Stability enhancement of ZnTPPS in acidic aqueous solutions by polymeric micelles

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稳定性和一致性是中国铸造业亟待解决的问题

稳定性和一致性是中国铸造业亟待解决的问题刘金城（欣特卡斯特—中国北京办公室，北京 100007）提要：分析指出了国内铸件稳定性和一致性较差，产品的可靠性不好，市场竞争力低的原因；提出了提高铸件质量稳定性和一致性的几项重要措施：控制铸件生产的每一工艺过程，严格执行工艺规范，采用先进可靠的工艺和设备，不断改进现有的生产工艺等；例举了国外生产稳定优质铸件的实例。

关键词：铸件质量；稳定性；一致性中图分类号：TG250文献标识码：A文章编号：1003－8345（2012）Z 2－0015－09DOI ：10.3969/j.issn.1003-8345.2012.z 2.001 Improving Stability and Consistency is Urgently Needed for Chinese Foundry IndustryLIU Jin-cheng（The Office in Beijing of Sinter Cast ，Beijing 100007，Chin a ）Abstract: The reason causing relatively lower stability and consistency ，poor reliability and low competing ability of Chinese foundrie s -produced castings was analyzed. The important measures to improve casting quality stability and consistency were proposed as following ：controlling every processes of casting production ；strictly observing process specifications ；adopting advanced and reliable productive processes and equipments ；constantly improving existing productive process ，etc. Some high quality casting - producing foundries of developed countries was introduced as examples. Key words: casting quality ；stabilit y ；consistency位居世界第一；2007 年，中国铸件产量 3 126.9 万 t ，占世界铸件产量的 1/3，比第 2 至第 4 位的美国、俄罗斯、印度的总和还多 524 万 t ，接近第 2 至第 5 位的美国、俄国、印度和日本的总和；2008 年，中国铸件产量更达到 3 350 万 t ；2009 年，世界铸件产量比 2008 年减产 14%，但是 2009 年中国铸件产量却继续增长，达到 3 530 万 t ，比第 2 到第10 位国家的总和（3 518 万t ）还要多，并占世界产量 8 034 万 t 的 43.9%。

Enhanced Photocatalytic Hydrogen Evolution over Cu-Doped ZnIn2S4 under Visible Light Irradiation

Enhanced Photocatalytic Hydrogen Evolution over Cu-Doped ZnIn 2S 4under Visible Light IrradiationShaohua Shen,Liang Zhao,*Zhaohui Zhou,and Liejin GuoState Key Laboratory of Multiphase Flow in Power Engineering,Xi’an Jiaotong Uni V ersity,Xi’an,ShaanXi 710049,P.R.ChinaRecei V ed:May 22,2008;Re V ised Manuscript Recei V ed:July 25,2008A series of Cu-doped ZnIn 2S 4photocatalysts has been synthesized by a facile hydrothermal method,with the copper concentration varying from 0wt%to 2.0wt%.The physical and photophysical properties of these Cu-doped ZnIn 2S 4photocatalysts were characterized by X-ray diffraction (XRD),photoluminescence spectroscopy (PL),scanning electron microscopy (SEM),and UV -visible diffuse reﬂectance spectroscopy (UV -vis).The diffuse reﬂectance and photoluminescence spectra of Cu-doped ZnIn 2S 4shifted monotonically to longer wavelengths as the copper concentration increased from 0wt%to 2.0wt%,indicating that the optical properties of these photocatalysts greatly depended on the amount of Cu doped.Meanwhile,the layered structure of ZnIn 2S 4would be destructed gradually by Cu doping.The photoactivity of ZnIn 2S 4was enhanced when Cu 2+was doped into the crystal structure.The highest photocatalytic activity was observed on Cu (0.5wt%)–doped ZnIn 2S 4,with the rate of hydrogen evolution to be 151.5µmol/h under visible light irradiation (λ>430nm).On the basis of the calculated energy band positions and optical properties,the effect of copper as a dopant on the photocatalytic activity of Cu-ZnIn 2S 4was studied.1.IntroductionPhotocatalytic water splitting into H 2and O 2using semicon-ductor photocatalysts has been regarded as an attractive solution to resolve the global energy and environmental problems.Many effective photocatalysts have been developed;however,most of them only work in the ultraviolet region because of their wide band gap.1-4Thus,developing highly active photocatalysts with visible light response to use solar energy is important,as the ultraviolet light occupies only 2-3%of solar energy.Over the past few years,considerable effort has been made to narrow the band gap of catalysts to improve visible light response.Recent progress includes single-phase oxide PbBi 2Nb 2O 9for isopropyl alcohol degradation and water de-composition,5GaN-ZnO solid solution,6and titanium disilicide 7for pure water decomposition to H 2and O 2.One effective way to increase the absorption of photocatalyst is to form donor levels in the forbidden band by introducing foreign elements into active photocatalysts with a wide band gap.TiO 2codoped with Ni and Ta,8ZnS doped with Cu or Ni,9,10and ZnS codoped with Pb and halogens 11have been reported as active photocata-lysts under visible-light irradiation.In particular,the InTaO 4doped with Ni was found to be an active photocatalyst for overall water splitting in the visible light region.12On the other hand,chalcogenides such as CdS have been studied extensively,since they have ideal edge positions of the valence and conduction bands for hydrogen production from aqueous electrolyte solutions containing a sacriﬁcial agent (Na 2S or/and Na 2SO 3)under visible light irradiation.13,14Unfortunately,they also have a fatal disadvantage of photocorrosion,i.e.,photogenerated holes in the valence band tend to react with chalcogenides themselves.15Although incorporation of chalco-genides into interlayers 16or mesoporous materials 17,18was efﬁcient for stabilizing the chalcogenides and producing hy-drogen from water,the photocatalytic efﬁciency is still low.Recently,some multicomponent metal sulﬁdes have been reported to be more stable and show higher photocatalytic activity under visible light.19-21Moreover,the CdZnS doped with Cu showed greatly improved stability and photocatalytic activity even without Pt as a cocatalyst.22Ternary sulﬁde ZnIn 2S 4,as the only member of the AB 2X 4family semiconductor with a layered structure,has attracted far-ranging interests because of its potential applications in different ﬁelds such as charge storage,23thermoelectricity,24and photo-conduction.25In 2003,Lei et al.26synthesized ZnIn 2S 4by a simple hydrothermal method and ﬁrst treated ZnIn 2S 4as an efﬁcient visible-light-driven photocatalyst for hydrogen produc-tion.In 2006,Gou et al.27hydrothermally prepared the ZnIn 2S 4solid or hollow microspheres in the presence of a surfactant such as cetyltrimethylammonium bromide (CTAB)or poly(eth-ylene glycol)(PEG).In our previous research,28,29the photo-catalytic activity of ZnIn 2S 4could be further enhanced when hydrothermally prepared in the presence of CTAB.Thus,ZnIn 2S 4turned to be a good candidate for hydrogen production from water under visible light.In the present study,a series of ZnIn 2S 4doped with different amounts of Cu was synthesized by a CTAB-assisted hydrothermal method.The effects of Cu doping on the morphology,optical properties,and photocatalytic activities of ZnIn 2S 4were discussed in detail.2.Experimental Section2.1.Synthesis of Cu-Doped ZnIn 2S 4.All chemicals are of analytical grade and used as received without further puriﬁca-tion.ZnIn 2S 4products were prepared by a hydrothermal synthetic method.27In a typical procedure,0.735g of ZnSO 4·7H 2O,1.615g of In(NO 3)3·4H 2O,0.65g of cetyltrimethylam-monium bromide (CTAB),and a double excess of thioacetamide (TAA)were dissolved in 50mL of distilled water.The mixed solution was then transferred into a 70-mL Teﬂon-lined auto-clave.The autoclave was sealed and kept at 160°C for 12h*To whom correspondence should be addressed.Phone:+86-29-82668287.Fax:+86-29-82669033.E-mail address:lzhao@.J.Phys.Chem.C 2008,112,16148–161551614810.1021/jp804525q CCC:$40.75 2008American Chemical SocietyPublished on Web 09/20/2008and then cooled to room temperature naturally.A yellow precipitate was obtained,which was then ﬁltered and washed with absolute ethanol and distilled water for several times.After being dried in a vacuum at 80°C,ZnIn 2S 4was obtained.For the synthesis of Cu-doped ZnIn 2S 4,a desired amount of 0.1M Cu(NO 3)2solution was added into the mixed solution before transferring into the autoclave.ZnIn 2S 4doped with different amounts of Cu is denoted as Cu(X )-ZnIn 2S 4;the value of X ,from 0wt%to 2.0wt%,is used to describe the weight content of Cu.2.2.Characterization.The X-ray diffraction (XRD)patterns were obtained from a PANalytical X’pert MPD Pro diffracto-meter using Ni-ﬁltered Cu K R irradiation (Wavelength 1.5406Å).The diffuse reﬂection of the samples was determined by a Hitachi U-4100UV -vis -near-IR spectrophotometer.The analysis of photoluminescence spectra (PL)was carried out at room temperature using a PTI QM-4ﬂuorescence spectropho-tometer.The sample morphology was observed by a JEOL JSM-6700FE scanning electron microscope.2.3.Evaluation of Photocatalytic Activity.Photocatalytic hydrogen evolution was performed in a gas-closed circulation system with a top window Pyrex cell.A 300W Xe lamp was used as the light source,and the UV part of the light was removed by a cutoff ﬁlter (λ>430nm).Hydrogen evolved was analyzed by an online thermal conductivity detector (TCD)gas chromatograph (NaX zeolite column,nitrogen as a carrier gas)every 10min.In all experiments,the photocatalyst powder (0.2g)was dispersed by a magnetic stirrer in 150mL of 0.25M Na 2SO 3/0.35M Na 2S aqueous solution.Here,Na 2SO 3/Na 2S mixed sacriﬁcial agent was used to scavenge photogenerated holes.Nitrogen was purged through the cell before reaction to remove oxygen.Pt (1wt%)as a cocatalyst for the promotion of hydrogen evolution was photodeposited in situ on the photocatalysts from the precursor of H 2PtCl 6·6H 2O.The tem-perature for all the photocatalytic reactions was kept at 25(0.5°C.The blank experiments showed no appreciable H 2evolution in the absence of irradiation or photocatalyst.Apparent quantum yield deﬁned by the eq 1was measured using a 420nm band-pass ﬁlter and an irradiatometer.A.Q.Y.(%))the number of reacted electronsthe number of incident photons×100)the number of evolved H 2molecules ×2the number of incident photons×100(1)2.4.Band Structure Calculation.The plane-wave-based density functional theory (DFT)calculation was carried out for ZnIn 2S 4with hexagonal structure by employing the CASTEPprogram to obtain further information about the energy structure of the Cu-ZnIn 2S 4photocatalysts.30The core electrons were treated using ultrasoft pseudopotentials,31and the valence electronic conﬁgurations for Zn,In,and S are 3d 104s 2,4d 105s 25p 1,and 3s 23p 4,respectively.The kinetic energy cutoff was taken to be 400eV for ZnIn 2S 4.The exchange and correlation interactions were modeled using the generalized gradient approximation (GGA).The calculation was carried out using the primitive unit cell of [ZnIn 2S 4]2,which had 31occupied orbitals.The atomic coordinates of ZnIn 2S 4were obtained from Gou et al.273.Results and Discussion3.1.Crystal Structure.Figure 1A shows X-ray diffraction patterns of Cu(X )-ZnIn 2S 4photocatalysts (X )0wt%to 2.0wt%).Without Cu doping,the diffraction peaks of the obtained ZnIn 2S 4sample can be readily indexed as a pure phase hexagonal ZnIn 2S 4(ICSD-JCPDS card No.01-072-0773,a )3.85Å,c )24.68Å),and no other impurities such as ZnS,In 2S 3,oxides,or organic compounds related to reactants were detected.When ZnIn 2S 4was doped with Cu,the XRD patterns of the obtained Cu(X )-ZnIn 2S 4were almost the same as that of the hexagonal ZnIn 2S 4,except that the diffraction peaks were slightly shifted to higher angles with the amount of Cu doped increasing,as shown in Figure 1B.This observation suggested that Cu 2+was homogeneously incorporated into the lattice of ZnIn 2S 4,because the ionic radius of Cu 2+(0.72Å)is smaller than the radius of Zn 2+(0.74Å)and In 3+(0.81Å).32Furthermore,Cu 2+may occupy the Zn 2+site,since charge compensation was very easy in this case,as deduced by Shionoya et al.33An XRD pattern of CuS around 2θ)30°could be easily observed while the amount of Cu doped was close to 2.0wt%.This was due to the limitation of doping amount in the ZnIn 2S 4lattice.113.2.Morphology.Figure 2shows SEM images for Cu(X )-ZnIn 2S 4with X )0wt%to 2.0wt%.During the hydrothermal process,addition of Cu ion directly affects the morphology of Cu-ZnIn 2S4.When none of the Cu was doped,ZnIn 2S 4exhibited a lot of separate microspheres with diameters of 1-2µm,as shown in Figure 2a.Further observation showed that all the microspheres were composed of numerous petals/sheets.This growth tendency of lamellar structures might be related to the layered feature of hexagonal ZnIn 2S 4.27When X )0.1wt%to 0.5wt %,ZnIn 2S 4products still appeared in the shape of microspheres;however,increasing the amount of Cu doped led to gradual decrease in the diameter of Cu(X )-ZnIn 2S 4micro-spheres.The diameter of microsphere was about 0.5-1µmforFigure 1.X-ray diffraction patterns of Cu(X )-ZnIn 2S 4;the values of X were (a)0.0wt%,(b)0.1wt%,(c)0.3wt%,(d)0.5wt%,(e)0.7wt%;(f)0.9wt%,(g)1.2wt%,(h)1.6wt%,(i)2.0wt%.Enhanced Photocatalytic Hydrogen Evolution J.Phys.Chem.C,Vol.112,No.41,200816149Figure 2.Part 1of 2.16150J.Phys.Chem.C,Vol.112,No.41,2008Shen et al.Cu(0.5wt%)-ZnIn 2S 4.As X increased further,the shape of microspheres for Cu(X )-ZnIn 2S 4was destructed partially and even throughly,as shown in Figure 2e -g,as well as the petals/sheets presented to be more irregular.When X )1.6wt%to 2.0wt %,instead of microspheres and petals/sheets,Cu(X )-ZnIn 2S 4turned out to be a bulky conglomeration with a rough surface,and petals/sheets could be hardly observed.The morphology of the Cu(X )-ZnIn 2S 4samples obtained in the same synthetic condition varies regularly with the increasing amount of Cu doped.That is to say,the layered structure of hexagonal ZnIn 2S 4,as well as the shape of microspheres,could be destructed gradually by the increasing Cu dopant.3.3.Optical Properties.Figure 3shows the UV -vis diffuse reﬂectance spectra of Cu(X )-ZnIn 2S 4with X )0wt%to 2.0wt%.The onset of the absorption edge of ZnIn 2S 4was at about 495nm,corresponding to the band gap of 2.51eV.Moreover,ZnIn 2S 4had an intense absorption band with a steep edge in the visible-light region.This shape indicated that the UV -vis absorption was due to the band gap transition but not due to the transition from impurity levels to the conduction band of ZnIn 2S4.As X increased,a new absorption shoulder around 500nm was observed,and the absorption edge of Cu(X )-ZnIn 2S 4shifted monotonously from 575to 650nm with an increase inX from 0.1wt%to 1.2wt%,corresponding to the narrowing of the band gap from 2.16to 1.91eV.The absorption shoulder with a long tail on the low energy side,which was characteristic of doped photocatalysts 34,35and indicated that intraband gap states were formed by the dopants in the forbidden band,couldFigure 2.Part 2of 2.Scanning electron microscope images of Cu(X )-ZnIn 2S 4;the values of X were (a)0.0wt%,(b)0.1wt%,(c)0.3wt%,(d)0.5wt%,(e)0.7wt%;(f)0.9wt%,(g)1.2wt%,(h)1.6wt%,(i)2.0wt%.Figure 3.Diffuse reﬂectance spectra of Cu(X )-ZnIn 2S 4;the values of X were (a)0.0wt%,(b)0.1wt%,(c)0.3wt%,(d)0.5wt%,(e)0.7wt%;(f)0.9wt%,(g)1.2wt%,(h)1.6wt%,(i)2.0wt%.Enhanced Photocatalytic Hydrogen Evolution J.Phys.Chem.C,Vol.112,No.41,200816151be assigned to the transition from the Cu3d level above the valence band to the conduction band of ZnIn 2S 4.In addition,a broad band (λ>750nm)was observed for Cu (1.6wt%to 2.0wt%)-ZnIn 2S 4.This was due to the impurity CuS phase,as indicated by X-ray diffraction.The PL spectra of Cu(X )-ZnIn 2S 4,with X )0wt%to 2.0wt%,were obtained using an excitation wavelength of 330nm,as shown in Figure 4.The PL intensity and response range of Cu(X )-ZnIn 2S 4were inﬂuenced by Cu doping.The PL spectra,in company with the diffuse reﬂect spectra,shifted successively to longer wavelength with the change in the amount of Cu doped,indicating that the energy structure of Cu(X )-ZnIn 2S 4depended on the value of X.Similar phenomena has been reported by Kudo et al.in the (AgIn)x Zn 2(1-x )S 2solid solutions.19However,as shown in Table 1,the emission spectra of Cu(X )-ZnIn 2S 4(X )0.0wt%to 0.7wt%)was somewhat red-shifted vis-a-vis the absorption edge.This is because the PL emission of Cu(X )-ZnIn 2S 4presented here is broadband,36or donor -acceptor defect (such as sulfur vacancy)based,37in nature.In constrast,the absorption edge of Cu(X )-ZnIn 2S 4(X )0.9wt%to 2.0wt%)shifted to longer wavelength when compared to the emission spectra.This may be due to the excess of Cu doping,resulting in the formation of CuS,which has a total absorption in the visible-light region.Thus,as reported by Peng et al.on Cu-ZnS,38the PL emission of Cu(X )-ZnIn 2S 4may arise from the recombination between the shallow donor level (sulfur vacancy)and the t 2level of Cu 2+(splitting from Cu3d).As the energy level of sulfur vacancy relative to the valence band nearly stays constant in these samples despite the variation in Cu 2+concentration,it can be concluded that the t 2energy level ofCu 2+ions is farther from the valence band with increasing Cu 2+concentration.In addition,it could be found from Figure 4that the PL intensity of Cu(X )-ZnIn 2S 4gradually increased as the Cu content increased and arrived at the highest degree when the Cu content was 0.5wt%.While the Cu content continued to increase,namely more than 0.5wt%,the PL intensity began to decrease.In Mn-ZnS 39and Cu-ZnS,38a similar photolumi-nescence phenomenon was also observed,which can be explained by the effect of ion doping.As the foregoing analysis shows,these PL spectra were related to native defects (e.g.,sulfur vacancy).When Cu 2+was doped into ZnIn 2S 4,more defect states would be introduced.Therefore,it is reasonable that the defect-related PL intensities were enhanced for the Cu 2+-doped samples compared with the undoped sample.As for the decrease of the PL intensity with the Cu 2+concentration above 0.5wt%,it may be caused by the formation of CuS,though the XRD measurement did not detect the existence of the copper sulﬁde phase.In Eu-doped GaN,40a similar concentration quenching phenomenon was also observed,which was mainly attributed to the formation of EuN compound.3.4.Band Structures.Figure 5A shows the band structure and the density of state (DOS)of ZnIn 2S 4.The density contour maps for the lowest unoccupied molecular orbitals (LUMO)and highest occupied molecular orbitals (HOMO)of ZnIn 2S 4are shown in Figure 5B.We can observe clearly that both the top of valence band and the bottom of the conduct band lay at the G point of the Brillouin zone from Figure 5A.So the pure ZnIn 2S 4crystal is a direct gap band semiconductor.The theoretical value of the direct gap at G is 0.4eV,which is less than the experimental value of about 2.51eV.Such an underestimation of the band gap is a well-known artifact of GGA.The density of states (Figure 5A)indicates that the S3p orbitals make a signiﬁcant contribution to the valence band top of ZnIn 2S 4and that the highest occupied molecular orbital (HOMO)levels are composed mainly of the hybridized S3p and Zn3d orbitals.The In5s orbitals locate at more negative energy levels than that of S3p orbitals and do not contribute much to the valence band top.The lowest unoccupied molecular orbital (LUMO)levels are composed mainly of the In5s5p and S3p orbitals.The Zn4s4p orbitals locate at more positive energy levels and do not contribute much to the conduction band bottom.Based on the optical properties and DFT calculations,the schematic energy level diagram of Cu(X )-ZnIn 2S 4is shown in Figure 6.As for ZnIn 2S 4,upon photoexcitation,electrons would transfer from the valence band (hybridized S3p and Zn3d orbitals)to the conduction band (hybridized In5s5p and S3p orbitals),leaving photogenerated holes in the valence band.As aforementioned,the PL emission has been known to be due to the photoluminescence transition from the sulfur-vacancy-related donor level or the conduction band to the valence band.Therefore,the energy difference between the absorption edge and the emission spectra of ZnIn 2S 4can be explained.Taking the Cu doping into account,the t 2state,splitting from discrete Cu3d levels,will form above the edge of valence band of ZnIn 2S 4,which is consistent with those reported by Peng 38and Xu 41in Cu-ZnS.A similar orbital-splitting phenomenon has been observed by Ye 42and Zou 43for Cr-3d and Ni-3d orbtials in In 12NiCr 2Ti 10O 42and Ca 2NiWO 6.The t 2(Cu3d)level,pro-duced by doping Cu 2+into ZnIn 2S 4,works as the donor level and acceptor level for photoexcitation and PL emission,respec-tively,44as shown in Figure 6.With the amount of Cu doped increasing,the t 2(Cu3d)level will be elevated farther fromtheFigure 4.Photoluminescence spectra of Cu(X )-ZnIn 2S 4;the values of X were (a)0.0wt%,(b)0.1wt%,(c)0.3wt%,(d)0.5wt%,(e)0.7wt%;(f)0.9wt%,(g)1.2wt%,(h)1.6wt%,(i)2.0wt%,excited at 330nm.TABLE 1:Band Gap,Absorption Edge,PL Emission and Emission Intensity of Cu(X )-ZnIn 2S 4,with X )0.0wt%to 2.0wt%X (wt%)band gap a (eV)absorption edge (nm)PL emission (nm)emission intensity(normalized,a.u.)0.0 2.514955600.330.1 2.165755970.720.3 2.115876110.760.5 2.05604617 1.000.7 2.026146260.740.9 1.946396320.561.2 1.916506390.421.6 1.737156550.202.01.657506660.19aCalculated from absorption edge.16152J.Phys.Chem.C,Vol.112,No.41,2008Shen et al.valence band,which results in the redshift of absorption edge and PL emission for Cu(X )-ZnIn 2S 4.3.5.Photocatalytic Activities of Cu(X )-ZnIn 2S4.Figure 7shows the dependence of photocatalytic H 2evolution from an aqueous Na 2SO 3/Na 2S solution over Cu(X )-ZnIn 2S 4under visible-light irradiation (λ>430nm).Either nondoped orCu-Figure 5.(A)Band structure and density of states for ZnIn 2S 4calculated by the density functional method.(B)Density contour maps for the LUMO and HOMO of ZnIn 2S 4.Figure 6.Schematic energy level diagram of Cu(X )-ZnIn 2S 4.Vs stands for sulfurvacancy.Figure 7.Photocatalytic H 2evolution under visible-light irradiation over Cu(X )-ZnIn 2S 4;the values of X were (a)0.0wt%,(b)0.1wt%,(c)0.3wt%,(d)0.5wt%,(e)0.7wt%,(f)0.9wt%,(g)1.2wt%,(h)1.6wt%,(i)2.0wt%.Enhanced Photocatalytic Hydrogen Evolution J.Phys.Chem.C,Vol.112,No.41,200816153doped ZnIn 2S 4was active and stable for splitting water to hydrogen.The rate of H 2evolution over nondoped ZnIn 2S 4was 26.1µmol ·h -1.The apparent quantum yield at 420nm was calculated to be 9.6%by eq 1.As the amount of doped Cu was increased,the photocatalytic activity of Cu(X )-ZnIn 2S 4was increased,because the visible-light absorption band of Cu(X )-ZnIn 2S 4grew.11The highest activity was obtained when 0.5wt %of Cu was doped,the rate of hydrogen evolution reached at 151.5µmol ·h -1,with the apparent quantum yield determined to be 14.2%.As the concentration of Cu doped was above 0.5wt%,the activity was decreased,though the visible-light absorption band grew further.Such a similar dependence of photocatalytic H 2evolution upon the amount of dopant has been observed for several other photocatalysts.11,44,45These observa-tions indicated that the photocatalytic activites depended upon not only the visible-light absorption (i.e.,band gap)but also some other factors.One of the reasons for the decrease in photocatalytic activity may be due to the impurity phase of CuS,resulted from the excess of Cu doping,as proved by XRD results.The CuS impurity may work as recombination sites between photogenerated electrons and holes.Another possible inactivation factor for the ZnIn 2S 4doped with excessive Cu is that the layered structure could be destructed gradually with the amount of Cu increased further,as revealed by SEM images.Some perovskite photocatalysts with layered structure have also shown good photocatalytic activity for splitting water to hydrogen,as the dipole moment along layers seems to enhance the charge separation,resulting in high activity.46,47Figure 8shows the photocatalytic activity and photolumi-nescence intensity as a function of Cu content in the Cu(X )-ZnIn 2S 4.The change in photoluminescence intensity was concurrent to that in photocatalytic activity,as both photolu-minescence intensity and photocatalytic activity reached the highest level when 0.5wt %of Cu was doped.Photolumines-cence depends on various factors such as the densities of photoexcited charges and recombination centers,the extent of nonradiation process,and the mobility of photoexcited charges.44It is difﬁcult to determine which process is mainly responsible for changes in photoluminescence intensity with Cu content.However,in association with the change in photocatalytic activity,a plausible explanation can be made as follows.During the PL process,vacancies (such as sulfur vacancy)and defects can easily bind photoinduced electrons to form excitons,so that the PL signal can easily occur.48When Cu 2+ions were doped into ZnIn 2S 4,more vacancies (such as sulfur vacancy)or defect states would be introduced.38The larger the content of vacancy or defect,the stronger the PL signal.Meanwhile,an increasein Cu content not only raised the t 2(Cu3d)level to narrow the band gap of Cu(X )-ZnIn 2S 4,which has been demonstrated by the UV -vis diffuse reﬂectance spectra,but also enhanced the density of the t 2(Cu3d)levels and increased the concentration and the mobility of the photoexcited electrons.44These could be related to the enhancement of photocatalytic activity.However,further increase in the amount of Cu doped would result in the increased absorption to longer wavelength,which was likely due to the formation of CuS,as discussed previously.Thus,the CuS impurity weakened the photoluminescence,40as well as lowered photocatalytic activity of Cu-doped ZnIn 2S 4.114.ConclusionsIn summary,we have synthesized a series of Cu-doped ZnIn 2S 4photocatalysts by a simple hydrothermal method.The photocatalytic activity of ZnIn 2S 4was remarkably enhanced by Cu doping.The optimized Cu (0.5wt%)-doped ZnIn 2S 4photocatalyst showed the highest activity for splitting water into H 2,with the rate of hydrogen evolution to be 151.5µmol ·h -1.With increasing concentration of Cu doped,the UV -vis spectra and PL emission peak were systematically shifted to longer wavelength.Moreover,there were certain intrinsic relationships between the PL emission intensity and photocatalytic activity of Cu-doped ZnIn 2S 4.That is to say,the change in photolumi-nescence intensity was concurrent to that in photocatalytic activity,both depending on the increasing concentration of Cu doped.Acknowledgment.The authors gratefully acknowledge the ﬁnancial support of the National Natural Science Foundation of China (No.50521604)and National Basic Research Program of China (No.2003CB214500).The authors also would like to thank the molecular simulating platform and National High Performance Computing Center (Xi’an)at Xi’an Jiaotong University for the calculation resource support.References and Notes(1)Domen,K.;Kudo,A.;Ohnishi,T.J.Catal.1986,102,92.(2)Hwang,D.W.;Kim,H.G.;Kim,J.;Cha,K.Y.;Kim,Y.G.;Lee,J.S.J.Catal.2000,193,40.(3)Kato,H.;Asakura,K.;Kudo,A.J.Am.Chem.Soc.2003,125,3082.(4)Sato,J.;Saito,N.;Yamada,Y.;Maeda,K.;Takata,T.;Kondo,J.N.;Hara,M.;Kobayashi,H.;Domen,K.J.Am.Chem.Soc.2005,127,4150.(5)Kim,H.G.;Hwang,D.W.;Lee,J.S.J.Am.Chem.Soc.2004,126,8912.(6)Maeda,K.;Teramura,K.;Lu,D.;Takata,T.;Saito,N.;Inoue,Y.;Domen,K.Nature 2006,440,295.(7)Ritterskamp,P.;Kuklya,A.;Wu ¨stkamp,M.;Kerpen,K.;Weidentha-ler,C.;Demuth,M.Angew.Chem.,Int.Ed.2007,46,7770.(8)Niishiro,R.;Kato,H.;Kudo,A.Phys.Chem.Chem.Phys.2005,7,2241.(9)Kudo,A.;Sekizawa,M.Catal.Lett.1999,58,241.(10)Kudo,A.;Sekizawa,mun.2000,15,1371.(11)Tsuji,I.;Kudo,A.J.Photochem.Photobiol.A 2003,156,249.(12)Zou,Z.G.;Ye,J.H.;Sayama,K.;Arakawa,H.Nature 2001,414,625.(13)Bubler,N.;Meier,K.;Reber,J.F.J.Phys.Chem.1984,88,3261.(14)Naman,S.A.;Gra ¨tzel,M.J.Photochem.Photobiol.A 1994,77,249.(15)Inoue,T.;Watanabe,T.;Fujishima,A.;Honda,K.J.Electrochem.Soc.1977,124,719.(16)Shangguan,W.;Yoshida,A.J.Phys.Chem.B 2002,106,12227.(17)Shen,S.;Guo,L.J.Solid State Chem.2006,179,2629.(18)Shen,S.;Guo,L.Mater.Res.Bull.2008,43,437.(19)Tsuji,I.;Kato,H.;Kobayashi,H.;Kudo,A.J.Am.Chem.Soc.2004,126,13406.(20)Tsuji,I.;Kato,H.;Kudo,A.Angew.Chem.,Int.Ed.2005,44,3565.(21)Jang,J.S.;Choi,S.H.;Shin,N.;Yub,C.;Lee,J.S.J.Solid State Chem.2007,180,1110.Figure 8.Dependence of photocatalytic activity for H 2evolution and PL emission intensity over Cu(X )-ZnIn 2S 4,with X )0.0wt%to 2.0wt%.16154J.Phys.Chem.C,Vol.112,No.41,2008Shen et al.(22)Liu,G.;Zhao,L.;Ma,L.;Guo,mun.2008,9,126.(23)Romeo,N.;Dallaturca,A.;Braglia,R.;Sberveglieri,G.Appl.Phys. Lett.1973,22,21.(24)Seo,W.S.;Otsuka,R.;Okuno,H.;Ohta,M.;Koumoto,K.J.Mater. Res.1999,14,4176.(25)Romeo,N.;Tarricone,L.;Zanotti,L.Il Nuo V o Cim.D1983,2, 2007.(26)Lei,Z.;You,W.;Liu,M.;Zhou,G.;Takata,T.;Hara,M.;Domen, K.;Li,mun.2003,17,2142.(27)Gou,X.;Cheng,F.;Shi,Y.;Zhang,L.;Peng,S.;Chen,J.;Shen, P.J.Am.Chem.Soc.2006,128,7222.(28)Shen S.;Zhao L.;Guo L.Mater.Res.Bull.,2008,doi:10.1016/ j.materresbull.2008.03.027.(29)Shen S.;Zhao L.;Guo L.Int.J.Hydrogen Energy,2008, doi:10.1016/j.ijhydene.2008.05.043.(30)Segall,M.D.;Lindan,P.J.D.;Probert,M.J.;Pickard,C.J.;Hasnip, P.J.;Clark,S.J.;Payne,M.C.J.Phys.:Condens.Matter2002,14,2717.(31)Vanderbilt,D.Phys.Re V.B1990,41,7892.(32)Lei,Z.;Ma,G.;Liu,M.;You,W.;Yan,H.;Wu,G.;Takata,T.; Hara,M.;Domen,K.;Li,C.J.Catal.2006,237,322.(33)Shionoya,S.;Tamoto,Y.J.Phys.Soc.Jpn.1964,19,1142.(34)Konta,R.;Ishii,T.;Kato,H.;Kudo,A.J.Phys.Chem.B2004, 108,8992.(35)Miyauchi,M.;Takashio,M.;Tobimatsu,ngmuir2004,20, 232.(36)Spanhel,I.;Anderson,M.A.J.Am.Chem.Soc.1991,113,2826.(37)Castro,S.L.;Bailey,S.G.;Raffaelle,R.P.;Banger,K.K.;Hepp,A.F.J.Phys.Chem.B2004,108,12429.(38)Peng,W.Q.;Cong,G.W.;Qu,S.C.;Wang,Z.G.Opt.Mater. 2006,29,313.(39)Ghosh,P.K.;Ahmed,Sk.F.;Jana,S.;Chattopadhyay,K.K.Opt. Mater.2007,29,1584.(40)Bang,H.;Morishima,S.;Sawahata,J.;Seo,J.;Takiguchi,M.; Tsunemi,M.;Akimoto,K.;Nomura,M.Appl.Phys.Lett.2004,85,227.(41)Xu,S.J.;Chua,S.J.;Liu,B.;Gan,L.M.;Chew,C.H.;Xu,G.Q. Appl.Phys.Lett.1998,73,478.(42)Wang,D.;Zou,Z.;Ye,J.Chem.Phys.Lett.2005,411,285.(43)Li,D.;Zheng,J.;Zou,Z.J.Phys.Chem.Solids2006,67,801.(44)Arai,N.;Saito,N.;Nishiyama,H.;Domen,K.;Kobayashi,H.;Sato, K.;Inoue,Y.Catal.Today2007,129,407.(45)Nishimoto,S.;Matsuda,M.;Miyake,M.Chem.Lett.2006,35, 308.(46)Kudo,A.;Kato,H.;Nakagawa,S.J.Phys.Chem.B2000,104, 571.(47)Hwang,D.W.;Kim,H.G.;Lee,J.S.;Kim,J.;Li,W.;Oh,S.H. J.Phys.Chem.B2005,109,2093.(48)Jing,L.;Qu,Y.;Wang,B.;Li,S.;Jiang,B.;Yang,L.;Fu,W.;Fu,H.;Sun,J.Sol.Energy Mater.Sol.Cells2006,90,1773.JP804525QEnhanced Photocatalytic Hydrogen Evolution J.Phys.Chem.C,Vol.112,No.41,200816155。

油水分离英文文献

Comparison of polyole ﬁn biocomposites prepared with wastecardboard,microcrystalline cellulose,and cellulose nanocrystals via solid-state shear pulverizationKrishnan A.Iyer a ,Amanda M.Flores a ,John M.Torkelson a ,b ,*a Dept.of Chemical and Biological Eng.,Northwestern University,Evanston,IL 60208,USA bDept.of Materials Science and Eng.,Northwestern University,Evanston,IL 60208,USAa r t i c l e i n f oArticle history:Received 14May 2015Received in revised form 4August 2015Accepted 15August 2015Available online 18August 2015Keywords:CellulosePolypropylene Polyethylenea b s t r a c tAs a signi ﬁcant part of municipal solid waste (MSW),waste cardboard (CB)is a sustainable,inexpensive,and rich source of cellulose.Previous studies of polyole ﬁn/CB composites have reported modest enhancement to major reduction in modulus and major reduction in elongation at break values relative to neat polymer.Here,green hybrids of low density polyethylene (LDPE)and polypropylene (PP)with 5e 25wt%CB are made by solid-state shear pulverization (SSSP),which achieves both size reduction of 2e 3cm sized CB pieces to the micron level and dispersion in polymer.The properties obtained with CB incorporation in LDPE and PP are compared and contrasted with those obtained with incorporation of microcrystalline cellulose (MCC)and cellulose nanocrystal (CNC).Polyole ﬁn composites with CB made by SSSP exhibit major enhancement in Young's modulus (63%and 71%increases for 10wt%CB in LDPE and 15wt%CB in PP,respectively).The PP/CB composites exhibit a broad range of property enhancements relative to neat PP,including a nearly 50%nucleating ef ﬁciency,as much as an 8%increase in PP crys-tallinity,and a factor of ~3decrease in crystallization half-time.Well-dispersed CB particles improve LDPE and PP thermo-oxidative stability as shown by thermogravimetric analysis (~5e 20 C increase in 20%mass loss temperature in air with 15e 20wt%CB addition)and isothermal shear ﬂow rheology.Similarly,post-SSSP high-temperature,long-time melt mixing results in no apparent degradation of LDPE/CB and MCC composites whereas LDPE/CNC composites show major degradation.When incorpo-rated into polyole ﬁn composites,low cost,cellulose-rich MSW can often produce reinforcement similar to glass ﬁbers and thus has potential as ﬁller for structural composite applications.©2015Elsevier Ltd.All rights reserved.1.IntroductionThe last two decades has witnessed rising interest in using nano ﬁllers for the preparation of polymer nanocomposites [1e 12].Such nanoscopic ﬁllers have the potential to improve material properties of the composite at much lower ﬁller loadings (typically <10wt%)when compared to microscopic or macroscopic ﬁllers.Recent literature studies have thus focused on reducing ﬁller size to the nanoscale,with the aim of achieving better property en-hancements in composites [7e 12].Environmental concerns over depleting petrochemical resources have also prompted researchers to explore alternative,greener ﬁllers [12e 19].Green polymercomposites based on polyole ﬁns that employ renewable sources as reinforcements offer sustainable ecological and structural bene ﬁts.Studies have thus investigated incorporating cellulose and ligno-cellulosic materials including wood ﬂour,natural ﬁbers,soy ﬂour,rice husks and lignin into polymers as greener alternatives to synthetic ﬁllers [20e 30].Green ﬁllers offer bene ﬁts such as biodegradability,reduced reliance on fossil fuel-based raw mate-rials,and reduced part weight,carbon footprint and wear to pro-cessing equipment [27e 30].Such advantages make biocomposites attractive for structural applications in the automotive industry,while adding value to waste materials obtained from agricultural and municipal sources [14e 19].In this regard,cellulose has good potential as a green reinforcing ﬁller for polymers.It is the most abundant renewable material accounting for 50e 90%of all plant matter [31].Single cellulose nanocrystals (CNCs)possess excellent modulus with values of*Corresponding author.Dept.of Chemical and Biological Eng.,Northwestern University,Evanston,IL 60208,USA.E-mail address:j-torkelson@ (J.M.Torkelson).Contents lists available at ScienceDirectPolymerjournal homepage:www.elsev /locate/polymer/10.1016/j.polymer.2015.08.0290032-3861/©2015Elsevier Ltd.All rights reserved.Polymer 75(2015)78e 87137GPa or higher[32e34].The presence of amorphous domains and defects reduces the modulus of cellulose to29e36GPa [32e34].Discoveries of these excellent properties have led to re-ports of polymer composites incorporating cellulosicﬁllers ranging from nanocellulose to macroscale cellulose-rich municipal solid waste(MSW)materials[32e58].Corrugated cardboard(CB)and waste paper account for almost one-third of the total MSW generated in the United States[59].Kraft pulping of wood employed for the production of cardboard results in the partial elimination of hemicellulose and lignin[58,60,61].Corrugated cardboard is chemically made up of~75%cellulosics,~15%lignin, and the rest being binders/adhesives such as starch and acrylam-ides[60,61].The hemicellulosic part is primarily made up of mannose,galactose and xylose.Despite advancements in recycling technologies,with increasing number of recycling operations the quality of cellulose ﬁbers in CB decreases.As a result,almost25million tons of CB waste are discarded annually into landﬁlls in the United States[59]. Lack of effective processing techniques results in extremely low valuation of~$95/ton for paper scrap[62];in contrast,the highly reﬁned form of cellulose known as microcrystalline cellulose(MCC) that is used in the pharmaceutical industry is priced at~$2500/ton [63].Cardboardﬁbers are known to possess other attractive prop-erties like high speciﬁc strength and high aspect ratio(~100)[44]. Similar to wood-based polymer composites,thermoplastic com-posites with waste CB are speculated to be useful in load-bearing applications,frames,car interiors,etc[44].Despite their potential,the majority of studies producing such composites via melt processing have reported poor or mixed re-sults.Yuan et al.[45]noted,“Because of the poor compatibility of polypropylene(PP)and paperﬂour,it is nearly impossible to pre-pare…PP/paperﬂour blends with good mechanical properties.”(The presence of hydroxyl groups on cellulose makes it inherently incompatible with the hydrophobic polyoleﬁn matrices.)Thus,all literature reports attempting to produce such composites have utilized surface modiﬁcation,particle size reduction,extraction and/or compatibilizer addition for the preparation of polyoleﬁn/CB composites[42e58].Chibani et al.[46]reported no improvement in tensile modulus with incorporation of up to28wt%unmodiﬁed CB in PP composites prepared via melt processing.They further suggested the addition of maleated PP as a compatibilizer to improve material properties.Salmah et al.[47]utilized intensive grinding to obtain waste paper particles that were an average of 31m m in size.Incorporating20wt%of thisﬁller in low density polyethylene(LDPE)resulted in a125%increase in modulus but a 90%decrease in elongation at break compared to neat LDPE.Ashori and Nourbakhsh[56]incorporated10e40wt%of old corrugated cardboardﬁber into PP by melt mixing;all composites exhibited tensile modulus values well below(as much as50%below)that of neat PP.Drzal and coworkers incorporated recycled celluloseﬁber (average20m m diameter)extracted from waste paper into PP via melt processing and observed a64%increase in modulus for30wt%ﬁller content[49e51].The extra steps employed in these studies such as particle size reduction,extraction and compatibilization not only add to the time and cost of processing but also reduce the green aspect of theﬁller.We previously reported on property enhancements achieved by incorporating CNC in polyoleﬁns via solid-state shear pulverization (SSSP)[39].For example,in90/10wt%LDPE/CNC composites made by SSSP,there was a70%increase in tensile modulus and no reduction within error in elongation at break relative to neat LDPE [39].The ambient conditions and solid-state nature of SSSP enabled high shear and compressive forces to be imparted to the materials, resulting in excellent CNC dispersion and strong suppression of ﬁller degradation that accompanies high-temperature melt processing of cellulose-basedﬁllers[39].Past studies have shown the ability of SSSP to produce excellent dispersion of pristineﬁllers ranging from bundled carbon nanotubes and graphite to waste materials from natural sources[27e30,39,64e69].Excellent dispersion of immiscible blends has also been achieved by SSSP [70e72].Studies have also taken advantage of ambient conditions in SSSP to achieve functionalization and long-chain branching of PP without major molecular weight reduction[73e75].Here,we compare the reinforcing ability of well-dispersed cel-lulose-rich CB waste to well-dispersed,synthetic sources of cellu-lose such as MCC and CNC in polyoleﬁn composites.The CB is fed to the SSSP apparatus in several-centimeter-sized pieces with SSSP achieving both major particle size reduction and dispersion.For commercial viability of such composites as well as for sustainability considerations,it is important to compare low cost,cellulose-rich waste materials with much higher cost celluloseﬁllers.(At pre-sent,CNC production is at the pilot-plant scale rather than involving large-scale,commercial production.)We show that well-dispersed,cellulose-rich CB from MSW can often provide property enhancements similar to those achieved by highly reﬁned,micro-crystalline and nanocrystalline cellulose.2.Experimental section2.1.MaterialsTwo PP samples,PP1(Total3276)and PP2(Total3270)were used as received.As reported by the supplier(Total Petrochemi-cals),both samples had the same density(0.905g/cm3)and melt ﬂow index(MFI,2g/10min).Low density polyethylene(Exxon-Mobil LD103)with density of0.919g/cm3and MFI of1.1g/10min (190 C and2.2kg load)was supplied by ExxonMobil.Randomly chopped cardboard pieces(average size of~2e3cm)procured locally were used as-received without deinking.Microcrystalline cellulose(lattice NT with average particle size of~50m m and aspect ratio of~1.4as reported by the supplier)was supplied by FMC Biopolymers and used without modiﬁcation.Unmodiﬁed cellulose nanocrystals were produced at the Forest Products Laboratory in Madison,WI as described in Ref.[76].(Data related to polyoleﬁn/ CNC nanocrystals and used for comparative purposes are taken from Ref.[39].)2.2.Preparation of polyoleﬁn/cellulose compositesPolyoleﬁn pellets were fed to a Berstorff ZE-25pulverizer with a K-tron S-60feeder at a~100g/h feed rate.(A commercial-scale apparatus has processed polyoleﬁns at rates exceeding150kg/h [27,28].)The CB pieces(~2e3cm)were fed to the pulverizer via the K-tron S-60feeder whereas powdery MCC and CNC were added with a powder feeder(Brabender Technologies Inc.DDSR12-1 volumetric feeder)at different feed rates to obtain desiredﬁller content.The composites were produced using a200rpm screw speed and a screw design that yielded high speciﬁc energy(see Ref.[77]for a detailed description of screw design and energy in-puts).The pulverizer barrels were cooled by a recirculating ethylene glycol/water mix(À7 C,Budzar Industries WC-3chiller). Other details and process conditions are available in Refs.[27e30,39].2.3.Characterization of polyoleﬁn/cellulose compositesField-emission scanning electron microscopy(FE-SEM)samples were prepared by melting and extruding material obtained from SSSP with an Atlas Electronic Devices MiniMax molder(cup-and-rotor mixer).Morphologies of cryo-fractured sections wereK.A.Iyer et al./Polymer75(2015)78e8779obtained via an SU8030instrument after sputtering with gold/ palladium(Denton DeskIII).The FE-SEM images of as-received MCC were acquired after casting from water onto Si wafers.The mor-phologies of pristine CNC and polyoleﬁn/CNC composites produced by SSSP have been reported[39].Uniaxial tensile test samples of~0.7mm thickness were pre-pared by compression molding using a PHI(Model0230C-X1)press at180 C or140 C depending on the matrix polymer for5min with 5ton ram force.Dog-bone shaped specimens were cut using a Dewes-Gumbs die and tested using an MTS Sintech2S tensile tester according to ASTM D1708with a5kN load cell using a crosshead speed of50mm/min.Polymer crystallization was characterized by differential scan-ning calorimetry(DSC;Mettler-Toledo822e).After heating samples above the melt temperature,a10 C/min cooling rate was used to determine the non-isothermal crystallization onset temperature (T c).The percent polymer crystallinity was obtained by dividing the speciﬁc enthalpy from the area associated with the crystallization part of the nonisothermal cooling curve by the polymer mass fraction;this value was divided by the theoretical heat of fusion for neat polyethylene or PP of285.9and207.1J/g,respectively[78,79]. Since the PP matrices used for the preparation of CB and synthetic cellulose(MCC and CNC)composites are different,a nucleating efﬁciency(NE)was calculated based on the calorimetric efﬁciency scale proposed by Lotz and coworkers[65,80]:NEð%Þ¼ÀT cÀT c;lowÁ ÀT c;maxÀT c;lowÁÂ100(1)where T c,low is the onset crystallization temperature for a non-nucleated PP(equal to T c for neat PP1and PP2,117.1and121.4 C, respectively),T c,max is the onset crystallization temperature for a self-nucleated PP(both PP in this study had T c,max of140.2 C),and T c is the non-isothermal onset temperature of crystallization.(All onset temperatures were recorded at a cooling rate of10 C/min.) Isothermal crystallization half-times for the PP-based composites were determined at140 C after cooling from the melt at40 C/min.Thermo-oxidative degradation was monitored via thermo-gravimetric analysis(TGA;Mettler Toledo851e)under air.~5mg samples were heated from25 C to700 C at a10 C/min heating rate.At least three samples were run to show reproducibility.(Neat PP leaves behind no residue within error at700 C.)In order to understand the effect of the differentﬁllers on the thermal stability of polyoleﬁns under isothermal shear meltﬂow,shear storage modulus was monitored as a function of time at200 C using small amplitude oscillatory shear measurements at10rad/s(TA In-struments ARES rheometer;25mm parallel plateﬁxture).Water absorption measurements were performed on compres-sion molded discs(thickness¼~0.125inch and diameter¼2inch) following ASTM D570.Specimens were dried at80 C for24h, cooled in a desiccator,and immediately weighed(w1).Specimens were then immersed in distilled water at~23 C.Samples were periodically removed,dried with absorbent paper,and weighed (w2).The percentage water absorption(WA)is calculated as follows:WAð%Þ¼ðw2Àw1Þ=w1Â100(2) 3.Results and discussion3.1.Dispersion and morphology of polyoleﬁn/cellulose compositesFig.1a shows~2e3cm sized CB pieces that were employed in the present study.The large shear and compressive forces imparted to the material during solid-state processing leads to majorﬁller size reduction in the polymer composites.Fig.1b and c shows SEM images of fractured surfaces of LDPE/CB and PP/CB composites with 10wt%CB.The originally centimeter-sized CB pieces are reduced via a single-step SSSP process to particles in the range of1e10m m in size that are wetted into the polymer matrix.In addition,the fractured surfaces show no signs of pull-out,indicating the absence of majorﬁller agglomeration.Fig.1d shows SEM images of as-received MCC.Agglomerates of MCC can be as large as 100e200m m due to the strong interparticle afﬁnity arising from the numerous hydroxyl groups on the cellulose surface.Similar to polyoleﬁn/CB composites,SEM images of LDPE/MCC and PP/MCC composites(Fig.1e and f)show very good dispersion.The highly agglomerated MCC particles underwent major size reduction to particles no larger than1m m.In an earlier study,excellentﬁller dispersion was obtained in polyoleﬁn/CNC composites made by SSSP[39].Previous studies have reported challenges in achieving excellent dispersion of cellulosicﬁllers in polyoleﬁns via melt mixing.Chi-bani et al.[46]observed severeﬁller agglomeration,debonding and ﬁber pull-out,indicating poor adhesion between the CBﬁbers and PP matrix.In their study,5wt%PP grafted with maleic anhydride was used as compatibilizer to improve the interfacial adhesion which seemingly enhanced theﬁller dispersion.Ganster et al.[35] observed similarﬁber pull-out and poorﬁller dispersion when MCC was incorporated in polyethylene by melt mixing.Wetting and dispersion similar to that achieved in our study were obtained only after the addition of maleated PP.In short,solid-state processes are able to achieve excellentﬁller dispersion and particle size reduc-tion;this leads to the production of polyoleﬁn/CB composites with morphologies similar to those observed by employing MCC or CNC ﬁllers.3.2.Mechanical properties of polyoleﬁn/cellulose composites3.2.1.Tensile properties of polyoleﬁn/CB compositesTable1summarizes the effect of CB on the mechanical proper-ties of LDPE/CB composites made by SSSP.Excellent dispersion and particle size reduction led to major improvements in Young's modulus.For example,relative to neat LDPE,incorporation of5wt% CB results in a~38%increase in modulus and20wt%CB results in a 190%increase.The yield strength of LDPE/CB composites shows a 22%increase relative to neat polymer for5wt%CB and values unchanged from that of neat LDPE at other CB loadings.These re-sults compare well with those obtained by incorporating MCC and CNC into LDPE.The63%increase in modulus seen with90/10wt% LDPE/CB is within error the same as that obtained with90/10wt% LDPE/MCC and LDPE/CNC(Fig.2a and Table1).Similarly,the90/ 10wt%LDPE/CB composites retain yield strength that is within error invariant from those of neat LDPE and the90/10wt%LDPE/ MCC composite and only slightly lower than that of90/10wt% LDPE/CNC.In addition,the excellentﬁller dispersion and particle size reduction achieved by SSSP processing led to unparalleled reten-tion of elongation at break values in LDPE composites.As shown in Fig.2b,90/10wt%LDPE/MCC and LDPE/CNC composites have elongation at break values that are within error unchanged from that of neat LDPE.Due to the slightly larger size scales of CB par-ticles in the polymer matrix(yet less than10m m in size),the95/5 and90/10wt%LDPE/CB composites exhibit reductions in elonga-tion from500%for neat LDPE to390%and260%,respectively. Notably,LDPE/CB composites produced by SSSP retain sufﬁcient elongation at break to be viable for commercial applications atﬁller loadings as high as20wt%.As shown in Table2,relative to neat PP1with a modulus of 910MPa,PP1composites with5and25wt%CB exhibit24and92% increases in Young's modulus,respectively.In addition,all PP1/CBK.A.Iyer et al./Polymer75(2015)78e87 80composites produced here show yield strength similar to neat PP1.Due to minor degradation of CB during compression molding,the 95/5wt%PP1/CB composite retains an elongation at break of 40%while the 75/25wt%PP1/CB composite has a value of 8%.None-theless,all composites exhibit ductile behavior except the 75/25wt %PP1/CB composite with a barely ductile fracture.These results are comparable to those obtained with MCC and CNC composites;relative to neat PP2with a 1200MPa modulus,90/10wt%PP2/MCC and 90/10wt%PP2/CNC composites show ~33%and ~53%increases in modulus,respectively.parison with literature data for polyole ﬁn/cellulose based compositesFew literature studies have investigated the fabrication of polyole ﬁn/CB composites via melt mixing,all of which have employed particle size reduction steps prior to melt processing in order to achieve CB particles that are less than 50m m in size [46,47].Salmah et al.[47]utilized intensive grinding to produce,on average,31-m m-sized waste paper particles,that were subsequently incor-porated into LDPE via melt mixing.The LDPE composites with 23wt%ﬁller showed a ~100%increase in modulus relative to neat LDPE (modulus of 80MPa).In contrast,the 80/20wt%LDPE/CB composite produced via SSSP shows a 190%increase in modulus.The severe ﬁller agglomeration and void formation during melt processing result in dramatically reduced elongation at break values in the composite.Salmah et al.[47]reported major reduction in elongation at break from 400%for neat LDPE to only 50%for composites with 9wt%ﬁller produced via melt processing.Dramatically superior performance is observed with an SSSP pro-cessed composite of similar ﬁller content,showing a 260%elon-gation at break (neat LDPE has 500%elongation).Chibani et al.[46]incorporated up to 15wt%CB ﬁbers in PP via melt mixing and observed no improvement in tensile modulus.In comparison,in the present study,an 85/15wt%PP/CB composite shows a ~71%increase in Young's modulus relative to neat PP.Poor outcomes have also been reported when synthetic cellu-lose ﬁllers were incorporated in composites prepared via melt processing or solution mixing.Spoljaric et al.[36]produced a 90/10wt%PP/MCC composite using ultrasonication in solution and reported a ~30%increase in modulus relative to neat PP.OurstudyFig.1.a)Photographs of ~2e 3cm size CB pieces employed in preparing polyole ﬁn/CB composites.Field-emission scanning electron micrographs of b)90/10wt%LDPE/CB,c)85/15wt%PP/CB,d)as-received MCC,e)90/10wt%LDPE/MCC and f)90/10wt%PP/MCC composites prepared via SSSP.Table 1Mechanical properties of LDPE/cellulosic ﬁller composites produced by SSSP.SampleYoung's modulus E (MPa)Yield strength s (MPa)Elongation at break ε(%)Neat LDPE160±510.0±0.3500±3095/5wt%LDPE/CB 220±1012.2±1.0390±3090/10wt%LDPE/CB 260±2010.7±0.6260±1580/20wt%LDPE/CB 465±3510.1±0.233±1090/10wt%LDPE/MCC 260±2011.0±0.1485±2090/10wt%LDPE/CNC270±1013.0±1.0460±30Note:Data for LDPE/CNC composites are from Ref.[39].K.A.Iyer et al./Polymer 75(2015)78e 8781reports a similar 33%increase for the same MCC loading using the industrially scalable,solventless,continuous SSSP process.As shown in Ref.[39],polyole ﬁn/CNC composites produced by SSSP have the highest reported enhancement in modulus relative to similar composites produced via melt or solution mixing in litera-ture studies.Moreover,no study has produced PP/CNC composites using industrially scalable,melt processing techniques due to concerns with CNC thermal degradation.Alternatively,such com-posites can be manufactured by using ambient temperature,solid-state processes that are able to achieve very good dispersion.We further demonstrate here that effective agglomerate breakup and superior dispersion of macroscopic cellulose rich MSW achieved by SSSP give rise to property enhancements that are comparable to those seen with microscale or nanoscale cellulose.Well-dispersed cellulosic ﬁllers thus provide excellent reinforcement to poly-ole ﬁns,making the plastic stiffer and more durable.3.3.Water uptake of polyole ﬁn/cellulose based compositesWater absorption behavior is important in applications related to structural materials for outdoor use.The overall water absorp-tion of a composite depends on moisture content of the ﬁller,void fraction,quality of dispersion,permeability,ﬁller hydrophilicity,etc [46].Fig.3shows the percentage weight gain as a function of the square root of time with increasing ﬁller content in composite samples (thickness ¼0.125inch and diameter ¼2.0inch,following ASTM D570).Neat LDPE and PP show no appreciable water ab-sorption after 300h immersion.Hence,water uptake in these composites is a result of ﬁller incorporation.Under the same conditions,LDPE composites show marginal water absorption.For example,after 24h immersion,LDPE com-posites with 10wt%CNC,MCC,and CB show 0.12,0.15,and 0.19wt%water gain,respectively;none of the composites reaches a constant,equilibrium sorption value after 300h immersion.Similarly,after 24h immersion,PP composites with 10wt%CNC,MCC and 15wt%CB show 0.09,0.13,and 0.08wt%water absorption;none of the PP composites reaches equilibrium after 300h immersion.Via melt mixing,Tajvidi et al.[54]incorporated 15wt%waste paper in PP and observed ~0.50%water absorption after 24h,a factor of six greater than that observed with 85/15wt%PP1/CB produced via SSSP (samples were tested according to ASTM D570in their study).The very low water absorption reported in the current study is consis-tent with excellent ﬁller dispersion and absence of voids within the composites.In addition,increasing the cellulose crystallinity by extraction of microscopic and nanoscopic crystallite does not signi ﬁcantly reduce water absorption in the composite.Overall,the very low moisture absorption with cellulose-based composites makes them appealing in load bearing and outdoorapplications.Fig.2.a)Young's modulus values of LDPE/CB (blue dots),LDPE/MCC (red lines)and LDPE/CNC (green checkered)composites prepared by SSSP,and b)Elongation at break values of LDPE/CB (blue dots),LDPE/MCC (red lines)and LDPE/CNC (green checkered)composites prepared by SSSP.(For interpretation of the references to color in this ﬁgure legend,the reader is referred to the web version of this article.)Table 2Mechanical properties of PP/cellulosic ﬁller composites produced by SSSP.SampleYoung's modulus E (MPa)Yield strength s (MPa)Elongation at break ε(%)Neat PP1910±5032.0±0.7740±4095/5wt%PP1/CB 1130±9031.2±1.040±1085/15wt%PP1/CB 1560±8032.6±1.710±275/25wt%PP1/CB 1750±9032.7±0.98±3Neat PP21200±2036.0±1.0700±4090/10wt%PP1/MCC 1600±5035.6±1.110±290/10wt%PP1/CNC a1830±7038.0±1.012±3Note.PP1and PP2samples employed in this study had different tensile properties despite having the same MFI values (as reported by suppliers).aData for PP/CNC composites are from Ref.[39].K.A.Iyer et al./Polymer 75(2015)78e 87823.4.Nucleating ef ﬁciency of polyole ﬁn/CB compositesFig.4and Table 3summarize the effects of well-dispersed CB,MCC and CNC on the crystallization of LDPE and PP.Cellulosic ﬁllers are often good nucleating agents for polymer crystallization.However,the extent of enhancement in crystallization depends strongly on ﬁller dispersion and size reduction and the inherent crystallizability of the polymer.The LDPE used in this study has a very fast crystallization rate,and hence incorporating cellulosic ﬁllers provides no additional bene ﬁt.Within error,all LDPE/CB composites retain crystallization behavior similar to that of neat LDPE.On the other hand,excellent particle size reduction and very good dispersion of CB pieces lead to major increases in PP crystal-lization rate.Relative to neat PP1with on onset temperature of crystallization (T c )of 117.1 C,incorporating 5wt%and 15wt%CB results in 10.2 C and 11.4 C increases in T c ,respectively.En-hancements are also seen in overall crystallinity of PP in the com-posite;neat PP1is 44.7%crystalline whereas in a 75/25wt%PP1/CBFig.3.Water uptake of neat polyole ﬁn and SSSP-processed composites plotted as a function of square root of time for a)LDPE,LDPE/CB,LDPE/MCC,and LDPE/CNC and b)PP1,PP1/CB,PP2/MCC and PP2/CNC (Note.PP1and PP2had similar water absorptionbehavior).Fig.4.a)Nonisothermal crystallization curves for neat PP1and PP1/CB composites prepared via SSSP.b)Isothermal crystallization curves (140 C)for neat PP1and PP1/CB composites prepared via SSSP.K.A.Iyer et al./Polymer 75(2015)78e 8783。

拉曼光谱分析(二)

Semi-quantitati v e analysis of indigo by surface enhanced resonance Raman spectroscopy (SERRS)using sil v er colloidsI.T.Shadi,B.Z.Chowdhry,M.J.Snowden,R.Withnall *Vibrational Spectroscopy Centre,School of Chemical and Life Sciences,Uni v ersity of Greenwich,Pembroke,Chatham Maritime CampusChatham,Kent ME44TB,UKRecei v ed 13June 2002;accepted 2September 2002AbstractIn this paper we report for the first time semi-quantitati v e analysis of indigo using surface enhanced Raman spectroscopy (SERS)and surface enhance resonance Raman spectroscopy (SERRS).Indigo,a dye widely used today in the textile industry,has been used,historically,both as a dye and as a pigment;the latter in both paintings and in printed material.The molecule is uncharged and largely insoluble in most sol v ents.The application of SERS/SERRS to the semi-quantitati v e analysis of indigo has been examined using aggregated citrate-reduced sil v er colloids with appropriate modifications to experimental protocols to both obtain and maximise SERRS signal intensities.Good linear correlations are obser v ed for the dependence of the intensities of the SERRS band at 1151cm (1using laser exciting wa v elengths of 514.5nm (R 00.9985)and 632.8nm (R 00.9963)on the indigo concentration o v er the range 10(7Á10(5and 10(8Á10(5mol dm (3,respecti v ely.Band intensities were normalised against an internal standard (sil v er sol band at 243cm (1).Resonance Raman spectra (RRS)of aqueous solutions of indigo could not be collected because of its low solubility and the presence of strong fluorescence.It was,howe v er,possible to obtain RS and RRS spectra of the solid at each laser excitation wa v elength.The limits of detection (L.O.D.)of indigo by SERS and SERRS using 514.5and 632.8nm were 9ppm at both exciting wa v elengths.Signal enhancement by SERS and SERRS was highly pH dependent due to the formation of singly protonated and possibly doubly protonated forms of the molecule at acidic pH.The SERS and SERRS data pro v ide e v idence to suggest that an excess of monolayer co v erage of the dye at the surface of sil v er colloids is obser v ed at concentrations greater than 7.85)10(6mol dm (3for each exciting wa v elength.The data reported herein also strongly suggest the presence of multiple species of the indigo molecule.#2003Else v ier B.V.All rights reserved.Keywords:Indigo;Colloids;Sil v er sol;Surface enhanced resonance Raman spectroscopy (SERRS);Resonance Raman spectroscopy (RRS);Semi-quantitati v e analysis;Internal standard1.IntroductionIndigo,a dye widely used today in the textile industry [1],is also of archaeological and historical importance [2]ha v ing been used as a dye and a pigment,the latter in both paintings and printed*Corresponding author.Tel.:'44-208-331-8691;fax:'44-208-331-9983.E-mail address:r.withnall@ (R.Withnall).Spectrochimica Acta Part A 59(2003)2213Á2220www.else v /locate/saa1386-1425/03/$-see front matter #2003Else v ier B.V.All rights reserved.doi:10.1016/S1386-1425(03)00065-9material.A v ailable e v idence suggests the use of the dye pre-dates the Christian era by at least4000 years[3,4].The molecule is uncharged and rela-ti v ely insoluble in most sol v ents.To our knowl-edge a surface enhanced Raman spectroscopy (SERS)/surface enhanced resonance Raman spec-troscopy(SERRS)in v estigation of this molecule using sil v er colloids has not been reported in the literature.Howe v er,analytical in v estigations of this molecule ha v e largely been carried out using HPLC,resonance Raman scattering(RRS)[2]and FT Raman[5],the last two techniques ha v ing been applied to solid material.In this study SERS and SERRS of indigo ha v e been obtained by adding methanolic solutions to aqueous sil v er sols.Spec-tra were obtained through modification of a pre v iously used experimental protocol and the SERS/SERRS signal output optimised.SERRS signal enhancement arises from a com-bination of signal intensification,v ia RRS and surface enhanced Raman scattering mechanisms, which can increase the efficiency of the Raman scattering process by10-fold[10]or greater[6]. For maximum sensiti v ity,SERRS requires con-trolled aggregation of the colloidal sol used[7]. Surface enhancement of the Raman signals is dependent on the size of the colloidal particles as well as the exciting wa v elength employed.This is because the surface plasmon absorption bands of metals such as sil v er and gold show wa v elength dependent shifts with metal particle size,and surface enhancement is achie v ed by choosing the Raman exciting wa v elength to coincide with the plasmon band[8].Spectra were subsequently collected using a LabRam spectrometer,equipped with argon ion and heliumÁneon lasers which pro v ided exciting radiation of wa v elengths equal to514.5and632.8 nm,respecti v ely.The exciting wa v elength of632.8 nm lies within the electronic absorption band of solutions of indigo in methanol which peaks at611 nm,con v ersely the exciting wa v elength of514.5 nm lies in the short wa v elength wing.SERRS has been shown to ha v e significant potential for the quantitati v e determination of analytes,e.g.SERRS studies,using citrate reduced and borohydride reduced sil v er sols,in an in v es-tigation of alcian blue8GX,re v ealed different properties for each sol.Furthermore,it was demonstrated that it was possible to combine the linear regions obser v ed in SERRS with that of RRS(upon normalisation against an internal standard)extending the quantifiable linear con-centration range[9].SERRS has also been applied to a study of the detection and identification of specific sequences of labelled DNA suggesting a potential approach towards detecting specific sequences of DNA,which could ultimately replace the need to amplify DNA using polymerase chain reaction(PCR)procedures[10].Vibrational spec-tra of LH2complex isolated from two photosyn-thetic bacteria were obtained using SERRS[11]. Metallation kinetics of a free base porphyrin, where the SERRS sil v er colloid system has been employed as a probe,has been reported for the in v estigation of porphyrinÁnucleic acids interac-tion[12].The SERRS technique has also been applied successfully to measure Raman spectra from an oxygenic photosynthetic pigmentÁprotein complex by excitation within the Q(y)transition [13].and SERRS spectra of porphyrin and metal-loporphyrin species in systems ha v e been obtained using sil v er nanoparticles modified by anionic organosulfur spacers[14].These examples illus-trate some of the di v erse applications of the SERRS technique.The in v estigation reported herein was under-taken with the specific aim of de v eloping appro-priate experimental protocols for optimization of signal intensities,with subsequent determination and comparison of the extent of the linearity of the signal dependence on concentration and the limits of detection(L.O.D.)for the semi-quantitati v e analysis of indigo by SERS and SERRS.2.Experimental2.1.ReagentsIndigo(Aldrich),poly(L-lysine)hydrobromide M r4000Á15000(Sigma),sil v er nitrate(BDH), methanol(Fisher),tri-sodium citrate(Fisher), ascorbic acid(Fisher),sodium hydroxide(Fisher) and hydrochloric acid(Fisher)were of analytical grade.The dye was used without further purifica-I.T.Shadi et al./Spectrochimica Acta Part A59(2003)2213Á2220 2214tion.Double de-ionised water was used for all experiments.2.2.InstrumentationSERS/SERRS and RS spectra were obtained using a Labram Raman spectrometer(Instruments S.A.,Ltd.)equipped with an1800g mm(1 holographic grating,a holographic super-notch filter(Kaiser),an Olympus BX40microscope,and a Peltier-cooled CCD(MPP1chip)detector.A heliumÁneon laser and an argon ion laser pro v ided 632.8and514.5nm exciting radiation,respecti v ely which was attenuated by a10%neutral density filter,resulting in a laser power of0.8mW at the static sol.All SERS/SERRS and RRS spectra were collected by using a1808back-scattering geome-try.An Olympus microscope objecti v e,ha v ing a magnification of)10and a numerical aperture of 0.25,was used both to focus the incident laser light and to collect the back-scattered Raman light.2.3.Colloid preparationA sil v er colloid was prepared according to a modified LeeÁMeisel procedure[7,15].All glass-ware was acid washed with aqua regia[HNO3ÁHCl(1:3,v/v)]followed by gentle scrubbing with a soap solution.Sil v er nitrate(90mg)was suspended in500ml of de-ionised water at458C and rapidly heated to boiling before a1%solution of tri-sodium citrate(10ml)was added under v igorous stirring.The solution was held at boiling for90min with continuous stirring upon cooling; the v olume was made up to500ml with de-ionised water.The quality of the resulting colloid was checked by determining the wa v elength of the absorption maximum in the v isible region on a PerkinÁElmer Lambda-2UVÁVis spectrometer. Good quality sil v er colloids for SERS apparently ha v e an absorption maximum at approximately 404nm and full width half height(FWHH)ofB 60nm[6].The nature of the LeeÁMeisel colloid [15,16],often used for SERS,has been examined using v isible absorption,photon correlation and NMR spectroscopic techniques which confirm that the surface of the sil v er particles are co v ered with a layer of citrate with pendent negati v ely charged groups.Howe v er,the subsequent addition of poly(L-lysine)again coats the surface resulting in pendent positi v ely charged groups on the colloidal surface[17].2.4.Indigo solutionsFor SERS/SERRS in v estigation solutions,ha v-ing a final indigo concentration in the range of 10(8Á10(5mol dm(3were prepared in methanol. For RRS in v estigation,a10(5mol dm(3dye concentration(maximum solubility)was used. Samples were always made up fresh,immediately before analysis was carried out.The suppliers of the indigo(structure shown in Fig.1)confirm it has a purity of95%.2.5.RS of solidFor RRS in v estigation of the solid the dye was used,directly from the suppliers bottle without further purification.2.6.Sample preparationAggregation of the sil v er colloid particles was induced by poly(L-lysine).One hundred and fifty microlitres of a0.01%aqueous solution of poly(L-lysine)was added to1ml of sil v er colloid which had been diluted with1ml of de-ionised water, followed by150m l of the methanolic indigo solution and35m l of a1mol dm(3aqueous solution of ascorbic acid.In subsequent experi-ments poly(L-lysine)was not used.Instead aggre-gation of the sol was induced with35m l of1mol dm(3HCl before adding150m l of the methanolic indigosolution.Fig.1.Schematic structure of indigo.I.T.Shadi et al./Spectrochimica Acta Part A59(2003)2213Á222022152.7.ReproducibilitySERRS spectra were collected approximately5 min after mixing the indigo solution with the sil v er sol.2.8.Concentration dependence of indigo (normalization)The concentration dependence of indigo was determined by plotting the log intensity of the 514.5and632.8nm excited SERRS bands at582, 986and1151cm(1of indigo v s log indigo concentration.The same bands were normalized against the internal standard(sil v er sol band at 243cm(1).The intensities of the Raman bands were measured as the peak area after baseline correction.2.9.SERRS pH dependenceA pH profile of a10(5mol dm(3indigo dye concentration was obtained o v er the pH range of 0.5Á6.5using an exciting wa v elength of514.5nm.2.10.Packing effects at colloidal surface Packing effects at the colloidal surface were determined by plotting wa v enumber shifts for the band at1717cm(1v s log dye concentration.3.Results and discussion3.1.SERRSThe theory of SERS enhancement of analytes is well known[8,10,16].In the current study it was found that aggregation of the colloidal particles, using poly(L-lysine),pre v ented collection of SERS/ SERRS spectra.In a subsequent series of experi-ments a modified protocol was applied in which poly(L-lysine)was not used.It was also apparent that adsorption of indigo molecules to sil v er colloids was highly pH dependent.We were able to further optimise signals in a subsequent set of experiments by substituting ascorbic acid with1 mol dm(3HCl.Aggregation of the sol was induced by addition of35m l of1mol dm(3HCl to the diluted sol to which150m l of the aqueous dye was added.SERS/SERRS pH profiles were obtained for each exciting wa v elength and opti-mum signal intensification for this molecule was found to be at approximately pH1.75.SERS spectra of the aqueous dye solutions using 514.5nm excitation(Fig.2a)show strong SERS bands at242,582,986,1151,1366,1624and1717 cm(1.For SERRS in v estigations using632.8nm Fig.2.(a)Representati v e514.5nm excited SERS spectra of indigo in the signal v s concentration range examined.Concen-trations of the dye,from top to bottom are:7.85)10(5, 3.95)10(5, 1.98)10(5,7.85)10(6, 3.95)10(6, 1.98) 10(6,7.85)10(7and3.95)10(7mol dm(3.SERS v ibra-tional bands used for analysis are indicated by solid arrows, dashed arrow represents the sil v er sol band used as internal standard.(b)Log concentration dye v s log signal intensity (peak area)o v er the concentration range examined for the bands at582j(I),986m(II)and1151cm(1'(III).(c) Bands at582j(I)and986m(II)and1151cm(1'(III) normalised against the sil v er sol band at242cm(1.I.T.Shadi et al./Spectrochimica Acta Part A59(2003)2213Á2220 2216excitation (Fig.3a)strong bands were obser v ed at 243,583,806,988,1151,1238,1323,1464,1626and 1717cm (1.It is worth noting that the same bands were obser v ed for each exciting wa v elength with two exceptions,the profile of both the spectra and the relati v e intensities of bands for each exciting wa v elength differed significantly (Fig.2a and Fig.3a).3.2.Linear regionsFor each exciting wa v elength fluorescence was completely quenched with good linear correlations [(R 00.9985and 0.9963)]pro v iding L.O.D.s of 9ppm using the band at 1151cm (1for the dye concentrations of 3.95)10(7and 1.98)10(7mol dm (3using 514.5and 632.8nm exciting wa v elengths,respecti v ely.A linear concentration range of 3orders of magnitude was obtained for each exciting wa v elength (Fig.2b and Fig.3c).This v alue reflects the plots that pro v ided the best linear correlations.It was obser v ed that there was no marked impro v ement in linear correlations for 514.5nm excited bands,upon normalisation using the 243cm (1sil v er sol band as internal standard.The re v erse is true for 632.8nm excited bands,where a significant impro v ement to linear correla-tions was obser v ed for all bands examined upon normalisation (see Table 1).This appears to be due to the resonance effect obser v ed in 632.8nm excited SERRS spectra.3.3.General proﬁleIn pre v ious studies [9]of dyes it has been obser v ed that the highest concentration of dye gi v es a comparati v ely low Raman intensity signal (due to the surface of the colloidal sil v er particles being in excess of a full monolayer co v erage).When compared to subsequent samples of lower concentration,where Raman intensities increase and peak,thereafter signal intensities decrease as a function of concentration down to the L.O.D.;this region shows a linear dependence of the SERS/SERRS signal with concentration.Indigo does not follow this profile most probably due to its low solubility.Spectra appear to be obtained as a direct consequence of protonation of the dye and subsequent adsorption directly to the colloidal sil v er surface resulting in what appears to be monolayer co v erage.The phenomenon of self-absorption of scattered radiation is not obser v ed for the dye concentrations used in this study,instead,it appears spectra for the highest concen-tration of indigo examined (maximum solubility)are obtained in what would be considered the upper linear region of a SERRSconcentrationFig.3.(a)Representati v e 632.8nm excited SERRS spectra of indigo in the signal v s concentration range examined.Concen-trations of dye from top to bottom are:7.85)10(5,3.95)10(5, 1.98)10(5,7.85)10(6, 3.95)10(6, 1.98)10(6,7.85)10(7,3.95)10(7and 1.98)10(7mol dm (3.SERRS v ibrational bands used for analysis are indicated by solid arrows,dashed arrow represents the sil v er sol band used as internal standard.(b)Log concentration of dye v s log signal intensity (peak area)o v er the concentration range examined for the bands at 583j (I)and 986m (II)and 1151cm (1'(III).(c)Bands at 583j (I),986m (II)and 1151cm (1'(III)normalised against the sil v er sol band at 242cm (1.I.T.Shadi et al./Spectrochimica Acta Part A 59(2003)2213Á22202217study (profile)as obser v ed with other dyes.For 514.5and 632.8nm exciting wa v elengths max-imum signals were obser v ed for a dye concentra-tion of 7.85)10(5mol dm (3(Fig.2b and Fig.3b),thereafter,band intensities decreased as a function of concentration,and linearity for the signal dependence on dye concentration is ob-ser v ed down to 3.95)10(7and 1.98)10(7mol dm (3for each exciting wa v elength,respecti v ely.3.4.Packing effectsThe data (Fig.2b and c,Fig.3b and c)appear to suggest a monolayer co v erage of the dye on the colloidal surfaces.Howe v er,closer examination of the wa v enumber shifts for the v ibrational band at 1717cm (1(due to C ÄO)as a function of log dye concentration seems to suggest that an excess of monolayer co v erage is in fact obser v ed in the concentration range 10(6Á10(5mol dm (3(Fig.4c)for each exciting wa v elength.3.5.Solution RRSThe low solubility of the dye,in methanol,together with strong fluorescence did not re v eal dye bands (only methanol bands were obser v ed)using 514.5(Fig.4a (II))and 632.8nm (not shown)excitation.3.6.RRS of solidGood spectra were obtained for each exciting wa v elength.The spectrum obtained using 514.5nm excitation is shown in Fig.4a (I).3.7.SERRS pH dependencepH profiles were obtained,using a dye concen-tration of 10(4mol dm (3,for each exciting wa v elength re v ealing an optimum pH at approxi-mately 1.75(the pH profile obtained using 514.5nm excitation is shown in Fig.4b).3.8.Identiﬁcation of multiple species of the dye Spectra collected across the pH range examined (0.5Á6.5)strongly suggest the presence of twoT a b l e 1P a r a m e t e r s o b t a i n e d f r o m m u l t i l i n e a r r e g r e s s i o n f o r a n a l y s i s o f i n d i g oT e c h n i q u e (n m )B a n d (c m (1)S l o p e I n t e r c e p tC o r r e l a t i o n c o e f f i c i e n tC o n c e n t r a t i o n r a n g e (m o l d m (3)R .S .D .(9)L .O .D a (p p m )O r d e r s o f M a g n i t u d e bS E R S 514.55820.475.370.991810(7Á10(50.053193S E R S 514.5c5820.600.210.990510(7Á10(50.073833S E R S 514.59861.278.570.980010(6Á10(50.1808112S E R S 514.5c9861.483.780.984010(6Á10(50.1760152S E R S 514.511510.535.760.998510(7Á10(50.025693S E R S 514.5c11510.660.580.993210(7Á10(50.067663S E R R S 632.85830.888.820.992010(7Á10(50.1108103S E R R S 632.8c5830.863.200.9956710(7Á10(50.077673S E R R S 632.89860.979.030.973010(6Á10(50.1560172S E R R S 632.8c9860.923.330.982410(6Á10(50.1196102S E R R S 632.811510.446.540.980610(7Á10(50.0844133S E R R S 632.8c 11510.430.970.996310(7Á10(50.035793aT h r e e t i m e s s t a n d a r d d e v i a t i o n o f i n t e r c e p t /s l o p e .bF o r l i n e a r r e g i o n s .cN o r m a l i s e d a g a i n s t t h e v i b r a t i o n a l b a n d a t 243c m (1.I.T.Shadi et al./Spectrochimica Acta Part A 59(2003)2213Á22202218forms of the same dye.It was apparent that the ratios of se v eral bands differed significantly,as a function of pH.This was further substantiated on closer examination of the dye bands in spectra from the SERS/SERRS concentration study where it was clear that the intensities of se v eral bands decreased at a faster rate than other bands.Further e v idence for this can be seen when the slopes using 514.5and 632.8nm exciting wa v e-lengths are compared for the v ibrational bands at 582and 984cm (1(see Table 1and Fig.2c and Fig.3c).4.ConclusionIn this study it has been shown that SERS/SERRS o v ercomes the difficulties associated with obtaining RRS spectra of aqueous solutions of indigo for semi-quantitati v e analysis.Both 514.5and 632.8nm exciting wa v elengths re v ealed simi-lar quantifiable linear concentration ranges of 3orders of magnitude in the concentration range 10(8Á10(5mol dm (3.In this study it was possible to normalise dye bands against an internal standard,resulting in significant enhancement of RSD fits for 632.8nm excited SERRS spectra but made little difference to 514.5nm excited SERS spectra.The molecule was shown to be highly pH sensiti v e,the data re v ealing the presence of pro-tonated forms of the molecule.AcknowledgementsR.W.and B.Z.C.wish to acknowledge the EPSRC (ref.GR/L85176)and Instruments S.A.,Ltd.for jointly funding the purchase of the Labram Raman Spectrometer.References[1]H.A.Lubs,The chemistry of synthetic dyes and pigments,A.C.S.Monograph Series,Malabar (1955).[2]R.Withnall,A.Derbyshire,S.Thiel,M.J.Hughes,Proc.SPIE 4098(2000)217.[3]M.R.Fox,J.H.Pierce,Textile Chemist Colorist 22(1990)13.[4]A.S.Tra v is,Textile Chemist Colorist 22(1990)18.[5]E.Tatsch,B.Schrader,J.Raman Spectrosc.26(1995)467Á473.[6]C.Rodger,V.Rutherford,P.C.White,W.E.Smith,J.Raman Spectrosc.29(1998)601.[7]C.Rodger,W.E.Smith,G.Dent,M.Edmondson,J.Chem.Soc.,Dalton Trans.5(1996)791.[8]J.A.Creighton,C.G.Blatchford,M.G.Albrecht,J.Chem.Soc.,Faraday Trans.75(2)(1979)790Á798.[9]I.T.Shadi,B.Z.Chowdhry,M.J.Snowden,R.Withnall,Appl.Spectrosc.54(2000)384Á389.[10]D.Graham,B.J.Mallinder,W.E.Smith,Biopolymers 57(2000)85Á91.[11]G.Chumano v ,R.Picorel,I.O.deZarate,T.M.Cotton,M.Seibert,Photochem.Photobiol.71(2000)589Á595.[12]M.Prochazka,P.Y.Turpin,J.Stepanek,J.Bok,J.Molec.Struct.483(1999)221Á224.Fig.4.(a)Raman scattering (RS)spectra for solid indigo (I)and a 2)10(4mol dm (3methanolic solution (II)of indigo using 514.5nm excitation.(b)514.5nm excited SERS pH proﬁle in the pH range 0Á7,for the v ibrational band at 582cm (1,of indigo at a dye concentration 7.85)10(5mol dm (3.(c)Plot of wa v enumber shift for the C ÄO band around 1717cm (1across the concentration range examined for 514.5and 632.8nm exciting wa v elengths.I.T.Shadi et al./Spectrochimica Acta Part A 59(2003)2213Á22202219[13]R.Picorel,G.Chumano v,E.Torrado,T.M.Cotton,M.Selbert,J.Phys.Chem.102(1998)2609Á2613.[14]B.Vicko v a,P.Smejkal,P.Michl,M.Prochazka,P.Mojzes,F.Lednicky,J.Pﬂeger,J.Inorg.Biochem.79 (2000)295Á300.[15]P.C.Lee,D.Meisel,J.Phys.Chem.86(1982)3391.[16]C.H.Munro,W.E.Smith,M.Garner,J.Clarkson,P.C.White,Langmuir11(1995)3712Á3720.[17]C.H.Munro,W.E.Smith,D.R.Armstrong,P.C.White,J.Phys.Chem.99(1995)879.I.T.Shadi et al./Spectrochimica Acta Part A59(2003)2213Á2220 2220。

微纳金属结构光吸收增强英文

微纳金属结构光吸收增强英文Enhanced Light Absorption in Micro-Nano Metal Structures.The field of photonics has witnessed remarkable advancements in recent years, with a particular focus on enhancing light absorption in micro-nano metal structures. This enhancement is crucial for various applications ranging from solar cells, photodetection, and sensing to plasmonic devices. The unique optical properties of metals at the nanoscale offer opportunities for manipulatinglight-matter interactions, leading to improved performance in these areas.1. Plasmonic Resonance in Metal Nanostructures.The key to understanding light absorption enhancement in micro-nano metal structures lies in the concept of plasmonic resonance. Plasmons are collective oscillations of electrons in a metal that can be excited by incidentlight. When the frequency of incident light matches the natural frequency of these oscillations, a resonance condition is achieved, leading to a significant enhancement of the electromagnetic field around the metal structure. This enhanced field in turn increases the light absorption by the metal.2. Nanostructuring for Enhanced Absorption.Nanostructuring metals offers a powerful means to control plasmonic resonances and thereby enhance light absorption. By reducing the dimensions of metal structures to the nanoscale, it becomes possible to tune the plasmonic resonances to match the desired wavelength of light. This tuning can be achieved by varying the size, shape, and composition of the nanostructures.3. Materials Considerations.The choice of metal material is also crucial for light absorption enhancement. Noble metals such as gold andsilver are commonly used due to their strong plasmonicresponse. However, these metals often suffer from high ohmic losses that limit their performance. Alternatively, alternative metals with lower losses, such as aluminum and magnesium, have been explored. Furthermore, the use of alloys and composite materials can further optimize the plasmonic response and absorption properties.4. Applications of Enhanced Light Absorption.Enhanced light absorption in micro-nano metal structures finds applications in diverse fields. In solar cells, for example, plasmonic nanostructures can increase the absorption of sunlight, leading to improved conversion efficiencies. Similarly, in photodetection and sensing applications, the enhanced absorption can enhance the sensitivity and response speed. In plasmonic devices, the strong localization of light at the nanoscale offers opportunities for nanoscale imaging, spectroscopy, and manipulation of light.5. Challenges and Future Directions.Despite the significant progress made in enhancinglight absorption in micro-nano metal structures, several challenges remain. One of the primary challenges is the limited stability of plasmonic nanostructures, especially under harsh environmental conditions. Additionally, the integration of these structures into practical devices requires further research and development. Futuredirections include exploring new materials and design strategies to overcome these challenges and further improve light absorption enhancement.In conclusion, enhanced light absorption in micro-nano metal structures holds promise for revolutionizing various photonic applications. By harnessing the unique optical properties of metals at the nanoscale, it is possible to manipulate light-matter interactions and achieve remarkable improvements in light absorption. While challenges remain, ongoing research and development in this field are expected to lead to transformative advancements in the near future.。

Effect of valence electron concentration on stability of fcc or bcc phase in high entropy alloys

See discussions, stats, and author profiles for this publication at: /publication/229595062 Effect of valence electron concentration on stability of fcc or bcc phase in high entropy alloysARTICLE in JOURNAL OF APPLIED PHYSICS · MAY 2011Impact Factor: 2.19 · DOI: 10.1063/1.3587228CITATIONS 80DOWNLOADS143VIEWS4104 AUTHORS, INCLUDING:Sheng GuoChalmers University of Technology29 PUBLICATIONS 329 CITATIONSSEE PROFILEAvailable from: Sheng GuoRetrieved on: 16 September 2015Effect of valence electron concentration on stability of fcc or bcc phase in high entropy alloysSheng Guo,1Chun Ng,1Jian Lu,2and C.T.Liu1,a)1Department of Mechanical Engineering,The Hong Kong Polytechnic University,Hung Hom,Kowloon,Hong Kong,People’s Republic of China2College of Science and Engineering,City University of Hong Kong,Kowloon,Hong Kong(Received8March2011;accepted3April2011;published online16May2011)Phase stability is an important topic for high entropy alloys(HEAs),but the understanding to it isvery limited.The capability to predict phase stability from fundamental properties of constituentelements would beneﬁt the alloy design greatly.The relationship between phase stability andphysicochemical/thermodynamic properties of alloying components in HEAs was studiedsystematically.The mixing enthalpy is found to be the key factor controlling the formation of solidsolutions or compounds.The stability of fcc and bcc solid solutions is well delineated by thevalance electron concentration(VEC).The revealing of the effect of the VEC on the phase stabilityis vitally important for alloy design and for controlling the mechanical behavior of HEAs.V C2011American Institute of Physics.[doi:10.1063/1.3587228]I.INTRODUCTIONHigh entropy alloys(HEAs)constitute a new type of metallic alloys for structural and particularly high-tempera-ture applications,due to their high hardness,wear resistance, high-temperature softening resistance and oxidation resist-ance.1–3HEAs are typically composed of more thanﬁve me-tallic elements in equal or near-equal atomic ratios,and interestingly they tend to form solid solution structure (mainly fcc and/or bcc)rather than multiple intermetallic compounds as expected from general physical metallurgy principles.They were termed as HEAs because the entropy of mixing is high when the alloying elements are in equia-tomic ratio,and it was initially believed that the high entropy of mixing leads to the formation of the solid solution struc-ture rather than intermetallic compounds.The generally used alloying elements in HEAs are fcc-type Cu,Al,Ni,bcc-type Fe,Cr,Mo,V and hcp-type Ti,Co (crystal structure at ambient temperature).When these alloy-ing elements are mixed with different combination,or with same combination but different amount of certain elements, fcc,bcc or mixed fcc and bcc structures may form.For example,cast CoCrCuFeNi(in atomic ratio,same after-wards)has the fcc structure while AlCoCrCuFeNi has the fccþbcc structure;4and the amount of Al in the Al x CoCrCu-FeNi system can tune the crystal structure from fcc to fccþbcc and to fully bcc4.The structure directly affects the mechanical properties,and to take again the Al x CoCrCuFeNi system as an example:with increasing x,the structure changes from fcc to fccþbcc andﬁnally to bcc;the hardness and strength increase with the increasing amount of bcc phases but the alloys get brittle.4,5Although the embrittle-ment mechanism by bcc phases still needs further explora-tion,it is certainly important to be able to control the formation of bcc phases.The target of this work is hence to ﬁnd out the physical parameters that control the stability for the fcc and bcc phases in HEAs.II.ANALYSISWang et al.brieﬂy discussed the reason of addition of Al in the Al x CoCrCu1Àx FeNiTi0.5system causing the struc-tural transition from fcc to bcc.6They claimed that the alloy-ing of larger Al atoms introduces the lattice distortion energy,and the formation of a lower atomic-packing-efﬁ-ciency structure,such as bcc,can decrease this distortion energy.This does make sense but is far away from being sat-isfactory;besides,it can not quantitatively predict when the bcc structure will form as a function of Al additions.Ke et al.claimed that,in the Al x Co y Cr z Cu0.5Fe v Ni w system,Ni and Co are fcc stabilizers and Al and Cr are bcc stablizers;1.11Co is equivalent to Ni as the fcc stablizers and2.23Cr is equivalent to Al for the bcc stablizers.Furthermore,if the equivalent Co%is greater than45at.%,the alloy has an fcc structure,and the alloy has a bcc structure if the equivalent Cr%is greater than55at.%.7This empirical rule is useful but it has no scientiﬁc merits and is valid only for the speciﬁc alloy systems.The establishment of scientiﬁc principles to control the crystal structures in HEAs can also contribute to the alloy design of HEAs with desirable properties.For example,we can use less expensive Ni to partially or com-pletely replace more expensive Co;or we can reduce the amount of Cu which is known to cause segregation issue because the mainly positive enthalpy of mixing between Cu and other alloying elements.4As a test to the equivalency of Ni and Co as fcc stabil-izers,we prepared a series of Al x CrCuFeNi2(0.2x 1.2) alloys to study the effect of Al amount on the phase stability in this alloy system,in comparison to the well studied Al x CoCrCuFeNi system.The alloys were prepared by arc-melting a mixture of the constituent elements with purity better than99.9%in a Ti-gettered high-purity argon atmos-phere.Repeated melting was carried out at leastﬁve times toa)Author to whom correspondence should be addressed.Electronic mail:mmct8tc@.hk.0021-8979/2011/109(10)/103505/5/$30.00V C2011American Institute of Physics109,103505-1JOURNAL OF APPLIED PHYSICS109,103505(2011)improve the chemical homogeneity of the alloy.The molten alloy was drop-cast into a10mm diameter copper mold.The phase constitution of the alloy was examined by X-ray dif-fractometer using Co radiation(Bruker AXS D8Discover). The X-ray diffraction patterns are shown in Fig.1where it is clear that at x0.8,the alloys have a single fcc structure and the bcc phase starts to appear at x¼1.0.In the Al x CoCrCu-FeNi system,fully fcc structure is obtained at x0.5and bcc phase starts to appear at x>0.8.4The experimental results indicate that Co is not necessarily required in obtain-ing the solid solution structure in HEAs,which is good foralloy design from economy concerns.This new alloy systemalso provides more data to study the phase stability in HEAs,ideally from the consideration of the fundamental propertiesof constituent alloying elements.Zhang et al.studied the relationship between the phasestability and the atomic size difference,d(¼100ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃP Ni¼1c ið1Àr i=rÞ2q,r¼P ni¼1c i r i,where c i and r i areatomic percentage and atomic radius of the i th component),and also the mixing enthalpy,D H mix(¼P ni¼1;i¼jX ij c i c j,X ij¼4D AB mix,where D AB mix is the mixing enthalpy of binaryliquid AB alloys)for multi-component alloys.8They foundthat the solid solution tends to form in the region delineatedbyÀ15KJ/mol D H mix5KJ/mol and1d 6.Therequirement of atomic size difference for formation of thesolid solution structure is not surprising as basically it is inline with the well established Hume-Rothery rule.9Othertwo requirements from the Hume-Rothery rule to form thesolid solution are electronegativity and electron concentra-tion.Fang et al.deﬁned the electronegativity difference in amulti-component alloy system as D v(¼ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃP ni¼1c iðv iÀvÞ2q,v¼P ni¼1c i v i,where v i is the Pauling electronegativity forthe i th component).10The effect of electron concentration isa little bit more complex.There are basically two deﬁnitionsof the electron concentration:average number of itinerantelectrons per atom,e/a,and the number of total electronsincluding the d-electrons accommodated in the valenceband,valence electron concentration or VEC.11,12e/a orVEC for a multi-component alloy can be deﬁned as theweighted average from e/a or VEC of the constituent compo-nents:e/a¼P ni¼1c iðe=aÞi or VEC¼P ni¼1c iðVECÞi,where(e/a)i and(VEC)i are the e/a and VEC for the individual ele-ment.Hume-Rothery rule works with the e/a deﬁnition ande/a has clear effect on the crystal structure for the so-calledelectron compounds or Hume-Rothery compounds.9How-ever,the HEAs comprise mainly transition metals(TMs)ande/a for TMs are very controversial.11Very recently,Mizutanireviewed the various deﬁnitions of e/a for TMs and con-cluded that e/a for TMs are small positive numbers.11Unfortunately,not all e/a for TMs have been determined ande/a for a TM element even varies in different environment.For convenience,VEC was used here to study the electronconcentration effect on the phase stability in HEAs.III.RESULTSFollowing Zhang et al.’s method,8the atomic size dif-ference,d,and the mixing enthalpy,D H mix for the Al x CoCr-CuFeNi4and Al x CrCuFeNi2systems are plotted in Fig.2.The electronegativity difference,D v,and VEC are also plot-ted to show how these factors referred in the Hume-Rotheryrule affect the solid solution formation.D H mix,D v and VECare all plotted as a function of d in Fig.2for convenience,and this does not indicate these parameters are mutually de-pendent.For comparison,d,D H mix,D v and VEC for threeadditional systems of HEAs[CoCrCuFeNiTi x(see Ref.13),Al0.5CoCrCuFeNiTi x(see Ref.14),Al0.5CoCrCuFeNiV x(see Ref.15)],where compounds will form in the originallyfcc-typed alloy by increasingly doping the amount of onealloying element(Ti or V),are also plotted in Fig.2.The cal-culation required physicochemical and thermodynamicFIG.1.(Color online)X-ray diffraction patterns for Al x CrCuFeNi2alloys(x¼0.2$1.2).FIG.2.(Color online)Relationship between the mixing enthalpy,D H mix(a),the Electronegativity,D v(b)and the valence electron concentration,VEC,(c),and the atomic size difference,d,forﬁve HEA systems:Al x CoCrCu-FeNi,CoCrCuFeNiTi x,Al0.5CoCrCuFeNiTi x,Al0.5CoCrCuFeNiV x,andAl x CrCuFeNi2.Note on the legend:fully closed symbols for sole fcc phases;fully open symbols for sole bcc phase;top-half closed symbols for mixes fccand bcc phases;left or right-half closed symbols for phases containing atleast one compound phase(left or right half simply indicates different typesof compounds).parameters for the constituent alloying elements are from Refs.16–19and some of them are listed in Table I .As seen from Fig.2,using the deﬁnitions of atomic size difference,mixing enthalpy,valence electron concentration and electronegativity deﬁned here,D H mix is the only effec-tive parameter that can predict the formation of sole solid solutions (hence no formation of compounds)in HEAs.Solid solution form when À5KJ/mol D H mix 5KJ/mol,and compounds would form once D H mix is more negative.On the other hand,d ,D v and VEC all fail to effectively predict the formation of solid solution phases or compounds.Figure 2provides some clues to obtain the solely solid solution struc-ture in HEAs based simply on the fundamental properties of constituent elements.This is certainly useful but from Fig.2it is still unclear when the bcc phase will form and what is the determining factor controlling the bcc phase formation.A careful examination of Fig.2,however,suggests that bcc phases start to form when VEC reaches $8.0[Fig.2(c)].The other three parameters,D H mix ,d ,and D v do not behave such a clear indicator function.To make the point clearer,VEC for three HEA systems,Al x CoCrCuFeNi (see Ref.4),Al x CoCrCu 0.5FeNi (see Ref.7),and Al x CoCrCuFeNi 2(this work)in which increasingly doping of the same element Al would cause phase constitution from sole fcc to mixed fccand bcc,are plotted in Fig.3.Figure 3clearly shows that VEC can be used to quantitatively predict the phase stability for fcc and bcc phases in HEAs:at VEC !8.0,sole fcc phase exists;at 6.87 VEC <8.0,mixed fcc and bcc phases will co-exist and sole bcc phase exists at VEC <6.87.Note that at the boundary VEC ¼8.0,sometimes bcc phases also form but they are minor phases (see Fig.1and Ref.4).Although there is one exception for the Al x CoCrCu 0.5FeNi alloy where 6.87 VEC <8.0but the stable phase is sole bcc (not fcc þbcc),we suspect this VEC -deﬁned phase stability shall work effectively for most cases.To prove this,VEC for more HEA systems with fcc,fcc þbcc,or bcc structure containing other alloying elements like Ti,V,Mn,Nb,Mo,Ta,W even metalloid B and C,are plotted in Fig.4(data are from litera-tures in Ref.7and 20–24).Although there are still some exceptions,the fcc/bcc phase boundary can clearly be delineated by VEC .With a note to those exceptions,the VEC -deﬁned fcc/bcc phase boundary seems to work unsatis-factorily for Mn-containing HEA systems.TABLE I.Physiochemical properties for commonly used elements in HEAs.Element Atom radius (A˚)Pauling electronegativityVEC Al 1.4321.613B 0.8202.043C 0.773 2.554Co 1.251 1.889Cr 1.249 1.666Fe 1.241 1.838Mn 1.350 1.557Mo 1.363 2.166Nb 1.429 1.65Ni 1.246 1.9110Ta 1.430 1.505Ti 1.462 1.544V 1.316 1.635W1.3672.366FIG.3.(Color online)Relationship between VEC and the fcc,bcc phase sta-bility for three HEA systems:Al x CoCrCuFeNi,Al x CrCuFeNi 2and Al x CoCr-Cu 0.5FeNi.Note on the legend:fully closed symbols for sole fcc phases;fully open symbols for sole bcc phase;top-half closed symbols for mixes fcc and bccphases.FIG. 4.(Color online)Relationship between VEC and the fcc,bcc phase sta-bility for more HEA systems further to Fig.3.Note on the legend:fully closed symbols for sole fcc phases;fully open symbols for sole bcc phase;top-half closed symbols for mixes fcc and bcc phases.IV.DISCUSSIONThe effect of the VEC on the phase stability has been studied before by the current authors for the intermetallic compounds only.One example is on the(Fe,Co,Ni)3V inter-metallic alloys with long-range-ordered(LRO)structures.25 We found that these LRO alloys are characterized by speciﬁc sequences of stacked close-packed ordered layers and the stacking character can be altered systematically by control-ling the VEC of these alloys.With the decreasing VEC by partial substitution of Co and Ni by Fe,the LRO changes from purely hexagonal,to L12-type cubic ordered structure, through different ordered mixtures of hexagonal and cubic layers.As the hexagonal structure exhibits brittle fracture while the cubic ordered structures are ductile,the control of VEC can hence be used to tune the mechanical properties of LRO alloys.We also investigated the role of VEC in the phase stability of NbCr2-based transition-metal Laves phase alloys.26It was found that when the atomic size ratios were kept nearly identical,the VEC is the dominant factor in con-trolling the phase stability(C14,hexagonal or C15,cubic)in this type of high-temperature structural alloys.Our results in the present work prove that VEC also plays a decisive role in the stability of fcc and bcc solid solution phases in the multi-component HEAs.Mizutani has shown that VEC is crucial in determining the Fermi level whenﬁrst-principles band calcu-lations are carried out to study the band structure.11In the ﬁrst-principles band calculations,the integration of the den-sity of states(DOS)actually results in VEC,which includes not only s-and p-electrons but also d-electrons forming the valence band.11Mizutani emphasized that the parameter VEC,instead of e/a,should be used in realistic electronic structure calculations to take into account the d-electron con-tribution.11More theoretical work needs to be carried out to understand the physical basis for the mechanism behind the VEC rule on the phase stability,for example from the VEC-electronic structure-bind structure energy perspective.27 Two issues need to be emphasized here for the discussion of the VEC rule on the phase stability.First,the VEC ranges for different phases to be stable might overlap and these ranges also vary depending on the speciﬁc alloy systems.A very close example is in some ternary Mg alloys that possess typical Laves structures.9It was found that the electron con-centration(e/a though)ranges for MgCu2-type(cubic,with packing ABCABCABC),MgNi2-type(hexagonal,with pack-ing ABACABAC)and MgZn2-type(hexagonal,with packing ABABAB)structures differ in various alloy systems,and the e/a ranges for MgNi2-type structure and MgZn2-type struc-ture overlap for the Mg-Cu-Al system.This can probably explain the exceptions that appear in Figs.3and4.Second, the phases referred in this work are all identiﬁed in the as-cast state and they are hence very possibly in the metastable state. However,evidences have shown that these metastable phases have quite good thermal stability28–31and can hence be regarded as very close to the stable phases.This gives conﬁ-dence to the general applicability of the VEC rule,consider-ing it works so well for such an extended series of various alloy systems.More work is certainly needed to further verify this.Admitting these two issues mentioned above,one solid result out of our study is that,in HEAs the bcc phase is stable at lower VEC while the fcc phase is stable at higher VEC. This trend already sheds some light on the alloy design,and the fact that most HEA alloy systems satisfying the VEC (<6.87,bcc;!8,fcc)rule even simpliﬁes the process.As the VEC rule on the phase stability between the fcc and bcc phases is tested only for the HEAs in this work,its applicabil-ity to other alloy systems other than the nearly equiatomic HEAs(i.e.,in the traditional alloys where only one or two pri-mary elements dominate),awaits further analysis.In addition, it would be interesting to know whether this VEC rule can be used to predict the phase stability for other structured phases, like the hcp-typed phases.More work along these directions is under way.V.CONCLUSIONSIn summary,the phase stability in HEAs and its relation-ship to the physicochemical and thermodynamic properties of constituent alloying elements are systematically studied. The mixing enthalpy determines whether the solid solution phases or compounds form in the nearly equiatomic multi-component alloy systems.Most importantly the VEC is found to be the physical parameter to control the phase sta-bility for fcc or bcc solid solutions.Fcc phases are found to be stable at higher VEC(!8)and instead bcc phases are sta-ble at lower VEC(<6.87).This work provides valuable input for understanding of the phase stability and to design ductile crystal structures in HEAs. ACKNOWLEDGMENTSThis research was supported by the internal funding from HKPU.1B.Cantor,I.T.H.Chang,P.Knight,and A.J.B.Vincent,Mater.Sci. Eng.A375,213(2004).2W.H.Wu,C.C.Yang,and J.W.Yeh,Ann.Chim.Sci.Mater.31,737(2006). 3J.W.Yeh,Ann.Chim.Sci.Mater.31,633(2006).4C.J.Tong,Y.L.Chen,S.K.Chen,J.W.Yeh,T.T.Shun,C.H.Tsau, S.J.Lin,and S.Y.Chang,Metall.Mater.Trans.36A,881(2005).5C.W.Tsai,M.H.Tsai,J.W.Yeh,and C.C.Yang,J.Alloys Compd.490, 160(2010).6F.J.Wang,Y.Zhang,and G.L.Chen,J.Alloys Compd.478,321(2009). 7G.Y.Ke,S.K.Chen,T.Hsu,and J.W.Yeh,Ann.Chim.Sci.Mater.31, 669(2006).8Y.Zhang,Y.J.Zhou,J.P.Lin,G.L.Chen,and P.K.Liaw,Adv.Eng. Mater.10,534(2008).9R.W.Cahn and P.Hassen,Physical Metallurgy,4th ed.(North Holland, Amsterdam,1996),Vol.1.10S.S.Fang,X.Xiao,X.Lei,W.H.Li,and Y.D.Dong,J.Non-Cryst.Sol-ids321,120(2003).11U.Mizutani,Hume-Rothery Rules for Structurally Complex Alloy Phases (CRC Press,Boca Raton,2011).12T.B.Massalski,Mater.Trans51,583(2010).13X.F.Wang,Y.Zhang,Y.Qiao,and G.L.Chen,Intermetallics15,357 (2007).14M.R.Chen,S.J.Lin,J.W.Yeh,S.K.Chen,Y.S.Huang,and C.P.Tu, Mater.Trans.47,1395(2006).15M.R.Chen,S.J.Lin,J.W.Yeh,S.K.Chen,Y.S.Huang,and M.H. Chuang,Metall.Mater.Trans.37A,1363(2006).16A.Takeuchi and A.Inoue,Mater.Trans.41,1372(2000).17A.Takeuchi and A.Inoue,Mater.Trans.46,2817(2005).18O.N.Senkov and D.B.Miracle,Mater.Res.Bull.36,2183(2001).19WebElements:the periodic table on the web,available at:http://www. /.20C.C.Tung,J.W.Yeh,T.T.Shun,S.K.Chen,Y.S.Huang,and H.C. Chen,Mater.Lett.61,1(2007).21H.Y.Chen,C.W.Tsai,C.C.Tung,J.W.Yeh,T.T.Shun,C.C.Yang, and S.K.Chen,Ann.Chim.Sci.Mater.31,685(2006).22O.N.Senkov,G.B.Wilks,D.B.Miracle,C.P.Chuang,and P.K.Liaw, Intermetallics18,1758(2010).23C.Li,J.C.Li,M.Zhao,L.Zhang,and Q.Jiang,Mater.Sci.Technol.24, 376(2008).24Y.F.Li,L.J.Kong,Z.H.Gan,and Z.X.Yuan,J.Wuhan,Univ.Sci. Technol.32,60(2009).25C.T.Liu,Inter.Met.Rev.29,168(1984).26J.H.Zhu,P.K.Liaw,and C.T.Liu,Mater.Sci.Eng.A239–240,260 (1997).27D.Nguyen-Manh and D.G.Pettifor,Intermetallics7,1095(1999).28L.H.Wen,H.C.Kou,J.S.Li,H.Chang,X.Y.Xue and L.Zhou,Interme-tallics17,266(2009).29C.M.Lin,H.L.Tsai,and H.Y.Bor,Intermetallics18,1244(2010).30C.M.Lin and H.L.Tsai,pd.489,30(2010).31O.N.Senkov,G.B.Wilks,J.M.Scott,and D.B.Miracle,Intermetallics 19,698(2011).。

Enhancement of CO2 Adsorption and CO2_N2 Selectivity on ZIF-8 via Postsynthetic Modi

Enhancement of CO2Adsorption and CO2/N2Selectivity on ZIF-8via Postsynthetic ModiﬁcationZhijuan ZhangSchool of Chemistry and Chemical Engineering,South China University of Technology,Guangzhou,510640,P.R.ChinaDept.of Chemistry and Chemical Biology,Rutgers University,Piscataway,New Jersey,08854Shikai Xian,Qibin Xia,Haihui Wang,and Zhong LiSchool of Chemistry and Chemical Engineering,South China University of Technology,Guangzhou,510640,P.R.ChinaJing LiDept.of Chemistry and Chemical Biology,Rutgers University,Piscataway,New Jersey,08854DOI10.1002/aic.13970Published online January11,2013in Wiley Online Library()Imidazolate framework ZIF-8is modiﬁed via postsynthetic method using etheylenediamine to improve its adsorption per-formance toward CO2.Results show that the BET surface area of the modiﬁed ZIF-8(ED-ZIF-8)increases by39%,and its adsorption capacity of CO2per surface area is almost two times of that on ZIF-8at298K and25bar.H2O uptake on the ED-ZIF-8become obviously lower compared to the ZIF-8.The ED-ZIF-8selectivity for CO2/N2adsorption gets signiﬁcantly improved,and is up to23and13.9separately at0.1and0.5bar,being almost twice of those of the ZIF-8. The isosteric heat of CO2adsorption(Q st)on the ED-ZIF-8becomes higher,while Q st of N2gets slightly lower com-pared to those on the ZIF-8Furthermore,it suggests that the postsynthetic modiﬁcation of the ZIF-8not only improves its adsorption capacity of CO2greatly,but also enhances its adsorption selectivity for CO2/N2/H2O signiﬁcantly. V C2013American Institute of Chemical Engineers AIChE J,59:2195–2206,2013Keywords:ZIF-8,modiﬁcation,adsorption/gas,isosteric heat of adsorption,selectivityIntroductionCO2has often been cited as the primary anthropogenicgreenhouse gas(GHG)as well as the leading culprit inglobal climate change.The development of a viable carboncapture and sequestration technology(CCS),is therefore,ascientiﬁc challenge of the highest order.1–4Currently,a vari-ety of methods,such as membrane separation,chemicalabsorption with solvents,and adsorption with solid adsorb-ents,have been proposed to sequester CO2from theﬂuegases of power plant.Thereinto,the adsorption is consideredto be one of the most promising technologies for capturingCO2fromﬂue gases because of their easy control,low oper-ating and capital costs,and superior energy efﬁciency.5–7Many adsorbents have been investigated for CO2adsorptionincluding activated carbons,zeolites,hydrotalcites and metaloxides.8–14However,although some zeolite materials havebeen claimed to be most adequate for CO2separation fromﬂue streams,it is difﬁcult to regenerate them without signiﬁ-cant heating which leads to low productivity and greatexpense.15,16Recently,metal-organic frameworks(MOFs)haveattracted great attention and present a promising platform forthe development of next-generation capture materialsbecause of their high capacity for gas adsorption and tunablepore surfaces that can facilitate highly selective binding ofCO2.17–26To optimize a MOF for a particular application,itis important to be able to tailor its pore metrics and function-ality in a straightforward fashion.However,tailoring MOFsmaterials by modifying their textural properties(e.g.,surfacearea and pore volume)and surface chemistry(acid–baseproperties,functional groups)for adsorption application isstill a difﬁcult task.27Many researchers have given insightinto modiﬁcation of the MOF materials so as to develop newand better adsorbents.Strategies reported include ligandfunctionalization,24,28–39framework interpenetration,22,23introduction of alkali-metal cations,40–42control of poresize32,43–47and incorporation of open metal sites(OMSs).39,48–51However,because of the instability underconditions for the synthesis of MOFs or the competitivereaction with some framework components,it may be difﬁ-cult for certain functional groups to incorporate into MOFsusing aforementioned strategies.Another strategy for gener-ating desired functionalities in MOFs is the postsynthesis Additional Supporting Information may be found in the online version of thisarticle.Correspondence concerning this article should be addressed to Z.Li atcezhli@.V C2013American Institute of Chemical EngineersAIChE Journal2195June2013Vol.59,No.6modiﬁcation of preconstructed,robust precursor MOFs.52–55 For example,An et al.33demonstrated that postsynthetic exchange of extra-framework cations within anionic bio-MOF-156can be used as a means to systematically modify its pore dimensions and metrics.Farha et al.57synthesized a series of cavity modiﬁed MOFs by replacing coordinated sol-vents with several different pyridine ligands.They found that a p-(CF3)NC5H4-modiﬁed MOF showed considerable improvements in the CO2/N2selectivities compared to the parent framework.46Long and his coworkers58previously reported the grafting of ethylenediamine(en)within a water-stable MOF H3[(Cu4Cl)3(BTTri)8](CuBTTri),and found that the en modiﬁed sample had more greater attraction of CO2 at low pressures and the CO2/N2selectivity also increased over the entire pressure range measured.More recently, Long and coworkers59incorporated the N,N0-dimethylethyle-nediamine(mmen)into the CuBTTri MOF,and showed that the CO2uptake was drastically enhanced.Zhang et al.60 reported that after ZIF-8was modiﬁed by ammonia impreg-nation,the surface basicity was greatly increased and there-fore the CO2uptake was enhanced.Park et al.61reported a postsynthetic reversible incorporation of organic linkers3,6-di(4-pyridyl)-1,2,4,5-tetrazine(bpta)into SNU-30 [Zn2(TCPBDA)(H2O)2]Á30DMFÁ6H2O through single-crystal-to-single-crystal transformations,and found that the desol-vated SNU-310exhibited enhanced selective adsorption of CO2over N2.Xiang et al.62incorporated the CNTs into HKUST-1,and then modiﬁed it with Li1.The results showed that the hybrid Li@CNT@[Cu3(btc)2],which is formed by the combination of Li doping and CNT incorpora-tion,having an enhancement of CO2uptakes by about 305%.However,to this date,no work has been reported out on the postsynthetic modiﬁcation of ZIF-8to enhance its functionality.In this work,the postsynthetic modiﬁcation of the ZIF-8is proposed to prepare a novel adsorbent with higher CO2 adsorption capacity and CO2/N2selectivity.The postsyn-thetic modiﬁcation of the ZIF-8crystals would be carried out by using ethylenediamine treatment.Then the surface groups of the modiﬁed ZIF-8samples(ED-ZIF-8)would be characterized.Single-component isotherms of CO2and N2 on the modiﬁed ZIF-8samples would be measured sepa-rately.Furthermore,the CO2/N2selectivity is estimated by using IAST on the basis of single-component isotherms of CO2and N2.The inﬂuence of the textural structures and sur-face chemistry of the original and modiﬁed ZIF-8samples on their adsorption capacities for CO2and selectivity of CO2/N2would be discussed and reported here.This informa-tion will be valuable for selecting appropriate adsorbents for CO2capture process.Methods and MaterialsMaterials and instrumentsZinc nitrate hexahydrate(Zn(NO3)2Á6H2O,98%,extra pu-rity)and2-methylimidazole(H A MeIM)(99%purity)were purchased from J&K Chemicals.N,N A Dimethylacetamide (DMF)was purchased from Qiangshen Chemicals Co.,Ltd. of Jiangshu(Jiangshu,China),and it was further puriﬁed by 4A molecular sieve to eliminate the water.Maganetic suspension balance RUBOTHERM was sup-plied by Germany.Its precision was0.000001g.ASAP 2010sorptometer was supplied by Micromeritics Co., Norcross,GA,USA.AdsorbentsSynthesis of ZIF-8was performed following the reported procedures63with a few modiﬁcations.First,a solid mixture of zinc nitrate hexahydrate Zn(NO3)2Á6H2O(0.956g, 3.2 mmol)and2-methylimidazole(H A MeIM)(0.24g, 3.4 mmol)was dissolved in70mL of DMF solvent.The mixture was quickly transferred to a100mL autoclave and sealed. Second,the autoclave was heated at a rate of5K/min to 413K in a programmable oven and held at this temperature for24h under autogenous pressure by solvothermal synthe-sis,followed by cooling at a rate of0.3K/min to room tem-perature.Third,after removal of mother liquor from the mix-ture,chloroform(40mL)was added to the autoclave.The as-synthesized ZIF-8crystals were then isolated byﬁltration. Colorless polyhedral crystals were collected from the upper layer,washed with DMF(10mL33),and dried at383K overnight.To further remove the guest species from the framework and prepare the evacuated form of ZIF-8crystals for modiﬁ-cation and gas-sorption analysis,the as-synthesized ZIF sam-ples were immersed in methanol at ambient temperature for 48h,and evacuated at ambient temperature for5h,and sub-sequently at an elevated temperature673K for2h. Postsynthetic modiﬁcation of adsorbentsThe as-synthesized ZIF-8crystals(labeled as ZIF-8)were dried at383K for24h for postsynthetic modiﬁcation.The subsequent treatment applied to the modiﬁcation of ZIF-8crystals consists of the following steps:The modiﬁed ZIF-8sample(labeled as ED-ZIF-8)was synthesized using ethylenediamine as a linker.In a typical procedure,the ZIF-8sample was added to30%ethylenediamine solution and then the mixture was placed in a stainless high-pressure autoclave.The autoclave was heated in an oven at416K for 1h and then381K for6h.The light yellow product wasﬁl-tered and washed with deionized water.Finally,the sample was dried at383K overnight.Characterization of adsorbentsThe speciﬁc surface area and pore volume of original ZIF-8and modiﬁed ZIF-8crystals were measured on a Micrometrics gas adsorption analyzer ASAP2010instrument equipped with commercial software for calculation and analysis.Powder X-ray diffraction data were collected using a D8 advance h-2h diffractometer(Bruker)in reﬂectance Bragg-Brentano geometry employing Cu K a line focused radiation with40kV voltages and40mA current.The X-ray scanning speed was set at2 /min and a step size of0.02 in2h.A Jade5XRD pattern processing software(MDI,Inc.,Liver-more,CA)was used to analyze the XRD data collected on the ZIF-8samples.The surface organic molecules were analyzed by taking FTIR spectra on a Bruker550FTIR instrument equipped with a diffuse reﬂectance accessory that included a reaction cell.Data acquisition was performed automatically using an interfaced computer and a standard software package.The samples were dried in vacuo at423K prior to mixing with KBr powder.The samples were run in ratio mode allowing for subtraction of a pure KBr baseline.The sample chamber2196DOI10.1002/aic Published on behalf of the AIChE June2013Vol.59,No.6AIChEJournalwas kept purged with nitrogen during the entire experiment.The spectrometer collected 64spectra in the range of 400–4,000cm 21,with a resolution of 4cm 21.CO 2and N 2adsorption measurementsThe CO 2and N 2adsorption-desorption isotherms at 298K,308K,318K,and 328K were obtained on a RUBO-THERM magnetic suspension balance.The initial activa-tion of the modiﬁed sample was carried out at 423K for 12h in a vacuum environment.He (ultra-high purity,U-sung)was used as a purge gas in this study.The adsorp-tion processes were carried out using high purity CO 2and N 2(99.999%)gas.A feed ﬂow rate of 60mL/min of CO 2,40mL/min of N 2and 30mL/min of He,respec-tively,were controlled with the mass ﬂow controllers (MFC)to the sample chamber.Both adsorption and de-sorption experiments were conducted at the same tempera-ture.The temperature of the sorption chamber can be adjusted and maintained constant by an internal tempera-ture sensor.However,the pressure can be changed step-wise through the gas ﬂow rate.Typically,there are four steps for ﬁnishing determination of an isotherm of CO 2or N 2by using Rubotherm magnetic suspension balance.These detail steps are shown by the operation manual of Rubotherm maganetic suspension balance.H 2O adsorption measurementsThe water adsorption measurements were conducted on a computer-controlled DuPont Model 990TGA.The partial pressure of water was varied by changing the blending ratios of water-saturated nitrogen and pure nitrogen gas streams.Before measurement,the modiﬁed ZIF-8samples were acti-vated at 423K for 6h.Results and DiscussionStructure and pore characterizationFigure 1exhibits the adsorption-desorption isotherms of N 2at 77K on the two samples ZIF-8and ED-ZIF-8.It can be seen that both samples show type-I behavior,indicating they are microporous in nature.Table 1lists structure param-eters of the two samples.These data indicate that the BET surface area and micropore volume of the ED-ZIF-8sample are signiﬁcantly higher than those of the original ZIF-8sam-ple,with an increase of $39%and 35.6%,respectively.Yaghi and his coworkers reported a pore volume of 0.66cm 3/g for ZIF-8from the single crystal structure.For the ZIF-8sample,the total pore volume is calculated to be 0.54cm 3/g,because part of the pores might be blocked.However,after the postsynthetic modiﬁcation,the blocked pores were reopened,and at meanwhile,some new pores were formed.64,65Thus,the total pore volume of the ED-ZIF-8sample is greatly improved.Figure 2shows the powder X-ray diffraction (PXRD)pat-tern of the modiﬁed ZIF-8sample.It can be seen that the main peaks of the modiﬁed ZIF-8sample are very clear,and similar to those of the original ZIF-8sample,indicating that the integrity of the modiﬁed ZIF-8sample maintains well af-ter the postsynthetic modiﬁcation.However,for a deep look-ing,it can be found that the major peaks of ED-ZIF-8all shifted to the left side (low-angle area)a little bit,which means after modiﬁcation,the lattice distance increased.In order to obtain information concerning changes in the surface groups,FTIR experiments were carried out to char-acterize the samples.Figure 3a shows the FTIR spectra of the original ZIF-8and the ED-ZIF-8sample.It is noticed that the spectra for the two samples show high similarities,and the main peaks of both ZIF-8samples match well with the published FTIR spectra for the ZIF-8.However,someTable 1.Porous Structure Parameters of the Modiﬁed ZIF-8CrystalsSample BET surface area (m 2.g 21)Langmuir surface area (m 2.g 21)Micropore volume(cm 3.g 21)Total pore volume (cm 3.g 21)Micropore diameter (nm)Mesopore diameter (nm)ZIF-8102513520.450.540.352 4.43ED-ZIF-8142818970.610.750.5444.53Figure 1.N 2adsorption-desorption isotherms of ZIF-8and ED-ZIF-8samples.[Color figure can be viewed in the online issue,which is available at .]Figure2.PXRD patterns of ZIF-8and ED-ZIF-8samples.[Color figure can be viewed in the online issue,which is available at .]AIChE Journal June 2013Vol.59,No.6Published on behalf of the AIChE DOI 10.1002/aic2197differences are also observed.For example,the spectrum of the ED-ZIF-8sample is different from that of the ZIF-8sam-ple in that (1)as shown in Figure 3b there is a new peak at 3381cm 21which is assigned to N A H group appeared on the spectrum of the ED-ZIF-8sample,suggesting some N A H groups have been introduced on the surfaces of the sample ED-ZIF-8,and (2)a peak at 3626cm 21assigned to O A H of the adsorbed H 2O is present in the spectrum of the ZIF-8sample,which is absent in the spectrum of the ED-ZIF-8sample,as shown in Figure 3b.CO 2and N 2adsorption isothermsFor comparison,Figure 4shows the isotherms of CO 2on the ZIF-8and ED-ZIF-8samples.It is visible that the amount adsorbed of CO 2increases as temperature decreases.This suggests that the adsorption of CO 2is mainly physical adsorption.More importantly,it is found that the ED-ZIF-8sample had higher CO 2adsorption capacities compared to the ZIF-8sample,indicating that the adsorption capacities of the modiﬁed ZIF-8toward CO 2are greatly improved,nearly being twice as much as the ZIF-8.One of the reasons is that the surface area (BET)of the ED-ZIF-8increases by 39%,as indicated in Table 1.The other reason is that adsorptioncapacity per unit surface area of the ED-ZIF-8for CO 2increases due to an introduction of N A H groups by postsyn-thetic modiﬁcation.To further understand that,Figure 4a and 4b are separately transferred into Figure 5a and 5b in which the equilibrium uptakes of CO 2based on unit surface area (BET)of the two samples are plotted as a function of CO paring Figure 5b and Figure 5a shows that the CO 2uptake per surface area (BET)of the ED-ZIF-8is obvi-ously higher than that of the ZIF-8,which is mainly ascribed to the introduction of N A H groups,as shown in Figure 3.Figure 6a and 6b show the N 2adsorption isotherms on the two samples.It is visible that the N 2uptakes on the modiﬁed ZIF-8samples are slightly higher than that on the ZIF-8due to its larger surface area and pore volume after modiﬁcation.However,after Figure 6a and 6b are converted into Figure 7a and 7b in which the equilibrium uptakes of N 2based on unit surface area of the two samples are plotted as a function of pressure,it is found from Figure 7that the equilibrium uptakes of N 2per surface area of the ED-ZIF-8are slightly lower than that of the ZIF-8,which means that ED-ZIF-8sample has less afﬁnity toward N 2than ZIF-8sample.This will be helpful to enhance the adsorption selectivity for CO 2/N 2.Figure 3.a.FTIR spectra of the modified ZIF-8crystalsbetween 4,000–400cm 21;b.FTIR spectra of the modified ZIF-8crystals between 4000–2,400cm 21.[Color figure can be viewed in the online issue,which is available at .]Figure 4.a.Isotherms of CO 2on the ZIF-8sample withdifferent temperatures; b.isotherms of CO 2on the ED-ZIF-8sample with different temperatures.[Color figure can be viewed in the online issue,which is available at .]2198DOI 10.1002/aicPublished on behalf of the AIChE June 2013Vol.59,No.6AIChEJournalMultiple cycles of CO 2adsorption-desorption on the ED-ZIF-8To evaluate the regeneration performance of the modiﬁed sample or the reversibility of CO 2adsorption on the modi-ﬁed sample,the experiments of multiple cycles of CO 2adsorption-desorption on the ED-ZIF-8were performed in the Rubotherm system at 298K.For adsorption process,the adsorption pressure were targeted for 25bar;while for de-sorption process the system pressure was targeted for 1mbar,and then the desorption system was quickly depressur-ized by using vacuum pumping.Figure 8shows the variation curve of the amounts adsorbed of CO 2on the ED-ZIF-8dur-ing four consecutive cycles of CO 2adsorption-desorption experiments at 298K.It was visible clearly that during the desorption,the amounts adsorbed of CO 2on the ED-ZIF-8sample decreased sharply with time,and then reached a very low content,about 2.21wt %of residual CO 2which was present on the sample after desorption at 1mbar.The efﬁ-ciency of CO 2desorption was nearly up to 98%over the entire four circles.It indicated further that CO 2adsorption was reversible with very little accumulation of irreversible bound CO 2on the ED-ZIF-8framework.In addition,it wasalso observed from Figure 8that the curves representing the cycles of CO 2adsorption-desorption experiments were very similar,suggesting that adsorption and desorption properties of the sample ED-ZIF-8for CO 2were stable or repeatable.It also proved that the pressure swing was effective in strip-ping adsorbed CO 2from the ED-ZIF-8.H 2O adsorption isothermsFigure 9shows the water isotherms on the modiﬁed ZIF-8samples at 298K.The water uptake on the ED-ZIF-8sample is less than that on the ZIF-8sample,indicating that the sur-face of the modiﬁed sample became more hydrophobic com-pared to the ZIF-8sample.It also means that the interaction of the water molecule with the modiﬁed sample became weaker as compared to that with the ZIF-8.Ideal adsorbed solution theory (IAST)selectivity of CO 2/N 2The ideal adsorbed solution theory (IAST)developed by Myers and Praunitz 66provides an effective method to predict the adsorption selectivity and the adsorption equilibrium of gas mixtures from the isotherms of the pure components.Figure 5.a.Isotherms of CO 2on the ZIF-8samplebased on unit surface area;b.isotherms of CO 2on the ED-ZIF-8sample based on unit surface area.[Color figure can be viewed in the online issue,which is available at .]Figure 6.a.Isotherms of N 2on the ZIF-8sample atdifferent temperatures;b.isotherms of N 2on the ED-ZIF-8sample at different temperatures.[Color figure can be viewed in the online issue,which is available at .]AIChE JournalJune 2013Vol.59,No.6Published on behalf of the AIChE DOI 10.1002/aic2199Previous work reported that the IAST can accurately predict gas mixture adsorption in a number of zeolites and MOF materials.10,48,67–70The IAST assumes that the adsorbed mixture is an ideal solution at constant spreading pressure and temperature,where all the components in the mixture conform to the rule analogous to Raoult’s law,and the chemical potential of the adsorbed solution is considered equal to that of the gas phase at equilibrium.From the IAST,the spreading pressure p is given byp 0i ðp 0i Þ5RT A ðp 0iqd ln p (1)p Ã5p A 5ðp 0i 0q i dp (2)Where A is the speciﬁc surface area of the adsorbent,p andp *are the spreading pressure and the reduced spreading pres-sure,separately.p 0i is the gas pressure of component i corre-sponding to the spreading pressure p of the gas mixture.At a constant temperature,the spreading pressure of single component is the samep Ã15p Ã25…5p Ãn 5p(3)For binary adsorption of component 1and 2,the IASTrequiresy 1p t 5x 1p 1ð12y 1Þp t 5ð12x 1Þp 2(4)Where y 1and x 1denote the molar fractions of component 1in the gas phase and in the adsorbed phase,respectively.p t is the total gas pressure,p 1and p 2are the pressures of com-ponent 1and 2at the same spreading pressure as that of the mixture,respectively.Adsorption selectivity in a binary mixture of component 1and 2is deﬁned asS 125x 1x 2 y 2y 1 (5)For the application of IAST to predict adsorption separa-tion selectivity,the following two conditions are necessary:good quality adsorption data of each single component;and excellent curve ﬁtting model for such data.48,71,72In order to perform the integrations of Eqs.(1)and (2)required by IAST,the single-component isotherms should be ﬁtted by a proper isotherm model.In practice,several meth-ods are available.In this work,it is found that the dual-site Langmuir-Freundlich (DSLF)equation can be successful to ﬁt this set of adsorption data.The dual-site Langmuir-Freundlich model can be expressed as followsq 5q m ;13b 1p 1=n 111b 1p 11q m ;23b 2p 1=n 211b 2p 2(6)Where p is the pressure of the bulk gas at equilibrium with the adsorbed phase (kPa),q m,1,q m,2are the saturation capaci-ties of sites 1and 2(mmol/g),b 1and b 2are the afﬁnity coefﬁcients of sites 1and 2(1/kPa),and n 1and n 2are the deviations from an ideal homogeneous surface.Figure 10shows a comparison of the model ﬁts and the isotherm data.It is visible that the DSLF model can be applied favorably for ﬁtting experimental data of CO 2and N 2adsorption.Table 2presents the ﬁtting parameters ofFigure 7.a.Isotherms of N 2on the ZIF-8sample basedon unit surface area;b.isotherms of N 2on the ED-ZIF-8sample based on unit surface area.[Color figure can be viewed in the online issue,which is available at .]Figure 8.Recycle runs of CO 2adsorption-desorptionon the ED-ZIF-8at 298K and 25bar for adsorption and 1mbar for desorption.[Color figure can be viewed in the online issue,which is available at .]2200DOI 10.1002/aicPublished on behalf of the AIChE June 2013Vol.59,No.6AIChEJournalDSLF equation as well as the correlation coefﬁcients (R 2).Examination of the data shows that this DSLF model is able to ﬁt the adsorption data well since the correlation coefﬁ-cients R 2are up to 0.9997.In this work,the equilibrium adsorption data of single component CO 2as well as N 2are available,and the DSLF model can ﬁt the experimental isotherms of CO 2and N 2adsorption very well.Therefore,the DSLF model can be combined with the ideal adsorbed solution theory (IAST)to predict the mixture adsorption isotherms and calculate the selectivities of the two samples for CO 2/N 2adsorption.Figure 11a and 11b present,respectively,the adsorption isotherms predicted by IAST for equimolar mixtures of CO 2/N 2in the samples ZIF-8and ED-ZIF-8as a function of total bulk pressure.It can be seen that CO 2is preferentially adsorbed over N 2on the two samples because of stronger interactions between CO 2and the ZIF-8sample,and the amount adsorbed of N 2is much lower in the mixtures than that in single-component adsorption because of competition adsorption from CO 2,which adsorbs more strongly.Figure 12shows the IAST-predicted selectivities of the two samples for equimolar CO 2and N 2mixtures at 298K as a function of total bulk pressure.It can be seen that the adsorption selectivity of the two samples for CO 2/N 2dropped with an increase in the pressure.More importantly,Figure 9.H 2O adsorption isotherms on the modifiedZIF-8samples at 298K.[Color figure can be viewed in the online issue,which is available at .]Table 2.The Fitting Parameters of the Dual-site Langmuir-Freundlich Equations for the Pure Isotherms of CO 2and N 2at 298KZIF-8ED-ZIF-8CO 2N 2CO 2N 2R 20.99970.99990.99970.9999q m,1(mmol/g)27.2527.8748.8828.32q m,2(mmol/g) 2.122 1.919 4.672 1.847b 1(atm 21)0.015330.0011700.012590.001388b 2(atm 21)0.0068950.026090.029480.02504n 1 1.6000.7875 1.4040.7704n 20.32440.96340.44300.8671Figure 10.DSLF fitting of the CO 2and N 2isotherms onZIF-8and ED-ZIF-8at 298K.[Color figure can be viewed in the online issue,which is available at .]Figure11.a.The IAST -predicted isotherm forequimolar CO 2/N 2mixtures of the ZIF-8sample at 298K as a function of total bulk pressure; b.the IAST -predicted isotherm for equimolar CO 2/N 2mixtures of the ED-ZIF-8sample at 298K as a function of total bulk pressure.[Color figure can be viewed in the online issue,which is available at .]AIChE Journal June 2013Vol.59,No.6Published on behalf of the AIChE DOI 10.1002/aic2201the adsorption selectivity of CO 2/N 2on the sample ED-ZIF-8is always higher than that on the sample ZIF-8,especially in the low-pressure region.For example,at 0.1and 0.5bar,the selectivity of the sample ED-ZIF-8for CO 2/N 2were up to 23and 13.9separately,which is almost twice of those of the sample ZIF-8.Figure 13a and 13b show,respectively,the IAST-pre-dicted selectivities of the samples ZIF-8and ED-ZIF-8for CO 2/N 2at different mixture compositions and different pres-sures.It is noticed that the selectivity increases rapidly as the gas-phase mole fraction of N 2approaches unity.For example,at yN 250.9,a typical feed composition of ﬂue gas,high selectivities are obtained.Even at yN 250.5,the selectivity of the ED-ZIF-8for CO 2/N 2is in the range of 6–24,much higher than those on the ZIF-8sample and many other MOF samples such as ZIF-7030,ZIF-6830and MOF-508b.73This property is very important since some separa-tion processes could be operated at low pressures,such as vacuum swing adsorption (VSA),which could be extremely efﬁcient by using the sample ED-ZIF-8because its selectiv-ity increases dramatically with decreasing pressure.Ideal adsorbed solution theory (IAST)selectivity of CO 2/N 2/H 2OThe major challenge of CO 2capture from power plant ﬂue gas wastes is the separation of CO 2/N 2.In addition,competition adsorption of water molecule must be taken into account,because these ﬂue gas wastes are usually saturated with certain amount of water (5–7%by volume)for the industrial postcombustion processes.Thus,for real industrial use of adsorbents,the effect of water on CO 2/N 2selectivity is another crucial factor that needs to be considered and evaluated.Here,the IAST was adopted to evaluate the ter-nary mixture CO 2/N 2/H 2O adsorption on the modiﬁed ZIF-8samples.First,the experimental isotherms of water on the modiﬁed ZIF-8samples at 298K were ﬁtted using the DSLF model.Table 3presents the ﬁtting parameters of DSLF equation as well as the correlation coefﬁcients.It can be seen that theDSLF model ﬁts the H 2O adsorption on both samples very well.Second,the DSLF model was combined with the ideal adsorbed solution theory (IAST)to predict the mixture adsorption isotherms,and then calculate the selectivities of the two samples for CO 2/N 2adsorption.Figure 14shows the predicted isotherms of ternary mix-ture CO 2/N 2/H 2O on the modiﬁed ZIF-8samples at 298K.It can be observed that in comparison with the ZIF-8,after modiﬁcation,the CO 2adsorption capacity of the ED-ZIF-8in the ternary mixture obviously increased,and its N 2adsorption capacity somewhat increased,which made CO 2/N 2adsorption selectivity of the ED-ZIF-8increase.More importantly,its water adsorption capacity in the ternary mix-ture became lower compared to the ZIF-8,and it was also lower than the single component water uptake.It means the competition adsorption of H 2O in the ternary mixture was weakened on the surfaces of the ED-ZIF-8sample.Figure 12.The IAST -predicted selectivity for equimolarCO 2and N 2at 298K as a function of total bulk pressure.[Color figure can be viewed in the online issue,which is available at .]Figure 13.a.The IAST predicted selectivities atdifferent mixture compositions and different pressures for the ZIF-8sample at 298K;b.the IAST predicted selectivities at different mixture compositions and different pressures for the ED-ZIF-8sample at 298K.[Color figure can be viewed in the online issue,which is available at .]2202DOI 10.1002/aicPublished on behalf of the AIChE June 2013Vol.59,No.6AIChEJournal。

离子掺杂对提高锐钛型TiO2高热稳定性的研究

离子掺杂对提高锐钛型TiO2高热稳定性的研究刘艳敏1，张萍2，李平蕊1，张艳峰1，魏雨1(1.河北师范大学化学与材料科学学院，河北石家庄050016 2. 石家庄学院河北石家庄)摘要：结合本课题组的工作，归纳分析了离子掺杂对二氧化钛由锐钛矿型向金红石型转化的抑制作用，对相关文献数据分析得出不同掺杂离子对TiO2相转化温度和粒径具有较大影响的结论。

本课题组以TiCl4为原料，通过添加少量磷酸二氢钠，采用强迫水解法制备的纯锐钛相纳米TiO2，相变温度提高到了1000℃，有效抑制了TiO2粒径的长大，与文献结果一致。

但掺杂后TiO2的相变机理尚处于探索阶段，如何选择适当添加剂实现高热稳定性锐钛矿型纳米TiO2产业化是今后研究的重点。

关键词：锐钛矿相纳米TiO2；相变；掺杂；高热稳定性中图分类号：TF123 文献标识码：A 文章编号Research on Improvement of High Thermal Stability of AnataseTitania by Doping IonsResearch on Improvement of Ion Dopants on High ThermalStability of Anatase TitaniaLIU Yan-min1, ZHANG Ping2, LI Ping-rui1, ZHANG Yan-feng1, WEI Yu1(1.College of Chemistry and Material Sciences,Hebei Normal University,HebeiShijiazhuang 050016,China;2. China）Abstract:The suppressing effects on the anatase-to-rutile phase transformation by doping ions were systematically concluded combining with our research group’s work. And we came to the conclusion that the ion dopants have large influences on the phase transition temperature and particle size through analysing interrelated literatures. Anatase TiO2 was prepared by forced hydrolysis under boiling reflux method using TiCl4 as the raw material and NaH2PO4 as the additive in our laboratory. The obtained sample has a high stability at 1000℃and the crystallite size was effectively inhibited, which is in accordance with the literatures. However, the mechanism of the phase transformation of TiO2 is still in the exploratory stage, how to choose the appropriate additives to achieve the industrial production of anatase TiO2 with high thermal stability is the emphasis in future research.Key words:Anatase TiO2；phase transformation; doping; high thermal stability1.引言：纳米TiO2凭借其独特的光电特性、自清洁、化学稳定性、无毒和低成本等优势，在高级涂料、环境保护、半导体材料、高级油漆、化妆品、催化剂等领域得到了广泛应用[1-3]。

植物糖原负载提高姜黄素的稳定性和生物活性

植物糖原负载提高姜黄素的稳定性和生物活性韩兴曼，樊金玲*，王攀，朱文学，任国艳（河南科技大学食品与生物工程学院，河南洛阳 471023）摘要：植物糖原（phytoglycogen，PG）是一种碳水化合物天然纳米粒，以PG为载体负载姜黄素（curcumin，CCM）制备PG-CCM复合物，可显著提高CCM的溶解度。

本实验进一步研究PG负载对CCM的稳定性、生物活性及释放的影响，探讨负载前后以及不同复合物中CCM的稳定性和生物活性变化的可能机制。

通过制备不同PG质量分数的PG-CCM复合物（1% PG-CCM、3% PG-CCM和5% PG-CCM），使用激光粒度仪测定负载前后纳米粒的粒径和表面电位，分析不同复合物中CCM的负载特征；通过测定紫外光加速光解、不同pH值环境等条件下CCM的保留率，研究复合物中CCM的稳定性；同时，采用总还原力和2,2’-联氮-双-3-乙基苯并噻唑啉-6-磺酸阳离子自由基清除实验研究复合物的抗氧化活性，采用噻唑蓝法检测复合物对MCF-7和A549癌细胞的抑制活性，采用体外实验研究不同复合物在模拟胃、肠液中释放行为。

结果表明，CCM负载前后，PG纳米粒的粒径和表面电位无明显变化，分别为70～75 nm、0 mV（pH 7.0）。

负载于PG后，CCM的紫外稳定性、抗氧化活性及癌细胞抑制活性均明显增强；生物活性的提高与负载后CCM具有更好的分散性有关。

“突释”是PG-CCM复合物中CCM释放的共同特征，CCM 在胃液中的释放率高于肠液。

PG-CCM复合物制备时使用的PG质量分数极大影响CCM的负载特征、释放规律、稳定性以及生物活性。

1% PG-CCM和5% PG-CCM复合物中分布于载体表面的CCM比例分别为37.5%和17.3%。

5% PG-CCM复合物的紫外稳定性和酸碱稳定性均显著优于1% PG-CCM复合物。

1% PG-CCM复合物在体外模拟胃、肠液中的释放率以及对两种癌细胞的抑制作用均高于5% PG-CCM复合物。

Enhanced activity and stability of papain immobilized onCNBr-activated sepharose

International Journal of Biological Macromolecules 75(2015)373–377Contents lists available at ScienceDirectInternational Journal of BiologicalMacromoleculesj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /i j b i o m acEnhanced activity and stability of papain immobilized on CNBr-activated sepharoseAhmad Homaei ∗Department of Biochemistry,Faculty of Sciences,University of Hormozgan,PO Box 3995,Bandar Abbas,Irana r t i c l ei n f oArticle history:Received 1December 2014Received in revised form 16January 2015Accepted 19January 2015Available online 4February 2015Keywords:PapainImmobilization Thermal stability ActivityExtreme pHsa b s t r a c tImmobilization of papain was carried out by covalent attachment on Sepharose 6B activated by using cyanogen bromide.Immobilization process brought about signiﬁcant enhancement of storage and ther-mal stability,stability at extreme pHs,and resistance against the inhibitory effects of various bivalent metal ions with respect to papain.The optimum temperature of papain increased by 20◦C (from 60to 80◦C)and its optimum pH was shifted from 6.5to 8.0upon immobilization.The activation energy of the enzymatic reaction for immobilized papain showed a signiﬁcant increase as compared with its free form (1.87kcal mol −1K −1for free and 4.69kcal mol −1K −1for immobilized enzyme).The kinetic parameters,K m and k cat ,were estimated to be 0.62␮M and 162×10−4s −1for free and 0.79␮M and 102×10−4s −1for immobilized papain,respectively.©2015Elsevier B.V.All rights reserved.1.IntroductionEnzymes are often not sufﬁciently stable in the desired media.This still is an essential drawback of enzymes.As even slight con-formational changes can cause an enormous decline in activity,retention of activity is a stringent criterion for the integrity of a protein molecule.Enzymes deactivate under a range of condi-tions such as extremes of temperature or pH value,physical forces and aqueous-organic or gas liquid interfaces [1].The speciﬁcities of enzymes and the abilities to enhance reaction rates promise improvements in many applications.Improvements in enzyme sta-bility can enable further practical applications.There have been several strategies to increase the enzyme stability:immobilization,chemical modiﬁcation,protein engineering and medium engineer-ing [2].Compared with their free forms,immobilized enzymes are generally more stable and easier to handle.In addition,the reaction product is not contaminated with the enzyme (especially useful in the food and pharmaceutical industries)[3]and,in the case of pro-tease,the rate of the autolysis process can be dramatically reduced upon immobilization [4].Papain,a thiol protease,present in the latex of Carica papaya exhibits broad proteolytic activity and is an enzyme of industrial use and of high research interest.Papain has a variety of indus-trial applications,especially in food industry.It is used to tenderize meat and meat products,in the manufacture of protein hydrolysate,∗Tel.:+987617665054;fax:+987616670716.E-mail address:a.homaei@hormozgan.ac.irin brewing industry for clarifying juice and beer,in dairy industry for cheese,in baking industry,and in the extraction of ﬂavor and color compounds from plants.Papain can also be used in forage industry to increase utilizing and transforming rate of protein and in resolving plant and animal protein to make high health prod-ucts [5–7].The need for the immobilization of papain has been due to its great industrial applications,and in many instances,there are some of the key advantages of immobilized papain over their soluble counterpart.Although the covalent coupling of papain on CNBr-activated Sepharose and other sugar supports have been reported earlier [8,9],however extensive investigations have not been performed related to stability and other enzyme characteristics in details.In the present work,we report the advantages of papain immobiliza-tion on CNBr-activated Sepharose 6B with respect to stability and catalytic activity.It was shown that immobilization process could signiﬁcantly enhance the storage and thermal stability,stability at extreme pHs,and resistance against the inhibitory effects of biva-lent metal ions.The immobilized papain was also compared with its free form in terms of temperature and pH proﬁles and kinetic parameters.2.Materials and methods2.1.ChemicalsSepharose 6B and cyanogen bromide (CNBr)were purchased from Sigma (St.Louis,MO,USA).All other chemicals were from Merck (Darmstadt,Germany)and were reagent grade./10.1016/j.ijbiomac.2015.01.0550141-8130/©2015Elsevier B.V.All rights reserved.374A.Homaei /International Journal of Biological Macromolecules 75(2015)373–3772.2.Activation of sepharose and immobilization of papainSepharose 6B was activated with cyanogen bromide.The titra-tion method of activation was performed for activating Sepharose and papain coupled to the CNBr-activated Sepharose at a concen-tration of 5mg/mL according to the procedure described by March and others [10].The ratio of gel/protein solution (v/v)was 1.5:1.The gel was treated with 2M glycine to block the remaining activated group on the matrix after immobilization.2.3.Determination of protease activity and protein concentrationProtease activity was determined at room temperature in 50mM phosphate buffer containing 5mM EDTA and 5mM cysteine chloride,pH 7.5,using casein as the substrate by the method of Homaei [11].50␮L of enzyme solution was added to a tube con-taining 350␮L of the buffer.400␮L of 0.45mM casein was then added and the reaction mixture incubated at room temperature for 10min.The reaction was stopped by addition of 800␮L of 10%trichloroacetic acid (TCA)solution.The mixture was incubated at room temperature for 30min,centrifuged at 12,000×g for 10min and the absorbance of the supernatant was measured at 280nm.One unit of protease is deﬁned as the amount of enzyme that hydrolyses casein to produce equivalent absorbance to 1␮mol of tyrosine/min with tyrosine as standard.In the case of the immobi-lized papain,the reaction mixture was continuously stirred during the reaction.Protein concentration was estimated by the Bradford method [12],using bovine serum albumin as standard.2.4.Determination of optimum pH and temperatureThe pH proﬁles of free and immobilized papain were determined at room temperature in various pH of a mixed buffer containing 50mM of acetate,phosphate and glycine.For determining tem-perature proﬁles of free and immobilized papain,the activity of the enzymes was determined at several temperatures (from 30to 90◦C)in the phosphate buffer pH 7.5as described above.2.5.Effect of pH and temperature on enzyme stabilityTo determine the thermal stability,free and immobilized papain were incubated at 80and 90◦C in 50mM phosphate buffer,pH 7.5for a series of time intervals,cooled on ice,and ﬁnally the residual activity was determined under assay conditions.The pH stability was studied for free and immobilized papain by incubation of the enzyme in 50mM of mixed buffer (pH 3and 12)for a series of time intervals at room temperature,then adjusted to pH 7.5and ﬁnally the residual activity was determined under assay conditions.Activity of the same enzyme solution kept on ice in the thermal stability and in the buffer,pH 7.5in the pH stability experiments were considered as controls (100%).2.6.Effect of bivalent metal ions on enzyme activityThe activity of free and immobilized enzyme were measured in the presence of various chloride salts of bivalent metal ions and EDTA with ﬁnal concentrations of 5,10,20,and 40mM under assay conditions and the relative activity of the enzyme was determined.2.7.Determination of storage stability and reusability studiesThe activity of free and immobilized papain stored in 50mM phosphate buffer,pH 7.5at 4◦C and room temperature up to 60days was measured under assay conditions.Also the stability of the immobilized papain was measured by reusing it seven times.The immobilized enzyme was used as described in Section 2.3but for several cycles.At the end of each cycle,the derivative was washed with distilled water and activity buffer and a new substrate solution was added to start a new round of reaction.2.8.Determination of kinetic parametersCatalytic activities of free and immobilized papain were investi-gated at different substrate concentrations under assay conditions.K m and V max were determined from the Lineweaver–Burk plots.3.Results and discussionThe coupling efﬁciency of immobilization with 200mg of CNBr per milliliter of Sepharose 6B and 5mg/mL of papain in 0.2M NaHCO 3at pH 9.5(1:1.5ratio of gel/protein solution,v/v)was 7.3mg of protein per milliliter of packed activated gel.The activity yield and the immobilization yield of immobilization were about 53%and 76%respectively.3.1.Effect of immobilization on thermostabilityIrreversible thermo inactivation of free and immobilized papain was determined at 80and 90◦C.As shown in Fig.1,the immobilized papain exhibited a marked increase in thermostability as compared with its free counterpart.The half lives of free enzyme were 18and 6min at 80and 90◦C respectively,while the half life of immobi-lized enzyme was 40min at 90◦C.After 60min of incubation at 80and 90◦C,the immobilized papain retained 80%and 45%of its orig-inal activity respectively.Under the same conditions,theresidual204060801001200 10 20 30 40 5060Time (min)A c t i v i t y (%)0204060801001201401600102030 40 5060Time (min)A c t i v i t y (%)Fig.1.Irreversible thermo inactivation of free ( )and immobilized ( )papain at 80◦C (a)and 90◦C (b).Further details are described under Section 2.A.Homaei/International Journal of Biological Macromolecules75(2015)373–377375Fig.2.(a)Storage stability of free(triangles)and immobilized(squares)papain at4◦C(solid)and at room temperature(hollow).(b)Catalyst recycling of the immobilized papain.activity of free papain signiﬁcantly decreased.However,activation was obtained for immobilized enzyme in the initial times of incu-bation,particularly at80◦C.Immobilization of papain on Sepharose 6B caused an increase in conformational rigidity of protein struc-ture and limited its freedom to undergo drastic conformational changes,thus resulting in increased stability toward thermal dena-turation[13].On the other hand,theﬁxation of enzyme on the support can lead to a lower degree of autolysis and consequently increasing the stability of the enzyme.The improvement of ther-mal stability of papain via immobilization has also been reported by others[14–16],but improving thermal stability achieved in this work for papain was not observed.Immobilization of papain on CNBr caused an increase in conformational rigidity of protein struc-ture and limited its freedom to undergo drastic conformational changes.This resulted in an increased stability toward thermal denaturation[11].3.2.Effect of immobilization on storage stability and catalyst recyclingIn addition to improving thermal stability,the storage stability of papain exhibited a signiﬁcant increase upon immobilization.As indicated in Fig.2a,free papain lost all of its initial activity after30 and60days of incubation at4◦C and room temperature respec-tively,while under these condition,substantial activities remained after2months for immobilized papain.Fig.2b shows the residual activity as a function number of cycles.The results showed that the immobilized papain remained83%of its initial activity after7 cycles.3.3.Effect of immobilization on enzyme stability at extreme pHsThe stability of free and immobilized papain was measured at two extreme pHs(pH3.0and12).As shown in Fig.3,the immo-bilized enzyme was more stable as compared with free enzyme not only at pH3.0but also at pH12.After60min of incubation at these pH values,the immobilized papain retained about50%of its residual activity.Under the same conditions,a nearly complete inactivation of free papain was witnessed.This indicates that the immobilization appreciably enhanced the stability of papain both in the acidic and basic pHs.Improving papain resistance through immobilization to extreme pHs has been reported elsewhere,but none has considered pH values in the present study[15,17].3.4.Effect of immobilization on temperature and pH proﬁlesThe inﬂuence of temperature and pH on the activity of free and immobilized enzyme is shown in Fig.4.A signiﬁcant shift to higher temperature was observed upon immobilization.As shown in Fig.4a,maximum activity for free and immobilized papain was observed at60and80◦C respectively.However,the free papain is active in a broad temperature range.It exhibited at least80%of maximum activity in the range of30–70◦C,but it retained only60% of activity at80◦C(optimum temperature of immobilizedenzyme).204060801001200102030405060Time (min)Activity(%)204060801001200102030405060Time (min)Activity(%)Fig.3.pH stability at pH3.0(a)and12(b)for free( )and immobilized( )papain.376A.Homaei /International Journal of Biological Macromolecules 75(2015)373–377204060801001200 2 4 68 10 1214pHA c t i v i t y (%)0204060801001202030405060708090100temperature (oC)A c t i v i t y (%)Fig.4.(a)Effect of temperature on the activities of free ( )and immobilized ( )enzyme.The inset is Arrhenius plots corresponding to free ( )and immobilized ( )forms of the enzyme.(b)Effect of pH on the activities of free ( )and immobilized ( )papain.At 90◦C,the free papain displayed about 30%of optimal activity,whereas its immobilized counterpart had about 70%of its maxi-mum activity.Enhancement of the catalytic activity of the enzyme at high temperature presumably occurs as a result of the preven-tion of autolysis,which is facilitated at high temperature due to ﬁxing the enzyme on the support.The Arrhenius plots of the data presented in Fig.4a,inset were prepared in the temperature range of 30–60◦C and 30–70◦C for papain and its immobilized form respectively.The acti-vation energy of the enzymatic reaction,calculated from the slopes of the plots,signiﬁcantly increased upon immobilization (1.87kcal mol −1K −1for free and 4.69kcal mol −1K −1for immobi-lized enzyme),which suggests an increasing in conformational rigidity of the enzyme.This was also purposed previously (Fig.1)which is commonly reﬂected by increase in thermal stability [14,18].The optimum pH of the enzyme is shifted from 6.5to 8.0upon immobilization.Furthermore,the immobilized form of papain showed a broad pH activity proﬁle compared with the free papain.As indicated in Fig.4b,the immobilized form of enzyme showed higher activity both in acidic and basic pH ranges when compared to its free form.While the free form of papain exhibited onlyTable 1Kinetic parameters for free and immobilized papain.Enzyme formk cat (S −1)×10−4K m (␮M)Speciﬁc activity (␮M min −1mg −1)Free162±1.350.62±0.09232±3.72Immobilized102±1.170.79±0.11205±2.61about 10%and 20%of activity at pH 2.0and 12,two quiet extreme pHs,the immobilized form retained more than 40%and 50%of activity at pHs 2.0and 12respectively.The shift in optimum pH of covalently coupled papain to the solid support has also been reported by others [15,16,19].The enzyme sees be more stable,that may explain the altered pH/activity proﬁle.If equilibrated,the pH that the enzyme suffers should be the same than in free solution,and they ﬁnd positive pHs at both acidic and alkaline pH values.Conformational changes produced by the immobilization or avoided by the enzyme stability may explain the change in optimal pH [6,11].3.5.Effect of immobilization on kinetic parametersAs indicated in Table 1,a slight increase in K m and signiﬁcant decrease in k cat of immobilized papain at room temperature com-pared with its free counterpart are observed.The slight increase in K m value may be due to diffusion limitation,the steric hindrance of the active site,and/or the loss of enzyme ﬂexibility necessary for substrate binding by immobilization [20,21].The decrease in k cat could be due to the restricted diffusion of substrate to the active site and the higher structural rigidity of immobilized enzyme.IncreaseTable 2Effect of various metal ions and their concentrations on free and immobilized papain.aMetal ionRelative activityFreeImmobilized Control (no add)11Ca 2+5mM 0.780.9410mM 0.570.8720mM 0.340.7240mM0.100.48Mg 25mM 0.810.9610mM 0.600.8820mM 0.400.7740mM0.200.57Ba 2+5mM 0.760.9110mM 0.470.7220mM 0.280.5740mM0.130.38Co 2+5mM 0.540.7010mM 0.250.5820mM 0.060.4740mM0.20Zn 2+5mM 0.490.6510mM 0.220.5420mM 0.010.4540mM0.16Fe 2+5mM 0.560.6810mM 0.280.5620mM 0.090.4740mM0.16Mn 2+5mM 0.560.6910mM 0.290.6020mM 0.100.4840mM0.18aAll metal ions were added as chloride salts.A.Homaei/International Journal of Biological Macromolecules75(2015)373–377377in K m and decrease in k cat values upon immobilization have been frequently reported[3,20–23].3.6.Effect of bivalent metal ions on the activity of free and immobilized enzymeRelative activates of papain and its immobilized form in the absence and presence of various bivalent metal ions,which are known to be strong inhibitors of papain[14–26],in the different concentrations are depicted in Table2.As indicated,substantial improvement toward inhibition by the metal ions was achieved upon immobilization.These data clearly indicate that the sen-sitivity of the enzyme declines against the inhibitory effects of bivalent metal ions through the process of immobilization. Such protection may be due to masking of binding sites on the enzyme as well as the diffusion limitations[27].Probably biva-lent metal ions react nonspeciﬁcally with the protein hydrophobic groups,resulting in salting out of these residues from the sur-face into the interior of the enzyme macromolecule[28,29]but more extended research is needed in order to draw the exact mechanism.4.ConclusionMany of industrial processes are performed in conditions quite different from their natural conditions.A major limitation to the use of enzymes in non-natural conditions is their stability. Therefore,the enzyme stability could be very important in many bio-processes.On the other hand,the decrease of enzyme activ-ity during storage is also an important drawback,especially in the case of proteases.The results obtained in this study clearly showed that thermal and storage stability as well as resistance to extreme pHs of papain increased signiﬁcantly due to its immobilization on Sepharose6B.The interesting point observed in this immobiliza-tion process was that increase in K m and decrease in k cat that is, decrease in catalytic efﬁciency,which is a common in most immobi-lized enzymes,was not very signiﬁcant here.It was also shown that immobilized papain was highly resistant to the inhibitory effects of bivalent ions compared to the free enzyme.It was concluded that immobilization process used in this study is highly efﬁcient in improving the stability of papain in various extreme conditions. However,we are still trying to improve the catalytic efﬁciency of the immobilized enzyme,the results of which will be reported in due course.AcknowledgementsThe authors are grateful to the University of Hormozgan for their ﬁnancial support.References[1]A.Homaei,R.Sariri, F.Vianello,R.Stevanato,J.Chem.Biol.6(2013)185–205.[2]J.Kim,J.W.Grate,P.Wang,Chem.Eng.Sci.61(2006)1017–1026.[3]R.Reshmi,G.Sanjay,S.Sugunan,mun.7(2006)460–465.[4]L.Gianfreda,M.R.Scarﬁ,Mol.Cell.Biochem.100(1991)97–128.[5]R.Monti,C.A.Basilio,H.C.Trevisan,J.Contiero,Braz.Arch.Biol.Tech.43(2000)501–507.[6]A.Homaei,R.H.Sajedi,R.Sariri,S.Seyfzadeh,R.Stevanato,Amino Acids38(2010)937–942.[7]A.Sumantha,rroche,A.Pandey,Food Technol.Biotechnol.44(2006)211–220.[8]R.Axen,S.Ernback,Eur.J.Biochem.18(1971)351–360.[9]A.Kilara,K.M.Shahani,Biotechnol.Bioeng.19(1977)1703–1714.[10]S.C.March,I.Parikh,P.Cuatrescasas,Anal.Biochem.60(1974)149–152.[11]A.Homaei,R.Etemadipour,Int.J.Biol.Macromol.72(2015)1176–1181.[12]M.M.Bradford,Anal.Biochem.72(1976)248–254.[13]D.S.Jiang,S.Y.Long,J.Huang,H.Y.Xiao,J.Y.Zhou,Biochem.Eng.J.25(2005)15–23.[14]S.Afaq,J.Iqbal,Electron.J.Biotechnol.4(2001)120–124.[15]K.Sangeetha,T.E.Abraham,J.Mol.Catal.B:Enzymol.38(3–6)(2006)171–177.[16]R.S.Rao,P.S.Borkar,C.N.Khobragade,A.D.Sagar,Enzyme Microb.Technol.39(2006)958–962.[17]H.Lei,W.Wang,L.L.Chen,X.C.Li,B.Yi,L.Deng,Enzyme Microb.Technol.35(2004)15–21.[18]C.Silva,Q.Zhang,J.Shen,A.Cavaco-Paulo,Enzyme Microb.Technol.39(2006)634–640.[19]J.V.Shah,R.C.Chang,F.F.Wang,Y.J.Wang,Biotechnol.Bioeng.35(1990)132–137.[20]G.D.Altun,S.A.Cetinus,Food Chem.100(2007)964–971.[21]S.A.Cetinus,H.N.Öztop,Enzyme Microb.Technol.32(2003)889–894.[22]A.Arslan,S.Kiralp,L.Toppare,Y.Yagci,Int.J.Biol.Macromol.35(2005)163–167.[23]E.Sahmetlioglu,H.Yürük,L.Toppare,I.Cianga,Y.Yagci,React.Funct.Polym.66(2006)365–371.[24]H.A.Sathish,P.Kaul,V.Parkash,Indian J.Biochem.Biophys.37(2000)18–27.[25]Y.Shukor,N.A.Baharom,F.Abd Rahman,M.Puad Abdullah,N.Shamaan,S.M.Arif,Anal.Chim.Acta566(2006)283–289.[26]L.A.Sluyterman,Biochim.Biophys.Acta139(1967)430–438.[27]A.Homaei,A.Bahari,R.Sariri,E.Kamrani,R.Stevanato,S.M.Etezad,K.Khajeh,J.Photochem.Photobiol.B125(2013)131–136.[28]A.M.Klibanov,Adv.Appl.Microbiol.29(1983)1–29.[29]G.Mousumi,N.Geeta,FEBS Lett.330(1993)275–278.。

数字图像处理-冈萨雷斯-课件(英文)Chapter03-空域图像增强

- Histogram matching To make histogram as the desire
Monotonically Increasing Function = Function that is only increasing or constant
Ds Dr
Smaller Dr yields wider Ds = increasing Contrast
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Gray Level Slicing
Contrast Stretching
Contrast means the difference between the brightest and darkest intensities
Before contrast enhancement
After
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Images in the spatial domain are pictures in the xy plane
where the word “distance” is meaningful.
Using the Fourier
transform, the word “distance” is lost but the word “frequency” becomes alive.
Image Negative
L-1 White

基于声学指数的神农架国家公园声音多样性动态变化

果显示ＡＣＩ指数不能很好地反映日变化趋势，但ＢＩ指数和ＮＤＳＩ指数具有明显的日变化趋势，且变化趋势符合
物种黎明／黄昏合唱的习性；声学指数随海拔梯度的空间变化结果表明，ＡＣＩ、ＢＩ指数在中海拔区域具有最大值，
且ＡＣＩ指数与海拔相关性较强，ＮＤＳＩ指数没有显著的变化趋势。【结论】ＢＩ、ＮＤＳＩ指数能较好地反映动物声音
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基于响应面法的地热钻采碳纳米管复合水泥基材料的研究

第43卷第2期2024年2月硅㊀酸㊀盐㊀通㊀报BULLETIN OF THE CHINESE CERAMIC SOCIETY Vol.43㊀No.2February,2024基于响应面法的地热钻采碳纳米管复合水泥基材料的研究向㊀杰,王㊀胜,李玉杰,王文杰(成都理工大学地质灾害防治与地质环境保护国家重点实验室,成都㊀610059)摘要:针对现有导热固井水泥存在的性能不足问题,本文研制了一种新型地热钻采碳纳米管复合水泥基材料(CNTs-CC)㊂首先,选用石墨㊁氮化硅作为主要导热填料,硅微粉作为热稳定材料,碳纳米管作为协同增强填料,初步研制出纳米复合水泥材料基础液;其次,基于响应曲面法Box-Behnken 试验设计,开展17组配比优化试验,构建了以2d 抗压强度和导热系数为响应指标的二次多项式预测模型,结合方差分析和响应曲面考察了各因素对响应指标的影响,并得到胶凝材料最优配比;最后,对复合水泥基材料的工程性能进行评估,并结合XRD 与SEM 研究了材料的水化机理㊂结果表明:复合水泥基材料的导热性能与抗压强度受多因素交互作用影响,其中早强剂与减水剂交互影响显著;CNTs-CC 水泥石28d 抗压强度达8.15MPa,导热系数为2.236W /(m㊃K);导热填料不参与水化过程,碳纳米管粉可发挥填充及桥连效应,外加剂调控水化进程㊂关键词:地热钻采;水泥基材料;石墨;氮化硅;碳纳米管;响应曲面;水化中图分类号:TQ172㊀㊀文献标志码:A ㊀㊀文章编号:1001-1625(2024)02-0495-14收稿日期:2023-09-19;修订日期:2023-11-17基金项目:国家自然科学基金(42072339,U19A2097);地质灾害防治与地质环境保护国家重点实验室(SKLGP2022Z006);成都理工大学珠峰技术研究计划(80000-2020ZF11411)作者简介:向㊀杰(1998 ),男,硕士研究生㊂主要从事水泥相关的研究㊂E-mail:1345491887@通信作者:王㊀胜,博士,教授㊂E-mail:yongyuandewangsheng@Carbon Nanocomposite Cement-Based Materials for Geothermal Drilling and Production Based on Response Surface MethodXIANG Jie ,WANG Sheng ,LI Yujie ,WANG Wenjie(State Key Laboratory of Geological Hazard Prevention and Geological Environmental Protection,Chengdu University of Technology,Chengdu 610059,China)Abstract :A novel carbon nanocomposite cement-based material for geothermal drilling and production (CNTs-CC)was developed to solve the problem of insufficient performance of existing thermal cementing cement.Firstly,with graphite and silicon nitride as main thermal conductivity filler,silicon powder as heat stabilization material and carbon nanotubes as co-reinforcing filler,the nano composite cement material base liquid was preliminarily developed.Secondly,based on the Box-Behnken experiment design of response surface method,17-sets of ratio optimization experiments were carried out,and a quadratic polynomial prediction model with 28d compressive strength and thermal conductivity as the response indexes was constructed.The influences of various factors on the response indexes were investigated by combining analysis of variance and response surface,and the optimal ratio of cementable materials was obtained.Finally,the engineering properties of the cement-based composite materials were evaluated,and the hydration mechanism of the cement-based composite materials was studied by XRD and SEM.The results show that the thermal conductivity and compressive strength of cement-based composite materials are influenced by the interaction of many factors,in which the interaction betweenearly strength agent and water reducing agent is significant.The 28d compressive strength of CNTs-CC cement stone is8.15MPa,and the thermal conductivity is 2.236W /(m㊃K).The thermal conductive filler does not participate in the hydration process,and the carbon nanotube powder can play a "filling"and "bridging"effect,and the admixture regulates the hydration process.496㊀水泥混凝土硅酸盐通报㊀㊀㊀㊀㊀㊀第43卷Key words:geothermal drilling and production;cement-based material;graphite;silicon nitride;carbon nanotube;response surface;hydration0㊀引㊀言地热能具有绿色环保㊁储量丰富等优点,推广开发地热能,有益于缓解我国对化石能源的依赖,对环境保护及生态系统健康发展具有重要意义[1]㊂目前,我国中深层地热资源(井深约3000m,温度介于90~150ħ)的开采研究还处于缓慢发展阶段[2]㊂已有研究[3-5]表明,提升同轴换热系统固井水泥环的导热性能可有效改善地热井的取热效率㊂学者们对适用于地热开采的导热水泥展开了系统研究,但仍存在一定的研究缺陷㊂Song等[6]研究了石墨㊁铁粉及铜粉各自对水泥石孔隙率㊁导热系数及抗压强度的影响,并得出了填料最优掺量范围,但却未指明材料的施工应用特性㊂近年来,Yang等[7]将石墨㊁铁粉㊁石英砂和油井水泥按照一定比例复配,研制出了48h抗压强度为23.38MPa㊁导热系数为2.003W/(m㊃K)的水泥材料,但样品的养护方式仅为60ħ水浴养护,忽略了高温高压养护条件对样品性能的影响,这削弱了材料在中深层地热开采固井工程应用中的借鉴意义,且材料在导热性能方面还有提升空间㊂Wang等[8]兼顾考虑了样品的高温高压养护条件(150ħ,20.7MPa),并将复合水泥的导热系数提升至2.141W/(m㊃K),但该水泥体系1d抗压强度仅为7.05MPa,14d强度低至4.57MPa,强度不足将会影响固井质量,不利于地热井的完整性㊂可见,如何保证水泥材料在高温高压条件下兼具优异的导热性能和抗压强度已成为地热固井工程的技术瓶颈,研发新型导热水泥材料对提高地热井固井效果及热能利用率仍具有十分重要的工程意义和科学价值㊂已有研究[9-11]表明,水泥导热性能主要受养护温度㊁水灰比(water-cement ratio,W/C)和外加剂等因素影响㊂在研究材料最优设计比时,若各因素间存在交互作用,那么采用单因素试验法或正交设计法得出的结果往往不适用于实际情况分析[12]㊂相比而言,响应面法是一种综合试验设计优化方法,可以较好评估各个因素对响应值的线性作用㊁交互作用,并取得各影响因素的最优水平值[13]㊂因此,本文采用响应面法作为优化设计方法,在研制出纳米水泥材料基础液后,使用Design-Expert软件的Box-Behnken模块,以水灰比大小㊁早强剂添加量㊁减水剂添加量为自变量,水泥石导热性能㊁抗压强度为响应值,建立了二次多项式模型,并结合方差分析和响应曲面考察了各因素对响应目标的影响主次关系及因素间的交互作用,最终得到最佳配比㊂本文针对当前地热固井工程存在的技术瓶颈,研制出了适用于中深层地热开采的新型纳米复合水泥材料,其既具有可供热能高效开采的优异导热性能,又具备可支撑深井软弱地层的良好力学强度㊂同时,探究了采用响应面法设计导热固井水泥配合比的可行性,并从微观层面对水泥水化机理作出阐述,为中深层地热钻采胶凝材料配比设计及工程应用提供了理论依据㊂1㊀实㊀验1.1㊀试验材料选用G级油井水泥作为基本胶凝材料(购自四川乐山嘉华水泥厂),其主要化学成分见表1;选用200目(74μm)石墨(记作SM-200,购自江西硕邦新材料科技有限公司)和400目(38μm)氮化硅(记作Si3N4-400,购自上海肴弋合金材料有限公司)作为导热填料,两者的技术参数分别见表2和表3;选用300目(50μm)硅微粉(记作GF-300,购自江苏徐州市新沂市林志石英厂)作为热稳定材料,其主要成分为SiO2,纯度大于99%;选用碳纳米管(carbon nanotubes,CNTs,购自江苏宿市迁烯谷纳米科技有限公司)作为协同增强材料,其主要技术参数见表4;选用减水剂(一种改性聚羧酸醚类高效分散减水剂,记作JSL,购自巴斯夫建材助剂有限公司)㊁早强剂(AR级无水硫酸钠,记作ZQS,纯度大于99%,购自国药集团化学试剂有限公司)㊁结构稳定剂(一种高分子聚合物类黏度改性剂,记作STA,购自巴斯夫建材助剂有限公司)优化调控水泥基材料性能㊂㊀第2期向㊀杰等:基于响应面法的地热钻采碳纳米管复合水泥基材料的研究497表1㊀水泥的主要化学成分Table1㊀Main chemical composition of cementComposition CaO SiO2Fe2O3Al2O3MgO SO3Other Mass fraction/%64.0721.43 4.76 3.48 1.98 1.57 4.04表2㊀石墨粉的技术参数Table2㊀Technical parameters of graphite powderCarbon content/%Particle size/μm Density/(g㊃m-3)Thermal conductivity/(W㊃m-1㊃K-1) 99742350~2000表3㊀氮化硅的技术参数Table3㊀Technical parameters of silicon nitridePurity/%Particle size/μm Specific surface area/(m2㊃g-1)Density/(g㊃m-3)Crystal form99.938.065.0 3.4Alpha phase表4㊀碳纳米管的技术参数Table4㊀Technical parameters of carbon nanotubesPurity/%Specific surface area/(m2㊃g-1)Powder resistivity/(Ω㊃mm2㊃m-1)Pipe diameter/nm Pipe length/μm98.4243.0817.28~205~151.2㊀试验方法1.2.1㊀水泥石性能测试水泥石的抗压强度通常会在高温环境下衰退,参考‘油井水泥试验方法“(GB/T19139 2012),在90~ 150ħ(我国中深层地热资源温度)养护温度下,推荐水泥石养护压力为20.7MPa㊂为确保固井质量,除特别说明外,文中水泥石的养护条件均设定为150ħ㊁20.7MPa,采用加压养护釜对入模后的水泥浆施加温度和压力,养护至规定龄期后采用全自动水泥抗折抗压试验机对水泥石进行力学强度测试㊂采用上海和晟仪器科技有限公司生产的HS-DR-5型导热系数测试仪测试水泥石导热系数,仪器参考标准‘塑料制品导热系数和热扩散系数的测试法第2部分:瞬态平面热源法“(ISO22007-2:2022)㊂1.2.2㊀水泥浆液性能测试参考‘水泥基灌浆材料应用技术规程“(GB/T50448 2015),采用圆锥截模法测试浆液的初始流动度㊂由四川乐山嘉华特种水泥股份有限公司测试水泥浆液高温稠化特性,试验严格遵循‘油井水泥试验方法“(GB/T19139 2012)㊂1.2.3㊀微观形貌分析取终止水化并烘干后的水泥石粉末样品用于X射线衍射分析(XRD),采用仪器型号为D8ADVANCE㊂采用NOVA NANOSEM450型扫描电子显微镜(SEM)对样品的微观形貌进行识别分析㊂1.3㊀试验设计试验以水泥石2d导热系数Y1㊁抗压强度Y2为响应指标值,水灰比大小X1㊁早强剂添加量X2㊁减水剂添加量X3为自变量(全文所述百分比添加量均是指占水泥质量的百分比),根据Box-Behnken模块设计三因素三水平试验(共17组),设计因素编码水平见表5,表中-1㊁0㊁1分别代表编码变量的低㊁中㊁高水平㊂表5㊀因素水平编码Table5㊀Level coding of factorsFactor Level-101 X10.630.680.73X2/% 1.5 2.0 2.5X3/%0.050.100.15498㊀水泥混凝土硅酸盐通报㊀㊀㊀㊀㊀㊀第43卷2㊀结果与讨论借鉴文献[14]思路,本文先确定导热填料及热稳定材料,优选纳米材料和外加剂,再进行响应面优化试验,最终研制出纳米复合水泥优化配方㊂2.1㊀纳米复合水泥基材料基础浆液研制2.1.1㊀导热填料筛选图1㊀常用导热填料对水泥性能的影响Fig.1㊀Effects of common thermal conductive fillers on cement properties 13种常用导热填料在10%单掺条件下对水泥石高温抗压强度及导热性能的影响结果如图1所示,每种填料均选用600目(23μm)及1200目(11μm)两种粒度以避免误差㊂从图1可以看出:石墨粉最有利于提升传热性能,但并不参与水泥水化,且其鳞片状结构极易引入空气,会导致水泥高温强度衰退[15];α-Si 3N 4力学强度提升效果最优,但其对导热性能的改善效果不及石墨;铜包石墨粉的成本过高,且整体效果不如石墨㊂综合考虑,选用石墨及α-Si 3N 4共同作为基础导热填料㊂图2为不同粒径石墨及α-Si 3N 4在10%掺量下对水泥性能的影响㊂由图2(a)可知,伴随石墨粒径减小,水泥石高温抗压强度整体表现为先增后减趋势,而导热系数及浆液流动度呈降低趋势,其中200目石墨最有益于提升材料传热性能㊂如图2(b)所示,随着氮化硅填料尺寸的减小,水泥石(除5000目外)抗压强度㊁导热系数及流动度几乎保持稳定,以400目氮化硅对水泥石的性能改善最优㊂故此,最终选择200目石墨(记作SM-200)及400目氮化硅(记作Si 3N 4-400)进行添加量优化及复配研究㊂图2㊀不同粒径导热填料对水泥性能的作用效果Fig.2㊀Effects of thermal conductive fillers with different particle size on cement properties 图3为不同SM-200及Si 3N 4-400添加量对水泥性能的影响㊂试验结果表明,20%石墨几乎最大化打通导热通路,实现了水泥石的高效热传导;伴随石墨添加量持续提升,水泥石高温抗压强度及浆液流动性严重恶化㊂氮化硅可显著提升水泥石力学强度,但随着用量逐渐增多,其改善效果开始趋于缓和,水泥石导热系数增幅也逐渐饱和,同时浆液流动性逐渐降低㊂综上所述,确定SM-200添加量为20%以保障较优导热性能,并在此基础上掺入Si 3N 4-400进行复配研究,导热填料复配添加量对水泥性能的影响(W /C =0.68)见图4(提升水灰比至0.68以确保浆液较优的流动性,养护龄期为2d)㊂第2期向㊀杰等:基于响应面法的地热钻采碳纳米管复合水泥基材料的研究499㊀图3㊀导热填料添加量对水泥性能的影响(W /C =0.55)Fig.3㊀Effect of thermal conduction filler addition on cement properties (W /C =0.55)图4㊀导热填料复配添加量对水泥性能的影响(W /C =0.68)Fig.4㊀Effect of compound addition of thermal conductive filler on cement properties (W /C =0.68)㊀㊀由图4可知,随氮化硅添加量提升,水泥浆液流动度直线下降,水泥石高温抗压强度呈先增后减趋势,而导热性能稳定在一定水平范围内㊂分析认为,氮化硅自身的导热性能远低于石墨,使得其在均匀分布的情况下,也无法像石墨那样大幅提升材料导热性能,持续提升氮化硅添加量至20%亦无显著效果,故最终确定Si 3N 4-400的添加量为15%㊂此后,通过开展类似试验,确定使用300目硅微粉(记作GF-300)作为热稳定剂(添加量5%)以延缓高温下水泥强度衰退,得出复合水泥基础浆液(base slurry,BS),配方即:G 级油井水泥+20%SM-200+15%Si 3N 4-400+5%GF-300(W /C =0.68)㊂2.1.2㊀纳米材料优选以上获得的BS 配方水泥石2d 抗压强度仅为8.904MPa,这并不利于保障良好的固井质量,且导热系数仅为1.8624W /(m㊃K),这与实际岩层导热系数(2~3W /(m㊃K))还存在一定差距[7],不能有效提升地热井换热效率㊂前期试验表明,继续增大石墨或氮化硅添加量已无明显性能提升效果,而纳米材料可以优化水泥石微观结构[16],改善内部缺陷,故掺入高导热纳米材料协同增强水泥性能㊂表6为不同纳米材料对BS 水泥性能的影响㊂数据表明,CNTs 最有益于提升BS 水泥石的导热性能与抗压强度,这源自其极高的导热系数及其尺寸效应㊂随后开展添加量优化试验,试验参数如表7所示,CNTs 在0.4%添加量下对水泥性能改善效果最优㊂分析认为,尽管碳纳米材料分子间存在极强的范德华力,会导致CNTs 发生缠结团聚[17],但仍可发挥填充及桥联效应[18],其独特的线型结构[19]可承载微观裂纹扩展应力,有利于基体性能的提升㊂故此,最终选用CNTs 协同增强材料性能,其添加量为0.4%,得出纳米复合水泥材料基础浆液(记作BS +CNTs),配方即BS +0.4%CNTs㊂表6㊀不同纳米材料对BS 水泥性能的影响Table 6㊀Effects of different nanomaterials on properties of BS cementBasic formula Types of nanomaterial Dosage /%2d thermal conductivity /(W㊃m -1㊃K -1)2d compressive strength /MPa Fluidity /cm 0 1.802110.01215.0Nano boron nitride 0.5 1.75429.53014.0BS Nano silicon nitride 0.5 1.65968.84214.0Graphene nanosheet powder 0.5 1.89249.12012.0Carbon nanotube powder 0.5 1.902410.33113.5Carbon nanotube slurry0.5 1.89918.97412.0500㊀水泥混凝土硅酸盐通报㊀㊀㊀㊀㊀㊀第43卷表7㊀纳米材料添加量优化试验参数Table7㊀Test parameters of nanomaterial addition optimizationBasic formula Types of nanomaterial Dosage/%2d thermal conductivity/(W㊃m-1㊃K-1)2d compressive strength/MPa Fluidity/cm0.2 1.877210.16514.00.3 1.865410.20314.0BS Carbon nanotube powder0.4 1.920710.53214.00.5 1.902410.33113.50.6 1.84749.57312.0 2.1.3㊀外加剂优选当前研制的纳米复合水泥体系水泥石力学强度及导热性能仍处于较低水平,且存在浆液初始流动度低㊁长期力学性能不足㊁沉降稳定性差的问题,这会降低固井水泥的工程应用价值㊂针对上述问题,分别采用减水剂㊁早强剂㊁结构稳定剂进行优化调控㊂表8为常用减水剂对水泥性能的影响,通过调控减水剂添加量,确保水泥浆液初始流动度为22cm左右[8]㊂在养护至规定龄期后,以水泥石高温抗压强度及导热系数作为主要评估指标㊂观察表8数据可知,木质素类(CMN)㊁奈系(NQ)㊁胺系(F10)及部分工业合成产品(如MX-1㊁MX-2)使纳米复合水泥浆严重缓凝,致使水泥石出现了断层现象(上下分层)㊂而聚羧酸减水剂(HLX)㊁改性聚羧酸醚类减水剂(JSL)及工业品(CP19)的作用效果不一,以JSL效果最优㊂故减水剂最终选用JSL,通过添加量优化试验确定其添加量宜控制在0.05%~0.15%㊂表8㊀常用减水剂对水泥性能的影响Table8㊀Effects of common water reducers on cement propertiesSlurry composition Water reducer Fluidity/cm2d compressivestrength/MPa 2d thermal conductivity/ (W㊃m-1㊃K-1)None14.010.532 1.9207CMN22.0NQ21.5F1022.5 BS+0.4%CNTs HLX22.09.687 1.8564MX-122.5MX-222.0JSL22.511.023 2.0017CP1922.010.157 1.8721㊀㊀Note: indicates that the cement is layered above and below.表9为常用早强剂对水泥性能的影响(以各自推荐添加量添加)㊂数据表明,不同早强剂对水泥石高温抗压强度并没有展现出明显的适用性,其中仅以2%添加量的无水硫酸钠(ZQS)对复合水泥性能起到明显的协同增强效果,通过添加量优化试验确定其用量宜控制在1.5%~2.5%㊂表9㊀常用早强剂对水泥性能的影响Table9㊀Effects of common early strength agents on cement propertiesSlurry composition Early strength agent Dosage/%Fluidity/cm2d compressivestrength/MPa 2d thermal conductivity/ (W㊃m-1㊃K-1)022.511.023 2.0017Triethanolamine0.521.08.976 1.8951BS+0.4%CNTs+0.1%JSL Mechanicals7042 1.023.59.087 1.9422Mechanicals7100 2.023.511.219 1.8763CaCl2 2.022.011.254 1.8482ZQS 2.022.012.856 2.2064最后研究了两种结构稳定剂对复合水泥体系性能的影响,如表10所示㊂分析表中数据可知,两种结构第2期向㊀杰等:基于响应面法的地热钻采碳纳米管复合水泥基材料的研究501㊀稳定剂对复合水泥体系均起到一定的降泌水作用,其中STA结构稳定剂可显著降低水泥浆游离液体积,保水性更强㊂同时,STA在不同添加量下对水泥其他性能无显著影响,而SMC会使水泥性能出现不同程度的衰退㊂故最终选用STA作为结构稳定剂,其添加量宜控制在0.02%左右㊂表10㊀结构稳定剂对水泥性能的影响Table10㊀Effects of structural stabilizers on cement propertiesSlurry composition Stabilizer Dosage/%Free fluid/%Fluidity/cm2d compressivestrength/MPa 2d thermal conductivity/ (W㊃m-1㊃K-1)0 3.7322.012.856 2.2064STA0.01 1.1422.012.679 2.2748STA0.02 1.0622.012.763 2.2856BS+0.4%CNTs+0.1%JSL+2%ZQS STA0.03 1.0321.512.664 2.2542SMC0.05 2.6021.011.685 2.1359SMC0.08 2.5120.011.763 2.1654SMC0.10 2.2319.011.602 2.14462.2㊀响应面试验设计优化2.2.1㊀试验测试结果水泥导热性能受水灰比㊁外加剂等因素影响㊂同时在试验过程中发现,水灰比大小㊁JSL添加量及ZQS 添加量的不同均会引起复合水泥性能显著变化㊂故此,根据表5开展优化试验,测试结果见表11,以此探究因素间交互作用及影响主次关系,并得到最优配比㊂表11㊀响应面优化测试结果Table11㊀Test results of response surface optimizationTest No.Code value Response valueX1X2X32d thermal conductivity/(W㊃m-1㊃K-1)2d compressivestrength/MPa1-1-10 2.315913.39621-10 2.087210.6613-110 1.983011.8214110 1.88298.6285-10-1 2.093011.896610-1 1.84398.6977-101 1.984711.9728101 1.86948.50490-1-1 2.098311.8561001-1 1.99379.878110-11 2.124711.97312011 1.88289.33613000 2.287612.29814000 2.234511.59915000 2.222112.65116000 2.287011.92617000 2.228412.1082.2.2㊀模型方差分析及可靠性检验对表11试验数据进行回归分析,分别建立了水泥石导热性能㊁抗压强度与三个因素间的四种回归模型,如表12㊁表13所示㊂一般地,P<0.01说明该因子在模型中非常显著,P<0.05为显著,反之则不显著[20]㊂由表12㊁表13可知,二次多项式模型P值均小于0.01,为非常显著;而失拟项P分别为0.3480和0.7353,均大于0.05,不显著;校正相关系数Adj.R2和预测相关系数Pre.R2均较大且接近理想值1㊂因此选用二次多项式模型分析因素间的定量关系,采用该模型对表11中的试验数据进行拟合,得出二次多项式,如式(1)㊁式(2)所示㊂502㊀水泥混凝土硅酸盐通报㊀㊀㊀㊀㊀㊀第43卷Y1=2.25-0.0866X1-0.1105X2-0.0209X3+0.0321X1X2+0.0335X1X3-0.0343X2X3-0.1309X21-0.0538X22-0.1733X23(1)Y2=12.12-1.5700X1-1.0300X2-0.0677X3-0.1145X1X2-0.0672X1X3-0.1648X2X3-0.7417X21-0.2482X22-1.1100X23(2)表12㊀水泥石导热性能回归模型对比Table12㊀Comparison of regression models of thermal conductivity of cement stoneModel P-value Lack of fit P-value Adj.R2Pre.R2Linear model0.08410.00340.24860.0626 Two-factor interaction model0.90380.00180.0747-0.5556 Quadratic polynomial model<0.00010.34800.95050.8020Cubic polynomial model0.34800.9589表13㊀水泥石力学性能回归模型对比Table13㊀Comparison of regression models of mechanical properties of cement stoneModel P-value Lack of fit P-value Adj.R2Pre.R2Linear model0.00030.04650.69340.6189 Two-factor interaction model0.97730.02500.60900.3283Quadratic polynomial model0.00050.73530.94970.8864Cubic polynomial model0.73530.9339为评价模型可靠度和精确性,通过方差分析对导热性能和力学性能模型误差来源进行显著性检验,结果如表14㊁表15所示㊂通常采用显著性检验指标F值和概率P值共同判定回归模型的显著性,F值越大,P 值越小表示模型假设不成立的概率越小,模型显著性越强,模拟精度越高[21]㊂分析表14㊁表15中参数可知,导热性能模型和力学性能模型F值分别为35.17㊁34.58,且P值都小于0.0001,这表明两个二次多项式模型都具有极高的显著性;复相关系数R2分别为0.9784㊁0.9780,说明97.84%㊁97.80%的响应值变化与选取三个因素变化相关;模型校正相关系数Adj.R2分别为0.9505㊁0.9497,表明其中95.05%㊁94.97%的响应指标值可以由模型解释,能较好地拟合导热系数㊁抗压强度与三因素之间的响应关系;预测相关系数Pre.R2分别为0.8020㊁0.8864,表明预测可靠㊂观察各因素㊁交互因素的P值大小可知,水灰比大小X1及早强剂添加量X2对水泥石导热性能和抗压强度的影响都最为显著㊂具体来看,单因素影响导热系数的显著性排序为X2>X1>X3,影响抗压强度的显著性排序为X1>X2>X3;各因素交互作用影响导热系数的显著性排序为X2X3>X1X3>X1X2,影响抗压强度的显著性排序为X2X3>X1X2>X1X3㊂表14㊀导热性能模型方差分析Table14㊀Variance analysis of thermal conductivity modelsSource Sum of squares Degree of freedom Mean square F-value P-value Significance Model0.404890.045035.17<0.0001Significant X10.060110.060146.960.0002X20.097610.097676.31<0.0001X30.003510.0035 2.740.1421X1X20.004110.0041 3.230.1153X1X30.004510.0045 3.500.1036X2X30.004710.0047 3.680.0964X210.072110.072156.400.0001X220.012210.01229.520.0177X230.126410.126498.83<0.0001Residual0.009070.0013Lack of fit0.004730.0016 1.480.3480Insignificant Pure error0.004240.0011Sum0.413816㊀㊀Note:R2=0.9784,Adj.R2=0.9505,Pre.R2=0.8020.㊀第2期向㊀杰等:基于响应面法的地热钻采碳纳米管复合水泥基材料的研究503表15㊀力学性能模型方差分析Table15㊀Variance analysis of mechanical property modelsSource Sum of squares Degree of freedom Mean square F-value P-value Significance Models36.889 4.1034.58<0.0001Significant X119.83119.83167.30<0.0001X28.4518.4571.31<0.0001X30.036710.03670.30980.5951X1X20.052410.05240.44240.5272X1X30.018110.01810.15260.7077X2X30.108610.10860.91600.3704X21 2.321 2.3219.540.0031X220.259410.2594 2.190.1826X23 5.161 5.1643.570.0003Residual0.829770.1185Lack of fit0.206930.06900.44290.7353Insignificant Pure error0.622840.1557Sum37.7116㊀㊀Note:R2=0.9780,Adj.R2=0.9497,Pre.R2=0.8864.2.2.3㊀实际值与预测值对比分别以水泥石2d导热系数㊁抗压强度实际测量值为X轴,模型预测值为Y轴,绘制了如图5所示的模型可靠性评估散点图㊂由图5(a)㊁(b)可知,水泥石导热系数和抗压强度预测值与实际值相关性都较高,实际测量值均匀分布于直线及其两侧,离散性较小,说明模型拟合精度高,可靠性好,所建模型可以对复合水泥的导热性能和抗压强度进行分析和预测㊂图5㊀模型可靠性评估Fig.5㊀Model reliability assessment2.2.4㊀响应曲面分析为直观分析各因素交互作用对响应值的影响,并获得性能最优值,构建了如图6所示三维曲面图㊂图6(a)为水灰比和早强剂交互作用对水泥石导热性能的影响,由图可知,水泥石导热系数随水灰比提升呈先增后减的趋势;随着早强剂添加量增加表现为小幅度的先增后减趋势,整体来看,在水灰比和早强剂交互作用下存在一个交叉点使水泥石导热性能最优㊂图6(b)展示了水灰比和减水剂交互作用对水泥石导热性能的影响,随着水灰比提升,水泥石导热性能呈显著的先增后减趋势;随着减水剂添加量提升,性能变化趋势类似,可见两者位于中值附近时导热性能最优㊂早强剂与减水剂交互作用对水泥石导热性能的影响如图6(c)所示,提升早强剂添加量,导热系数先略微提升后加速下降;提升减水剂用量,先增后减趋势更为明显,整体来看,在早强剂和减水剂交互作用下亦存在一个交叉点使水泥石导热性能最优㊂图6(d)为水灰比与早强剂交互作用对抗压强度的影响,由图可知,水灰比增大会导致水泥石抗压强度加速衰退;早强剂添加量提升亦会产生同样效果,可见两者取较低水平时有利于水泥石强度的发展㊂504㊀水泥混凝土硅酸盐通报㊀㊀㊀㊀㊀㊀第43卷图6(e)展示了水灰比和减水剂交互作用对抗压强度的影响,伴随着减水剂添加量提升,水泥石抗压强度呈先增后减趋势;随着水灰比缓慢提升,抗压强度先略微增加后加速衰减,可见,水灰比取较低水平㊁减水剂取中值水平时有利于水泥石强度的发展㊂早强剂与减水剂交互作用对力学性能的影响如图6(f)所示,提升早强剂添加量,水泥石抗压强度呈现出缓慢降低的趋势;随着减水剂用量逐渐提升,水泥石抗压强度呈显著的先增后减趋势,可见减水剂取中值水平㊁早强剂取较低掺量时,水泥石力学性能较优㊂图6㊀响应面分析Fig.6㊀Response surface analysis2.2.5㊀响应面最优化结果预测与验证经响应曲面分析,探究了水灰比大小㊁早强剂添加量㊁减水剂添加量对水泥石导热性能及力学强度的交互作用和显著性影响,随后基于模型最大期望值得出了纳米复合水泥基材料优化配方(记作CNTs-CC),如表16所示㊂模型计算结果表明,水泥石2d抗压强度为13.448MPa,导热系数为2.323W/(m㊃K)㊂通过室内重复性试验测试了优化配方的综合性能,如表17所示,其中水泥石48h抗压强度为12.860MPa,导热系数为2.241W/(m㊃K)㊂模型预测值与试验实际测量值吻合度高,这表明响应面试验设计科学有效,对纳米复合水泥配比优化有较好指导意义㊂表16㊀纳米复合水泥基材料优化配方Table16㊀Optimal formulation of nano-composite cement materialOptimize formula Formula composition W/C Early strength agent/%Water reducer/%Structural stabilizer/% CNTs-CC BS+0.4%CNTs0.65 1.600.100.02表17㊀优化配方的综合性能Table 17㊀Compressive properties of optimized formulationsOptimize formula 2d compressive strength /MPa 2d thermal conductivity /(W㊃m -1㊃K -1)Fluidity /cm High temperature pumpable period /min CNTs-CC 12.860 2.24121.0652.3㊀纳米复合水泥基材料工程性能评估2.3.1㊀高温稠化特性在地热钻采固井中,通常要求水泥具备适宜的初始流动度和稠度,以确保其较优的可泵性㊂同时,浆液需在施工泵送期间缓慢水化㊁施工完成后迅速稠化[22]㊂因此,开展了CNTs-CC 配方高温稠化特性研究(试验条件为150ħ㊁76.5MPa㊁74min),以评估水泥浆现场施工可行性㊂图7为CNTs-CC 高温高压稠化特性,纳米复合水泥浆液初始稠度为10Bc 左右,伴随模拟深井温度及压力逐步提升,当到设定值后,优化配方水泥浆液迅速完成稠化(稠度值达到100Bc),稠化总时长为70min,展现出明显的直角稠化特性,具备施工可行性㊂2.3.2㊀抗压强度在当前高温高压固井施工领域中,相关规范要求水泥石24及48h 抗压强度应分别高于3.5和7.0MPa [23],故此,以150ħ㊁20.7MPa 作为养护条件,探究CNTs-CC 能否适用于实际的地热开采固井工程,相关试验数据如图8所示㊂由图可知,随着养护龄期的增加,抗压强度呈先增后减趋势,这是由于水泥前期还在缓慢反应形成有利于强度发展的水化硅酸钙,而后期高温下非晶态的水化硅酸钙会转化为不利于强度发展的结晶相水化硅酸二钙,进而导致水泥性能衰退[24]㊂即便如此,样品28d 抗压强度仍具有8.15MPa,可保障其对深井软弱地层的有力支撑(>7MPa)㊂图7㊀CNTs-CC 高温高压稠化特性Fig.7㊀High temperature and pressure thickening properties ofCNTs-CC 图8㊀CNTs-CC 高温力学性能Fig.8㊀High temperature mechanical property of CNTs-CC 2.3.3㊀导热系数图9为CNTs-CC 导热性能随养护龄期的变化㊂由图9可知,随着养护龄期的延长,水泥石导热系数整体呈先增后减㊁最后保持稳定的趋势㊂优化配方养护35d 后,导热系数变化趋于平缓,受时间与温度的影响不显著,其导热性能并未发生本质性的改变,稳定性较强㊂最终取CNTs-CC 导热系数为2.236W /(m㊃K),这足以满足我国中深层地热井对固井水泥的导热性能需求(>2.0W /(m㊃K))[7]㊂2.4㊀纳米复合水泥基材料微观机理分析2.4.1㊀X 射线衍射分析图10为复合水泥基础浆液配方BS㊁纳米协同增强配方BS +CNTs 及最终优化配方CNTs-CC 三种复合体系水化2d 后的样品XRD 谱㊂由图10可知,各对照样品的主要物相成分均为斜方硅钙石(Ca 24Si 16O 56)㊁氢氧化钙(Ca(OH)2,后文简写为CH)㊁水化硅酸二钙(C 2SH)㊁硬硅钙石(C 6S 6H)㊁托贝莫来石(C 5S 6H 5)㊁氮化硅(Si 3N 4)及石墨(C,记作。

心脏核磁共振参数预测ST段抬高型心肌梗死患者急诊血运重建后心功能改善的价值

-临床研究•心脏核磁共振参数预测ST段抬高型心肌梗死患者急诊血运重建后心功能改善的价值刘丹顾佳宁韩凯月邸若岷杨晨曦杨奕清徐迎佳【摘要】目的：探讨心脏核磁共振（CMR）特征追踪（FTI）、首过灌注成像（PFI）、延迟钆强化技术（LGE）获得的参数对于预测ST段抬高型心肌梗死（STEMI）患者急诊血运重建后心功能改善的价值。

方法:连续入选2018年1月至2020年1月行急诊经皮冠状动脉介入术（PCI）的初次诊断STEMI患者58例，术后即刻超声心动图检查提示左室射血分数（LVEFX40%，在成功实施血运重建后3〜5d行CMR检查。

先后应用SSFP电影序列、T2W STIR-FSE序列、LGE进行扫描并分别获取FTI、PFI及LGE图像，利用后处理分析软件分别计算左室整体收缩期峰值圆周应变（GCS）和纵向应变（GLS）、心肌挽救指数（MSI），并在12个月后复查超声心动图。

结果：12个月随访发现27例（47%）心功能改善（LVEF增加>5%）o GCS判断患者心功能改善的临界值为—19.1%,敏感性为76%、特异性为85%［曲线下面积（AUC）=0.86,95%CI：0.71〜0.92,P<0.001］，优于GLS（AAUC=014,P=0.01）。

MSI的临界值为61.5%,其敏感性为85%、特异性为91%,均优于GCS（AAUC=007,P<0.05）。

多元回归分析显示，GCS和MSI是预测心功能改善的独立影响因素（HR=1.5,95%CI： 1.0〜1.9和HR=1.4,95%CI： 1.1〜1.7,P均<0.05）。

结论:FTI技术估测的GCS在无需额外注射钆造影剂的情况下能预测STEMI患者PCI术后心功能改善，但MSI的诊断效能更高。

【关键词】急性心肌梗死；经皮冠状动脉介入术；心脏核磁共振;心功能恢复doi：103969/jissn1673-6583202103014Value of CMR in predicting cardiac function recovery after emergency revascularization in patients with STsegment elevation myocardial infarction LIU Dnn,GU Jianing,HAN Kaiyue,DI Ruomin,YANGChemi,YANG Yiqing,XU Yingjia Department of Cardiology,Shanghai Fifth People'sHospital,Fudnn University,Shanghai200040,China【Abstract】Objective：To investigate the predictive value of different parameters concerned withimproving emeryency revascularization acquired by cardiac magnetic resonance(CMR):including featuretracking(FTI)first p ass perfusion imaging(PFI)and delayed gadolinium enhancement(LGE)inpatients with ST segment elevation myocardial infarction(STEMI).Methods:A total of58patients withSTEMIunderwentprimarypercutaneouscoronaryintervention(PCI)fromJanuary2018toJanuary2020,with left ventricular ejection fraction(LVEF)less than40%tested by transthoracic echocardiography(TTE)immediately after PCI,were consecutively enrolled in this study.CMR wasperformed3-5days after successful revascularization.We used SSFP cine sequence,T2W STIR-FSEsequence and LGE sequence to acquire FTI,PFI and LGE images,respectively.The global systolic peakcircumferential strain(GCS),longitudinal strain(GLS)and myocardial salvage index(MSI)werecalculated by postprocessing analysis software.After12-month follow-up,TTE was reexamined.基金项目：上海市卫生健康委员会（201740064）作者单位：200040复旦大学附属上海市第五人民医院心内科通信作者:徐迎佳,E-mail:xuyingjia@Results:After12-month follow-up,27patients(47%)showed improvement in cardiac function(LVEF increase》5%).The cut-off value of GCS was—19.1%for evaluating the improvement of cardiac function(AUC二0.86,95%CI0.71-0.92,P<0.001).The sensitivity and specificity of GCS were76% and85%,which were better than GLS(Z\AUC二0.14,P二0.01).The cut-o ff value of MSI was 61.5%.The sensitivity and specificity of MSI were85%and91%respectively,which were better than GCS(z\AUC二0.07,P<0.05).Multiple regression analysis showed that GCS and MSI were independent predictoss of cardiac function recovery(HR二1.5,95%CI1.0-1.9；HR二1.4,95%CI1.1-1.了，both P< 005)Concusions:GCSderivedfrom FTIcanpredictcardiacfunctionrecoveryinSTEMIpatients after PCI without additional gadolinium injection,but MSI is the most effective parameter.【Keywords】Acutemyocardialinfarction；Percutaneouscoronaryintervention；Cardiacmagnetic resonance；Cardiacfunctionrecovery心脏磁共振(CMR)具有高空间分辨率、高软组织对比度、无辐射、造影剂安全、能直接三维成像和“一站式”(同时提供血管解剖、心肌局部和整体功能信息)等优势，已成为评价心肌梗死后心肌纤维化和存活心肌的首选无创检查之一。

量子点增强太阳能电池

量子点增强太阳能电池英文回答：Quantum dots have emerged as promising materials for enhancing the efficiency of solar cells due to their unique optical and electronic properties. By incorporating quantum dots into the active layer of solar cells, it is possible to achieve improved light absorption, charge separation, and reduced recombination losses. This has led to a significant increase in the power conversion efficiency (PCE) of solar cells.One of the main advantages of quantum dots in solar cells is their ability to absorb light over a wider range of wavelengths compared to traditional semiconductor materials. This is due to the quantum confinement effect, which results in the quantization of energy levels in the quantum dots. By tailoring the size and composition of the quantum dots, it is possible to tune their bandgap and absorption spectrum, allowing for the efficient absorptionof light from the entire solar spectrum.Furthermore, quantum dots possess a high surface-to-volume ratio, providing a large number of active sites for charge separation and transport. This enhanced charge separation efficiency reduces recombination losses and improves the overall performance of the solar cell.In addition to their optical and electronic properties, quantum dots also offer advantages in terms of device fabrication. Quantum dots can be easily integrated into existing solar cell architectures using solution-based techniques, such as spin-coating or drop-casting. This compatibility with existing manufacturing processes enables the facile and cost-effective production of quantum dot-enhanced solar cells.Despite these advantages, there are still challenges that need to be addressed for the widespread adoption of quantum dot-enhanced solar cells. One challenge is the stability of quantum dots under harsh environmental conditions, such as exposure to high temperatures andmoisture. Another challenge is the integration of quantum dots into high-performance solar cell devices without compromising the stability and efficiency of the device.Ongoing research efforts are focused on addressingthese challenges and further improving the performance of quantum dot-enhanced solar cells. By optimizing thematerials and device design, it is expected that quantumdot-enhanced solar cells will play a significant role inthe development of high-efficiency and cost-effective photovoltaic technologies.中文回答：量子点因其独特的光学和电子特性而成为一种用于提高太阳能电池效率的有前途的材料。

Sensitivity-enhancement

Sensors and Actuators B 206(2015)463–470Contents lists available at ScienceDirectSensors and Actuators B:Chemicalj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /s nbSensitivity enhancement of a surface plasmon resonance based ﬁber optic sensor using ZnO thin ﬁlm:a theoretical studySarika Shukla,Navneet K.Sharma ∗,Vivek SajalDepartment of Physics and Materials Science and Engineering,Jaypee Institute of Information Technology,A-10,Sector-62,Noida 201307,Indiaa r t i c l ei n f oArticle history:Received 25June 2014Received in revised form 22September 2014Accepted 23September 2014Available online 2October 2014Keywords:Surface plasmon resonance Optical ﬁber ZnO Sensora b s t r a c tA surface plasmon resonance (SPR)based ﬁber optic sensor with bi layers of metal–ZnO is proposed and theoretically studied.Three metals:gold (Au),silver (Ag)and copper (Cu)have been exercised in the study.The top ZnO layer is shown to protect the metallic layer from oxidation and to enhance the sensitivity of the SPR sensor.Besides,increase in thickness of Au/Ag/Cu layer increases the sensitivity of SPR sensor for all thicknesses of ZnO layers.For a ﬁxed thickness of ZnO layer,the sensitivity of sensor is larger for Au layer than that of Ag/Cu layer.Sensitivity also increases with increase in ZnO layer thickness for all thicknesses of Au/Ag/Cu layers.The SPR sensor based on bi layers of 40nm Au–15nm ZnO demonstrates the maximum sensitivity of 3161nm/RIU.©2014Elsevier B.V.All rights reserved.1.IntroductionDuring last three decades,surface plasmon resonance (SPR)phenomenon has attracted huge attention due to fast and accu-rate optical sensing of various physical,chemical and biochemical parameters [1–4].Surface plasmons are the collective oscillations of free electrons in a metal and propagate along the metal–dielectric surface.This transverse electromagnetic wave is known as sur-face plasmon wave.Being transverse in nature,surface plasmon wave can be excited by exponentially decaying evanescent ﬁeld of incident p -polarized light only.When the wave vector and fre-quency of incident p -polarized light match with those of surface plasmon wave,this light resonantly excites the surface plasmon wave.The resonance condition depends on the incident angle,wavelength of the incident light and the dielectric constants of both metal as well as dielectric.The resonance condition (reso-nance angle/wavelength)is very sensitive to the variations in the refractive index of the dielectric adjacent to the metal.Therefore,the variations in the refractive index of the sensing medium can be determined by monitoring the resonance condition.For study-ing SPR,Kretschmann’s conﬁguration based on attenuated total internal reﬂection (ATR)is generally used [5–7].In Kretschmann’s∗Corresponding author.Tel.:+911202594365;fax:+911202400986.E-mail address:navneetk.sharma@jiit.ac.in (N.K.Sharma).conﬁguration,a high refractive index prism is coated with a thin metal layer and this metal layer touches the sample.Surface plas-mon waves are excited by evanescent wave from prism at the total reﬂection condition.The prism based SPR sensing has vari-ous disadvantages such as bulky size of sensor and inapplicability for remote sensing.However,optical ﬁber based SPR sensing pro-vides several beneﬁts over prism based SPR sensing like simpliﬁed and ﬂexible optical design,development of remote sensing,contin-uous analysis and in situ monitoring [8–10].In optical ﬁber based SPR sensor,the prism is replaced by the core of the optical ﬁber.Optical ﬁber based SPR sensing has been demonstrated both exper-imentally and theoretically in a large number of research studies [11–15].Gold (Au),silver (Ag)and copper (Cu)metals are normally used as plasmonic materials.However excluding Au,Ag and Cu are not chemically much stable because being prone to oxidation.The problem of oxidation of these metals is automatically eliminated by coating another material on it.In addition of protecting the inner metallic layer against oxidation by the outer layer,the sensitivity and the resolution of the SPR sensor are signiﬁcantly improved [16].Semiconductors offer many advantages over metals such as their carrier densities can expand to several orders of magnitudes using various doping techniques.Further,the carrier concentration of the active semiconductor ﬁlm can be tuned to match its SPR frequency to the exact frequency of the light source leading to miniaturiza-tion of SPR based devices [17].Wide band gap semiconductors,/10.1016/j.snb.2014.09.0830925-4005/©2014Elsevier B.V.All rights reserved.464S.Shukla et al./Sensors and Actuators B206(2015)463–470Fig.1.Schematic diagram of SPR basedﬁber optic sensor. particularly oxides are more chemically inert and stable than metals and hence could be used as sensors in extreme adverse conditions.Recently,zinc oxide(ZnO)has attracted considerable research interest.ZnO is a wide band gap semicondctor(band gap∼3.37eV)and is extensively used in several applications such as transparent conductingﬁlms,photonic crystals,gas sen-sors,bio sensors,light emitting diodes,solar cells,lasers,photo electrochemical cells and electrodes[18–22].Compared to other semiconductors,ZnO does not get easily oxidized when comes in contact with the surrounding environment.In addition,ZnO has high thermal and chemical stability,large mechanical strength, large piezoelectric coefﬁcient,high exciton binding energy and optical gain,making it an ideal material to realize excitonic devices at room temperature[18].In general,undoped ZnO thinﬁlms typically exhibit n-type conduction with a background electron concentration of1021cm−3[23].In this study,we theoretically discuss a SPR basedﬁber optic sensor with bi layers of metal–ZnO.Three metals:Au,Ag and Cu have been considered.The top ZnO layer has been shown to not only protect the metallic layer from oxidation but also to improve the sensitivity and stability of the SPR sensor.SPR produced by coupling of evanescent light to surface plasmons is employed as the sensing scheme and the wavelength interrogation method is used for the analysis of SPR basedﬁber optic sensor.In wave-length interrogation method,the wavelength of incident light from the white light source is changed and the corresponding trans-mitted power through the opticalﬁber is determined.A sharp dip in the transmitted power is observed at the resonance wave-length.The effects of thicknesses of Au,Ag,Cu and ZnO layers on the sensitivity of the sensor have also been studied.The top ZnO layer over Au/Ag/Cu layer enhances the sensitivity of the SPR sensor.Besides,increase in thickness of Au/Ag/Cu layer increases the sensitivity of SPR sensor for all thicknesses of ZnO layers.Fur-ther,for aﬁxed thickness of ZnO layer,the sensitivity of sensor is larger for Au layer than that of Ag and Cu layers.The sensi-tivity also increases with increase in ZnO layer thickness for all thicknesses of Au/Ag/Cu layers.The SPR basedﬁber optic sensor with bi layers of40nm Au–15nm ZnO possesses high sensitivity of 3161nm/RIU.2.TheoryThe SPR sensing is based on the principle of attenuated total reﬂection(ATR)with Kretschmann’s conﬁguration.In the proposed SPR basedﬁber optic sensor,the sensing system consisting of a ﬁber core-metal layer-ZnO layer-sensing medium is considered as shown in Fig.1.Three metals,i.e.Au,Ag and Cu have been consid-ered for the study.The plastic cladding around the core from the middle portion of a step index multimode plastic clad silica(PCS)ﬁber (numerical aperture=0.24andﬁber core diameter=600␮m)is removed and is then coated with a thin metal layer,which is then further coated with a ZnO layer.These bi layers of metal–ZnO are ﬁnally enclosed by the sensing medium.The light from a broadband source is launched into one of the ends of the opticalﬁber with proper optics and the transmitted light is detected at the other end of the opticalﬁber.At resonance wavelength,a sharp dip in the transmitted power emerges.The resonance wavelength depends on the refractive index of the sensing medium.2.1.Fiber coreLayer I is composed of core of opticalﬁber.The core of the opti-calﬁber is assumed to be made of fused silica.The refractive index of fused silica varies with wavelength according to Sellmeier dis-persion relation as,n1( )=1+a1 22−b21+a222−b22+a322−b23(1)where is the wavelength in␮m and a1,a2,a3,b1,b2and b3are Sellmeier coefﬁcients.The values of these coefﬁcients are given as,a1=0.6961663,a2=0.4079426,a3=0.8974794, b1=0.0684043␮m,b2=0.1162414␮m and b3=9.896161␮m [24].2.2.Metal layerLayer II is made of metal,i.e.Au/Ag/Cu.The dielectric constant of a metal is written according to Drude model as,εm( )=εmr+iεmi=1−2 c2p( c+i )(2)Here, p and c are the plasma wavelength and the collision wavelength of metal respectively.Where, p=1.6826×10−7m, 1.4541×10−7m, 1.3617×10−7m and c=8.9342×10−6m, 1.7614×10−5m,4.0852×10−5m for Au,Ag and Cu respectively [25].2.3.ZnO layerLayer III is made of ZnO.The dielectric constant of ZnO is written according to Drude model as[17],ε(ω)=ε∞−ω2pω2+ 2+iω2pω(ω2+ 2)(3)whereε∞is the high frequency dielectric constant,ωp is the plasma frequency and is the damping frequency.Here,ε∞=3.40,ωp=2×1015Hz and =1.5×1014Hz for ZnO[26].2.4.Sensing mediumLayer IV is composed of sensing medium.The dielectric con-stant of the sensing medium isεs.If n s is the refractive index of the sensing medium,thenεs=n2s.The resonance condition for excita-tion of surface plasmon wave is given as,2n1sinÂ=Re{K sp}(4) where K sp=ωcεmεsεm+εs=2εm n2sεm+n2sis the propagation con-stant of the surface plasmon wave and c is the speed of light inS.Shukla et al./Sensors and Actuators B206(2015)463–470465 Fig.2.Variations of resonance wavelength of SPR sensor with refractive index of sensing medium for10nm,20nm,30nm and40nm thick Au layers withﬁxed(a)0nm(without ZnO layer)(b)5nm(c)10nm and(d)15nm thick ZnO layers.vacuum.The left hand side of Eq.(4)denotes the propagation con-stant of the light incident at an angleÂand the right hand sideshows the real part of the propagation constant of the surfaceplasmon wave.If the refractive index of the sensing medium ischanged,the right hand side of Eq.(4)gets modiﬁed and thereforethe resonance condition will be satisﬁed at some other value of thewavelength.By observing the shift in the resonance wavelength,a change in the refractive index of the sensing medium can bemeasured.2.5.Transmitted powerThe expression for the reﬂection coefﬁcient(reﬂectance)of p-polarized incident light is obtained by using matrix method for N-layer model[27].Considering that all the guided rays are launchedin theﬁber using a collimated source and a microscope objective,the angular power distribution of rays guided in theﬁber is givenas[28],dP∝n21sinÂcosÂ(1−n21cos2Â)2dÂ(5)whereÂis the angle of the ray with the normal to the core-cladding interface.Also,n1is the refractive index of the core of the ﬁber.To calculate the effective transmitted power,the reﬂectance (R p)for a single reﬂection is raised to the power of the num-ber of reﬂections the speciﬁc propagating angle undergoes with the sensor interface.Hence,for p-polarized light,the generalized expression for the normalized transmitted power in an opticalﬁber based SPR sensor will be given as,P trans=/2ÂcrR N ref(Â)pn21sinÂcosÂ(1−n21cos2Â)2dÂ/2Âcrn21sinÂcosÂ(1−n21cos2Â)2dÂ(6)Where,N ref(Â)=LD tanÂ(7) AndÂcr=sin−1n cln1(8)Here N ref(Â)is the total number of reﬂections performed by a ray making an angleÂwith the normal to the core–metal layer interface in the sensing region.L and D are the length of the exposed sensing region and theﬁber core diameter respectively.Also,Âcr is466S.Shukla et al./Sensors and Actuators B206(2015)463–470Fig.3.Variations of resonance wavelength of SPR sensor with refractive index of sensing medium for10nm,20nm,30nm and40nm thick Ag layers withﬁxed(a)0nm (without ZnO layer)(b)5nm(c)10nm and(d)15nm thick ZnO layers.the critical angle of theﬁber and n cl is the refractive index of the cladding of theﬁber.2.6.SensitivityThe sensitivity of a SPR sensor with wavelength interrogation is deﬁned as the change in resonance wavelength per unit change in refractive index of the sensing medium[29].Also,it is signiﬁcant to mention here that in the present work, a white light source has been used to couple the incident light into the opticalﬁber.However,if a laser source is assumed to couple the incident light into the opticalﬁber then the coupling of laser mode into surface plasmons can be understood easily.The mode conversion of TM mode of a laser into surface plasmon wave in a metal coated opticalﬁber is facilitated by a surface ripple of suitable wave number[30–32].There is always a wave number mismatch between the TM mode and the surface plasmon wave in an optical ﬁber.This wave number mismatch corresponds to the required rip-ple wave number for resonant mode conversion.When a laser beam in TM mode propagates through the opticalﬁber,it induces oscilla-tory velocity on the electrons lying at metal surface.This oscillatory velocity beats with the space modulated density to produce a cur-rent,driving the surface plasmon wave on the boundary between metal and free space.Theﬁeld of surface plasmon waves polarizes the metal particles present on metal surface,enhancing localﬁelds at resonance condition.3.Results and discussionIn proposed SPR basedﬁber optic sensor,the sensing system consisting of aﬁber core-metal layer-ZnO layer-sensing medium is considered.Three metals;Au,Ag and Cu have been exercised in the present study.Furthermore,various solutions of glycerine in water with concentrations that provide refractive indices of1.30,1.31, 1.32,1.33,1.34,1.35,1.36and1.37are considered as the sensing mediums.SPR basedﬁber optic sensor with bi layers of metal–ZnO detects the refractive indices of these solutions.The sensing mech-anism of proposed SPR sensor can be explained as the change in dielectric function of ZnO layer due to the presence of solutions of different refractive indices.As solutions of various refractive indices come in contact with ZnO layer,the refractive index and hence the dielectric constant of ZnO layer changes,which in turn changes the resonance wavelength of the SPR spectrum.For numerical calcula-tions,the refractive index of sensing medium is changed from1.30 to1.37(in steps of0.01)and following values of parameters have been used:Numerical aperture of theﬁber=0.24,ﬁber core diameter D=600␮m,length of the exposed sensing region L=15mm.Fur-ther,three combinations of bi layers(metal–ZnO),i.e.Au–ZnO, Ag–ZnO and Cu–ZnO have been considered in the present study. Thickness of ZnO layer is assumed to be0nm(i.e.without ZnO layer),5nm,10nm and15nm.In addition,to optimize the thick-nesses of metal layers,the transmitted output power of SPR basedS.Shukla et al./Sensors and Actuators B206(2015)463–470467 Fig.4.Variations of resonance wavelength of SPR sensor with refractive index of sensing medium for10nm,20nm,30nm and40nm thick Cu layers withﬁxed(a)0nm (without ZnO layer)(b)5nm(c)10nm and(d)15nm thick ZnO layers.ﬁber optic sensor has been calculated for various thicknesses i.e. 10nm,20nm,30nm and40nm of Au,Ag and Cu layers.Fig.2a shows the variation of resonance wavelength of SPR sensor with refractive index of sensing medium for10nm,20nm, 30nm and40nm thick Au layers withﬁxed0nm thick ZnO layer (i.e.without ZnO layer).It can be seen that the resonance wave-lengths for all thicknesses of Au layer increase linearly with increase in refractive index of sensing medium.Similarly,Fig.2b–d depict the plots of resonance wavelength with refractive index of sensing medium for10nm,20nm,30nm and40nm thick Au layers with ﬁxed5nm,10nm and15nm thick ZnO layers respectively.Again, the resonance wavelengths increase with enhancement in refrac-tive index of sensing medium for all thicknesses of Au and ZnO layers.The rationale behind these expansions in SPR resonance wavelengths with increase in refractive index of sensing medium for various thicknesses of Au and ZnO layers can be explained by Eq.(4).The real part of propagation constant(K sp)of surface plas-mon wave will be smaller for small value of refractive index of sensing medium and hence its resonance condition is satisﬁed at smaller wavelength[27].Similarly,for larger value of refractive index of sensing medium,the resonance condition is satisﬁed at longer wavelength due to the largest real part of K sp.Likewise,Fig.3a–d represent the variations of resonance wave-length of SPR sensor with refractive index of sensing medium for10nm,20nm,30nm and40nm thick Ag layers withﬁxed 0nm(without ZnO layer),5nm,10nm and15nm thick ZnO lay-ers respectively.The resonance wavelengths vary linearly with increase in refractive index of sensing medium for all thicknesses of Ag and ZnO layers.In the same way,Fig.4a–d illustrate the vari-ations of resonance wavelength of SPR sensor with refractive index of sensing medium for10nm,20nm,30nm and40nm thick Cu layers withﬁxed0nm(without ZnO layer),5nm,10nm and15nm thick ZnO layers respectively.Once more,the resonance wave-lengths follow the similar trend of linear variation with refractive index of sensing medium for all thicknesses of Cu and ZnO layers.Fig.5a–c reveal the plots of sensitivity of SPR sensor with thick-ness of Au/Ag/Cu layer forﬁxed0nm(without ZnO layer),5nm, 10nm and15nm thick ZnO layer respectively.It is evident from theseﬁgures that increase in thickness of Au/Ag/Cu layer enhances the sensitivity of SPR sensor for all thicknesses of ZnO layers.In addition,for aﬁxed thickness of ZnO layer,the sensitivity of sensor is greater for all thicknesses of Au layer than that of Ag as well as Cu layers and has been found to be in the order of Au layer>Ag layer>Cu layer.The reason for this fact is attributed to the real part of K sp as it is responsible for the shifting of resonance con-dition/wavelength.Au layer shows higher sensitivity than Ag/Cu layer because Au illustrates large value of real part of its dielectric function at all wavelengths[27].Thus,Au layer increases the shift between resonance wavelengths for a given change of refractive index of sensing medium and therefore the sensitivity of the sen-sor increases.Further,for aﬁxed thickness of Au/Ag/Cu layer,the sensitivity of sensor becomes larger as the thickness of ZnO layer is raised from0nm to15nm.This happens because of the change of refractive index of ZnO as ZnO layer shows high value of real part468S.Shukla et al./Sensors and Actuators B206(2015)463–470Fig.5.Variations of sensitivity of SPR sensor with thickness of(a)Au layer(b)Ag layer and(c)Cu layer forﬁxed0nm(without ZnO layer),5nm,10nm and15nm thick ZnO layers.of its dielectric function and hence its refractive index[33].There-fore,it can be understood that the top ZnO layer over Au/Ag/Cu layer enhances the surface plasmon resonance and hence the sen-sitivity of the SPR sensor.Besides it,the top ZnO layer protects the Au/Ag/Cu layer from oxidation.Fig.6a–c display the variations of sensitivity of SPR sensor with thickness of ZnO layer forﬁxed10nm,20nm,30nm and40nm thick Au/Ag/Cu layer respectively.Again,the sensitivity increases with increase in ZnO layer thickness for all thicknesses of Au/Ag/Cu plementarily,for aﬁxed thickness of ZnO layer,the sen-sitivity keeps on increasing as the thickness of Au/Ag/Cu layer is enhanced from10nm to40nm.To achieve the maximum sensitiv-ity from the SPR basedﬁber optic sensor,the optimum thicknesses of Au,Ag,Cu and ZnO layers,should be identiﬁed.The sensitivities of SPR sensor for various thicknesses of Au/Ag/Cu and ZnO layers are compared in Table1.It can be viewed form Table1that the sensitivity of Au–ZnO bi layers based SPR sensor increases from702nm/RIU(for10nm Au–0nm ZnO)to3161nm/RIU(for40nm Au–15nm ZnO).Also, Ag–ZnO bi layers based SPR sensor demonstrates the minimum sensitivity of687nm/RIU(for10nm Ag–0nm ZnO)and maximum sensitivity of3054nm/RIU(for40nm Ag–15nm ZnO).In addition, the sensitivity of Cu–ZnO bi layers based SPR sensor enhances from 677nm/RIU(for10nm Cu–0nm ZnO)to3018nm/RIU(for40nm Cu–15nm ZnO).Hence,the sensitivity of Au–ZnO bi layers based SPR sensor for all thicknesses of Au and ZnO layers is larger than that of Ag–ZnO and Cu–ZnO bi layers.However,the optimized thick-nesses of Au/Ag/Cu layers are found to be40nm while that of ZnO layer is15nm.Besides it,detection accuracy(signal to noise ratio) of a SPR basedﬁber optic sensor is inversely proportional to the FWHM(full width at half maximum)of SPR transmittance curve. Therefore,for a good SPR sensor,smaller FWHM and larger peak amplitude are desirable because a deeper and narrower resonance spectrum offers high detection accuracy.In the present study,it has also been found that SPR sensor based on bi layers of40nm Au–5nm ZnO,40nm Au–10nm ZnO and40nm Au–15nm ZnO exhibits FWHM of215nm,211nm and205nm respectively.On the other hand,40nm thick Au layer based SPR sensor(without ZnO layer)shows FWHM of345nm.Similarly,SPR sensor based on bi layers of40nm Ag–5nm ZnO,40nm Ag–10nm ZnO and40nm Ag–15nm ZnO displays FWHM of327nm,311nm and300nm respectively.On the contrary,40nm thick Ag layer based SPR sensor (without ZnO layer)shows FWHM of355nm.In the same way,SPR sensor based on bi layers of40nm Cu–5nm ZnO,40nm Cu–10nm ZnO and40nm Cu–15nm ZnO illustrates FWHM of336nm,321nm and312nm respectively.Conversely,40nm thick Cu layer based SPR sensor(without ZnO layer)shows FWHM of360nm.There-fore,it can be easily seen that SPR sensor based on bi layers of Au–ZnO/Ag–Zno/Cu–ZnO reveals smaller(i.e.narrower)FWHM in comparison to the SPR sensor based on single metallic layer of Au/Ag/Cu and hence demonstrates high detection accuracy.In addi-tion,FWHM for SPR sensor based on bi layers of Au–ZnO is lesser than that of Ag–Zno and Cu–ZnO.Hence keeping all the above mentioned facts in to consider-ation,it is concluded that among all the bi layers combinations (Au–ZnO/Ag–ZnO/Cu–ZnO)used,the SPR sensor based on40nmS.Shukla et al./Sensors and Actuators B206(2015)463–470469Fig.6.Variations of sensitivity of SPR sensor with thickness of ZnO layer forﬁxed10nm,20nm,30nm and40nm thick(a)Au layers(b)Ag layers and(c)Cu layers. Table1Comparison of sensitivity of SPR basedﬁber optic sensor for different thicknesses of Au,Ag and Cu layers withﬁxed0nm,5nm,10nm,15nm thick ZnO layer.Thickness of ZnO layer(nm)Sensitivity(nm/RIU)Thickness of Au layer(nm)Thickness of Ag layer(nm)Thickness of Cu layer(nm)1020304010203040102030400702168522922667687154221552583677152420242446 51042190523812744970177423152702911174422862655 10142320832583297014112036254229521363200024702845 15174423332833316116552321275030541631224426313018thick Au layer with15nm thick top ZnO layer exhibits the highest sensitivity of3161nm/RIU.Recently,Zamarreno et al.[34] have studied ITO coated opticalﬁber refractive index sensors exper-imentally and have obtained an average sensitivity of3125nm/RIU, which is in close agreement with our theoretically obtained result of sensitivity.4.ConclusionsA SPR basedﬁber optic sensor with bi layers of metal–ZnO has been theoretically investigated.Three metals,viz Au,Ag and Cu have been considered.Apart from protecting the metallic layer from oxidation,the top ZnO layer over Au/Ag/Cu layer has been shown to increase the sensitivity as well as stability of the SPR sensor.In addition,increase in thickness of Au/Ag/Cu layer increases the sen-sitivity of SPR sensor for all thicknesses of ZnO layers.For aﬁxed thickness of ZnO layer,the sensitivity of sensor is larger for Au layer than that of Ag and Cu layers.Also,the sensitivity increases with increase in ZnO layer thickness for all thicknesses of Au/Ag/Cu lay-ers.The SPR sensor with bi layers of40nm Au–15nm ZnO displays high sensitivity of3161nm/RIU.AcknowledgementThe corresponding author,Navneet K.Sharma is thankful to Prof.B.D.Gupta for his motivation.References[1]B.Liedberg,C.Nylander,I.Sundstrom,Surface plasmon resonance for gas detec-tion and biosensing,Sens.Actuators B4(1983)299–304.[2]R.D.Harris,J.S.Wilkinson,Waveguide surface plasmon resonance sensors,Sens.Actuators B29(1995)261–267.[3]J.Homola,On the sensitivity of surface plasmon resonance sensors with spec-tral interrogation,Sens.Actuators B41(1997)207–211.470S.Shukla et al./Sensors and Actuators B206(2015)463–470[4]Z.Salamon,H.A.Macleod,G.Tollin,Surface plasmon resonance spectroscopyas a tool for investigating the biochemical and biophysical properties of mem-brane protein systems.II:Applications to biological systems,Biochim.Biophys.Acta1331(1997)117–129.[5]E.Kretschmann,H.Reather,Radiative decay of non-radiative surface plasmonsexcited by light,Naturforsch23(1968)2135–2136.[6]A.Otto,Excitation of non-radiative surface plasma waves in silver by themethod of frustrated total reﬂection,Z.Phys.216(1968)398–410.[7]E.Kretschmann,Die Bestimmung optischer Konstanten von Metallen durchAnregung von Oberﬂachenplasmashwingungen,Z.Phys.241(1971)313–324.[8]J.Homola,Opticalﬁber sensor based on surface plasmon excitation,Sens.Actu-ators B29(1995)401–405.[9]W.B.Lin,N.Jaffrezic-Renault,A.Gagnaire,H.Gagnaire,The effects of polariza-tion of the incident light-modeling and analysis of a SPR multimode optical ﬁber sensor,Sens.Actuators A84(2000)198–204.[10]A.K.Sharma,B.D.Gupta,Absorption basedﬁber optic surface plasmon reso-nance sensor:a theoretical evaluation,Sens.Actuators B100(2004)423–431.[11]S.K.Srivastava,B.D.Gupta,Inﬂuence of ions on the surface plasmon resonancespectrum of aﬁber optic refractive index sensor,Sens.Actuators B156(2011) 559–562.[12]S.K.Srivastava,V.Arora,S.Sapra,B.D.Gupta,Localized surface plasmon reso-nance basedﬁber optic U-shaped biosensor for the detection of blood glucose, Plasmon7(2012)261–268.[13]M.Rani,N.K.Sharma,V.Sajal,Localized surface plasmon resonance basedﬁberoptic sensor with nanoparticles,mun.292(2013)92–100.[14]N.K.Sharma,M.Rani,V.Sajal,Surface plasmon resonance basedﬁber opticsensor with double resonance dips,Sens.Actuators B188(2013)326–333. [15]M.Rani,S.Shukla,N.K.Sharma,V.Sajal,Theoretical study of nanocompositesbasedﬁber optic SPR sensor,mun.313(2014)303–314.[16]J.Dostalek,A.Kasry,W.Knoll,Long range surface plasmons for observation ofbiomolecular binding events at metallic surfaces,Plasmon2(2007)97–106.[17]E.Sachet,M.D.Losego,J.Guske,S.Franzen,J.P.Maria,Mid-infrared surfaceplasmon resonance in zinc oxide semiconductor thinﬁlms,Appl.Phys.Lett.102(2013)051111.[18]Y.Ma,G.T.Du,S.R.Yang,Z.T.Li,B.J.Zhao,X.T.Yang,T.P.Yang,Y.T.Zhang,D.L.Liu,Control of conductivity type in undoped ZnO thinﬁlms grown by metalorganic vapour phase epitaxy,J.Appl.Phys.95(2004)6268–6272.[19]C.L.Tsai,Y.J.Lin,Y.M.Chin,W.R.Liu,W.F.Hsieh,C.H.Hsu,J.A.Chu,Low-resistance nonalloyed ohmic contacts on undoped ZnOﬁlms grown by pulsed-laser deposition,J.Phys.D42(2009)095108.[20]R.K.Sharma,S.Patel,K.C.Pargaien,Synthesis,characterization and propertiesof Mn-doped ZnO nanocrystals,Adv.Nat.Sci.3(2012)035005.[21]S.K.Gupta,A.Joshi,M.Kaur,Development of gas sensors using ZnO nanostruc-tures,J.Chem.Sci.122(2010)57–62.[22]J.X.Wang,X.W.Sun,A.Wei,Y.Lei,X.P.Cai,C.M.Li,Z.L.Dong,Zinc oxidenanocomb biosensor for glucose detection,Appl.Phys.Lett.88(2006)233106.[23]T.Minami,H.Sato,H.Nanto,S.Takata,Group III impurity doped zinc oxide thinﬁlms prepared by RF magnetron sputtering,Jpn.J.Appl.Phys.24(1985)L781.[24]A.K.Ghatak,K.Thyagarajan,An Introduction to Fiber Optics,ﬁrst ed.,CambridgeUniversity Press,Cambridge(UK),1999,pp.82-83.[25]M.A.Ordal,L.L.Long,R.J.Bell,S.E.Bell,R.R.Bell,R.W.Alexander Jr.,C.A.Ward,Optical properties of metals Al,Co,Cu,Au,Fe,Pb,Ni,Pd,Pt,Ag,Ti,and W in the infrared and far infrared,Appl.Opt.22(1983)1099–1119.[26]L.S.Hsu,C.S.Yeh,C.C.Kuo,B.R.Huang,S.Dhar,Optical and transport propertiesof undoped and Al-,Ga-and In-doped ZnO thinﬁlms,J.Optoelectron.Adv.Mater.7(2005)3039–3046.[27]A.K.Sharma,B.D.Gupta,On the performance of different bimetallic combina-tions in surface plasmon resonance basedﬁber optic sensors,J.Appl.Phys.101 (2007)093111.[28]B.D.Gupta,A.Sharma,C.D.Singh,Evanescent wave absorption sensors basedon uniform and taperedﬁbers:a comparative study of their sensitivities,Int.J.Optoelectron.8(1993)409–418.[29]A.K.Sharma,B.D.Gupta,On the sensitivity and signal to noise ratio of a step-indexﬁber optic surface plasmon resonance sensor with bimetallic layers,Opt.Commun.245(2005)159–169.[30]C.S.Liu,G.Kumar,V.K.Tripathi,Laser mode conversion into a surface plasmawave in a metal coated opticalﬁber,J.Appl.Phys.100(2006)013304.[31]G.Kumar,D.B.Singh,V.K.Tripathi,Surface enhanced Raman scattering of asurface plasma wave,J.Phys.D39(2006)4436–4439.[32]A.V.Zayats,I.I.Smolyaninov,A.A.Maradudin,Nano-optics of surface plasmonpolaritons,Phys.Rep.408(2005)131–314.[33]M.Bao,G.Li,D.Jiang,W.Cheng,X.Ma,Surface plasmon optical sensor withenhanced sensitivity using top ZnO thinﬁlm,Appl.Phys.A107(2012)279–283.[34]C.R.Zamarreno,M.Hernaez,I.D.Villar,I.R.Matias,F.J.Arregui,ITO coated opticalﬁber refractometers based on resonances in the infrared region,IEEE Sens.J.10 (2010)365–366.BiographiesSarika Shukla received her B.Sc.degree from MJP Rohilkhand University,Bareilly in 2008and M.Sc.degree in physics from Banasthali Vidyapith,Banasthali,Rajasthan in2010.She is currently pursuing her Ph.D.in Department of Physics and Material Science&Engineering from JIIT Noida.Her main research interests are opticalﬁber devices.Navneet K.Sharma received his M.Sc.degree in physics(specialization in engi-neering physics)from University of Roorkee(now IIT Roorkee)in1997and the Ph.D.degree in Physics from IIT Delhi in2004.Currently,he is working as assistant professor in the Department of Physics and Materials Science&Engineering,JIIT Noida,India.His areas of research areﬁber optic sensors,surface plasmon resonance, plasmonics,photonics,THZ radiation generation and plasma physics.Vivek Sajal was born in Mawana on September23,1977.He received his M.Sc. degree in Physics in1999and the Ph.D.degree in parametric instabilities and related nonlinear phenomenon in laser produced plasma in2008from IIT Delhi.He is cur-rently working as assistant professor in JIIT Noida.His current interests include parametric instabilities,SPW,THZ radiation generation and electron acceleration by laser plasma-interaction.。

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