Flower-like TiO2 nanostructures with exposed {001} facets Facile synthesis

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Simple Synthesis of Flower-Like ln2S3 Structures and Their Use as Templates to Prepare CuS Particles

Hindawi Publishing CorporationJournal of NanomaterialsVolume2011,Article ID280216,5pagesdoi:10.1155/2011/280216Research ArticleSimple Synthesis of Flower-Like ln2S3Structures andTheir Use as Templates to Prepare CuS ParticlesXia Sheng,Lei Wang,Guanbi Chen,and Deren YangState Key Laboratory of Silicon Materials,Department of Materials Science and Engineering,Zhejiang University,Hangzhou310027,ChinaCorrespondence should be addressed to Deren Yang,mseyang@Received31May2010;Revised2August2010;Accepted6September2010Academic Editor:Quanqin DaiCopyright©2011Xia Sheng et al.This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use,distribution,and reproduction in any medium,provided the original work is properly cited.Flower-like structure In2S3particles are prepared by a simple and rapid method.The reaction proceeds in a polyalcohol system without using any complex precursors.The phase and morphology of the In2S3are investigated.Furthermore,ﬂower-like structure CuS particles are synthesized via the reaction of Cu2+ions with the obtained In2S3as templates.Both the In2S3and CuS particles can be used in preparing compound solar cell material CuInS2.1.IntroductionIndium sulﬁde(In2S3)is an important III-VI semiconductor and exists in mainly three phases:α-In2S3which is a defective cubic structure and stable up to693K;β-In2S3 which is a defective spinel structure and stable up to 1027K;γ-In2S3which is a higher temperature structure and stable above1027K[1,2].Among these phases,n-typeβ-In2S3with a band gap of2.0–2.8eV has the most wide applications.In particular,the nanostructure In2S3,owing to its unique catalytic,optical,electronic,and gas-sensing properties,can be used in manyﬁelds,such as catalysts,solar cells,optoelectronic devices,luminophores,and acoustic devices[3–12].In particular,In2S3nanostructures could be used as precursors to fabricate CuInS2thinﬁlm which is one of the most important thinﬁlm solar cells,and has been widely investigated in last two decades.So far, various shapes of nanostructure In2S3have been reported, such as nanoﬁbers,half shells,nanobelts,nanorods,ﬂower-like structures,and hollow microsphere[13–17].Among these structures,ﬂower-like structure is a kind of3D porous structure and has large surface area which will beneﬁt for the application in catalysts and optoelectronic devices such as solar cells.Therefore,in recent years,ﬂower-like structures have been prepared by diﬀerent tech-niques,such as templates,surfactants,complex precursors,solvents,thermal decomposition,or hydrothermal synthesis [18–22].However,those processes were complicated,and most fabricatedﬂower-like In2S3were larger than1μm in size.Furthermore,In2S3nanostructures exist as incompletely coordinated sulfur atoms and can serve as a host for other metal ions[8].It was reported that Cu2+and Zn2+could displace In3+in In2S3nanostructures[23].But,there are few reports about the synthesis of CuS nanostructures by using In2S3as templates.In this paper,we use a simple and rapid chemical method to synthesize In2S3ﬂower-like structures with a diameter about300–600nm.The synthesis proceeds in polyalcohol system below150◦C and does not use any complex agents.Furthermore,the obtained In2S3are used as templates to synthesizeﬂower-like CuS structures under room temperature.Both the In2S3and CuS can be used in preparing compound solar cell material CuInS2.2.Experimental Details2.1.Chemicals.All the used chemicals are analytical grade: indium(III)trichloride,InCl3·4H2O;copper(II)dichloride, CuCl2·2H2O;thiourea(TA);thioacetamide(TAA);hexade-cyl trimethyl ammonium bromide(CTAB);diethylene glycol (DEG).(751)(531)(800)(731)(444)(533)(440)(511)(422)(331)(400)(222)(311)(220)203040506070802θ0100020003000400050006000I n t e n s i t y(a)SSiInInIn(b)Figure 1:XRD pattern (a)and EDS spectrum (b)of the In 2S 3particles reacting by InCl 3and TA at 140◦C for 60minutes.(a)(b)(c)Figure 2:SEM ((a)and (b))and TEM (c)images of the In 2S 3particles reacting by InCl 3and TA at 140◦C for 60minutes.2.2.The Synthesis of In 2S 3Particles.The In 2S 3particles are synthesized through the following process.1mmol InCl 3·4H 2O is dissolved in 35mL DEG in a three-neck ﬂask.The solution is stirred under the protection of N 2atmosphere at 140◦C.Then 4mmol TA or TAA dissolved in 5mL DEG is slowly added into the solution.After 30–60minutes reaction,the ﬂask is removed from the heater and cooled to the room temperature.Then the particles are separated by centrifugation at 6500rpm for 5minutes and washed in ethanol for several times.At last,the particles are baked under 80◦C for several hours.2.3.The Synthesis of CuS Particles Using Obtained In 2S 3as Template.The obtained In 2S 3particles are dispersed in ethanol by a ultrasonic vibration equipment.Then 1mmol CuCl 2·2H 2O power is added into the solution,reacting by ultrasonic vibration at room temperature for 30minutes.The obtained particles are also washed and dried following a same procedure as that of In 2S 3particles.2.4.Materials Characterization.The particles are charac-terized by X-ray di ﬀraction (XRD),scanning electronmicroscopy (SEM),and transmission electron microscopy (TEM).XRD is carried out to study the crystal structures of all the samples,by using a X’Pert PRO (PANalytical)di ﬀractometer equipped with a CuK αradiation source.Data is collected by step scanning of 2θfrom 20◦to 80◦with a step of 0.02◦and counting time of 1s per step.Morphology of the particles is investigated by SEM and TEM.The SEM images are taken by using a SEM Hitachi S4800.The compositions of samples are determined by energy-dispersive X-ray spectroscopy (EDS)attached with SEM.The operating parameters for EDS are as follows:acceleration voltage 20kV ,measuring time 80s,working distance 15mm,and counting rate 2.3kcps.TEM Philips CM200UT is employed for TEM characterizations.3.Results and DiscussionSize,shape,and dimensionality strongly a ﬀect the properties of nanomaterials [8].In this paper,TA and TAA are used as two kinds of di ﬀerent S sources to synthesize In 2S 3.Due to their di ﬀerent release rates of S 2−ions,the obtained particles(a)(b)(c)Figure3:SEM((a)and(b))and TEM(c)images of In2S3particles reacting by InCl3and TAA at140◦C for30minutes.(a)200nm(b)(c)Figure4:SEM((a)and(b))and TEM(c)images of the In2S3particles using CTAB as surfactant reacting at140◦C for60minutes.may be diﬀerent in surface morphologies.Besides,we useCTAB as a kind of surfactant to adjust the shape of theparticles.The XRD pattern and EDS spectrum of In2S3particlesvia InCl3and TA reacting at140◦C for60minutes areshown in Figures1(a)and1(b).The similar XRD patternby using InCl3and TAA as reactants has been obtained,which is not shown in this paper.All the peaks shown inFigure1(a)can be readily indexed as a cubic phase ofβ-In2S3without any other phase.The peaks are considerably narrowand strong,which indicates that the obtained particles arewell crystallized.EDS spectrum of the In2S3particles inFigure1(b)shows that the samples are composed by In,Satoms(Si is from the substrate of the sample).Figures2(a)and2(b)show the diﬀerent magniﬁcationSEM images of the In2S3particles reacting by InCl3andTA at140◦C for60minutes;and Figure2(c)is their TEMimage which further conﬁrms the structure.It can be seenthat the In2S3particles are allﬂower-like porous structureswith a diameter in range of300–600nm,while most of themare about500nm.The“petals”of theﬂowers are about10–30nm through careful examination.Figures3(a)and3(b)show the diﬀerent magniﬁcationSEM images of In2S3particles reacting by InCl3and TAAat140◦C for30minutes.Similarly the images show that theIn2S3particles are alsoﬂower-like structures.But comparedwith Figure2,it is found that theﬂake“petals”are muchthinner,with a thickness of about5–10nm.Meanwhile,dueto the thinner petals,leading to much more surface areas,the particles are conjugated to each other.Furthermore,theproducts using TA as S source are more spherical,whereasthe products using TAA as S source are slightlyﬂuﬀy.TheTEM images which are shown in Figure3(c)also prove thisresult.For cubicβ-In2S3,the crystallites are self-organized intospherical assemblies with protruding petals with a puﬀyﬂower-like manifestation[17].TAA has faster release rates ofS2−ions than TA,leading to faster reaction speed with In3+.This can be seen by the reaction phenomenon(the solutionturns yellow quicker by using TAA).Thus,using TAA has avery fast growth rate along the petals.Therefore,the petalsseem thinner and the wholeﬂower-like structures areﬂuﬃer.Furthermore,the CTAB is added to adjust and controlthe shape of the particles.Figures4(a)and4(b)show theSEM images of the In2S3particles using InCl3and TA asreactants and using CTAB as surfactant.The TEM image isshown in Figure4(c).It can be seen that the samples are stillﬂower-like porous structures with a diameter around300–600nm and with a petal thickness about10–30nm.However,compared with Figure2,the products get lessﬂake petals,(105)(116)(203)(108)(110)(006)(103)(102)(101)203040506070802θ500100015002000250030003500I n t e n s i t y (c p s )(a)SiCuSCuCu(b)Figure 5:XRD pattern (a)and EDS spectrum (b)of the CuS synthesized by the reaction of In 2S 3particles and CuCl 2.(a)(b)(c)Figure 6:SEM ((a)and (b))and TEM (c)images of the CuS synthesized by the reaction of In 2S 3particles and CuCl 2.as well as the bigger pores between the petals.Since CTAB is a kind of amphoteric surfactant and more tend to act as cationic surfactant,it is generally used to prepare hollow structures [24].In this reaction,the CTAB and In 3+are together dissolved in the DEG ﬁrst.CTAB may scatter around In 3+.Then when S sources are added,S 2−is easily attracted with one side of CATB.In the nucleation process,the other side of CTAB molecules may cause repulsion between ﬂake petals and then make the ﬂowers expand bigger.Moreover,CuS particles are obtained by using the ﬂower-like structure In 2S 3as templates.In fact,CuS with ﬂower-like structure has been fabricated by some methods such as polyol route or hydrothermal route [25,26],and their structures are normally larger than 1μm.In our experiments,the CuS ﬂower-like structures with the diameter about 300–600nm are synthesized at room temperature via CuCl 2reacting with In 2S 3particles as shown in Figure 2.Figures 5(a)and 5(b)show the XRD pattern and EDS spectrum of the CuS nanostructures synthesized by the reaction of In 2S 3particles and CuCl 2.The XRD pattern shows that the obtained products are well-crystallized hexagonal phase CuS and no any In 2S 3peaks are found,indicating that In 2S 3is turned to CuS after reaction.EDS spectrum also veriﬁes this since no hints of In are found.Figures 6(a)–6(c)show the SEM and TEM images of the CuS synthesized by In 2S 3particles and CuCl 2.It can be seen that the obtained CuS particles are also ﬂower-like structures with a diameter around 300–600nm,indicating the CuS particles are synthesized by In 2S 3ﬂower-like structures as templates.The possible mechanism of this reaction is discussed as follows.In 2S 3nanostructures exist incompletely coordinated sulfur atoms [8],and the ﬂower-like structures appear a kind of porous surface and have large surface areas.Therefore there are numerous S 2−ions with high reactivity existing on the surface of ﬂower-like In 2S 3particles.And after Cu 2+ions are added,Cu 2+react with S 2−to form CuS.In addition,since the solubility degree of In 2S 3is much bigger than that of ZnS and CuS,ions like Cu 2+and Zn 2+can displace In 3+in In 2S 3nanostructure [23],whereas In 3+ions in the solutionare washed away during the centrifugation process and that is the reason why we have not detected any hints of In.So at last,theﬂower-like CuS particles of pure phase are obtained.4.ConclusionIn conclusion,In2S3particles are prepared by a simple and rapid method.The obtainedﬂower-like In2S3structures have a diameter around300–600nm.By changing the S sources and,or adding surfactant,the In2S3particles appear diﬀerent in surface morphologies.Moreover,Cu2+ions are added to react with In2S3particles,and CuS with the similar structures and size are obtained.The mechanism of this reaction is probably due to the Cu2+ions reacting with the high reactivity S2−ions on the surface ofﬂower-like In2S3 structures and in the same time displacing In3+ions. AcknowledgmentThe authors would like to appreciate theﬁnancial supports from973project(no.2007CB613403).References[1]A.Datta,G.Sinha,S.K.Panda,and A.Patra,“Growth,optical,and electrical properties of In2S3zigzag nanowires,”Crystal Growth and Design,vol.9,no.1,pp.427–431,2009.[2]L.J.Liu,W.D.Xiang,and J.S.Zhong,“Flowerlike cubicβ-In2S3microspheres:synthesis and characterization,”Journal of Alloys and Compounds,vol.493,pp.309–313,2010.[3]H.X.Bai,L.X.Zhang,and Y.C.Zhang,“Simple synthesis ofurchin-like In2S3and In2O3nanostructures,”Materials Letters, vol.63,no.9-10,pp.823–825,2009.[4]S.Gorai and S.Chaudhuri,“Sonochemical synthesis andcharacterization of cage-likeβ-indium sulphide powder,”Materials Chemistry and Physics,vol.89,no.2-3,pp.332–335, 2005.[5]A.Datta,S.Gorai,D.Ganguli,and S.Chaudhuri,“Surfactantassisted synthesis of In2S3dendrites and their characteriza-tion,”Materials Chemistry and Physics,vol.102,no.2-3,pp.195–200,2007.[6]X.Chen,Z.Zhang,X.Zhang,J.Liu,and Y.Qian,“Single-source approach to the synthesis of In2S3and In2O3crystallites and their optical properties,”Chemical Physics Letters,vol.407, no.4-6,pp.482–486,2005.[7]L.-Y.Chen,Z.-D.Zhang,and W.-Z.Wang,“Self-assembledporous3dﬂowerlikeβ∼-In2S3structures:synthesis,character-ization,and optical properties,”Journal of Physical Chemistry C,vol.112,no.11,pp.4117–4123,2008.[8]L.Liu,H.Liu,H.-Z.Kou et al.,“Morphology control ofβ-In2S3from chrysanthemum-like microspheres to hollow microspheres:synthesis and electrochemical properties,”Crys-tal Growth and Design,vol.9,no.1,pp.113–117,2009. 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TiO2_Nanoparticles_as_Functional_Building_Blocks

Review /CR
TiO2 Nanoparticles as Functional Building Blocks
Lixia Sang,† Yixin Zhao,‡ and Clemens Burda*,§
†
Key Laboratory of Enhanced Heat Transfer and Energy Conservation, Ministry of Education and Key Laboratory of Heat Transfer and Energy Conversion, Beijing Municipality, College of Environmental andniversity of Technology, Beijing 100124, China ‡ School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China § Center for Chemical Dynamics and Nanomaterials Research, Department of Chemistry, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States
7.2.1. Improving Charge Separation with Metal NPs 7.2.2. Core−Shell Metal@TiO2 7.2.3. Increasing UV and Visible Light Absorption with Plasmonics NPs 7.3. TiO2−Semiconductor Nanoheterostructures 8. TiO2 NPs as Charge Separation Centers 8.1. Photoinduced Charge Separation in TiO2 NPs 8.2. Charge Extraction for Photocatalytic Redox Reactions 8.2.1. Charge Extraction for Photocatalytic Puriﬁcation of Water and Air 8.2.2. Charge Extraction for Solar Water Splitting 8.2.3. Charge Extraction for Photocatalytic Reduction of CO2 8.3. Charge Separation and Injection in Grätzeltype Solar Cells 9. Outlook Author Information Corresponding Author Notes Biographies Acknowledgments References T U U V X X X X Y Z AA AB AB AB AB AB AC AC

Titanium Dioxide Crystals with Tailored Facets

© 2014 Americal Reviews number of papers published on TiO2 has seen a continuous increase, particularly since the beginning of this century (Figure S2). This is understandable when one considers the wide range of applications of TiO2 from the conventional areas (i.e., pigment, cosmetic, toothpaste, and paint) to the later developed functional areas such as photoelectrochemical cell,1−3 dye-sensitized solar cells (DSSCs),4−11 photocatalysis,12−24 catalysis,25−31 photovoltaic cell,32−34 lithium ion batteries,35−41 sensors,42−46 electron ﬁeld emission,47−51 microwave absorbing material, biomimetic growth, and biomedical treatments.52−57 Nearly all these functional applications of TiO2 fall in the scope of energy, environment, and health, which are deﬁnitely the three most important and challenging themes facing the Human race that need to be addressed in this century. Besides the apparent merits including nontoxicity, elemental abundance, good chemical stability, and easy synthesis, TiO2 has attracted strong research interest worldwide due to its physicochemical properties for realizing various functions.15,58,59 Especially, very encouraging progresses in photocatalysis and DSSCs with the involvement of TiO2 have greatly stimulated the rapid development of TiO2 crystals with controllable phase, size, shape, defect, and heteroatom.58,60−68 The interaction between molecules/ions and surface of TiO2 crystals is essential nearly in all the functional applications listed above. Photocatalysis requires the eﬀective adsorption of reactant molecules/ions (i.e., water, O2, CO2, and organic compounds) on the surface of TiO2 photocatalysts before surface electron transfer. In DSSCs, dye molecules as sensitizers are anchored on the surface of TiO2 nanocrystals by covalent bonding. The discharge/charge processes in lithium ion batteries with TiO2 based anodes are accompanied by the transport of lithium ions across the surface of TiO2. For speciﬁc molecules/ions, their adsorption states are intrinsically determined by surface atomic structures (atomic coordination and arrangement) of TiO2. The substantial role of diﬀerent surfaces in aﬀecting the interaction can be demonstrated by comparing water adsorption, dye anchoring, and lithium insersion on anatase (001) and (101) surfaces. (1) The anatase (001) surface allows the dissociative adsorption of water, while anatase (101) surface only allows the molecular adsorption of water.69 (2) The adsorption of C101 dye molecules on anatase (001) and (101) surfaces form two anchoring geometries diﬀering in the binding of the dye carboxylic groups to the TiO2 surfaces (bridged bidentate vs monodentate),70 and this is responsible for the remarkably diﬀerent dye loading and back electron transfer dynamics observed in the corresponding DSSCs.71,72 (3) An electrochemical study on anatase single crystals with the (101) and (001) facets exposed showed that Li+ insertion is favorable on the (001) surface but is unfavorable on (101) as evidenced by a higher standard rate constant for charge transfer (10−8 vs 2 × 10−9 cm/s).41 Controlling the essential interaction between molecules or ions and TiO2 surfaces required in various applications is therefore one inherent driving force to develop TiO2 with speciﬁc facets. The development of TiO2 crystals with speciﬁc facets is also driven by the inherent necessity of constructing heterostructures of TiO2 in a controllable manner. Constructing the heterostructures is attractive in not only improving the performance of the individual materials but also introducing some new and unusual properties the individual materials do not possess. Diﬀerent facets with diﬀerent surface atomic structures could exhibit distinct abilities in hosting guest materials. One typical example is the selective photodeposition

氧化钛纳米片材料的合成及其催化应用进展

CHEMICAL INDUSTRY AND ENGINEERING PROGRESS 2017年第36卷第7期·2488·化工进展氧化钛纳米片材料的合成及其催化应用进展李路1，2，徐金铭2，齐世学1，黄延强2（1烟台大学化学与化工学院，山东烟台 264005；2中国科学院大连化学物理研究所，航天催化与新材料研究室，辽宁大连 116023）摘要：氧化钛纳米片材料为一种新兴的二维层状材料，在催化、环境、能源和电子领域引起人们广泛的关注。

本文从催化研究的角度出发，综述了氧化钛纳米片材料的结构、制备方法、金属及非金属元素的掺杂、纳米片基复合材料和其在光催化、光电催化和热催化等方面的应用进展。

分析表明氧化钛纳米片材料拥有特殊的形貌和特别的物理化学性质，通过控制材料的组成及结构变化，能够实现氧化钛纳米片材料的多种功能化。

指出氧化钛纳米片材料虽然有着优良的性能，但是在实际应用中远不能满足要求。

因此，优化合成和探索新形式的二氧化钛纳米片材料，对其表面进行改性及开发具有特殊功能纳米复合材料是解决其瓶颈的有效途径。

探索催化反应过程中的反应机理，开发氧化钛纳米片基工业应用催化剂将是今后重要的研究方向。

关键词：氧化钛纳米片；层状钛酸盐；催化；合成；纳米材料中图分类号：O611.4 文献标志码：A 文章编号：1000–6613（2017）07–2488–09 DOI ：10.16085/j.issn.1000-6613.2016-2340Recent advances in titanium oxide nanosheets for catalytic applicationsLI Lu 1，2，XU Jinming 2，QI Shixue 1，HUANG Yanqiang 2（1College of Chemistry and Chemical Engineering ，Yantai University ，Yantai 264005，Shandong ，China ；2Laboratory of Catalysts and New Materials for Aerospace ，Dalian Institution of Chemical Physics ，Chinese Academy of Science ，Dalian 116023，Liaoning ，China ）Abstract: As a new class 2D layered materials ，Titanium oxide nanosheets have attracted great interest inthe fields of catalysis ，environment ，energy and electronics. In this work ，we provide an overview of the recent advance of titanium oxide nanosheets on their layered structure ，synthetic methods ，doping with metals or nonmetal ，as well as their nanocomposites and applications in catalysis. Recent researches indicate that titanium oxide nanosheets with unique structure and special physical and chemical properties can achieve multiple functions by controlling their compositions and structures. Although titanium oxide nanosheets have a lot of advantages ，they are still far from practical applications. Therefore it is demanded to explore new synthesis ，doping and modification methods ，and develop new composite materials. In addition ，the reaction mechanism in the catalytic reaction process and the industrial application of titanium oxide nanosheets will be important research directions in the future. Key words ：titanium oxide nanosheets ；layered titanate compounds ；catalysis ；synthesis ；nanomaterials助理研究员，从事有序介孔材料合成及表面修饰和生物质催化转化制化学品相关科研工作。

TiO2 nanowires sensitized with CdS quantum dots and the surface photovoltage properties

TiO 2nanowires sensitized with CdS quantum dots and the surface photovoltage propertiesMingxia Xia a ,Fuxiang Wang a ,Yicheng Wang a ,Anlian Pan a ,Binsuo Zou a ,Qinglin Zhang a ,b ,⁎,Yanguo Wang a ,c ,⁎aKey Laboratory for Micro-Nano Optoelectronic Devices of Ministry of Education,and State Key Laboratory for Chemo/Biosensing and Chemometrics,Hunan University,Changsha 410082,China bKey Laboratory of Low Dimensional Quantum Structures and Quantum Control,Ministry of Education,Hunan Normal University,Changsha 410082,China cInstitute of Physics,Chinese Academy of Sciences,P.O.Box 603,Beijing 100190,Chinaa b s t r a c ta r t i c l e i n f o Article history:Received 7March 2010Accepted 6May 2010Available online 12May 2010Keywords:TiO 2CdSNanowires PhotovoltageTiO 2nanowires prepared by thermal annealing of anodized Ti foil were sensitized with CdS quantum dots (QDs)via chemical bath deposition (CBD).Microstructural characterizations by SEM,TEM and XRD show that the CdS nanocrystals with the cubic structure have intimate contact to the TiO 2nanowires.The amount of CdS QDs can be controlled by varying the CBD cycles.The experiment results demonstrate that the surface photovoltage (SPV)response intensity was signi ﬁcantly enhanced and the surface photovoltage response region was also expanded obviously for the TiO 2NWs sensitized by CdS QDs.©2010Elsevier B.V.All rights reserved.1.IntroductionTitanium dioxide is one of the most important oxide semiconduc-tors with distinct photochemical activities and has been used widely in many areas such as photocatalysis and photovoltaic cells,etc.[1,2].Dye-sensitized solar cells (DSSCs)based on nanostructured TiO 2electrode have attracted intensive interest since they were ﬁrst reported by Grätzel in 1991[2].However,TiO 2absorbs only about 5%of the solar spectrum,resulting in poor conversion ef ﬁciency in solar cell applications.Because of high cost of t he typical organic dyes such as N3or N719,it is necessary to develop alternatively inexpensive light harvesters.CdS QDs with broadly tunable band gap (2.4–4.2eV)could give new opportunities to harvest light in the visible region of solar light [3–6],and inject the photo-induced electrons into the conduction band of wide band gap semiconductors,leading to the improvement of the energy conversion ef ﬁciency.Chemical bath deposition (CBD)is the most popular and attractive method for in situ synthesis of the QDs in mesoporous TiO 2substrates [7–9],since the synthesis of CdS QDs and sensitization of TiO 2can be achieved simultaneously.The improved photovoltaic performances were reported for the CdS sensitized mesoporous TiO 2in literatures [10–14].But the reported works were mainly focused on thesensitization of TiO 2nanoparticles or nanotubes synthesized through solution method.Recently,a simple method for preparation of TiO 2nanowires (NWs)with high crystallinity was reported at low temperature [15].High quality of TiO 2nanowires facilitates the charge carrier transport in the nanostructure,which help to optimize the performance of opto-electronic devices.In this letter,we report the sensitization of high crystallinity TiO 2NWs with CdS QDs via the CBD method.The transfer behavior of photo-generated charge carriers of the TiO 2NWs before and after sensitization has been investigated by the SPV technique.The results show that the deposition of CdS QDs can greatly enhance the SPV response intensity and broaden the SPV response region of TiO 2NWs.2.ExperimentsThe detailed synthesis of the TiO 2NWs was reported elsewhere [15].Simply,the anodization of Ti foil (99.6%in purity,Alfa Aesar)was ﬁrstly carried out in the electrolyte containing 0.1M NaF and 0.5M NaHSO 4for one hour.Secondly,Pd particles were attached on the Ti foil by immersing the anodized Ti foil into the ethanol solution of PdCl 2,which was then irradiated with a UV light source (365nm)for 5min.Finally,TiO 2NWs were obtained by annealling the Pd decorated Ti foil in a tube furnace at 780°C for one hour.The as-obtained TiO 2NWs were further sensitized with CdS via the CBD method.The CBD process includes dipping the TiO 2NWs in a 0.2M Cd (NO 3)2ethanol solution for 5min,rinsing it with ethanol and then dipping it in a 0.1M Na 2S methanol solution for another 5min,andMaterials Letters 64(2010)1688–1690⁎Corresponding authors.Key Laboratory for Micro-Nano Optoelectronic Devices of Ministry of Education,and State Key Laboratory for Chemo/Biosensing and Chemometrics,Hunan University,Changsha 410082,China.Tel.:+8673188820925,+861082648009;fax:+8673188822137,+861082648009.E-mail addresses:qinglinz@ (Q.Zhang),ygwang@ (Y.Wang).0167-577X/$–see front matter ©2010Elsevier B.V.All rights reserved.doi:10.1016/j.matlet.2010.05.003Contents lists available at ScienceDirectMaterials Lettersj o u r na l ho m e p a g e :w w w.e l s ev i e r.c o m /l o c a t e /m a t l e trinsing it again with methanol.These two-steps dipping procedure was recorded for one CBD cycle.The crystal structures of the TiO2NWs were examined by X-ray diffractometry(XRD,Siemens D-5000)with CuKa(λ=1.5405Å) radiation.The microstructures were characterized by FE-SEM(JSM 6700F,JEOL)and TEM(JEOL2010).The opto-electrical properties of the TiO2NWs sensitized by CdS QDs have been explored by an UV–vis spectrophotometer(Cary300,Varian,USA)and the surface photo-voltage measurement based on the lock-in ampliﬁer.3.Results and discussionsThe SEM image(Fig.1a)shows that the as-prepared TiO2NWs have a length of several tens of micrometers,with Pd particles founded at their tips.Fig.1b and c give the TEM images of representative single TiO2NWs without sensitization and with sensitization by CdS QDs with5CBD cycles,respectively.It is found that CdS nanoparticles,with an average diameter of∼3nm,are intimately deposited on the as-prepared TiO2NWs.XRD patterns of TiO2NWs and TiO2/CdS composites with different CBD circles are shown in Fig.2a,respectively.The XRD plot of the TiO2NWs without sensitization(0CBD)reveals a tetragonal phase of TiO2(rutile,JCPDS ﬁles86-0147).The peaks of2θ=27.43°,36.08°,41.24°,54.32°,56.62°can be assigned to the(110),(101),(111),(211),and(220)planes of rutile TiO2,respectively.Three new broad peaks appear at2θ=26°, 44°,and52°for the CdS QDs sensitized TiO2NWs,attributing to the cubic structured CdS(JCPDSﬁle10-454).The intensity of CdS diffraction peaks increases gradually with the increase of CBD cycles, resulting from the more deposition of CdS on theTiO2NWs.The amount of attached CdS QDs to TiO2NWs can also be qualitatively estimated through the UV-vis absorption measurement. Fig.2b gives the UV–vis absorption spectra of TiO2NWs and TiO2/CdS composites with different CBD cycles,respectively.It can be seen that the intensity of light absorption increases with the growing deposition of CdS.Typically,rutile TiO2has its featured absorption band in the region of300–420nm,while cubic CdS has the featured absorption band in the380–600nm region.The red shifts of the absorption edge with the CBD cycles imply the growth of the CdS QDs [16],which exhibits good agreement with the XRD results.However,the information of the photoelectric process about charge carriers generation,separation and transport cannot be really deduced from the absorption spectra.SPV measurement can give the fundamental information of both the light absorption and thebehavior of photo-generated charge carriers in semiconductor structures[8].Fig.3shows the SPV responses of TiO2NWs before and after sensitization by CdS QDs.The inset of Fig.3depicts the enlarged spectra of TiO2NWs and TiO2/CdS composite for5CBD cycles.It is clearly seen that the SPV response intensity increased and the SPV response region broadened simultaneously as the increase of CBD circles.The major feature of Fig.3is the shift of the maximum SPV response band of the TiO2/CdS nanostructures as increase of CBD cycles.The SPV response in the wavelength region of300–420nm is much stronger than that in the wavelength region of420–600nm when the CBD cycles are below10.In contrast,the SPV response band of420–600nm becomes dominant for the TiO2/CdS composites prepared by more than15CBD cycles.This phenomenon can be possibly explained by the transfer of the photo-generatedelectrons Fig.1.(a)SEM image of TiO2NWs,(b)TEM image of a representative TiO2NW,and(c)TEM image of a TiO2NW sensitized by CdS QDs.Inset of(a):SEM image of the tip of a TiO2NW.Fig.2.(a)XRD and(b)UV–vis absorption spectra of TiO2NWs sensitized by CdS QDswith different CBD cycles.1689M.Xia et al./Materials Letters64(2010)1688–1690from CdS QDs to TiO 2NWs.It is well known that the transfer of the photo-generated charge carriers between the sensitizer and the host material just happens at their interface.Therefore,only the photo-induced charge carriers generated near the interface can effectively transfer from sensitizer to the host material,leading to the prominent enhancement of the SPV response.For the TiO 2/CdS composites fabricated under 10CBD cycles,the CdS layer is so thin that both the ultraviolet and the visible light can reach the interface of TiO 2/CdS composites.The ultraviolet light can produce more photo-induced charge carriers transported to the TiO 2NWs than the visible light due to the absorption coef ﬁciency of CdS which is inversely proportional to the wavelength,resulting in the maximum SPV response band that appeared at 300–420nm.The high absorption coef ﬁciency of ultraviolet light also results in short penetration length in CdS.Consequently,only the visible light can reach the interface of TiO 2/CdS composites when the CdS layer on TiO 2NWs becomes thick enough,inducing the whole SPV response dominated in the visible light region,which is con ﬁrmed by the SPV response of the TiO 2/CdS composites produced by more than 15CBD cycles.The experimental results indicate that the TiO 2NWs were successfully sensitized by CdS QDs,which exhibit the enhanced SPV response intensity and the broaden SPV response region.4.ConclusionIn summary,TiO 2NWs have been successfully sensitized with CdS QDs with an average diameter of ∼3nm by the CBD method.The TiO 2/CdS composites show a wider absorption in the solar spectrum and an enhanced surface photovoltage response than those of the unsensi-tized wires.Theirs ﬁnding indicates that CdS QDs are good candidate as sensitizer of TiO 2NWs,and will have the potential to improve the solar energy conversion ef ﬁciency of TiO 2NWs based solar cells.AcknowledgementThe ﬁnancial support by the National natural Science foundation of China (Nos.60796078,10774174,20903038,90923014and 10974050),the Opening Project of Key Laboratory of Low Dimen-sional Quantum Structures and Quantum Control (Hunan Normal University),Ministry of Education (No.QSQC0912),and partly by “973”National Key Basic Research Program of China under Grant Nos.2007CB310500and 2007CB936301is acknowledged with gratitude.References[1]Fujishima A,Honda K.Nature 1972;238:37–8.[2]O'Regan B,Grätzel M.Nature 1991;353:737–40.[3]Barglik-Chory C,Remenyi C,Strohm H,Muller G.J Phys Chem B 2004;108:7637–40.[4]Vinodgopal K,Kamat PV.Eniron Sci Technol 1995;29:841–5.[5]Nasr C,Hotchandani S,Kim WY,Schmehl RH,Kamat PV.J Phys Chem B 1997;101:7480–7.[6]Sant PA,Kamat PV.Phys Chem Chem Phys 2002;4:198–203.[7]Chang CH,Lee YL.Appl Phys Lett 2007;91:053503.[8]Zhang Y,Xie TF,Jiang TF,Wei X,Pang S,Wang X,Wang DJ.Nanotech 2009;20:155707.[9]Tachibana Y,Umekita K,Otsuka Y,Kuwabata S.J Phys Chem C 2009;113:6852–8.[10]Shen Q,Kobayashi J,Diguna LJ,Toyoda T.J Appl Phys 2008;103:084304.[11]Akiyama HY,Torimoto T,Tachibana Y,Kuwabata S.Proc SPIE 2006;634063400H/63401–63413.[12]Tachibana Y,Umekita K,Otsuka Y,Kuwabata S.J Phys D Appl Phys 2008;41102002/102001–102005.[13]Tachibana Y,Akiyama HY,Ohtsuka Y,Torimoto T,Kuwabata S.Chem Lett 2007;36:88–9.[14]Tachibana Y,Umekita K,Otsuka Y,Kuwabata S.J Phys Chem C 2009;113:6852–8.[15]Xia MX,Zhang QL,Li HX,Dai GZ,Yu HC,Wang TH,Zou BS,Wang YG.Nanotech2009;20:055605.[16]Chang CH,Lee YL.Appl Phys Lett 2007;91:053503.Further reading[17]Kronik L,Shapira Y.Surf Sci Rep 1999;37:1–150.Fig.3.(a)SPV spectra of TiO 2NWs and TiO 2/CdS composites with different CBD cycles.Inset:enlargement of the SPV spectra of TiO 2NWs and TiO 2/CdS composite with 5CBD cycles.1690M.Xia et al./Materials Letters 64(2010)1688–1690。

留学美国签证研究计划模板大全

留学美国签证研究计划模板大全（1）Descriptions of the research planTitle: Synthesis, Formation Mechanism, and Properties of Different Metal/Metal Nanostructures Keywords: Multi-Shell Nanostructures, Ionic Liquids, Electrochemistry, Multi-Functionality,Porous Metal Materials, Low-Dimensionality, Green Chemistry Objectives: This program is to develop a novel method for fabricating heterogeneous or alloyed different metal/metal low-dimensional nanostructures, for example, multi-shell or porous Ag-Au nanowires, nanorods, and nanocubes using an ionic liquid as both the solvent and shape-inducing template. Synthesis of ionic liquids (ILs) with different alkyl chains and functional groups, as well as the formation of different metal/metal nanostructures with new properties are involved in this research plan. Alloyed or heterogeneous multi-shell nanostructures are generated by utilizing electrochemical (electroless) deposition or a simple galvanic replacement reaction in ILs. By controlling the size, shape, composition, crystal structure and surface properties of these structures, it enables us not only to uncover their intrinsic properties, but exploit their formation mechanism in ILs media, as well as their applications in catalysis, surface-enhanced Raman scattering (SERS), sensors, porous electrodes, etc. This green chemistry process also may be extended to synthesize other organic and inorganic nanostructures with novel properties, morphology and complex form. State-of-the-artMetal nanostructures have numerous applications as nanoscale building blocks, templates, and components in chemical and biological sensors, as well as electronic/optical devices, due to their interesting optical, catalytic and electrical properties that depend strongly on both size and shape. Over the past decade, impressive progress has been made towards the fairly good shape and size control of metal nanostructures [1][2]. For noble metals, more emphasis is placed on tuning the novel shape-dependent properties of these nanostructures in contrast to the size-dependency. A variety of metallic building blocks with unique properties have been synthesized including cubes [3][4], prisms [5], disks [6], and hollow nanostructures [7]. Currently the interests migrate to the synthesis and application of more complex structures with different metals, such as multi-shell and heterogeneous nanostructures having new properties[8][9], coupling a conception for optimizing preparative strategies in an environmentally benign system[10]. Therefore, besides creating novel nanostructures with unique properties, a problem arising from the utilization of volatile or poisonous organic solvents and additives is of much concern in view of cleaner technology throughout both industry and academia.Most of the current shape selective synthesis of metal nanostructures that their optical properties are markedly affected by their shape and aspect ratio are centered either on a solid substrate by physical methods or in aqueous or organic media through chemical procedures [2]. For instance, complex and highly regular crystalline silver inukshuk architectures can be produced directly on a germanium surface through a simple galvanic displacement reaction that only three ingredients were required: silver nitrate, water, and germanium [11]. Despite these advancements, however, limited reports have been reported on how the particle morphology and dimensionality could beregulated by the utilization of ILs[12].Recently, environmentally benign room-temperature ionic liquids (RTILs) have received increasing attention worldwide due to their favorable properties including excellent thermal and chemical stability, good solubility characteristics, high ionic conductivity, negligible vapor pressure, nonflammability, relatively low viscosity, and a wide electrochemical window. This class of fluid materials contains complicated molecular interactions such as ionic interactions, hydrogen bonding, л-л interactions, and amphiphilic polarization, rendering various molecular structures from merely local orderness up to macroscopic thermo tropic or lyotropic liquid crystalline phases [13]. These advantages make them actively being employed as green solvents for organic chemical reactions, extraction and separation technologies, catalysis, solar cells, and electrochemical applications[14][15].In contrast to tremendous growth in R&D on application of ionic liquids to chemical processing, the use of RTILs in inorganic synthesis is still in its infancy. There have been only a few reports on the shape-and-dimension controlled formation, by using RTILs, of hollow TiO2 microspheres [16] and nanowires of palladium [17], gold nanosheets [12], tellurium nanowires [18], flower-like ZnO nanostructures [19], and CuCl nanoplatelets [20]. So far, alloyed metal structures, either spherical nanoparticles or nanocomposite films, have been generated in RTILs using electrochemical deposition of nanocrystalline metals such as Al-Fe, and Al-Mn alloys on different substrates [21]. However, formation of multi-shell or hollow nanostructures by controlling both the shape and dimension in RTILs has not yet appeared in literature, especially using an electrochemical approach. It is therefore proposed in this program that a new route to optically or catalytically tune the properties of complex metal/metal nanostructures through the control of shape anisotropy and surface morphology is established in RTILs using a green chemistry approach. The reasons we choose RTILs as reaction media are not only in the view of environment protection, but in the consideration of their diversiform molecular structures, which could be used as shape-inducing templates for the synthesis of new nanostructures. It is very unlikely that ILs will entirely replace organic solvents or aqueous systems or gas phase processes for the fabrication of inorganic matter. Nevertheless, ionic liquids with different functional groups may provide a means to fabricate nanostructures that are not otherwise available. The applicant has accumulated good backgrounds in shape-controlled synthesis and characterization of metal and semiconductor low-dimensional nanostructures with unique optical properties. A series of approaches have been used to fabricate Ag-SiO2, and Ag-TiO2 core-shell nanostructures and Ag-SiO2-TiO2 nanocomposite films. During the Ph.D program, novel soft sol and polymer-assisted methods have been developed to form metal and semiconductor nanorods and wires, such as silver and gold nanowires, CdS and ZnS nanowires and rods, as well as anisotropic metal nanocrystals, for example, silver nanoprisms, gold nanocubes, nanodisks, and so on [22][23]. At the same time, tuning the optical properties through the interaction of nanostructures with femtosecond laser pulses to control the size, shape or dimension in nanometer regime has also been investigated [24]. As for the institution to which the applicant is applying and the group of Professor XXXXXXX, equipments including TEM, SEM, UV-Vis-NIR absorption spectrometer and other emission spectrometer (static, time-resolved and tempe rature dependent), as well as the group’s excellent research experience in semiconductor and metal nanomaterials [25][26] provide a sound foundation for the implementation of thisresearch plan, probably resulting in not only a better understanding of the utilization of RTILs in nanochemistry and electrochemistry, but creating new nanostructures, such as microporous Ag/Au multi-shell nanowires with promising applications in SERS, catalysis, etc.A multidisciplinary approach and the planned activitiesA multidisciplinary approach is designed in this proposal through integrating organic synthesis, electrochemistry, materials science and optoelectronics, aiming to fabricate different metal/metal multi-shell heterogeneous nanostructures including nanocubes, nanorings, nanoplates, nanowires and nanotubes. This research plan covers three aspects: The first one is to create novel structures through the reduction of different metal precursors in RTILs using reducing agents or electrosynthetic processes. The second is to produce porous low dimensional metal nanostructures by etching with specific solutions (e.g. concentrated ammonia or hydrochloric acid) or using galvanic displacement reaction and electrochemical anodization. The third is to investigate the formation mechanism and properties of these nanomaterials.1. Synthesis of metal nanostructures with tailored morphology2. Formation of porous low dimensional nanostructures.3. Properties of different metal/metal nanostructures.4. A possible extension of this research planAnother important direction is to fabricate magnetic/semiconducting core-shell nanocrystals, such as Fe3O4/CdSe, or dye molecule complexed rare earth metals to form Gd(BPy)/CdSe using RTILs as reaction media. These nanocrystals containing both fluorescence and magnetic resonance embedded in silica nanoparticles can be used as probes for the study of biological materials, especially in bio-imaging. The magnetic/semiconducting core-shell complex nanocrystals offer distinct advantages over conventional dye-molecules, magnetic resonance imaging (MRI), and simplex semiconductor nanocrystals not only in that they emit multiple colors of light and can be used to label and measure several biological markers simultaneously, but in the capability to target molecules with a good spatial resolution.Time schedule for the planMay 1, 2006-July 1, 2006Two months German learning in a Goethe InstituteJuly 1, 2006-Oct. 31, 20061. Discussion on the detailed research plan and the preparation of materials2. Synthesis and characterization of low-dimensional nanostructures in RTILs3. Publishing 1 papers4. Attending one international convention on nanostructures and applicationsNov. 1, 2007-Mar. 31, 20071. Further improvement of the optical and catalytic properties of nanostructures by controlling their composition, size, shape and morphology2. Formation of multi-shell and porous metal/metal nanomaterials and surface modification3. Applications of as prepared nanostructures in SERS and porous electrodes, ect.4. Publishing about 2-3 papersApr. 1, 2007-May 1, 20071. Summarization of experimental results and rethinking of the RTILs in synthesis of nanomaterials2. Discussion on the possible extension of this research plan留学美国签证研究计划模板大全（2）Advisor’s informationName:******Organization: Northwestern UniversityAcademic position: ****** ProfessorE-mail: ******@TEL: ******Address: ******, Chicago, IL 60611Research planBackground: A number of key transcription factors, including the Androgen Receptor, the Polycomb group protein EZH2, and the TMPRSS2:ERG gene fusions, have been related to epigenetic changes and implicated in prostate cancer. As transcriptional regulation, for instance those by EZH2, eventually leads to inheritable epigenetic changes and thus altered chromatin status. Epigenetic mechanisms may be fundamental to tumorigenesis. Based on lab’s previous work, we hypothesized that in aggressive tumors altered transcriptional controls and chromatin states lead to de-differentiation and a stem cell like cellular status. In our study we will reveal the link between transcriptional control and epigenetic changes including histone methylation, DNA methylation and the regulation of miRNAs.Therefore the proposed work seeks to find the mechanisms between epigenetic regulation andprostate cancer. We plan to do the following projects:Project 1: Cell Culture and In V itro Overexpression, Inhibition and Function Assays.From November 2010 to February 2011, I will conduct experiments on: cell lines culture, expression vector construct, RNA analysis by RT-PCR.Project 2: Protein Interaction Assay, ChIP-Seq Assays and Bioinformatics Analysis.From March 2011 to August 2011, I will perform the Assays on: Protein interaction between target genes, Chromatin immunoprecipitation using the histone methylation antibody and sequence the DNA fragments, Search the binding site sequence by Bioinformatics analysis.Project 3: Paper Writing and PublicationFrom September 2011 to October 2011, I will write my research paper and submit it to a high influence factor journal.Return planEpigenetic regulation, as one of the most fascinating research fields, has appeared in US & Europe since 2000’s. Now this discipline has emerged as a new research fr ontier and received more and more attention in the world. However, in China, epigenetics has only received little attention compared to overseas. In many universities and institutes, few people concentrate on epigenetic regulation. So plenty of researchers will be needed to work on this discipline in the near future. With good expertise in epigenetic research including histone methylation and DNA methylation acquired in National Key Laboratory of Crop Genetic Improvement in past seven years and a deeper insight into epigenetic regulation that will be acquired in Northwestern University, I am full of confidence that after the completion of my post-doctoral research program, I will be able to find a suitable academic position in some university or institute in littoral of China or my home province. With good training in U.S and profound knowledge in epigenetics, I am confident of myself that I will be more competitive and have a much better chance in China. In addition, I will share my research experience abroad with future colleagues in China.留学美国签证研究计划模板大全（3）Descriptions of the research planTitle: Synthesis of Metal-Organic Compound (Grubbs and Schrock-type) Using for PolymerizationKeywords: polymer, asymmetric catalyst, mechanism, polymerization1. Background and introduction of the research project:Conjugated polymers play an important role in various electronic applications. Apart from their conductivity, their photo- and electroluminescence properties are attracting great interest. Owing to their luminescence properties, they are also used in several electronic applications, such as organic lightemitting diodes (OLEDs), solar cells, photovoltaic devices, lasers, all-plastic full-color image sensors, and field effect transistors. In principle, ternary systems, well-defined Mo-based Schrock-type catalysts and fluorocarboxylate-modified Grubbs-type metathesis catalysts may be used for cyclopolymerization. Together with palladium-catalyzed reactions such as the Heck, Suzuki and Sonohashira-Hagihara reactions, metathesis reactions, particularly those that can be accomplished in an asymmetric way, belong nowadays to the most important C-C coupling reactions. Due to the achievements made with catalysts necessary to accomplish thesereactions, an almost unprecedented progress has been made in this area of research; nevertheless, the demand for new catalytic systems is a continuous and growing one.2. The aim and expection of the research project abroad:Its chemistry department can fulfill my project than any other domestic universities. Based on my professional knowledge, I can have a motivated research period and accomplish my Ph.D study. 3. The work plan after returning to China:After completing my Ph.D study, I would like to return to my homeland and make use of my knowledges to serve the people.Now I submit my application with full confidence in the hope of winning a favorable permit. Many thanks for your kind consideration!留学美国签证研究计划模板大全（4）Advisor’s informationName: +++++Organization: ++++++ UniversityAcademic position: +++++Professor of +++++DirectorE-mail: ***@TEL: 831 ***-*****Address: **********Research planBackground: ++++++++++Project 1: ++++++++++++++++Form October 2010 to January 2011, I will conduct experiments on +++++++++++++++++++Project 2: ++++++++++++++From February 2011 to September 2011, I will investigate ++++++++++++++++++Return planAfter one-year research in the United States, I will return to China to continue to be a college teacher in ++++++++ University. I will continue my research work and construct ++++++++++++++++++++++. In addition, I will share my research experience abroad with my colleagues and students. My research experience abroad will help me apply for a higher academic position.There is a list of my plans:Plan 1: ++++++++Plan 2: ++++++++Plan 3: +++++++++Plan 4: +++++++++留学美国签证研究计划模板大全（5）RESEARCH PROJECT:TITLE:BACKGROUND AND INTRODUCTION OF THE RESEARCH PROJECT:THE PREPARA TION WORK OF THE PROJECT IN CHINA:THE AIM AND EXPECTA TION OF THE RESEARCH PROJECT ABROAD:THE EXPERIMENTAL METHODS AND DA TA ANALYSIS METHODS:THE SCHEDULE OF THE RESEARCH PROJECT PLAN:THE WORK PLAN AFTER RETURNING TO CHINA:留学美国签证研究计划模板大全（6）课题研究项目/RESEARCH PROJECT)题目/TITLE: Fabrication and Modification of Different Electrocatalysts of Oxygen Reduction Reaction in Metal/ Air BatteryKeywords: Metal/ air battery, Oxygen reduction reaction, Electrocatalyst, Electrochemistry研究课题在国内外研究情况及水平THE CURRENT RESEARCH CONDITION AND LEVEL OF THE RESEARCH PROJECT A T HOME AND ABROAD:The electrocatalysts of oxygen reduction reaction (simply called ORR) are the key electrode materials for the metal/ air battery. Noble metal and alloy, such as Pt and alloy, are widely used as catalysts because of their highest catalytic activity and most stable performance in all the materials. Considering their high price, however, Pt and alloy are not suitable to be applied in large-scale industry. Therefore, it is significant to find a less expensive catalyst to replace Pt and alloy[1]. Recently three types of transition metal oxides are considered to be the excellent catalysts with wide application prospect due to low cost and high performance. In this essay I will introduce them as follows.The first type is the series of Manganese oxides. Manganese oxide is cheap and its source is abundant. It has been widely reported that the series of Manganese oxides show well catalytic activity on the decomposition of ORR and H2O2. They are usually prepared by adopting the method of thermal treatment. The temperature of pyrolysis influences greatly the activity of catalysts. L. Jaakko discovers that the activity of MnO2 prepared by using pyrolysis at 500℃ is very well. Z. D. Wei [2] fabricated MnO2 with high catalytic performance by the pyrolysis of Manganese Nitrate at 340℃. The optimal weight ratio of MnO2 in the electrode is 6.7%. T. X. Jiang[3] prepared low cost and high effective electrocatalyst with MnO2 and rare earth chloride. It is shown in the experimental results that the optimal temperature of calcining is 300℃, and the time is 20 hours. It is generally thought that catalytic activity of the series of Manganese oxide in ORR is realized by the Mn(Ⅳ)/Mn(Ⅲ) electrode. The catalytic activity of γ-MnOOH is the highest among a series of Manganese oxide. J. S. Y ang[4] synthesised nano finestra amorphismManganese oxide by adopting the method of low temperature liquid phase redox. Its catalytic activity center is considered to be more than that of crystal MnO2, and this type of material with poriferous structure is more suitable to be used to make poriferous electrode.Perovskite complex metal oxide is another type of catalyst studied by many researchers. The structure of perovskite complex metal oxides is ABO3, of which A is rare earth element and B is transition metal element. Due to its high conductivity (about 104 Ω-1•cm-1) and well ORR electrocatalytic activity, it is a kind of excellent double function ORR catalyst material. It is shown in researches[5] that the catalytic activity of oxide with structure of pure ABO3 is not very high. When A position is partly replaced by some low valence metal ions, the property of B position ion and vicinal oxygen ion can be improved. Complex valence of B position ion and vacancy of cation can be formed, which heightens the catalytic activity of complex oxide. The catalytic activity is better when A position ion is La or Pr, so the research of this respect is very common. B position ion plays a decisive role in the catalytic activity of this type of oxides. The sequency of catalytic activity is Co>Mn>Ni>Fe>Cr. The catalytic activity is the highest when B position is Fe. Both activity and stability of complex oxides are better when B position is Mn or Ni. There are several methods of fabricating perovskite complex metal oxide. The method of Acetate Decomposition (AD) is used commonly in the early stage. The temperature of calcining is between 800 and 900℃and time of calcining is as long as about 10 hours. The method of amorphism citric acid precursor (ACP) is a modified method of AD. The temperature of calcining is fall at 600℃and time is shortened to 2 hours. The sol-gel method can obtain nano material with larger specific surface area and better catalytic activity. Therefore, it is widely used in the fabricat ion of perovskite metal oxide catalyst.Finally, the spinel transition metal oxide is one type of catalyst with bright prospect. The general formula of its molecule is AB2O4. In this type of compound the vacancy of tetrahedron and octahedron and oxygen co-ordination was occupied by the transition metal ion with approximate radius. It is approved by many researchers that the catalytic mechanism of spinel transition metal oxide on ORR is similar with that of perovskite transition metal oxide.Although there are many kinds of material which can cause catalytic effect on ORR, few can be used in practical industry. The noble metal, such as Pt and alloy, possess high catalytic activity and stability, but it can not be used in large-scale industry because of their expensive price. Transition metal oxides are thought to have a wide application future because of their well catalytic activity, high stability and low cost. However, the catalytic mechanism is still unknown to us. The structure, the component and ratio of elements can not be designed under the direction of theory. Much exploration work need us to finish.研究课题的目的及预期目标THE AIM AND EXPECTA TION OF THE RESEARCH:I will engage in the research under the direction of Professor *** at *** University and Professor *** at *** University. They recommended me to research fabrication and modification of different electrocatalysts of oxygen reduction reaction in metal/ air battery, which will be very interesting in the future. Under their direction, theoritically, I will investigate the mechanism of fabrication of transition metal oxide, seek an effective and economical method to prepare the electrocatalyst, get the optimal experimental parameters of preparation process, and I will also explore the mechanism of ORR. During this period I will publish several papers or apply some patents related with my research if possible. And I will finish my dissertation of PhD./拟留学院校在此学科领域的水平和优势THE LEVEL AND ADV ANTAGE OF THE HOSTINGFOREIGN INSTITUTION ON THIS PROJECT:,The institution I wants to work in is the school of chemistry at Monash University. It has at least three advantages as follows. Firstly, there are advanced experiment instruments. Facilities in the laboratory are Zeta Potential and Size Analyzer, XRD, XRF, AFM, Electrochemical Impedance Analyzer, Polarization Apparatus, Capillary Electrophoresis, etc. And in the department there are also SEM, TEM, EPMA, etc. Secondly, solid basic research work has been done by the researchers in the laboratory. Great work about the research of electrocatalysts in metal/ air battery has been finished by them. Finally, excellent research environment has formed in the institution. The fabrication technology of electrocatalysts in metal/ air battery is advanced in Australian manufacture. There is frequent cooperation between these manufacturers and the institution, so I can learn the most advanced technology in this field.回国后工作/学习计划THE STUDY/WORK PLAN AFTER RETURNING TO CHINA:After I finish my PhD study and return to my home country, I will do some further reserch on the preparation of electrocatalysts in metal/ air battery. I will investigate the most proper method to fabricate the catalysts with high performance. And I wants to grasp the optimal parameters of the production technology. I hope the technology can be applied widely in the industry of my country.留学美国签证研究计划模板大全（7）Study/Research PlanNameE-mailCurrent UniversityDepartment of *************************UniversityEmployDepartment of **********, University of *******PositionMaster/PhD, Graduate Research Assistant/TAResearch Sponsor********** program,funds from University of ********Proposed PeriodFrom August, 2006 to June, 2008The period depends on the progress of the work.Contact in USDepartment of *********，ADDRESSKey Words***，****，***PurposeContentsMethodApplicationMy Career Goal。

以花瓣为模板制备TiO_2分层介孔纳米片

机染料的降解性能．
综上所述，本文以月季花花瓣为模板，在钛酸四丁酯前驱体的溶液中浸渍后于５０ｏ下煅烧，０Ｃ成
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的片层结构（度４ｎ和均匀的孔道结构（厚ｍ）尺寸４ｎ，强了捕捉光的能力．较薄的片层结构及煅ｍ）增
层结构有关，这些特殊的纳米结构使样品可以大量吸收可见光．与Ｐ５相比，仿生ＴＯ纳米薄片的吸２ｉ：收边红移了约２ｍ，带宽度也相应减小，这可能是由于仿生材料的独特结构以及生物模板煅烧后０ｎ禁
遗留下来的少量氮元素引起的氮掺杂造成的．ＥＳ能谱测试结果中氮元日嚣的存在证实了这一判断．Ｄ素一暑占一０
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赵晓兵等：以花瓣为模板制备ＴＯｉ分层介孔纳米片
构．发达的孔结构有利于吸附污染物，为ＴＯ的光催化提供了高浓度有机环境，而提高了光催化活ｉ：进性并加快了反应速度．

硫化铅量子点的能带调控

硫化铅量子点的能带调控曾鹏菀; 李炜【期刊名称】《《华南师范大学学报（自然科学版）》》【年(卷),期】2019(051)003【总页数】4页(P8-11)【关键词】硫化铅; 量子点; 带隙; 调控【作者】曾鹏菀; 李炜【作者单位】华南师范大学物理与电信工程学院广州510006【正文语种】中文【中图分类】O61量子点作为一种新型的半导体材料，由于其自身的量子效应，使得它具有特殊的光学和电学特性，因而在信息技术、生物医学和可再生能源等领域发挥着极其重要的作用. 硫化铅(PbS)作为一种特殊的半导体材料，具有较窄的直接带隙(0.41 eV)和较大的激子波尔半径(18 nm). 由于PbS产生的荧光可以覆盖整个传输窗口，因此它在光学器件中具有广泛的应用前景[1]，如红外探测器、发光二极管、光学开关、太阳能电池等，尤其是在太阳能电池领域. 近年来，PbS量子点(PbS QDs)引起了越来越多的关注，PbS的制备方法也逐渐成熟，主要包括物理方法、化学方法，甚至还有利用酵母的生物方法. 其中由于化学方法程序简单、反应可控，实验过程安全无危害，因而得到广泛应用. 目前应用比较多的化学方法包括水热合成法、微波法、超声化学法和化学还原法[2-4].近年来，国内外有关PbS QDs的研究报道越来越多，许多研究者采用不同的方法制备出了性质各异的量子点样品. LI等[5]采用一种新的双液相系统成功制备出平均粒径仅10 nm的PbS QDs，其光谱能带为1.34 eV. MAMIYEV等[6]制备出粒径为10～15 nm的PbS QDs，样品的光谱能带达到了3.36 eV.由于采用化学的液相法合成量子点具有步骤可控、条件简单且稳定安全的优点. 本文采用化学共沉积法制备了不同粒径的PbS QDs，并对其光谱能带进行了研究.1 实验部分1.1 试剂与仪器主要试剂有乙酸铅、硝酸铅、硫化钠、油酸、无水乙醇等均为分析纯，实验用水为去离子水. 主要仪器有X射线衍射仪(XRD,D8 ADVANCE,德国BRUKER)、透射电子显微镜(TEM，JEM-2100HR，日本JEOL)和紫外-可见分光光度计(UV-Vis,UV-2550，日本Shimadzu).1.2 制备方法采用乙酸铅和硝酸铅作为铅源、硫化钠作为硫源. 在样品的制备实验中，首先将0.05 mol硫化钠和1 mL油酸添加到装有100 mL去离子水的烧杯中，另用烧杯盛有100 mL去离子水，加入0.05 mol乙酸铅. 待两烧杯中的溶液搅拌至澄清(硫化钠溶液和乙酸铅溶液浓度均为0.5 mol/L)，将两溶液混合反应并不断搅拌，在反应一段时间后，黑色沉淀不断析出. 待反应完全后过滤得到黑色沉淀产物. 为了保证样品的纯度，分别使用乙醇和去离子水对产物进行清洗，循环操作4～5次，最终将得到的黑色沉淀放入鼓风干燥箱中在100 ℃下烘干12 h. 最后将烘干的样品研磨成粉体，即制备出PbS QDs.采用相同步骤制备不同粒径的PbS QDs，依据反应物(乙酸铅、硫化钠)溶液的浓度分别为0.05、0.20、0.50 mol/L，制备出平均粒径分别为7、10、15 nm的量子点，依次编号为：PbS(7 nm)、PbS(10 nm)、PbS(15 nm).采用X射线衍射仪、透射电子显微镜和紫外-可见吸收光谱仪对制备的PbS QDs进行表征.2 结果与讨论2.1 XRD分析由3种不同粒径PbS QDs的XRD谱(图1)可知，硫化铅属面心立方结构，在2θ分别为25.94°、30.03°、42.98°、50.89°、53.34°、62.50°、68.96°、70.91°、78.82°和84.88°处出现的衍射峰分别对应于(111)、(200)、(220)、(311)、(222)、(400)、(331)、(420)、(422)和(511)晶面，产生的衍射峰与硫化铅标准衍射卡(JCPDS Card No. 05-0592)结果一致，无杂质峰出现，表明形成的晶体纯度高. 窄细的半峰宽又体现了样品良好的结晶度.图1 不同粒径PbS QDs样品的XRD谱Figure 1 The XRD spectra of PbS QDs of different particle sizes除了从XRD谱中分析出量子点晶体性质外，还可通过Debye-Scherrer公式D=k/(β cos θ)(1)计算样品的平均粒径. 式中D表示颗粒的平均粒径，k为Scherrer常数(k=0.9)，表示X射线源的波长，β表示衍射峰的半高宽，2θ为衍射角. 利用式(1)计算出3个样品的平均粒径分别为7、10、15 nm. 结果表明：乙酸铅溶液和硫化钠溶液的浓度越小制备的样品粒径越小.2.2 形貌分析由PbS QDs的透射电子显微镜(TEM)图(图2)可知，该量子点呈圆点状，且均匀分散，粒径范围在2～7 nm，这与依据XRD谱计算的粒径结果一致. 这说明，可以通过改变实验条件(浓度)制备出不同形貌的量子点.图2 硫化铅量子点的TEM图Figure 2 The TEM micrograph of the synthesized PbS QDs通过比较研究，SHOMBE等[7]在生成量子点的反应过程中加入了蓖麻油作为一种表面活性剂成功合成了粒径分布在50～80 nm之间的硫化铅纳米片. 再如GOLABI等[8]通过使用黄嘌呤作为硫源反应合成了平均粒径为33 nm的硫化铅纳米颗粒，SALAVATI-NIASARI等[9]则通过水热合成法制备了平均粒径为20 nm的PbS QDs. 从大部分研究来看，对平均粒径小于10 nm的PbS QDs并且尺寸可控制的研究还不多.2.3 紫外-可见吸收光谱分析紫外-可见吸收光谱是研究半导体纳米材料量子尺寸效应[10-11]的常用方法. 图3为不同粒径PbS QDs的紫外-可见吸收光谱，3个样品均在可见光范围内有较强的吸收，明显在300、380、400 nm波段存在3个不同的吸收峰. 利用这3个不同的吸收带边可计算出3个样品的光谱能带.图3 硫化铅量子点的紫外-可见吸收光谱Figure 3 The UV-Vis spectra of PbS QDs相比于块体的硫化铅，PbS QDs的激子吸收峰位于 3 024 nm，对应的光谱能带为0.41 eV[12-14]，本文制备的样品其紫外-可见吸收光谱发生了明显的蓝移，即从红外区域向紫外-可见光区域方向移动，这种变化符合本文的预测. 通过改变量子点的粒径，可以调节量子点的光学性质，即减小量子点的粒径，可增大其光谱能带. 相关研究[8,15]表明：吸收峰波长分布在200～400 nm范围的PbS QDs对紫外-可见光的吸收也发生蓝移，其原因也是量子点粒径的变化.光谱能带可通过吸收光谱中的吸收边位置以及Tauc公式[16-17]αhv=A(hv-Eg)n,(2)计算得到，式中hv表示入射光子的能量，α是吸光度，Eg为被测样品的能带值；A是相对于不同材料的常数；n则表示半导体导带和价带之间的跃迁类型. 对于直接跃迁，取n=2；而对于间接跃迁，n=1/2. 硫化铅材料是一种直接跃迁型材料，将n=2代入式(2)，直接得到样品的光谱能带. 计算可得PbS(7 nm)和PbS(15 nm)的带隙Eg分别为2.4、0.8 eV(图4).图4 不同PbS量子点的能带Figure 4 The energy band graph of different PbS QDs图4所示的能带图进一步证实本文对量子点能带变化的猜想：粒径越小的样品其能带越高，对于粒径最小的PbS(7 nm)，其能带最高. 由于量子点的量子尺寸效应，本文实验的关键是通过改变反应条件来制备粒径较小的量子点，从而调节量子点的能带，达到调控光学性质的效果. 根据研究显示，对某一特定材料来说，其能带的大小不仅取决于自身的结构，而且尺寸大小也是一种控制因素. 一旦颗粒的大小达到纳米级，量子尺寸效应将发挥作用，并引起带隙的改变. 制备的PbS QDs其平均粒径(15 nm)接近理论值，而平均粒径最小的PbS(7 nm)在能带上具有较大的变化(从0.41 eV增大到2.4 eV)，其能带值与理论上的计算值相差1.99 eV，同大部分研究相比较也不同，例如GOLABI[8]成功合成了平均粒径为29 nm的PbS QDs，他们计算得到的能带值为2.3 eV，并将粒子对紫外-可见光吸收蓝移现象的关键因素归因于量子点的颗粒大小上. 研究表明：PbS(7 nm)具有2.4 eV的光谱能带. 在平均粒径小于10 nm的情况下，能带结果(2.4 eV)高于GOLABI等[8]报道的结果. 本文通过改变反应物浓度制备了不同粒径的量子点，进而调制其发光性质，获得了更高的光谱能带. 制备的样品从PbS(7 nm)、PbS(10 nm)到PbS(15 nm)，粒径可控，其能带也相应变化.3 结论采用化学共沉积法成功制备了硫化铅量子点及其粉体，并且通过控制反应溶液(乙酸铅、硝酸铅和硫化钠)的浓度以及添加表面活性剂(油酸)手段研究了量子点粒径与光谱性质的变化规律. 在室温下，混合溶液反应1 h，通过减小反应物浓度使量子点粒径减小. 在加入表面活性剂油酸等条件下，可进一步减小粒径. 采用XRD、TEM、紫外-可见分光光谱等表征方法，利用XRD谱以及谢乐公式计算了平均粒径. 结果表明：基于量子尺寸效应，通过减小样品粒径途经获得了更大的光谱能带. 本文通过对PbS QDs颗粒大小的控制实现了对颗粒光谱能带的调控. 利用量子点的光学特性可以很好地将其应用在太阳能电池等领域.参考文献：【相关文献】[1] PETERSON J J,KRAUSS T D. Fluorescence spectroscopy of single lead sulfide quantum dots[J]. Nano Letters,2006,6(3):510-514.[2] 郑品棋,熊予莹,黄志安,等. 化学沉淀法和溶胶-凝胶法制备纳米二氧化钛及其抑菌性的研究[J]. 华南师范大学学报(自然科学版),2006(3):65-69.ZHENG P Q,XIONG Y Y,HUANG Z A,et al. Study on TiO2 Nanoparticle prepared by chemistry precipitation method and its antibacterial property[J]. Journal of South China Normal University(Natural Science Edition),2006(3):65-69.[3] 张延霖,谢楚茹,蔡文娟,等. ZnO纳米线与硫掺杂TiO2微/纳复合材料的制备及其光催化活性[J]. 华南师范大学学报(自然科学版),2016,48(1):74-78.ZHANG Y L,XIE C R,CAI W J,et al. Preparation and photocatalytic activity of micro/nano-structured ZnO/S-doped TiO2 composites[J]. Journal of South China NormalUniversity(Natural Science Edition),2016,48(1):74-78.[4] 张宇,孙丰强,王红娟. 花状纳米结构SnO2颗粒的低温水浴合成及其光催化性能[J]. 华南师范大学学报(自然科学版),2012(1):90-93.ZHANG Y,SUN F Q,WANG H J. Preparation of flower-like nanostructured SnO2 particles by low-temperature water-bath method and their photocatalytic activity[J]. Journal of South China Normal University(Natural Science Edition),2012:90-93.[5] LI M,YANG Y,YUAN X,et al. A new two-liquid-phase system to synthesize PbS nanoparticles with narrow size distribution[J]. Materials Letters,2015,149:62-65.[6] MAMIYEV Z Q,BALAYEVA N O. Preparation and optical studies of PbS nanoparticles[J]. Optical Materials,2015,46:522-525.[7] SHOMBE G B,MUBOFU E B,MLOWE S,et al. Synthesis of hierarchical PbS nanostructures capped with castor oil[J]. Materials Letters,2016,185:17-20.[8] GOLABI P,AKBARZADEH R,DEHGHANI H. Facile preparation of PbS nanostructures and PbS/f-CNT nanocomposites using xanthate as sulfur source:thermal and optical characterization[J]. Journal of Alloys and Compounds,2015,647:539-547.[9] SALAVATI-NIASARI M,GHANBARI D. Hydrothermal synthesis of star-like and dendritic PbS nanoparticles from new precursors[J]. Particuology,2012,10:628-633.[10] BOUROPOULOS N,PSARRAS G C,MOUSTAKAS N,et al. Optical and dielectric properties of ZnO-PVA nanocomposites[J]. Physica Status Solidi:A,2008,205(8):2033-2037.[11] BOUROPOULOS N,TSIAOUSSIS I,POULOPOULOS P. ZnO controllable sized quantum dots produced by polyol method:an experimental and theoretical [J]. Materials Letters,2008,62(20):3533-3535.[12] NIKOLAEVA E V,OZERIN S A,GRIGORIEV A E,et al. Formation,structure and photoelectrical properties of poly-p-xylyene-PbS semiconductor nanocomposite films[J]. Materials Science and Engineering:C 1999,8/9(9):217-223.[13] NANDA K K,KRUIS F E,FISSAN H,et al. Band-gap tuning of PbS nanoparticles by in-flight sintering of size classified aerosols[J]. Journal of Applied Physics,2002,91(4):2315-2321.[14] ACOSTA M F,LERMA M S,CHAVEZ H A,et al. Excitonic absorption of spherical PbS nanoparticles in zeolite A[J]. Solid State Communications,2003,128(11):407-411.[15] SALAVATI-NIASARI M,GHANBARI D,LOGHMAN-ESTARKI M R. Star-shaped PbS nanocrystals prepared by hydrothermal process in the presence of thioglycolic acid[J]. Polyhedron,2012,35(1):149-153.[16] GREENWOOD D A. Amorphous and liquid semiconductors[J]. Optica Acta International Journal of Optics,1970,17(12):952-952.[17] ABAKER M,UMAR A,BASKOUTAS S,et al. Structural and optical properties of CuO layered hexagonal discs synthesized by a low-temperature hydrothermal process[J]. Journal of Physics D:Applied Physics,2011,44(15):155405/1-7.。

二氧化钛

Preparation of Hollow Anatase TiO2Nanospheres via Ostwald RipeningHua Gui Yang and Hua Chun Zeng*Department of Chemical and Biomolecular Engineering,Faculty of Engineering,National Uni V ersity ofSingapore,10Kent Ridge Crescent,Singapore119260Recei V ed:December10,2003;In Final Form:January20,2004In this work,we report a simple“one pot”approach to prepare hollow anatase TiO2nanospheres via Ostwaldripening under hydrothermal conditions.Inner nanospace and highly organized crystallites in the shell structureand surface regions can be created with a wide range of controlling parameters.The formation mechanismhas been investigated with TEM/ED/SEM/EDX/XRD/XPS methods.The approach shows a high versatilityfor structural engineering of various targeted morphological products,including inner material refills.IntroductionIn addition to the general core-shell nanostructures,1-4there has been an increasing interest in fabrication of hollow inorganic nanostructures owing to their important applications in optical, electronic,magnetic,catalytic,and sensing devices ranging from photonic crystals,to drug-delivery carriers,and nano-reactors.5-8 The inner“nanospace”of these nanostructures,when coupled with chemical functionality of boundary materials,creates both aesthetic beauty and scientific attractions.Among the many investigations in this area,polymeric colloidal particles have been commonly utilized as templates to support the materials of interest via layer-by-layer technique.5,6Hollow interiors can be generated by removing the polymeric core supports.Recently, sacrificial metal templates have been introduced to prepare metal nanoshells that have higher standard reduction potentials.7,8 During redox electrochemical reactions,these metal templates can be gradually evacuated through surface defects while the resultant metal shells preserve the shapes of original templates. In addition to the above two major methods,it would also be desirable to explore other wet-chemical means,aiming at a simple“one-pot”synthetic approach for important metal oxides. For example,hollow TiO2microspheres in the diameter range of10to20micrometers had been recently synthesized in ionic liquids.9In addition to this,smaller TiO2microspheres(ca.3µm in diameter)with mesoporous core-shell structures have also been prepared with a combination of wet(solvent used: EtOH/H2O)and solid-state reactions very recently.10In this article,we will report an aqueous synthetic scheme for prepara-tion of monodispersed hollow anatase TiO2nanospheres.With the hydrolysis of TiF4,solid TiO2spheres can be formed;hollow interiors can be further created in100%morphological yield via Ostwald ripening after a longer hydrothermal treatment. Owing to this new hollowing scheme,the crystallites formed in the nanosphere shell are well aligned;unique textural structures as well as inter-crystallite channels to the central interiors have been attained for the first time for the anatase hollow spheres.It is believed that the method will allow further preparations of other composite metal oxide nanospheres via a “refilling”process.Experimental SectionThe preparation of the tarting solution of TiF4has been detailed in our previous report.11In a typical experiment,30 mL of the TiF4solution(1.33-2.67mM)was added to a Teflon-lined autoclave,and the hydrothermal synthesis was conducted at140-220°C for1.5-100h in an electric oven.A total of37 experiments were carried out to examine various synthetic parameters.In certain experiments,additives such as thiourea, urea,and HF were further mixed,respectively,with the starting TiF4solution.After the reactions,white TiO2products were harvested by centrifuging and washing with deionized water. The products were then characterized with a range of analytical techniques,as had been detailed in our previous publications.11,12 In particular,scanning electron microscopy,energy-dispersive X-ray spectroscopy(SEM/EDX,JSM-5600LV),transmission electron microscopy,selected area electron diffraction(TEM/ SAED,JEM-2010F),X-ray photoelectron spectroscopy(XPS; AXIS-Hsi,Kratos),and powder X-ray diffraction(XRD, Shimadzu XRD-6000,Cu K R radiation)were employed in the present investigation.Results and DiscussionFigure1A illustrates the formation process of hollow TiO2 nanospheres.As indicated,the solid TiO2spheres are comprised of numerous smaller pared to those in the outer surfaces,the crystallites located in the inner cores have high surface energies,because they can also be visualized as a smaller sphere having a higher curvature(i.e.,higher surface energies and thus easy to be dissolved).When the reaction time is short, the TiO2spheres have a solid core(entirely dark;Figure1B).A hollowing effect is observed for those with a longer reaction time.Reported in Figure1C and1D,the inner nanospace(the lighter part)of the spheres is further increased in comparison to the shell(darker spherical circle)when the reaction time is longer(20h vs100h).Furthermore,a higher starting concen-tration of TiF4will give a thicker shell due to a higher growth rate.It should be mentioned that there was no such hollowing effect observed in our previous work,11because those TiO2 nanospheres were single-crystalline(they were epitaxially grown on the(010)surface of R-MoO3).There are two basic types of hollowed spheres,type(i)and type(ii),as indicated in Figure 1A.The nanospheres reported in Figure1D can be classified as the type(i)that has a relatively dense and smooth surface.*Corresponding author.E-mail:chezhc@.sg.3492J.Phys.Chem.B2004,108,3492-349510.1021/jp0377782CCC:$27.50©2004American Chemical SocietyPublished on Web02/24/2004The type(ii)spheres have a less compact surface where the extruding crystallites can be observed(will be shown soon). The XRD investigation shown in Figure2indicates that the crystallographic phase of all studied TiO2nanospheres prepared in this work belongs to the anatase-type(SG:I41/amd;JCPDS no.21-1272),and the measured lattice constants of a o and c o of this tetragonal phase are3.79and9.51Årespectively.In particular,the crystallinity of the products is indeed increased gradually with the reaction time(e.g.,from2to100h;Figure 2),which indicates that Ostwald ripening(crystallites grow at the expense of the smaller ones)13is an underlying mechanism operative in this hollowing process.The stoichiometric com-position of the anatase nano-products was further confirmed with our EDX analysis(atomic ratio of Ti/O,1:2,see Supporting Information).As reported in Figure3,XPS investigation on the titanium chemical state shows that the binding energy of Ti 2p3/2is equal to458.5eV and the binding energy of Ti2p1/2is equal to464.1eV,which are identical to that reported in the literature for the same anatase phase.14The chemical state of Ti IV is thus confirmed.On the basis of above TEM/XRD/EDX/XPS investigations, it is suggestive that Ostwald ripening is also associated with the chemical nature of ionic species present in the solution during the synthesis.This point is further addressed in theFigure1.(A)Schematic illustration(cross-sectional views)of the ripening process and two types(i&ii)of hollow structures.Evolution (TEM images)of TiO2nanospheres synthesized with30mL of TiF4 (1.33mM)at180°C with different reaction times:(B)2h(scale bar )200nm),(C)20h(scale bar)200nm),and(D)50h(scale bar)500nm).Figure2.Representative XRD patterns of anatase TiO2nanospheres. The samples were synthesized with30mL of TiF4(1.33mM)at180°C with reaction times of2,50,and100h,respectively.The intensity humps at2θ)15-25°are due to the signal generated by a silica sample holderused.Figure3.RepresentativeXPS spectra[Ti2p and S2p(inset)]of TiO2hollow structures.Synthetic conditions:(a)30mL of TiF4solution(1.33mM)at180°C for10h;and(b)30mL of TiF4solution(2.67mM)+100mg of thiourea at170°C for17h.Figure4.TEM images of TiO2nanospheres synthesized with30mLof TiF4(1.33mM)+25mg of thiourea for20h(180°C):(A)overallappearance,(B)center-projecting crystallites,(C)the texture of a shellfragment,and(D)TEM image of TiO2nanospheres synthesized with30mL of TiF4(2.67mM)for11h+0.4mL(HF10%)for another9h;both steps at180°C.Scale bars in(A)to(D)are equal to500,100,50,and500nm,respectively.Arrows indicate the projecting directionalong[001]while the dashed lines define the shell thickness.Figure 5.A representative TEM image and its related electrondiffraction pattern of anatase TiO2.Synthetic conditions:30mL ofTiF4solution(1.33mM)at180°C for50h.Preparation of Hollow Anatase TiO2Nanospheres J.Phys.Chem.B,Vol.108,No.11,20043493following three different synthetic experiments.When the solid TiO 2nanospheres (2h;Figure 1B)were separated from the mother liquor and heat-treated again in deionized water for another 18h,no hollowing was observed.This is understand-able,because there is no chemical species to generate necessary ionic transport in solution during the ripening process.When thiourea was added,as reported in Figure 4A -4C,the hollowing process could be accelerated,but no obvious effect was observed when using urea as an additive.The observed difference can be attributed to different chelating abilities of :S d C and :O d C to the titanium cations and different chemical natures of their hydrolysis products.Both EDX result (see Supporting Informa-tion)and XPS analysis on S 2p core electrons indicate that there is no sulfur contaminant on the samples synthesized with thiourea (see inset,Figure 3).It is interesting to note that the cellular crystallites of the TiO 2spherical shells are highly organized with respect to a common center (Figure 4B &4C).The diameter and length of these crystallites are in the ranges of 30-50nm and 150-250nm,respectively.Confirmed with SAED in Figure 5,the individual elongated TiO 2crystallites are largely single-crystalline with their axes pointing along [001]of the crystal.It is also noted that the hydrolysis of TiF 4will generate HF,a corrosive chemical that may also be responsible for this ripening process.To investigate this effect,a two-step reaction was carried out with a deliberate addition of HF in the second step (Figure 4D).Indeed,the evacuation of the TiO 2solid core has been significantly speeded up with the additional HF,giving away thinner shells comprising of well-faceted TiO 2nanocrystallites (30-70nm in size,Figure 4D).Note that some of the spheres are “fused”together forming a peanut-shell-like structure.In addition to the above TEM observations,where the observation of hollow interiors is largely based on the image contrast,the hollow interiors of the TiO 2nanospheres is also directly reconfirmed with our SEM investigation of Figure 6for the as-prepared nanospheres;the same hollow interiors are also observed more clearly for our crashed samples (not shown).Although size of these nanospheres may be relatively large (up to 1µm in diameter),it has been recently shown that the TiO 2microspheres with hollow interiors are also highly demanded in the application of chemical reactors,etc.9,10Regarding the formation of hollow interiors,it is recognized that the ripening process must involve the mass transfer between the solid core and outside chemical solution through inter-crystallite interstitials of the nanospheres.This is demonstrated in an evacuation-then-refilling process reported in Figure 7.With a high concentration of TiF 4,type (ii)hollow spheres were readily formed after 10h of reactions (Figure 7A).When moreFigure 6.SEM images of anatase TiO 2nanospheres.Hollow interiors of some fractured spheres are indicated with arrows.Synthetic conditions:the same as those in Figure 4A.Figure 7.Refilling process of TiO 2nanospheres (TEM images):(A)synthesized with 30mL of TiF 4(2.67mM)+10mg of thiourea at 180°C for 10h,and (B)synthesized with the same conditions of (A)for 11h,then added with 2mL of TiF 4(40mM)for another 9h (total 20h)at 180°C;both scale bars )500nm.Figure 8.TEM images of the anatase TiO 2spheres.Note that there are inter-crystallite spaces formed perpendicularly to the surface of spheres (whiter areas in the central area of Image A and in the edge area of Image B (the framed area of A).Synthetic conditions:30mL of TiF 4solution (1.33mM)at 180°C for 50h.3494J.Phys.Chem.B,Vol.108,No.11,2004Yang andZengTiF 4nutrient was supplied in a second stage of synthesis,the nanospheres synthesized from the stage one could be “refilled”with the TiO 2solid through the shell surfaces (Figure 7B),noting that this process did not cause obvious size change.In view of the well-aligned shell texture attained in Figure 4C,furthermore,it can be deduced that there must exist inter-crystallite inter-stitials formed perpendicularly to the sphere surface.Indeed,this postulation is further confirmed with our TEM examination reported in Figure 8,where the electron beam of TEM was focused perpendicularly to the sphere center.Brighter contrasts (with a diameter of about 10-25nm)in the central part of the sphere image reveal these “channels”for chemical entities traveling in and out of the sphere during either hollowing or refilling process.It should be mentioned that the oriented nanostructures fabricated and thus oriented nanochannels provide encapsulated materials with an easy access to the central cavities of the spheres.In addition to the general encapsulation applica-tion,this type of hollow nanospheres may also be utilized for synthesis of other composite nanospheres (or other core/shell nanostructures)with the refilling process investigated in Figure 7.Indeed,our recent preliminary investigations have shown that the same refilling process is applicable to other metal oxide inclusions.15By varying the reaction temperature,it has been found that an appreciable hollowing process commences at g 160°C,although the TiO 2nanospheres with a solid core can be formed at much lower temperatures.11Furthermore,core evacuation time can be significantly shortened by choosing a higher reaction temperature (220°C,5h),as exampled in Figure 9.The present method also shows a high versatility for structural and morphological engineering.In addition to the hollow structures,the solid core and surface region of a sphere can be further differentiated with a higher dose of thiourea in thesynthesis.As shown in Figure 10,an abrupt core -surface interface within the TiO 2spheres has been further attained.This structure can also be viewed as a variation of the type (ii)spheres with a solid core.ConclusionIn summary,we have developed a simple “one-pot”method to prepare hollow anatase TiO 2nanospheres via Ostwald ripening in aqueous mediums.Inner nanospace and highly organized crystallites in the shell and surface regions can be created with a wide range of controlling parameters.This approach shows a high versatility for structural engineering of various targeted morphological products.In addition to the general encapsulation,this type of hollow nanospheres could be utilized for synthesis of other composite core -shell nano-structures with a refilling process.Acknowledgment.The authors gratefully acknowledge the financial support of the Ministry of Education,Singapore.Supporting Information Available:Information on our EDX analysis.This material is available free of charge via the Internet at .References and Notes(1)Caruso,F.Ad V .Mater .2001,13,11.(2)Scha ¨rtl,W.Ad V .Mater .2000,12,1899.(3)Mandal,S.;Selvakannan,P.R.;Pasricha,R.;Sastry,M.J.Am.Chem.Soc.2003,125,8440.(4)Sobal,N.S.;Ebels,U.;Mo ¨hwald,H.;Giersig,M.J.Phys.Chem.B 2003,107,7351.(5)Caruso,F.;Caruso,R.A.;Mo ¨hwald,H.Science 1998,282,1111.(6)Go ¨ltner,C.G.Angew.Chem.,Int.Ed .1999,38,3155.(7)Sun,Y.;Xia,Y.Science 2002,298,2176.(8)Sun,Y.;Mayers,B.;Xia,Y.Ad V .Mater .2003,15,641.(9)Nakashima,T.;Kimizuka,N.J.Am.Chem.Soc.2003,125,6386.(10)Guo,C.-W.;Cao,Y.;Xie,S.-H.;Dai,W.-L.;Fan,mun.2003,700.(11)Yang,H.G.;Zeng,H.C.Chem.Mater.2003,15,3113.(12)Sampanthar,J.T.;Zeng,H.C.J.Am.Chem.Soc.2002,124,6668.(13)Ostwald,W.Z.Phys.Chem .1900,34,495.(14)Herman,G.S.;Gao,Y .Thin Solid Films 2001,397,157.(15)Yang,H.G.;Zeng,H.C.Work in process.Figure 9.A TEM image of the anatase TiO 2nanospheres synthesized at a higher temperature.Note that a much shorter reaction time is needed at higher temperatures.Synthetic conditions:30mL of TiF 4solution (2.67mM)+10mg of thiourea at 220°C for 5h.Figure 10.Sunflowerlike TEM images of TiO 2spheres with a less compact surface and a solid core:(A)overall appearance (scale bar )1000nm),and (B)a detailed view on the surface region (scale bar )200nm).Synthetic conditions:30mL of TiF 4(1.33mM)+300mg of thiourea at 180°C for 3h.Preparation of Hollow Anatase TiO 2Nanospheres J.Phys.Chem.B,Vol.108,No.11,20043495。

Hierarchical TiO2 flowers built from TiO2 nanotubes for efficient Pt-free based flexible dye-sensiti

Downloaded on 11 December 2012 Published on 08 August 2012 on | doi:10.1039/C2CP42746J
Received 6th August 2012, Accepted 6th August 2012 DOI: 10.1039/c2cp42746j A novel hierarchical TiO2 ﬂower consisting of anatase TiO2 nanotubes on a Ti foil substrate has been prepared via a mild hydrothermal reaction of TiO2 nanoparticles/Ti foil. The photovoltaic performance of DSSC based on hierarchical TiO2 ﬂowers/Ti (7.2%) is much higher than that of TiO2 nanoparticle/Ti (6.63%) because of its superior light scattering ability and fast electron transport. Moreover, full ﬂexible DSSC based on the novel hierarchical TiO2 ﬂowers/Ti foil photoelectrode and electrodeposited poly(3,4-ethylenedioxythiophene) (PEDOT) on indium tin oxide-coated poly(ethylene terephthalate) (ITO-PET) counter electrode shows a signiﬁcant power conversion eﬃciency of 6.26%, accompanying a short-circuit current density of 11.96 mA cmÀ2, an open-circuit voltage of 761 mV and a ﬁll factor of 0.69. Since O’Regan and Gra ¨ tzel reported a photovoltaic performance of 7.1% for a new type of solar cell based on the nanocrystalline titania photoelectrode in 1991,1 dye-sensitized solar cells (DSSCs) have attracted enormous academic and industrial interest due to the attractive power conversion eﬃciency, low cost for material and production. Recently, light weight ﬂexible DSSCs have been of tremendous interest for their wide and potential applications in wearable electronics and mobile electricity (e.g. lap-top computers, mobile phones, watches, etc.).2 Signiﬁcant progress has been made in the front-illumination ﬂexible DSSCs using an ITO-PET or an ITO-coated polyethylene naphthalate (ITO-PEN) substrate based photoanode prepared by spray pyrolysis, a press method or a doctor-blade method.3–5 However, the plastic substrates have thermal instability at high temperatures (450–550 1C) which are required for sintering TiO2 photoelectrodes of the DSSCs. Low temperature (o150 1C) sintering of the TiO2/plastic substrate results in poor connection between TiO2 particles which may hinder the further improvement of the photovoltaic performance.6 Hence, in order to overcome the high temperature sintering of the TiO2 photoelectrode/plastic substrate, various metal substrates

TiO2纳米花的制备及其生长机理研究

第 45 卷第 8 期2016 年 8 月Vol.45 No.8Aug.2016化工技术与开发Technology & Development of Chemical IndustryTiO 2纳米花的制备及其生长机理研究党威武（陕西国防工业职业技术学院机械工程学院，陕西西安 710300）摘要：利用水热法在导电玻璃基底上制备出TiO 2纳米花，反应温度和保温时间分别为160℃和12h。

表征结果显示，TiO 2纳米花是一种典型的金红石型结构，由一束底端聚集在一起的纳米棒形成。

进一步实验发现，随着温度和时间的增加，将在导电玻璃表面形成定向生长的TiO 2纳米棒。

同时，分析讨论了TiO 2纳米花的生长机理，为进一步推进TiO 2纳米材料的可控制备提供研究基础。

关键词：TiO 2；纳米花；生长中图分类号：TQ 134.1 文献标识码：A 文章编号：1671-9905(2016)08-0009-03作者简介：党威武（1985-），男，陕西渭南人，陕西国防工业职业技术学院讲师，硕士，主要从事纳米材料制备与应用方向研究。

E-mail：dww046@, dww_046@收稿日期：2016-05-27二氧化钛（TiO 2）是一种典型n 型优良半导体氧化物，也是目前被广泛研究的半导体材料，具有成本低廉、无毒无害、生物相容性和物化性能良好、带隙宽等特点，可应用于光催化、气体传感器、电子器件及杀菌消毒等领域[1-5]，是备受青睐的纳米材料。

为了更大层面上推广TiO 2应用，TiO 2纳米材料的可控制备，即通过可靠的实验方法，合成形貌可控的TiO 2纳米结构材料尤显重要。

随着TiO 2纳米材料研究的不断深入，科研工作者对实现TiO 2纳米材料各种结构的可控制备及其应用的研究开发，做了大量的研究工作[6-8]。

目前， TiO 2纳米材料的制备方法主要有气相法和液相法两种，其中，气相法因为设备昂贵，实验过程要求严格，实验稳定性差，重复性低等因素，其推广受到一定限制。

ACS Applied Materials And Interface Peiguang

Enhancement of Ethanol Vapor Sensing of TiO2Nanobelts by Surface EngineeringPeiguang Hu,†Guojun Du,†Weijia Zhou,†Jingjie Cui,†Jianjian Lin,†Hong Liu,*,†Duo Liu,†Jiyang Wang,†and Shaowei Chen‡State Key Laboratory of Crystal Materials,Center of Bio&Micro/Nano Functional Materials,Shandong University, 27Shandanan Road,Jinan250100,P.R.China,and Department of Chemistry and Biochemistry,University of California,1156High Street,Santa Cruz,California95064,United StatesABSTRACT TiO2nanobelts were prepared by a hydrothermal process,and the structures were manipulated by surface engineering, including surface coarsening by an acid-corrosion procedure and formation of Ag-TiO2heterostuctures on TiO2nanobelts surface by photoreduction.Their performance in the detection of ethanol vapor was then examined and compared by electrical conductivity measurements at varied temperatures.Of the sensors based on the four nanobelt samples(TiO2nanobelts,Ag-TiO2nanobelts,surface-coarsened TiO2nanobelts,and surface-coarsened Ag-TiO2nanobelts),they all displayed improved sensitivity,selectivity,and short response times for ethanol vapor detection,in comparison with sensors based on other oxide nanostructures.Importantly,the formation of Ag-TiO2heterostuctures on TiO2nanobelts surface and surface coarsening of TiO2nanobelts were found to lead to apparent further enhancement of the sensors sensitivity,as well as a decrease of the optimal working temperature.That is,within the present experimental context,the vapor sensor based on surface-coarsened Ag-TiO2composite nanobelts exhibited the best performance.The sensing mechanism was interpreted on the basis of the surface depletion model,and the improvement by oxide surface engineering was accounted for by the chemical sensitization mechanism.This work provided a practical approach to the enhancement of gas sensing performance by one-dimensional oxide nanomaterials.KEYWORDS:nanoscale Ag-TiO2heterostructure•hydrothermal method•surface coarsening•photoreduction•gas sensor1.INTRODUCTIONE thanol vapor sensors have been widely used in a widerange of areas,such as chemical,biomedical,andfood industries,wine-quality monitoring,and breath analysis(1,2).In these applications,it is desired that the ethanol vapor sensors exhibit features,such as high sensitiv-ity,high selectivity,high stability,low working temperature, short response and recovery times,etc.Therefore,a great deal of research effort has been devoted to the development of functional materials that may be exploited for the con-struction of high-performance ethanol vapor sensors.Among these,one-dimensional metal-oxide nanostructures have attracted particular attention,primarily because of their unique physical and chemical properties that arise from the large band gap energy,interesting surface chemistry,as well as high surface to volume ratio.In fact,a variety of1-D metal oxide nanostructures(1,3-5)have so far been designed and prepared and have shown good ethanol sensing character-istics.Yet most of these earlier studies were focused on ZnO (6-10),SnO2(11-15),V2O5(16),ZrO2(17),CuO(18),and WO3(19),where their practical applications in high-perfor-mance ethanol vapor sensing are impeded by the challenges in mass preparation of these1-D functional nanostructures.Furthermore,the performance of some of the ethanol vapor sensors(e.g.,those based on ZnO nanostructures)may be compromised by the structural instability upon exposure to even a small amount of water(e.g.,moisture in an ambient atmosphere)(20).TiO2is a unique functional material used in many areas (21),such as photocatalysis(22-25),solar cell(26-29), electrochemistry(30-33),biology(34-36),and gas sensors (37-39).Signiﬁcantly,TiO2is of lower cost,nontoxicity,and high chemical stability in comparison with other metal oxides such as SnO2and ZnO that have been commonly studied as ethanol vapor sensing materials.Previously,TiO2 nanostructures in the forms of thinﬁlms(40,41),nanotubes (42),and nanowires(43),have been examined as ethanol sensing materials,and the results suggest that TiO21-D nanostructures are remarkable candidates for ethanol vapor sensing.However,in these earlier studies,the sensing performance was found to be limited by several drawbacks, such as low sensitivity,high working temperature(which may result from the low surface area and poor surface structure),and complicated preparation process,etc.It thus remains a great challenge to develop new TiO21-D nano-structures for ethanol vapor sensing with low cost,high sensitivity,high reliability,low working temperature,short response time,and easy preparation process.Toward this end,TiO2nanobelts represent a unique structural building block in several areas(44-46)and should play an important role in ethanol vapor sensing.TiO2 nanobelts are1-D nanostructures with the length of several tens of micrometers,width of more than100nm,and*To whom correspondence should be addressed.E-mail:hongliu@ .Received for review August7,2010and accepted October14,2010†Shandong University.‡University of California.DOI:10.1021/am100707hXXXX American Chemical Societythickness of20-50nm.TiO2nanobelts can be mass-produced by a simple hydrothermal method followed by an acid exchange and calcination process without any capping agent or surfactant(44).Importantly,the gas sensing per-formance of the TiO2nanobelts may be further improved by surface engineering.Experimentally,the effective surface area may be increased by chemical treatments of TiO2 nanobelts that lead to surface coarsening and the formation of surface defects(47).In addition,the deposition of metal nanoparticles such as Au,Pd,Pt,etc.,onto nanostructures(48-50)has been demonstrated to improve the physical and chemical performance of those nanostructures,and accord-ingly as a consequence of the modulation of the oxide surface energy band structure and the recombination dy-namics of photogenerated electrons and holes,the decora-tion of1-D metal oxide nanostructures by metal nanopar-ticles was also found to be able to further enhance the photoelectronic and sensing properties of1-D metal oxide nanostructures(45,46,51-55).In this paper,TiO2nanobelts were synthesized by a hydrothermal method(44),and the structures were manipu-lated by acid corrosion for surface coarsening as well as deposition of Ag nanoparticles onto the oxide surface for the formation of nanoscale Ag-TiO2heterostructures(56).Both of these surface engineering procedures were found to markedly enhance the gas sensing performance toward ethanol.2.EXPERIMENTAL SECTIONAll chemicals used were of analytical grade and were used without further puriﬁcation.Solutions were freshly prepared with deionized mercial TiO2powder(P25,Degussa) was purchased from standard sources and used as received. Analytical reagents of AgNO3,NaOH,HCl(12M),and H2SO4 (18M)were all purchased from Sinopharm Chemical Reagents Co.Ltd.and were used without further treatment.2.1.Preparation of TiO2Nanobelts.TiO2nanobelts were prepared via an alkaline hydrothermal process by using com-mercial TiO2powders as the precursor.The synthetic procedure has been detailed elsewhere(44).Brieﬂy,0.1g of P25powder was dispersed in20mL of a10M NaOH aqueous solution.After it was stirred magnetically for10min,the solution was trans-ferred into a25mL Teﬂon-lined stainless steel autoclave,heated at200°C for48h,and cooled down to room temperature in air.The products were washed several times with deionized water in aﬁltration process.Subsequently,the wet powders were dispersed into a0.1M HCl aqueous solution for24h under slow magnetic stirring and washed thoroughly with deionized water to obtain H2Ti3O7nanobelts,which were then thermally annealed at600°C for1h to afford crystalline TiO2nanobelts.2.2.Preparation of Surface-Coarsened TiO2Nanobelts. Surface-coarsened TiO2nanobelts were prepared by an acid-assisted hydrothermal method.Brieﬂy,0.3g of H2Ti3O7nano-belts were added into20mL of a0.02M H2SO4aqueous solution under magnetic stirring.The solution was transferred into a Teﬂon-lined stainless steel autoclave,heated at100°C for12h, and cooled to room temperature in air.The wet powder was then washed thoroughly with deionized water,and annealed at600°C for1h to obtain surface-coarsened TiO2nanobelts.2.3.Preparation of Ag-TiO2and Surface-Coarsened Ag-TiO2Composite Nanobelts.Ag-TiO2and surface-coars-ened Ag-TiO2composite nanobelts were both synthesized by a photocatalytic reduction method(56)based on TiO2nanobelts and surface-coarsened TiO2nanobelts obtained from sections 2.1and2.2,respectively.In a typical process,20mg of TiO2or surface-coarsened TiO2nanobelts were dispersed into10mL of a0.1M AgNO3ethanol solution.The solution was then illuminated with a20W ultraviolet lamp under magnetic agitation.The illumination time was1.5min and the distance from the lamp to the liquid surface was10cm.2.4.Characterization.X-ray powder diffraction(XRD)pat-terns were recorded with a Bruker D8Advance powder X-ray diffractometer with Cu K R(λ)0.15406nm)radiation.Scan-ning electron microscopy(SEM)images were acquired using a Hitachi S-4800electron microscope.Transmission electron microscopy(TEM)images were acquired with a JEM-100CXΠelectron microscope.High-resolution TEM images were ac-quired with a JEOL JEM2100electron microscope.All experi-ments were carried out at room temperature.2.5.Ethanol Vapor Sensing.The schematic of the ethanol vapor sensors is depicted in Figure1a.TiO2nanobelts,surface-coarsened TiO2nanobelts,Ag-TiO2nanobelts,or surface-coarsened Ag-TiO2nanobelts were used as the sensing mate-rials.The nanobelts were mixed with a calculated amount of water to prepare slurry,which was then coated directly onto the outer surface of a ceramic tube and dried in air,followed by calcination at400°C for48h.The thickness of the as-preparedﬁlms are about40µm.(Figures S5and S6,Supporting Information)Two Au wires were inlaid onto the ceramic tube as electrodes and connected to two Pt wires to quantify theﬁlm conductance upon exposure to varied chemical environments. Temperature control was achieved by inserting a resistive heating wire into the ceramic tube.Vapor detection was carried out with a WS-30A gas sensing system(Zhengzhou Winsen Electronics Technology Co.Ltd., P.R.China)by using a static state gas distribution method.For ethanol detection,an ethanol-air mixed gas was prepared by injecting a certain volume of liquid ethanol into the test chamber on a heating platform where the evaporation of ethanol was aided by two small electric fans.The sensing electrical circuit is shown in Figure1b,and the electrical resistance of the sensors in air or in ethanol-air mixed gas is evaluated by R)[R L(V c-V out)]/V out,where R is the sensor resistance,R L is the load resistance,V c is the total loop voltage applied to the sensor electrical circuit,and V out is the output voltage across the load resistor.The sensors sensitivity(S)is deﬁned as S)R a/R g(13),where R a is the sensor resistance measured in air with the relative humidity of∼20%and R g is the resistance measured upon exposure to an ethanol-air mixed gas.The response/recovery time is deﬁned as the time required to reach90%of the total change of the voltage(V out). V h is the heater voltage.3.RESULTS AND DISCUSSION3.1.Structural Characterizations.The structures of the gas sensing materials,including TiO2nanobelts, Ag-TiO2nanobelts,surface-coarsened TiO2nanobelts,and surface-coarsened Ag-TiO2nanobelts,wereﬁrst character-ized by(HR)TEM and SEM measurements.Figure2depicts FIGURE1.Schematics of(a)the ethanol gas sensors and(b)the corresponding equivalent circuit.the representative (HR)TEM and SEM micrographs of these nanobelt samples.From panels a and b,it can be seen that the TiO 2nanobelts are 100-150nm in width,about 50nm in thickness,and several tens of micrometers in length with a very smooth surface.The (HR)TEM micrographs of Ag -TiO 2composite nanobelts are shown in panels c and d,where Ag nanoparticles exhibiting a dark contrast can be found to be deposited onto the smooth and crystalline surface of TiO 2nanobelts,and the diameter of the Ag nanoparticles ranges from 10to 30nm.In addition,the dimensions of the nanobelts,as compared to those in panels a and b,remain virtually unchanged.In particular,from panel d,it can be seen that the Ag nanoparticle is largely hemispherical in shape and in intimate contact with the oxide substrate,suggesting that the nanoparticle is not physically absorbed onto the oxide surface but nucleates and grows from the surface.In fact,a heterostructure between two distinctly different crystalline lattices can be clearly identiﬁed at the interface.This is consistent with the forma-tion of Ag nanoparticles by TiO 2photocatalytic reduction.The impacts of an acid corrosion treatment on the mor-phologies of the TiO 2nanobelts are illustrated in panels e and f,where one can see that the nanobelt surfaces were substantially coarsened.Furthermore,after the acid treat-ment,the width of these surface-coarsened nanobelts can be found to be around 100nm,which is somewhat smaller than that of the untreated nanobelts (panels a and b).The fact that the nanobelts now exhibited a highly porous structure with a number of TiO 2nanoparticles (about 30nm in diameter)attached on the surface indicates a signiﬁcant enhancement of the effective oxide surface area,as well as the formation of rampant surface defects that may facilitate adsorption of organic molecules.The HRTEM images of surface-coarsened Ag -TiO 2com-posite nanobelts are shown in panels g and h.From panel g,it can be seen that Ag nanoparticles of 20-30nm in diameter are successfully assembled on the porous TiO 2nanobelt surface,and the Ag particles are intimately at-tached to the protuberances on the nanobelts,again forming well-deﬁned nanoscale heterostructures at the Ag/TiO 2in-terface (as highlighted in panel d),similar to that observed in panel c.Further characterizations were carried out with XRD measurements.From Figure 3,it can be seen that the TiO 2nanobelts (left panel)mainly consist of anatase crystalline phase,with a small amount of -TiO 2,whereas surface-coarsened TiO 2nanobelts (right panel)exhibited a pure anatase crystalline phase.The silver nanoparticles on both nanobelts displayed a cubic lattice structure that is consistent with metallic silver (56).3.2.Ethanol Vapor Sensing.The performance of the varied nanobelts obtained above for ethanol vapor sensing was then examined by using the test apparatus shown in Figure 1.Experimentally,the sensor conductance was measured upon exposure to an ethanol -air mixed vapor with varied ethanol concentration at controlled temperatures.Figure 4(left panels)depicts the representative response/recovery curves at 200°C of the four ethanol vapor sensors based on TiO 2nanobelts,Ag -TiO 2nanobelts,surface-coarsened TiO 2nanobelts,and surface-coarsened Ag -TiO 2nanobelts.It can be seen that upon the exposure to ethanol vapor of varied concentrations (from 20to 500ppm),all sensors exhibited an apparent increase of V out ,and the increase becomes more signiﬁcant at higher concentrations.For instance,at 20ppm ethanol vapor,the value of V out is 0.118,0.112,0.337,and 0.390V,respectively;whereas at 500ppm ethanol vapor,V out increases markedly to 0.540,0.699,1.989,and 2.957V.From these measurements,it can be seen that the sensor performance increases in the order of TiO 2nanobelts <Ag -TiO 2nanobelts ≈surface-coarsened TiO 2nanobelts <surface-coarsened Ag -TiO 2nanobelts,suggesting the impacts of surface coarsening and formation of metal -TiO 2heterostructures on the sensor conductance and detection performance (vide infra,sensing mechanism section).Also,it should be noted that the response/recovery time for all four sensors was found to be 1-2s,which is comparable to that of SnO 2nanowires-based sensors (11)but much shorter than that of ZnO nanorods-based sensors(6).FIGURE 2.Representative (a)TEM and (b)SEM micrographs of TiO 2nanobelts,(c)Ag -TiO 2nanobelts,and (HR)TEM micrographs of (d)Ag -TiO 2nanobelts,(e,f)surface-coarsened TiO 2nanobelts,and (g,h)surface-coarsened Ag -TiO 2nanobelts.ARTICLEThe discrepancy of the sensor performance can be further illustrated in the sensitivity (R a /R g )proﬁles depicted in the right panel of Figure 4,where one can see that the sensitivity of all four sensors increases almost linearly with the con-centration of ethanol vapor.Notably,at 20ppm ethanol vapor,the sensitivity can be found to be 4.242,5.124,5.732,and 6.659for the four sensors,respectively;whereas at 500ppm,it increases drastically to 20.028,33.410,38.546,and 46.153.In other words,within the present experimental context,the vapor sensor based on surface-coarsened Ag -TiO 2nanobelts exhibit the best performance in ethanol vapor detection.Similar behaviors can be observed at other working temperatures (Figure S1,Supporting Information),and the sensor sensitivity is summarized in Figure 5which all exhibit peak-shaped dependence on the working temperature with the concentration of ethanol vapor up to 500ppm.There are at least two aspects that warrant attention here.First,at a speciﬁc working temperature and ethanol vapor concen-tration,coarsening of the nanobelt surface as well as deposi-tion of Ag nanoparticles onto the oxide surface lead to apparent enhancement of the detection sensitivity as com-pared to sensors based on untreated nanobelts.In fact,the sensor based on surface-coarsened Ag -TiO 2nanobelts con-sistently exhibits the best performance among the series interms of detection sensitivity.Second,the detection sensitiv-ity for sensors based on surface-coarsened (Ag -)TiO 2nano-belts reaches the maximum at 200°C (panels c and d),whereas for sensors based on smooth (Ag -)TiO 2nanobelts,the optimal working temperature is somewhat higher at 250°C (panels a and b).At lower temperatures (such as 150°C),the V out signals exhibited a noisy proﬁle with only a fraction of a volt even at 500ppm ethanol vapor.At higher temper-atures (e.g.,250-400°C),whereas the V out values are somewhat greater,the sensitivity (R a /R g )decreases rather substantially with increasing temperature,suggesting in-creasingly non-negligible background contributions in the conductance measurements.It should be noted that the electrical conductance (V out )of the vapor sensors remained virtually invariant between before exposure to ethanol vapor and after the test chamber was purged with fresh air,suggesting complete recovery and stability of the TiO 2nanobelt-based ethanol sensors.Fur-thermore,the stability and reproducibility of the gas sensors were evaluated by repeating the measurements at least four times under the same experimental conditions (e.g.,tem-perature and ethanol concentration),and the sensors re-sponses in the four measurements under the same condition were almost the same (Figure S2,SupportingInformation).FIGURE 3.XRD patterns of TiO 2nanobelts (left)and surface-coarsened TiO 2nanobelts(right).FIGURE 4.(left)Response curves and (right)sensitivity proﬁles of ethanol vapor sensors based on TiO 2nanobelts,Ag -TiO 2nanobelts,surface-coarsened TiO 2nanobelts,and surface-coarsened Ag -TiO 2nanobelts upon exposure to different concentrations of ethanol vapor at 200°C.The selectivity of the vapor sensors was then examined by exposing the sensors to other vapors or gas such as CH 3COCH 3,CO,CH 4,and H 2.It was found that all four sensors were totally insensitive to CO,CH 4,and H 2,and exhibited a much lower response to CH 3COCH 3than to ethanol under any condition (Figures S3and S4,Supporting Information).Furthermore,in comparison with other oxide nanostruc-tures,the vapor sensors derivatized from TiO 2nanobelts all exhibited markedly improved sensitivity (S )in ethanol sens-ing,which are summarized in Table 1.Additionally,the optimal working temperatures (200-250°C)were substan-tially lower those for ZnO nanowires (300°C)(8),ZnO nanopillars (350°C)(9),SnO 2nanorods (300°C)(11),and Pt -TiO 2nanowires (500°C)(43).Also,the nanobelt-basedvapor sensors exhibited response and recovery times (only 1-2s)that are comparable to those of SnO 2nanorods (11),but signiﬁcantly shorter than those of ZnO nanopilalrs (9)and Pt -TiO 2nanowires (43).3.3.Sensing Mechanism.The experimental obser-vations described above may be accounted for by the surface-depletion model (57),as shown in Figure 6.Similar to other vapor sensors based on metal -oxide semiconduc-tors,the operation of the present sensors is based on manipulation of the electrical resistance (conductance)of the oxide materials that results from the interactions between the target vapor molecules and the active complexes on the oxide surface (6,12,57).Mechanistically,as the lower edge of the TiO 2conduction band is higher than thechemicalFIGURE 5.Variation of sensitivity (R a /R g )with working temperature of the four different kinds of sensors based on (a)TiO 2nanobelts,(b)Ag -TiO 2nanobelts,(c)surface-coarsened TiO 2nanobelts,and (d)surface-coarsened Ag -TiO 2nanobelts to ethanol vapor of different concentrations.Table parison of Varied Oxide Nanostructures in Ethanol Vapor Sensingsamplefabrication methodethanol concentration(ppm)optimal temp (°C)/humidity (%)sensitivity S )R a /R gresponse time/recovery time (s)refZnO nanowires ZnO:Ga/glass as template 500300/in air 1.7548ZnO nanopillars a two-step solution approach500350/in air 3310/209SnO 2nanorodshydrothermal route 100300/25131/111Pt -TiO 2nanowires array naonpatterning process 3500500/in dry air 7.5>5/>1043TiO 2nanobelts hydrothermal method 500250/2033.6611-2this paper Ag -TiO 2nanobelts hydrothermal method +photocatalytic reduction method 500250/2041.7091-2this paper surface-coarsened TiO 2nanobeltshydrothermal method 500200/2038.5461-2this paper surface-coarsened Ag -TiO 2nanobeltshydrothermal method +photocatalytic reduction method500200/2046.1531-2this paperARTICLEpotential of O2(58),when TiO2is exposed to air,O2will be adsorbed dissociatively onto the TiO2surface,act as effective electron acceptors,capture electrons from the conduction band of TiO2,and form varied surface active complexes(e.g., superoxo-or peroxo-like species)(59).With the formation of the active complexes,a surface depletion region is created within the oxide matrix(the thickness of this region is denoted as L d)(60),leading to an increase of the electrical resistance of the TiO2layer as a result of the diminishment of charge carrier concentration.In fact,as the thickness of the TiO2nanobelts prepared above(Figure2)is only20-50 nm(i.e.,approximately twice that of L d),the depletion layer may extend throughout the entire nanobelt,resulting in minimal electrical conductance.However,upon exposure to reducing vapors such as ethanol,effective electron trans-fer occurs from the vapor molecules to TiO2(i.e.,ethanol undergoes oxidation reactions),such that the thickness of the surface depletion region decreases accordingly.The increase of charge carrier concentration therefore dimin-ishes the electrical resistance of the TiO2ﬁlm,reﬂected in the apparent enhancement of the V out response,as observed experimentally(Figure4).On the basis of this sensing mechanism,it can be seen that the detection performance will be strongly contingent upon the charge transfer dynamics between the ethanol molecules and the oxide matrix.One effective approach is to deposit metal nanoparticles onto the oxide surface,similar to the Ag-TiO2composite nanobelts described above.This is to take advantage of the spillover effects afforded by the metal nanoparticles as a result of the“chemical sensitiza-tion”mechanism(51,61-63).Speciﬁcally,because of their large Helmhotz double-layer capacitance,metal nanopar-ticles are efﬁcient electron sinks.Thus,when supported on reducible oxide surfaces(e.g.,TiO2),partial charge transfer may occur from the oxide metal centers to the metal nanoparticles,leading to the accumulation of negative charges on the metal nanoparticle surface.This may then facilitate the dissociative adsorption of oxygen onto the particle surface and consequently enhance the formation of electron-deﬁcient depletion layer.In fact,such a unique interfacial charge transfer phenomenon has been exploited in the electrocatalytic reduction of oxygen by using metal nano-particles supported on oxide surfaces(24,64,65).Addition-ally,the deposition of metal nanoparticles onto the oxide surface and hence the intimate interfacial contacts may lead to the formation of structural defects(e.g.,Figure2)and trap states within the oxide band gap.These may serve as the surface active sites for the adsorption of oxygen and alcohol vapor molecules,which is beneﬁcial to the improvement of the ethanol sensing sensitivity,as observed above(Figures 4and5).Experimentally,structural defects can also be created by surface coarsening,as manifested in Figure2.Both structural defects and the resulting increased effective surface area are anticipated to improve the ethanol sensing performance of TiO2nanobelts(66,67),consistent with the above observa-tions(Figures4and5),where the sensitivity increases and the optimal sensing temperature decreases by about50°C with surface-coarsened TiO2and Ag-TiO2nanobelts as compared to the smooth counterparts.4.CONCLUSIONIn this study,TiO2nanobelts were synthesized by a hydrothermal method,and the structures were further manipulated by surface engineering.For instance,the TiO2 nanobelt surface might be coarsened by an acid-corrosion procedure,and Ag-TiO2composite nanoscale heterostruc-tures were produced by depositing silver nanoparticles onto the TiO2nanobelt surfaces by photoreduction.The sensing activity of these four nanobelt materials in the detection of ethanol vapor was then examined and compared at con-trolled temperatures.It was found that surface coarsening and formation of Ag-TiO2nanoscale heterostructures(which results from deposition of Ag nanoparticles onto the TiO2 nanobelts surface)led to apparent improvement in the vapor sensing sensitivity as well as a diminishment of the optimal operation temperature.In fact,within the present experi-mental context,the vapor sensor based onsurface-coars-FIGURE6.Sensing mechanism of TiO2nanobelts to ethanol.ened Ag-TiO2composite nanobelts exhibited the best performance.The disparity of the sensing performance was accounted for by the surface depletion model where surface coarsening as well as formation of metal-TiO2composite nanoscale heterostructures were exploited as the chemical sensitization mechanism to manipulate the dynamics of interface charge transfer.Acknowledgment.This research was supported by an NSFC(NSFDYS50925205,50872070,50702031,Grant 50990303,IRG50721002),and the Program of Introducing Talents of Discipline to Universities in China(111program No.b06015).Supporting Information Available:Figures showing re-sponse curves,sensitivity proﬁles,variation of sensitivity,and sectional views of sensor I and II.This information is available free of charge via the Internet at . 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二氧化钛纳米材料的制备、改性及光催化性能研究

摘要二氧化钛纳米材料的制备、改性及光催化性能研究摘要随着人们生活水平的不断提高，越来越多的产品来自于石油、煤炭和天然气等不可再生的自然资源。

同时，产品在原材料的提取、运输和转化过程中都有可能给环境带来负面效应。

因此，环境污染和能源短缺现象成为人类目前应对的世界性难题。

半导体光催化技术在环境修复领域的作为不容忽视，已被证明是降解水体和大气环境中有害污染物的有效途径。

在解决能源危机方面，通过光分解水制氢、太阳能电池等方式实现了可再生能源的高效利用。

二氧化钛因其高稳定性，无毒性且低成本被认为是非常理想的光催化半导体材料。

光催化剂的表面积是决定污染物吸附量的重要因素，直接影响其光催化活性的强弱。

由于二氧化钛纳米材料的高表面能使得纳米粒子间倾向于聚集以达到体系的平衡状态，导致纳米粉体的团聚现象严重，无法获得较大的活性表面积。

因此，本文采用表面活性剂作为分散剂，并优化制备工艺进行改性，以获得均一分散的二氧化钛纳米体系是十分必要的。

主要研究内容如下：（1）综合溶胶-凝胶法和溶剂热法的制备优势，本论文采用溶胶-溶剂热改进工艺进行实验分析。

以钛酸丁酯为钛源，无水乙醇为溶剂，浓硝酸为抑制剂，按照n(Ti(OR)4):n(C2H5OH):n(H+):n(H2O)=1:15:0.35:4的反应物配比，制备纳米级二氧化钛材料。

（2）通过单因素实验与正交实验相结合的方式，以样品对甲基橙的光催化降解率为分析依据，探究溶剂热温度、溶剂热时间、煅烧温度和煅烧时间对于二氧化钛光催化活性的影响。

正交实验的结果表明，最佳工艺参数是：当溶剂热温度为150℃，溶剂热时间为24h，煅烧温度为450℃，煅烧时间为4h时，样品的光催化降解率最高，为82.88%。

同时XRD、SEM、TEM和EDS的图像表明，样品为结晶度良好的单一锐钛矿相，无任何杂质，但分散性一般。

（3）在最佳工艺参数的基础上，通过控制表面活性剂的种类和含量的不同，探究不同类型表面活性剂的最佳投料比，从而确定用于二氧化钛纳米粉体改性的最佳分散剂，并通过XRD、SEM、TEM和EDS等技术对样品进行表征。

Titanium Dioxide Nanomaterials Synthesis, Properties, Modifications, and

Titanium Dioxide Nanomaterials:Synthesis,Properties,Modifications,andApplicationsXiaobo Chen*and Samuel S.Mao†Lawrence Berkeley National Laboratory,and University of California,Berkeley,California94720Received March27,2006Contents1.Introduction28912.Synthetic Methods for TiO2Nanostructures28922.1.Sol−Gel Method28922.2.Micelle and Inverse Micelle Methods28952.3.Sol Method28962.4.Hydrothermal Method28982.5.Solvothermal Method29012.6.Direct Oxidation Method29022.7.Chemical Vapor Deposition29032.8.Physical Vapor Deposition29042.9.Electrodeposition29042.10.Sonochemical Method29042.11.Microwave Method29042.12.TiO2Mesoporous/Nanoporous Materials29052.13.TiO2Aerogels29062.14.TiO2Opal and Photonic Materials29072.15.Preparation of TiO2Nanosheets29083.Properties of TiO2Nanomaterials29093.1.Structural Properties of TiO2Nanomaterials29093.2.Thermodynamic Properties of TiO2Nanomaterials29113.3.X-ray Diffraction Properties of TiO2Nanomaterials29123.4.Raman Vibration Properties of TiO2Nanomaterials29123.5.Electronic Properties of TiO2Nanomaterials29133.6.Optical Properties of TiO2Nanomaterials29153.7.Photon-Induced Electron and Hole Propertiesof TiO2Nanomaterials29184.Modifications of TiO2Nanomaterials29204.1.Bulk Chemical Modification:Doping29214.1.1.Synthesis of Doped TiO2Nanomaterials29214.1.2.Properties of Doped TiO2Nanomaterials29214.2.Surface Chemical Modifications29264.2.1.Inorganic Sensitization29265.Applications of TiO2Nanomaterials29295.1.Photocatalytic Applications29295.1.1.Pure TiO2Nanomaterials:FirstGeneration29305.1.2.Metal-Doped TiO2Nanomaterials:Second Generation29305.1.3.Nonmetal-Doped TiO2Nanomaterials:Third Generation 29315.2.Photovoltaic Applications29325.2.1.The TiO2Nanocrystalline Electrode inDSSCs29325.2.2.Metal/Semiconductor Junction SchottkyDiode Solar Cell29385.2.3.Doped TiO2Nanomaterials-Based SolarCell29385.3.Photocatalytic Water Splitting29395.3.1.Fundamentals of Photocatalytic WaterSplitting2939e of Reversible Redox Mediators2939e of TiO2Nanotubes29405.3.4.Water Splitting under Visible Light29415.3.5.Coupled/Composite Water-SplittingSystem29425.4.Electrochromic Devices29425.4.1.Fundamentals of Electrochromic Devices29435.4.2.Electrochromophore for an ElectrochromicDevice29435.4.3.Counterelectrode for an ElectrochromicDevice29445.4.4.Photoelectrochromic Devices29455.5.Hydrogen Storage29455.6.Sensing Applications29476.Summary29487.Acknowledgment29498.References29491.IntroductionSince its commercial production in the early twentiethcentury,titanium dioxide(TiO2)has been widely used as apigment1and in sunscreens,2,3paints,4ointments,toothpaste,5etc.In1972,Fujishima and Honda discovered the phenom-enon of photocatalytic splitting of water on a TiO2electrodeunder ultraviolet(UV)light.6-8Since then,enormous effortshave been devoted to the research of TiO2material,whichhas led to many promising applications in areas ranging fromphotovoltaics and photocatalysis to photo-/electrochromicsand sensors.9-12These applications can be roughly dividedinto“energy”and“environmental”categories,many of whichdepend not only on the properties of the TiO2material itselfbut also on the modifications of the TiO2material host(e.g.,with inorganic and organic dyes)and on the interactions ofTiO2materials with the environment.An exponential growth of research activities has been seenin nanoscience and nanotechnology in the past decades.13-17New physical and chemical properties emerge when the sizeof the material becomes smaller and smaller,and down to*Corresponding author.E-mail:XChen3@.†E-mail:SSMao@.2891 Chem.Rev.2007,107,2891−295910.1021/cr0500535CCC:$65.00©2007American Chemical SocietyPublished on Web06/23/2007the nanometer scale.Properties also vary as the shapes of the shrinking nanomaterials change.Many excellent reviews and reports on the preparation and properties of nanomaterials have been published recently.6-44Among the unique proper-ties of nanomaterials,the movement of electrons and holes in semiconductor nanomaterials is primarily governed by the well-known quantum confinement,and the transport proper-ties related to phonons and photons are largely affected by the size and geometry of the materials.13-16The specific surface area and surface-to-volume ratio increase dramati-cally as the size of a material decreases.13,21The high surface area brought about by small particle size is beneficial to many TiO 2-based devices,as it facilitates reaction/interaction between the devices and the interacting media,which mainly occurs on the surface or at the interface and strongly depends on the surface area of the material.Thus,the performance of TiO 2-based devices is largely influenced by the sizes of the TiO 2building units,apparently at the nanometer scale.As the most promising photocatalyst,7,11,12,33TiO 2mate-rials are expected to play an important role in helping solvemany serious environmental and pollution challenges.TiO 2also bears tremendous hope in helping ease the energy crisis through effective utilization of solar energy based on photovoltaic and water-splitting devices.9,31,32As continued breakthroughs have been made in the preparation,modifica-tion,and applications of TiO 2nanomaterials in recent years,especially after a series of great reviews of the subject in the 1990s.7,8,10-12,33,45we believe that a new and compre-hensive review of TiO 2nanomaterials would further promote TiO 2-based research and development efforts to tackle the environmental and energy challenges we are currently facing.Here,we focus on recent progress in the synthesis,properties,modifications,and applications of TiO 2nanomaterials.The syntheses of TiO 2nanomaterials,including nanoparticles,nanorods,nanowires,and nanotubes are primarily categorized with the preparation method.The preparations of mesopo-rous/nanoporous TiO 2,TiO 2aerogels,opals,and photonic materials are summarized separately.In reviewing nanoma-terial synthesis,we present a typical procedure and repre-sentative transmission or scanning electron microscopy images to give a direct impression of how these nanomate-rials are obtained and how they normally appear.For detailed instructions on each synthesis,the readers are referred to the corresponding literature.The structural,thermal,electronic,and optical properties of TiO 2nanomaterials are reviewed in the second section.As the size,shape,and crystal structure of TiO 2nanomate-rials vary,not only does surface stability change but also the transitions between different phases of TiO 2under pressure or heat become size dependent.The dependence of X-ray diffraction patterns and Raman vibrational spectra on the size of TiO 2nanomaterials is also summarized,as they could help to determine the size to some extent,although correlation of the spectra with the size of TiO 2nanomaterials is not straightforward.The review of modifications of TiO 2nanomaterials is mainly limited to the research related to the modifications of the optical properties of TiO 2nanoma-terials,since many applications of TiO 2nanomaterials are closely related to their optical properties.TiO 2nanomaterials normally are transparent in the visible light region.By doping or sensitization,it is possible to improve the optical sensitiv-ity and activity of TiO 2nanomaterials in the visible light region.Environmental (photocatalysis and sensing)and energy (photovoltaics,water splitting,photo-/electrochromics,and hydrogen storage)applications are reviewed with an emphasis on clean and sustainable energy,since the increas-ing energy demand and environmental pollution create a pressing need for clean and sustainable energy solutions.The fundamentals and working principles of the TiO 2nanoma-terials-based devices are discussed to facilitate the under-standing and further improvement of current and practical TiO 2nanotechnology.2.Synthetic Methods for TiO 2Nanostructures2.1.Sol −Gel MethodThe sol -gel method is a versatile process used in making various ceramic materials.46-50In a typical sol -gel process,a colloidal suspension,or a sol,is formed from the hydrolysis and polymerization reactions of the precursors,which are usually inorganic metal salts or metal organic compounds such as metal plete polymerization and loss of solvent leads to the transition from the liquid sol into a solid gel phase.Thin films can be produced on a pieceofDr.Xiaobo Chen is a research engineer at The University of California at Berkeley and a Lawrence Berkeley National Laboratory scientist.He obtained his Ph.D.Degree in Chemistry from Case Western Reserve University.His research interests include photocatalysis,photovoltaics,hydrogen storage,fuel cells,environmental pollution control,and the related materials and devicesdevelopment.Dr.Samuel S.Mao is a career staff scientist at Lawrence Berkeley National Laboratory and an adjunct faculty at The University of California at Berkeley.He obtained his Ph.D.degree in Engineering from The University of California at Berkeley in 2000.His current research involves the development of nanostructured materials and devices,as well as ultrafast laser technologies.Dr.Mao is the team leader of a high throughput materials processing program supported by the U.S.Department of Ener-gy.2892Chemical Reviews,2007,Vol.107,No.7Chen and Maosubstrate by spin-coating or dip-coating.A wet gel will form when the sol is cast into a mold,and the wet gel is converted into a dense ceramic with further drying and heat treatment.A highly porous and extremely low-density material called an aerogel is obtained if the solvent in a wet gel is removed under a supercritical condition.Ceramic fibers can be drawn from the sol when the viscosity of a sol is adjusted into a proper viscosity range.Ultrafine and uniform ceramic powders are formed by precipitation,spray pyrolysis,or emulsion techniques.Under proper conditions,nanomaterials can be obtained.TiO2nanomaterials have been synthesized with the sol-gel method from hydrolysis of a titanium precusor.51-78This process normally proceeds via an acid-catalyzed hydrolysis step of titanium(IV)alkoxide followed by condensa-tion.51,63,66,79-91The development of Ti-O-Ti chains is favored with low content of water,low hydrolysis rates,and excess titanium alkoxide in the reaction mixture.Three-dimensional polymeric skeletons with close packing result from the development of Ti-O-Ti chains.The formation of Ti(OH)4is favored with high hydrolysis rates for a medium amount of water.The presence of a large quantity of Ti-OH and insufficient development of three-dimensional polymeric skeletons lead to loosely packed first-order particles.Polymeric Ti-O-Ti chains are developed in the presence of a large excess of water.Closely packed first-order particles are yielded via a three-dimensionally devel-oped gel skeleton.51,63,66,79-91From the study on the growth kinetics of TiO2nanoparticles in aqueous solution using titanium tetraisopropoxide(TTIP)as precursor,it is found that the rate constant for coarsening increases with temper-ature due to the temperature dependence of the viscosity of the solution and the equilibrium solubility of TiO2.63Second-ary particles are formed by epitaxial self-assembly of primary particles at longer times and higher temperatures,and the number of primary particles per secondary particle increases with time.The average TiO2nanoparticle radius increases linearly with time,in agreement with the Lifshitz-Slyozov-Wagner model for coarsening.63Highly crystalline anatase TiO2nanoparticles with different sizes and shapes could be obtained with the polycondensation of titanium alkoxide in the presence of tetramethylammonium hydroxide.52,62In a typical procedure,titanium alkoxide is added to the base at2°C in alcoholic solvents in a three-neck flask and is heated at50-60°C for13days or at90-100°C for6h.A secondary treatment involving autoclave heating at175and200°C is performed to improve the crystallinity of the TiO2nanoparticles.Representative TEM images are shown in Figure1from the study of Chemseddine et al.52A series of thorough studies have been conducted by Sugimoto et ing the sol-gel method on the formation of TiO2nanoparticles of different sizes and shapes by tuning the reaction parameters.67-71Typically,a stock solution of a0.50M Ti source is prepared by mixing TTIP with triethanolamine(TEOA)([TTIP]/[TEOA])1:2),followed by addition of water.The stock solution is diluted with a shape controller solution and then aged at100°C for1day and at140°C for3days.The pH of the solution can be tuned by adding HClO4or NaOH solution.Amines are used as the shape controllers of the TiO2nanomaterials and act as surfactants.These amines include TEOA,diethylenetri-amine,ethylenediamine,trimethylenediamine,and triethyl-enetetramine.The morphology of the TiO2nanoparticles changes from cuboidal to ellipsoidal at pH above11with TEOA.The TiO2nanoparticle shape evolves into ellipsoidal above pH9.5with diethylenetriamine with a higher aspect ratio than that with TEOA.Figure2shows representative TEM images of the TiO2nanoparticles under different initial pH conditions with the shape control of TEOA at[TEOA]/ [TIPO])2.0.Secondary amines,such as diethylamine,and tertiary amines,such as trimethylamine and triethylamine, act as complexing agents of Ti(IV)ions to promote the growth of ellipsoidal particles with lower aspect ratios.The shape of the TiO2nanoparticle can also be tuned from round-cornered cubes to sharp-edged cubes with sodium oleate and sodium stearate.70The shape control is attributed to the tuning of the growth rate of the different crystal planes of TiO2 nanoparticles by the specific adsorption of shape controllers to these planes under different pH conditions.70A prolonged heating time below100°C for the as-prepared gel can be used to avoid the agglomeration of the TiO2nano-particles during the crystallization process.58,72By heating amorphous TiO2in air,large quantities of single-phase ana-tase TiO2nanoparticles with average particle sizes between 7and50nm can be obtained,as reported by Zhang and Banfield.73-77Much effort has been exerted to achieve highly crystallized and narrowly dispersed TiO2nanoparticles using the sol-gel method with other modifications,such as a semicontinuous reaction method by Znaidi et al.78and a two-stage mixed method and a continuous reaction method by Kim et al.53,54By a combination of the sol-gel method and an anodic alumina membrane(AAM)template,TiO2nanorods have been successfully synthesized by dipping porous AAMs into a boiled TiO2sol followed by drying and heating processes.92,93In a typical experiment,a TiO2sol solution is prepared by mixing TTIP dissolved in ethanol with a solution containing water,acetyl acetone,and ethanol.An AAM is immersed into the sol solution for10min after being boiled in ethanol;then it is dried in air and calcined at400°C for 10h.The AAM template is removed in a10wt%H3PO4 aqueous solution.The calcination temperature can be used to control the crystal phase of the TiO2nanorods.At low temperature,anatase nanorods can be obtained,while at high temperature rutile nanorods can be obtained.The pore size of the AAM template can be used to control the size of these TiO2nanorods,which typically range from100to300 nm in diameter and several micrometers in length.Appar-ently,the size distribution of the final TiO2nanorods is largely controlled by the size distribution of the pores of the AAM template.In order to obtain smaller and mono-sized TiO2nanorods,it is necessary to fabricate high-quality AAM templates.Figure3shows a typical TEM for TiO2 nanorods fabricated with this method.Normally,the TiO2 nanorods are composed of small TiO2nanoparticles or nanograins.By electrophoretic deposition of TiO2colloidal suspensions into the pores of an AAM,ordered TiO2nanowire arrays can be obtained.94In a typical procedure,TTIP is dissolved in ethanol at room temperature,and glacial acetic acid mixed with deionized water and ethanol is added under pH)2-3 with nitric acid.Platinum is used as the anode,and an AAM with an Au substrate attached to Cu foil is used as the cathode.A TiO2sol is deposited into the pores of the AMM under a voltage of2-5V and annealed at500°C for24h. After dissolving the AAM template in a5wt%NaOH solution,isolated TiO2nanowires are obtained.In order toTitanium Dioxide Nanomaterials Chemical Reviews,2007,Vol.107,No.72893fabricate TiO 2nanowires instead of nanorods,an AAM with long pores is a must.TiO 2nanotubes can also be obtained using the sol -gel method by templating with an AAM 95-98and other organic compounds.99,100For example,when an AAM is used as the template,a thin layer of TiO 2sol on the wall of the pores of the AAM is first prepared by sucking TiO 2sol into the pores of the AAM and removing it under vacuum;TiO 2nanowires are obtained after the sol is fully developed and the AAM is removed.In the procedure by Lee and co-workers,96a TTIP solution was prepared by mixing TTIP with 2-propanol and 2,4-pentanedione.After the AAM was dipped intothisFigure 1.TEM images of TiO 2nanoparticles prepared by hydrolysis of Ti(OR)4in the presence of tetramethylammonium hydroxide.Reprinted with permission from Chemseddine,A.;Moritz,T.Eur.J.Inorg.Chem.1999,235.Copyright 1999Wiley-VCH.Figure 2.TEM images of uniform anatase TiO 2nanoparticles.Reprinted from Sugimoto,T.;Zhou,X.;Muramatsu,A.J.Colloid Interface Sci.2003,259,53,Copyright 2003,with permission from Elsevier.2894Chemical Reviews,2007,Vol.107,No.7Chen and Maosolution,it was removed from the solution and placed under vacuum until the entire volume of the solution was pulled through the AAM.The AAM was hydrolyzed by water vapor over a HCl solution for 24h,air-dried at room temperature,and then calcined in a furnace at 673K for 2h and cooled to room temperature with a temperature ramp of 2°C/h.Pure TiO 2nanotubes were obtained after the AAM was dissolved in a 6M NaOH solution for several minutes.96Alternatively,TiO 2nanotubes could be obtained by coating the AAM membranes at 60°C for a certain period of time (12-48h)with dilute TiF 4under pH )2.1and removing the AAM after TiO 2nanotubes were fully developed.97Figure 4shows a typical SEM image of the TiO 2nanotube array from the AAM template.97In another scheme,a ZnO nanorod array on a glass substrate can be used as a template to fabricate TiO 2nanotubes with the sol -gel method.101Briefly,TiO 2sol isdeposited on a ZnO nanorod template by dip-coating with a slow withdrawing speed,then dried at 100°C for 10min,and heated at 550°C for 1h in air to obtain ZnO/TiO 2nanorod arrays.The ZnO nanorod template is etched-up by immersing the ZnO/TiO 2nanorod arrays in a dilute hydro-chloric acid aqueous solution to obtain TiO 2nanotube arrays.Figure 5shows a typical SEM image of the TiO 2nanotube array with the ZnO nanorod array template.The TiO 2nanotubes inherit the uniform hexagonal cross-sectional shape and the length of 1.5µm and inner diameter of 100-120nm of the ZnO nanorod template.As the concentration of the TiO 2sol is constant,well-aligned TiO 2nanotube arrays can only be obtained from an optimal dip-coating cycle number in the range of 2-3cycles.A dense porous TiO 2thick film with holes is obtained instead if the dip-coating number further increases.The heating rate is critical to the formation of TiO 2nanotube arrays.When the heating rate is extra rapid,e.g.,above 6°C min -1,the TiO 2coat will easily crack and flake off from the ZnO nanorods due to great tensile stress between the TiO 2coat and the ZnO template,and a TiO 2film with loose,porous nanostructure is obtained.2.2.Micelle and Inverse Micelle MethodsAggregates of surfactant molecules dispersed in a liquid colloid are called micelles when the surfactant concentration exceeds the critical micelle concentration (CMC).The CMC is the concentration of surfactants in free solution in equilibrium with surfactants in aggregated form.In micelles,the hydrophobic hydrocarbon chains of the surfactants are oriented toward the interior of the micelle,and the hydro-philic groups of the surfactants are oriented toward the surrounding aqueous medium.The concentration of the lipid present in solution determines the self-organization of the molecules of surfactants and lipids.The lipids form a single layer on the liquid surface and are dispersed in solution below the CMC.The lipids organize in spherical micelles at the first CMC (CMC-I),into elongated pipes at the second CMC (CMC-II),and into stacked lamellae of pipes at the lamellar point (LM or CMC-III).The CMC depends on the chemical composition,mainly on the ratio of the head area and the tail length.Reverse micelles are formed in nonaqueous media,and the hydrophilic headgroups are directed toward the core of the micelles while the hydrophobic groupsareFigure 3.TEM image of anatase nanorods and a single nanorod composed of small TiO 2nanoparticles or nanograins (inset).Reprinted from Miao,L.;Tanemura,S.;Toh,S.;Kaneko,K.;Tanemura,M.J.Cryst.Growth 2004,264,246,Copyright 2004,with permission fromElsevier.Figure 4.SEM image of TiO 2nanotubes prepared from the AAO template.Reprinted with permission from Liu,S.M.;Gan,L.M.;Liu,L.H.;Zhang,W.D.;Zeng,H.C.Chem.Mater.2002,14,1391.Copyright 2002American ChemicalSociety.Figure 5.SEM of a TiO 2nanotube array;the inset shows the ZnO nanorod array template.Reprinted with permission from Qiu,J.J.;Yu,W.D.;Gao,X.D.;Li,X.M.Nanotechnology 2006,17,4695.Copyright 2006IOP Publishing Ltd.Titanium Dioxide Nanomaterials Chemical Reviews,2007,Vol.107,No.72895directed outward toward the nonaqueous media.There is no obvious CMC for reverse micelles,because the number of aggregates is usually small and they are not sensitive to the surfactant concentration.Micelles are often globular and roughly spherical in shape,but ellipsoids,cylinders,and bilayers are also possible.The shape of a micelle is a function of the molecular geometry of its surfactant molecules and solution conditions such as surfactant concentration,tem-perature,pH,and ionic strength.Micelles and inverse micelles are commonly employed to synthesize TiO2nanomaterials.102-110A statistical experi-mental design method was conducted by Kim et al.to optimize experimental conditions for the preparation of TiO2 nanoparticles.103The values of H2O/surfactant,H2O/titanium precursor,ammonia concentration,feed rate,and reaction temperature were significant parameters in controlling TiO2 nanoparticle size and size distribution.Amorphous TiO2 nanoparticles with diameters of10-20nm were synthesized and converted to the anatase phase at600°C and to the more thermodynamically stable rutile phase at900°C.Li et al. developed TiO2nanoparticles with the chemical reactions between TiCl4solution and ammonia in a reversed micro-emulsion system consisting of cyclohexane,poly(oxyethyl-ene)5nonyle phenol ether,and poly(oxyethylene)9nonyle phenol ether.104The produced amorphous TiO2nanoparticles transformed into anatase when heated at temperatures from 200to750°C and into rutile at temperatures higher than 750°C.Agglomeration and growth also occurred at elevated temperatures.Shuttle-like crystalline TiO2nanoparticles were synthesized by Zhang et al.with hydrolysis of titanium tetrabutoxide in the presence of acids(hydrochloric acid,nitric acid,sulfuric acid,and phosphoric acid)in NP-5(Igepal CO-520)-cyclohexane reverse micelles at room temperature.110The crystal structure,morphology,and particle size of the TiO2 nanoparticles were largely controlled by the reaction condi-tions,and the key factors affecting the formation of rutile at room temperature included the acidity,the type of acid used, and the microenvironment of the reverse micelles.Ag-glomeration of the particles occurred with prolonged reaction times and increasing the[H2O]/[NP-5]and[H2O]/[Ti-(OC4H9)4]ratios.When suitable acid was applied,round TiO2 nanoparticles could also be obtained.Representative TEM images of the shuttle-like and round-shaped TiO2nanopar-ticles are shown in Figure6.In the study carried out by Lim et al.,TiO2nanoparticles were prepared by the controlled hydrolysis of TTIP in reverse micelles formed in CO2with the surfactants ammonium carboxylate perfluoropolyether(PFPECOO-NH4+)(MW587)and poly(dimethyl amino ethyl methacrylate-block-1H,1H,2H,2H-perfluorooctyl meth-acrylate)(PDMAEMA-b-PFOMA).106It was found that the crystallite size prepared in the presence of reverse micelles increased as either the molar ratio of water to surfactant or the precursor to surfactant ratio increased.The TiO2nanomaterials prepared with the above micelle and reverse micelle methods normally have amorphous structure,and calcination is usually necessary in order to induce high crystallinity.However,this process usually leads to the growth and agglomeration of TiO2nanoparticles.The crystallinity of TiO2nanoparticles initially(synthesized by controlled hydrolysis of titanium alkoxide in reverse micelles in a hydrocarbon solvent)could be improved by annealing in the presence of the micelles at temperatures considerably lower than those required for the traditional calcination treatment in the solid state.108This procedure could produce crystalline TiO2nanoparticles with unchanged physical dimensions and minimal agglomeration and allows the preparation of highly crystalline TiO2nanoparticles,as shown in Figure7,from the study of Lin et al.1082.3.Sol MethodThe sol method here refers to the nonhydrolytic sol-gel processes and usually involves the reaction of titanium chloride with a variety of different oxygen donor molecules, e.g.,a metal alkoxide or an organic ether.111-119Figure6.TEM images of the shuttle-like and round-shaped(inset) TiO2nanoparticles.From:Zhang,D.,Qi,L.,Ma,J.,Cheng,H.J. Mater.Chem.2002,12,3677(/10.1039/b206996b). s Reproduced by permission of The Royal Society ofChemistry.Figure7.HRTEM images of a TiO2nanoparticle after annealing. Reprinted with permission from Lin,J.;Lin,Y.;Liu,P.;Meziani, M.J.;Allard,L.F.;Sun,Y.P.J.Am.Chem.Soc.2002,124,11514. Copyright2002American Chemical Society.TiX4+Ti(OR)4f2TiO2+4RX(1)TiX4+2ROR f TiO2+4RX(2)2896Chemical Reviews,2007,Vol.107,No.7Chen and MaoThe condensation between Ti -Cl and Ti-OR leads to the formation of Ti -O -Ti bridges.The alkoxide groups can be provided by titanium alkoxides or can be formed in situ by reaction of the titanium chloride with alcohols or ethers.In the method by Trentler and Colvin,119a metal alkoxide was rapidly injected into the hot solution of titanium halide mixed with trioctylphosphine oxide (TOPO)in heptadecane at 300°C under dry inert gas protection,and reactions were completed within 5min.For a series of alkyl substituents including methyl,ethyl,isopropyl,and tert -butyl,the reaction rate dramatically increased with greater branching of R,while average particle sizes were relatively unaffected.Variation of X yielded a clear trend in average particle size,but without a discernible trend in reaction rate.Increased nucleophilicity (or size)of the halide resulted in smaller anatase nanocrystals.Average sizes ranged from 9.2nm for TiF 4to 3.8nm for TiI 4.The amount of passivating agent (TOPO)influenced the chemistry.Reaction in pure TOPO was slower and resulted in smaller particles,while reactions without TOPO were much quicker and yielded mixtures of brookite,rutile,and anatase with average particle sizes greater than 10nm.Figure 8shows typical TEM images of TiO 2nanocrystals developed by Trentler et al.119In the method used by Niederberger and Stucky,111TiCl 4was slowly added to anhydrous benzyl alcohol under vigorous stirring at room temperature and was kept at 40-150°C for 1-21days in the reaction vessel.The precipitate was calcinated at 450°C for 5h after thoroughly washing.The reaction between TiCl 4and benzyl alcohol was found suitable for the synthesis of highly crystalline anatase phase TiO 2nanoparticles with nearly uniform size and shape at very low temperatures,such as 40°C.The particle size could be selectively adjusted in the range of 4-8nm with the appropriate thermal conditions and a proper choice of the relative amounts of benzyl alcohol and titanium tetrachloride.The particle growth depended strongly on temperature,and lowering the titanium tetrachloride concentration led to a considerable decrease of particle size.111Surfactants have been widely used in the preparation of a variety of nanoparticles with good size distribution and dispersity.15,16Adding different surfactants as capping agents,such as acetic acid and acetylacetone,into the reaction matrixcan help synthesize monodispersed TiO 2nanoparticles.120,121For example,Scolan and Sanchez found that monodisperse nonaggregated TiO 2nanoparticles in the 1-5nm range were obtained through hydrolysis of titanium butoxide in the presence of acetylacetone and p -toluenesulfonic acid at 60°C.120The resulting nanoparticle xerosols could be dispersed in water -alcohol or alcohol solutions at concentrations higher than 1M without aggregation,which is attributed to the complexation of the surface by acetylacetonato ligands and through an adsorbed hybrid organic -inorganic layer made with acetylacetone,p -toluenesulfonic acid,and wa-ter.120With the aid of surfactants,different sized and shaped TiO 2nanorods can be synthesized.122-130For example,the growth of high-aspect-ratio anatase TiO 2nanorods has been reported by Cozzoli and co-workers by controlling the hydrolysis process of TTIP in oleic acid (OA).122-126,130Typically,TTIP was added into dried OA at 80-100°C under inert gas protection (nitrogen flow)and stirred for 5min.A 0.1-2M aqueous base solution was then rapidly injected and kept at 80-100°C for 6-12h with stirring.The bases employed included organic amines,such as trimethylamino-N-oxide,trimethylamine,tetramethylammonium hydroxide,tetrabut-ylammonium hydroxyde,triethylamine,and tributylamine.In this reaction,by chemical modification of the titanium precursor with the carboxylic acid,the hydrolysis rate of titanium alkoxide was controlled.Fast (in 4-6h)crystal-lization in mild conditions was promoted with the use of suitable catalysts (tertiary amines or quaternary ammonium hydroxides).A kinetically overdriven growth mechanism led to the growth of TiO 2nanorods instead of nanoparticles.123Typical TEM images of the TiO 2nanorods are shown in Figure 9.123Recently,Joo et al.127and Zhang et al.129reported similar procedures in obtaining TiO 2nanorods without the use of catalyst.Briefly,a mixture of TTIP and OA was used to generate OA complexes of titanium at 80°C in1-octadecene.Figure 8.TEM image of TiO 2nanoparticles derived from reaction of TiCl 4and TTIP in TOPO/heptadecane at 300°C.The inset shows a HRTEM image of a single particle.Reprinted with permission from Trentler,T.J.;Denler,T.E.;Bertone,J.F.;Agrawal,A.;Colvin,V.L.J.Am.Chem.Soc.1999,121,1613.Copyright 1999American ChemicalSociety.Figure 9.TEM of TiO 2nanorods.The inset shows a HRTEM of a TiO 2nanorod.Reprinted with permission from Cozzoli,P.D.;Kornowski,A.;Weller,H.J.Am.Chem.Soc.2003,125,14539.Copyright 2003American Chemical Society.Titanium Dioxide Nanomaterials Chemical Reviews,2007,Vol.107,No.72897。

仿照荷花写水晶兰的作文

仿照荷花写水晶兰的作文英文回答：The Crystal Orchid (Monotropa uniflora), a member of the Ericaceae family, resembles a ghostly apparition in the dim forest understory. Its translucent, waxy stem and ethereal white flowers evoke an aura of mystery and intrigue. Unlike the showy lilies and roses that bask in the sun, the Crystal Orchid has adapted to thrive in the perpetual shade of towering trees.Its ghost-like appearance is a testament to its unique adaptation to its shadowy habitat. Its lack of chlorophyll, the green pigment that allows plants to photosynthesize, renders it incapable of producing its own food. Instead, it forms a symbiotic relationship with mycorrhizal fungi, which provide it with the nutrients it needs to survive.The Crystal Orchid's bell-shaped flowers are adorned with delicate white petals that are often tinged with pinkor purple. These petals, which lack nectar or scent, are primarily aimed at attracting pollinators through their visual appeal. The flowers bloom in late summer and autumn, casting an ethereal glow on the forest floor.Despite its fragile beauty, the Crystal Orchid is a resilient plant that can endure harsh conditions. It is found in a wide range of habitats, from coniferous foreststo deciduous woodlands. However, it is most commonly associated with beech trees, with which it forms a particularly strong symbiotic relationship.中文回答：水晶兰，幽暗森林中的幽灵。

模仿荷花写一种花的作文

模仿荷花写一种花的作文英文回答：The embodiment of grace and resilience, the lotus flower has captivated hearts for centuries with its exquisite beauty and profound symbolism. Its journey from the depths of murky waters to blooming with vibrant hues epitomizes the indomitable spirit of life.Like the lotus, its petals unfurl with an air of serenity, resembling delicate silk embroidered withintricate patterns. Their pure white or vibrant pink hues dance in harmony, creating a symphony of colors that captivates the eye. Each petal holds its own story, a testament to the flower's strength and adaptability.The lotus stem, strong and resilient, rises from the mud, anchoring the flower amidst the murky waters. It serves as a lifeline, transporting nourishment from the depths to the delicate petals above. Its presence serves asa reminder that even in the darkest of environments, beauty can thrive.The lotus flower's symbolism extends beyond itsphysical attributes. In many cultures, it represents purity, enlightenment, and spiritual growth. Its ability to bloom amidst adversity inspires hope and resilience in the faceof life's challenges. It is a constant reminder that evenin the most difficult of times, the potential for beautyand growth remains.中文回答：荷花，一种优雅与坚韧的化身，以其精美的外貌和深刻的象征意义，征服了世世代代的心。

Cu-Cu2O-TiO2 Nanojunction Systems with an Unusual Electron–Hole

DOI:10.1002/asia.201300019Cu ÀCu 2O ÀTiO 2Nanojunction Systems with an Unusual Electron–Hole Transportation Pathway and Enhanced Photocatalytic PropertiesJun Xing,[a]Zu Peng Chen,[a]Fang Yuan Xiao,[a]Xue Yan Ma,[a]Ci Zhang Wen,[a]Zhen Li,[b]and Hua Gui Yang*[a,c]IntroductionA photocatalytic reaction is a process in which photogener-ated electrons and holes (e–h)migrate to the surface of pho-tocatalysts and cause redox reactions.It takes place on semi-conductor materials and has various applications in photoca-talytic water splitting,CO 2reduction,pollutant decomposi-tion,sensors,and so forth.[1–7]During the photocatalytic re-action,recombination of photogenerated e–h is a crucial factor for low photocatalytic pared with single-phase photocatalysts with inherent electronic struc-tures and low separation efficiencies of photoinduced charge carriers,hybrid or integrated multi-semiconductor systems possess significant advantages in promoting the separation of e–h pairs and keeping reduction and oxidation reactions at two different reaction sites.[8]The type-II heterojunctionis the most typical heterostructure characterized by a stag-gered energy-level alignment that can lead to the spatial separation of e–h on different sides of the heterojunction.[9]However,one clear drawback of this mechanism is that the redox potential of transferred electrons/holes is greatly re-duced by the release of a portion of the potential energy.By contrast,direct Z-scheme-based heterostructures simultane-ously maintained charge separation and stronger oxidative holes and reductive electrons,which were isolated on differ-ent semiconductors by directly quenching the weaker oxida-tive holes and reductive electrons in the solid heterostruc-ture interfaces.[10,11]These heterostructures would have more advantageous photocatalytic properties than those of type-II heterostructures.However,it is still a challenge to construct direct Z-scheme-based heterostructures with suitable semi-conductors to realize desirable vectorial electron transfer and essential interface properties.To date,various TiO 2ÀCu-based nanojunctions have been designed and studied because of their superior photocatalyt-ic performance,including Cu particles loaded with TiO 2,[12,13]Cu 2O ÀTiO 2heterojunction thin-film cathodes,[14]Cu-or Cu 2O-doped TiO 2,[15,16]and TiO 2ÀCu 2O heterojunctions.[17]However,these heterojunctions lack effective structure con-trol,and multicomponent Cu ÀCu 2O ÀTiO 2heterojunctions that can promote electron transfer and e–h separation have not been reported.Herein,we describe the successful syn-thesis of Cu ÀCu 2O ÀTiO 2core–shell heterojunctions by a mild chemical process.The prolonged lifetime of photo-generated carriers and enhanced photocatalytic activities of these nanojunctions are also demonstrated.Based on experi-mental results,it can be confirmed that the existence of Abstract:Multicomponent Cu ÀCu 2O ÀTiO 2nanojunction systems were suc-cessfully synthesized by a mild chemi-cal process,and their structure and composition were thoroughly analyzed by X-ray diffraction,transmission elec-tron microscopy,field-emission scan-ning electron microscopy,and X-ray photoelectron spectroscopy.The as-prepared Cu ÀCu 2O ÀTiO 2(3and 9h)nanojunctions demonstrated higher photocatalytic activities under UV/Vis light irradiation in the process of thedegradation of organic compounds than those of the Cu ÀCu 2O,Cu ÀTiO 2,and Cu 2O ÀTiO 2starting materials.Moreover,time-resolved photolumines-cence spectra demonstrated that the quenching times of electrons and holes in Cu ÀCu 2O ÀTiO 2(3h)is higher than that of Cu ÀCu 2O ÀTiO 2(9h);this leads to a better photocatalytic performance of Cu ÀCu 2O ÀTiO 2(3h).The improve-ment in photodegradation activity and electron–hole separation of Cu ÀCu 2O ÀTiO 2(3h)can be ascribed to the ra-tional coupling of components and di-mensional control.Meanwhile,an un-usual electron–hole transmission path-way for photocatalytic reactions over Cu ÀCu 2O ÀTiO 2nanojunctions was also identified.Keywords:copper ·heterogeneous catalysis ·photochemistry ·semi-conductors ·titanium[a]J.Xing,Z.P .Chen,F.Y.Xiao,X.Y.Ma,C.Z.Wen,Prof.H.G.YangKey Laboratory for Ultrafine Materials of Ministry of Education School of Materials Science and EngineeringEast China University of Science and Technology 130Meilong Road,Shanghai 200237(P .R.China)Fax:(+86)21-64252127E-mail:hgyang@ [b]Dr.Z.LiARC Centre of Excellence for Functional Nanomaterials Australian Institute for Bioengineering and Nanotechnology The University of Queensland Brisbane,QLD 4072(Australia)[c]Prof.H.G.YangCentre for Clean Environment and Energy,Gold Coast Campus Griffith University,Gold Coast QLD 4222(Australia)Supporting information for this article is available on the WWW under /10.1002/asia.201300019.FULLPAPERa Cu metal core can change the photoinduced e–h transpor-tation pathway between Cu 2O and TiO 2in the Cu ÀCu 2O ÀTiO 2system,which can behave as a direct Z-scheme photo-catalyst.This is quite different from type-II heterojunctions,which are frequently applied to explain the e–h transmission pathway of TiO 2ÀCu 2O-based composite systems.[17]Results and DiscussionThe formation process for Cu ÀCu 2O ÀTiO 2nanojunctions is illustrated in Scheme 1.First,pure copper dendrites were prepared by a hydrothemal method,according to a previousreport.[18]It was demonstrated that the surface of copper could be slowly oxidized to Cu 2O in an ambient atmosphere until further exposure of copper was prevented by the oxide layer.[18,19]Inspired by this,in the second step,Cu ÀCu 2O was obtained by exposing freshly synthesized copper in air for more than two weeks.A thin Cu 2O layer was demonstrated by XRD,as shown in Figure S1in the Supporting Informa-tion.The three peaks at 43.3,50.4,and 74.18can be indexed as face-centered cubic (fcc)copper (Joint Committee on Powder Diffraction Standards (JCPDS)no.04-0836),and the peak at 36.48can be appropriately ascribed to the (111)diffraction of cuprite Cu 2O (JCPDS no.05-0667).Finally,anatase TiO 2was uniformly crystallized on the surface of Cu ÀCu 2O by a liquid-phase deposition (LPD)method to form multicomponent Cu ÀCu 2O ÀTiO 2nanojunctions (the amount of TiO 2is beyond the XRD detection limit).Field-emission scanning electron microscopy (FESEM)and transmission electron microscopy (TEM)images of the as-obtained Cu ÀCu 2O ÀTiO 2nanojunctions are shown in Figure 1.The FESEM image in Figure 1a shows that the nanojunctions display a three-dimensionally dendritic struc-ture assembled from a lone trunk and multiple branches with lengths of about 1m m.Spinous TiO 2particles uniformly cover the surface of the material (Figure 1b and c and Fig-ure S2in the Supporting Information).HRTEM images of the spinous area and the adjacent area are given in Fig-ure 1d and e.Two sets of fringes with a distance of 0.30nm and an angle of 1208match well with {110}planes of cubic fcc Cu 2O.A lattice fringe of 0.35nm is consistent with {101}planes of anatase TiO 2.Yang and Zeng developed a mild LPD method to fabricate various TiO 2-based nanocompo-sites.TiO 2in the composites was highly crystalline.[20]Here,the high crystallinity of TiO 2in Cu ÀCu 2O ÀTiO 2nanojunc-tions might be attributed to this unique LPD.All of the above results indicate that Cu ÀCu 2O ÀTiO 2nanojunctions were successfully synthesized with well-defined multiple core–shell structures.The outer TiO 2shell and inner Cu 2Oshell possess thicknesses of about 60and 30nm,respectively.X-ray photoelectron spectroscopy (XPS)data (Figure S2in the Supporting Information)further confirm the successful synthesis of Cu ÀCu 2O ÀTiO 2nanojunctions with a tiny amount of Cu 2+(Figure S3in the Supporting Informa-tion).[18,19,21–23]Previously,Yang et al.reported that the diam-eter and length of the TiO 2nanorods in the TiO 2/H 2Ti 5O 11·H 2O nanocomposites increased with increasing LPD treatment time.[20]For comparison,we obtained Cu ÀCu 2O ÀTiO 2with a thicker TiO 2layer by using a similar strategy.After LPD treatment for 9hours,the surface of the starting material Cu ÀCu 2O is fully wrapped in spinous TiO 2with a diameter of about 25nm,as shown in Figures S5and S6in the Supporting Information.UV/Vis absorption spectra of pure anatase TiO 2and Cu ÀCu 2O ÀTiO 2(3h)are shown in Figure 2a.Cu ÀCu 2O ÀTiO 2(3h)exhibits a broad absorption from 200to 800nm.A pre-vious report indicated that the UV/Vis absorption spectrum of Cu 2O was characterized by a broad absorption peak from 400to 600nm centered at 500nm.[24]Qian et al.synthesized copper nanowires with a diameter of about 85nm,which ex-hibited surface plasmon resonance (SPR)absorptions in the visible-light region.[18]The exact position of the absorption peak (570–650nm)also depends on its size and shape.[18,25]Here,the UV/Vis adsorption spectrum of the microsized Cu ÀCu 2O ÀTiO 2(3h)hierarchical structure also shows anal-ogous SPR adsorptions.Thus,the absorption of both ultra-violet and visible light by Cu ÀCu 2O ÀTiO 2(3h)should be at-tributed to synergetic effects from outer-shell TiO 2,inner-shell Cu 2O,and the Cu metal core.Time-resolved PL spectra were used to study the influ-ence of shell thickness on the recombination dynamics of e–h pairs in Cu ÀCu 2O ÀTiO 2nanojunctions;the emission decay kinetics are shown in Figure 2b.It is clear that the ra-diative recombination dynamics for the photogenerated e–h pairs are longer in Cu ÀCu 2O ÀTiO 2(3h)than those in Cu ÀCu 2O ÀTiO 2(9h).This observation indicates that the thin TiO 2layer leads to a prolonged lifetime of e–h pairs,which can be attributed to improved spatial e–hseparation.Scheme 1.Formation process of the Cu ÀCu 2O ÀTiO 2nanojunctions.Figure 1.FESEM (a),TEM (b and c),and corresponding high-resolution (HR)TEM (d and e)images of Cu ÀCu 2O ÀTiO 2.Scale bars in d)and e)are 5nm.To obtain Cu ÀCu 2O ÀTiO 2nanojunctions,as-prepared Cu ÀCu 2O was treated by a LPD method for 3h.Active hydroxyl radicals (C OH)obtained upon irradiation are considered as the most important reactive oxidative spe-cies (ROS)in photocatalytic reactions.Terephthalic acid can react with C OH in basic solution to generate 2-hydroxyter-ephthalic acid (TAOH),which emits a unique fluorescence signal with a peak at around 426nm.[26,27]Herein,tereph-thalic app:ds:acid was used as a fluorescence probe to studythe photodegradation effects of Cu ÀCu 2O ÀTiO 2samples.Asshown in Figure 2c,the relationship between fluorescence intensity and irradiation time is linear,which demonstrates the stability of Cu ÀCu 2O ÀTiO 2(3h).The formation of C OH on Cu ÀCu 2O and Cu ÀCu 2O ÀTiO 2nanojunctions excited byUV/Vis or visible light is illustrated in Figure 2d.For UV/Vis irradiation,both Cu ÀCu 2O ÀTiO 2(3h)and Cu ÀCu 2O ÀTiO 2(9h)present better photodegradation capabilities than that of the binary starting material Cu ÀCu 2O;Cu ÀCu 2O ÀTiO 2(3h)shows the best photocatalytic performance.For visible-light (l !420nm)irradiation,Cu ÀCu 2O ÀTiO 2(3h)and Cu ÀCu 2O ÀTiO 2(9h)show almost invariable fluores-cence intensity with time.These results indicate that Cu ÀCu 2O ÀTiO 2nanojunctions can only generate C OH under UV-light irradiation,whereas visible light cannot excite thesame nanojunctions to release detectable holes for C OH forma-tion.To further identify the out-standing e–h separation capa-bilities of Cu ÀCu 2O ÀTiO 2,pho-tocatalytic decomposition of an aqueous solution of methyl orange (MO)with prepared samples and reference samples,including Cu ÀCu 2O,Cu ÀTiO 2and Cu 2O ÀTiO 2,were carried out under UV/Vis irradiation.XRD patterns and SEM images of reference sample Cu 2O are shown in Figure S7in the Sup-porting Information.Under UV/Vis irradiation,almost no change in the concentration of MO was observed in the ab-sence of any photocatalyst.Fig-ure 3a shows the time depend-ence of the concentration of an aqueous solution of MO in the presence of photocatalysts under UV/Vis irradiation.After 80minutes of irradiation,thephotocatalytic decomposition ofMO by Cu ÀCu 2O ÀTiO 2nano-junction systems was nearly 90%;however,only a smallamount of MO could be de-composed by Cu ÀCu 2O,Cu ÀTiO 2,and Cu 2O ÀTiO 2under the same conditions.The mostefficient degradation of MO by the Cu ÀCu 2O ÀTiO 2nano-junction suggests excellent photoinduced e–h separation andstrong oxidative holes for such a nanojunction.It is clear that Cu ÀCu 2O ÀTiO 2(3h)exhibits better photocatalytic ac-tivity than Cu ÀCu 2O ÀTiO 2(9h)for the first 30minutes;this is the same order as that determined by ROS measurements.As demonstrated by time-resolved PL spectroscopy,the e–h quenching time was significantly delayed in Cu ÀCu 2O ÀTiO 2(3h).This result is much better than that of Cu ÀCu 2O ÀTiO 2(9h)with a thicker TiO 2layer,which can prolong the e–h transmission pathway,and thus,hinder their separation.Thestability of the highly efficient Cu ÀCu 2O ÀTiO 2nanojunction photocatalyst was further evaluated by recycling experi-ments for the degradation of MO.[28,29]Figure 3b shows that as-prepared Cu ÀCu 2O ÀTiO 2retains a similar degradation rate after five cycles,suggesting that the Cu ÀCu 2O ÀTiO 2nanojunctions exhibit high photocatalytic activity and stabil-ity during the degradation of MO,although slightly moreCu 2+is present during the photocatalytic reaction,according to XPS spectra (Figure S3in the Supporting Information).Based on the above observations and an energy-band dia-gram of the multicomponent nanojunctions,thereaction Figure 2.a)UV/Vis absorption spectra of anatase TiO 2,which was obtained by keeping an 8m m aqueous solu-tion of TiF 4at 708C for 9h in an oil bath (Figure S4in the Supporting Information),and Cu ÀCu 2O ÀTiO 2nanojunctions (3h).b)Time-resolved photoluminescence (PL)spectra of Cu ÀCu 2O ÀTiO 2nanojunctions LPDtreatment times of 3and 9h.Inset:spectra from 26to 42ns.c)Fluorescence spectra of the UV/Vis-irradiatedCu ÀCu 2O ÀTiO 2(3h)in 3m m terephthalic acid at different irradiation times.d)Time dependence of the fluo-rescence intensity at 426nm determined by photocatalytic reaction of Cu ÀCu 2O ÀTiO 2nanojunctions and start-ing material Cu ÀCu 2O under different conditions,including irradiation with light at l ex !420nm (&and ~)and UV/Vis light (3,*,and !).scheme in Figure 4is proposed.For UV/Vis irradiation,electrons and holes are photogenerated on both Cu 2O and TiO 2.Because the Fermi energy level of Cu is lower than that of p-type Cu 2O,electrons on the conduction band (CB)of Cu 2O migrate to Cu until the two Fermi levels are aligned.Holes in the valance band (VB)of Cu 2O recombine with electrons in the CB of TiO 2.More holes in the VB of TiO 2are separated from electrons and engage in C OH for-mation.For irradiation with light of l ex !420nm,only Cu 2O is photoexcited.Electrons in the CB of Cu 2O are trapped by highly conductive Cu,while migration of holes from the VB of Cu 2O to VB of TiO 2is difficult,and thus,the small amount of C OH generated can barely be detected.This transmission pathway is analogous to that of the Z-scheme system,in which holes in a hydrogen-evolution photocata-lyst and electrons in an oxygen-evolution photocatalyst re-combine with a redox mediator,such as IO 3À/I Àand Fe 3+/Fe 2+,in most cases or recombine directly in elaborately de-signed composites,and hydrogen-generation electrons and oxygen-generation holes are separated spatially.[2,10,11]The transmission pathway we propose herein is more feasible be-cause p-type semiconductor Cu 2O forms a contact with Cu metal to form an Ohm junction,which facilitates electron transmission from Cu 2O to Cu.[33]Holes in TiO 2are more easily trapped by OH Àunder alkaline conditions,[26]and holes in p-type Cu 2O and electrons in n-type TiO 2recom-bine instead of remaining to charge the components.[34–36]It is known that combinations of Cu 2O and TiO 2can form type-II heterojunctions,in which electrons transfer from Cu 2O to TiO 2,whereas holes transfer in the opposite direc-tion to achieve e–h separation.[17,32,37]The transmission path-way proposed herein is quite different from previous re-ports.We provide further evidence for our proposed elec-tron transmission from XPS data for Ti 2p and a terephthalic acid photodegradation test,which was carried out under vacuum and ambient conditions.The lack of a Ti 3+peak in the Ti 2p spectrum (Figure S3in the Supporting Informa-tion)indicates that the chance of electron transmission from the CB of Cu 2O to the CB of TiO 2is not likely for the gen-eration of Ti 3+by trapping electrons on the Ti 4+site.[32]In addition,it has been reported that oxygen molecules are strong electron scavengers,which can combine with elec-trons from the CB and thus prolong the lifetime of holes in the VB to enhance photocatalytic efficiency.[38,39]We con-firmed the role of O 2in Cu ÀCu 2O ÀTiO 2(3h)and P25TiO 2by comparison of a terephthalic app:ds:acid photodegrada-tion test performed in vacuum and under ambient condi-tions,as shown in Figure pared with the results ob-tained under vacuum,Cu ÀCu 2O ÀTiO 2(3h)showed reduced photocatalytic activity,whereas P25TiO 2showed enhanced photocatalytic activity under ambient conditions.These re-sults indicate that electrons make less contribution to the terephthalic acid photodegradation test in Cu ÀCu 2O ÀTiO 2(3h;Z-scheme heterostructure)than that in P25TiO 2(type-II heterostructure composed of anatase and rutilephases).Figure 3.a)Time profiles of the photocatalytic degradation of MO for different photocatalysts under UV/Vis irradiation and b)photodegrada-tion of a recycled sample of Cu ÀCu 2O ÀTiO 2(3h).Figure 4.Proposed reaction pathway for photoexcited e–h pairs in Cu ÀCu 2O ÀTiO 2nanojunctions.The band positions for Cu 2O and TiO 2were obtained from the literature.[30–32]NHE =normal hydrogenelectrode.Figure 5.Fluorescence spectra of UV/Vis-irradiated Cu ÀCu 2O ÀTiO 2(3h)and Degussa P25TiO 2in 3m m terephthalic acid.The ROS tests were performed under vacuum or in air.We assume that the reduction in the photocatalytic activity of CuÀCu2OÀTiO2(3h)under oxygen-rich conditions can be ascribed to perturbation of the Z-scheme transmission pathway by O2,which acts as an electron scavenger.For comparison,under vacuum conditions the solid CuÀCu2OÀTiO2Z scheme is favored for a lack of O2electron scaveng-ers,and further enhances the transmission efficiency of the CuÀCu2OÀTiO2Z scheme.ConclusionWe have prepared multicomponent CuÀCu2OÀTiO2nano-junctions by a facile method.The CuÀCu2OÀTiO2nanojunc-tions have photogenerated carriers with prolonged lifetimes and exhibit high photocatalytic activities and stabilities.Ra-tional coupling of components and dimensional control enable improved e–h separation and photo-oxidation activi-ty of the photocatalysts.Furthermore,we propose that the e–h transmission pathway of a CuÀCu2OÀTiO2nanojunction behaves as a Z-scheme photocatalyst instead of as a type-II heterojunction based on theoretical and experimental analy-ses.Experimental SectionSynthesis of NanojunctionsThe synthesis of CuÀCu2OÀTiO2nanojunctions was carried out by using a mild chemical process.1)Copper dendrites were fabricated by a modi-fied hydrothermal method.[18]In a typical experiment,distilled water (27.6g),NaOH(9g),glycerol(18mL),disodium hydrogen phosphate (1.947g),copper sulfate pentahydrate(0.5673g),and sodium dodecyl benzene sulfonate(0.055g)were introduced into a50mL Teflon-lined autoclave under vigorously stirring.Then the autoclave was maintained at1208C for20h.After cooling to room temperature,the red fluffy powder was harvested by centrifugation and washed with ethanol and distilled water several times.2)The as-prepared copper product was dried in vacuum and stored in air.After storage for more than two weeks,the surface of the copper was oxidized to cuprous oxide.3)Final-ly,CuÀCu2OÀTiO2nanojunctions were obtained by a LPD method.An aqueous solution of TiF4was prepared by a method reported previous-ly.[23]Briefly,the red powder(0.02g)obtained from step2)was added to an8m m aqueous solution of TiF4(40mL)and maintained at558C for3 or9h to obtain CuÀCu2OÀTiO2nanojunctions.The product in this step was separated by gravitational settling,washed with distilled water until the supernatant became clear,dried in vacuum,and then preserved in a dryer containing silica-gel desiccant.The reference sample CuÀTiO2 (3h)was synthesized according to the method described above without preserving the as-prepared Cu for more than two weeks.Cu2OÀTiO2was also prepared by a two-step method.Firstly,Cu2O was synthesized followed previous report.[40]Then,Cu2OÀTiO2nanojunctions were obtained by the LPD method mentioned above.Photoreactivity MeasurementsVarious photocatalysts,including the CuÀCu2O starting material and multicomponent CuÀCu2OÀTiO2nanojunctions(10mg),were dispersed in40mL of an aqueous solution containing0.01m NaOH and3.0m m ter-ephthalic acid.Before exposure to light irradiation,the solution was stirred in the dark for30min and then the photocatalysts were separated from solution by centrifugation.The clear supernatant was used for fluo-rescence spectroscopy measurements.During the photoreactions,no oxygen was bubbled into the suspension.The excitation light employed for recording the fluorescence spectra was l=320nm.The light source employed in photoreactions was a300W Xe lamp(CEL-HXUV300) with a wavelength range of200–2500nm.For visible-light irradiation, a l=420nm UV cutoff was used to eliminate l ex420nm irradiation. The photodegradation of an aqueous solution of MO was carried out under ambient temperatures.Typically,photocatalysts powders(50mg) were dispersed in MO solution(50mL,10mg LÀ1)under stirring.The suspension was stirred magnetically for1h in the dark to reach adsorp-tion equilibrium.The concentration of MO was determined by using a UV/Vis spectrophotometer.After irradiation every20min,the reaction solution was sampled to measure the change in concentration of MO.Characterization of the MaterialsCrystallographic information for the CuÀCu2O and CuÀCu2OÀTiO2 nanojunctions was obtained by XRD(Bruker D8Advanced Diffractome-ter,Cu K a radiation,40kV).The morphologies and structures of the sam-ples were characterized by HRTEM(JEOL JEM-2100F)and FESEM (Hitachi S4800);surface binding elements were analyzed by XPS(Kratos Axis Ultra DLD).All binding energies were referenced to the C1s peak (284.8eV)arising from surface hydrocarbons(or possible adventitious hydrocarbon).Prior to peak deconvolution,X-ray satellites and inelastic background(Shirley-type)signals were subtracted from all spectra.Fresh samples were redispersed in ethanol and dropped onto a carbon-coated copper grid with irregular holes for TEM analysis.The UV/Vis diffuse re-flectance spectra were obtained by using a UV/Vis spectrophotometer (Carry-500).Time-resolved fluorescence spectroscopy was performed at room temper-ature with a Horiba Jobin Yvon FluoroLog-3fluorescence spectropho-tometer.The instrument works on the principle of the time-correlated single-photon-counting(TCSPC)technique.The powder samples of the CuÀCu2OÀTiO2nanojunctions were excited by a l=340nm light-emit-ting diode(LED),and the fluorescence emission decay spectra were monitored at l=350nm by TCSPC.Acquisition of the emission decay spectrum was not stopped until the counting number of the fluorescence signal reached50007.The thickness of the quartz sample holder was 1cm.AcknowledgementsThis work was financially supported by the 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基于玫瑰花瓣的双模板法制备高光催化活性的有序大孔-介孔锐钛矿二氧化钛薄片

基于玫瑰花瓣的双模板法制备高光催化活性的有序大孔-介孔锐钛矿二氧化钛薄片赵健全;廖婵娟;陈霞;卢照;童华【摘要】以天然玫瑰花瓣和三嵌段共聚物P123(EO20 PO70 EO20)为双模板,有序大孔-介孔锐钛矿TiO2薄片通过溶胶-凝胶法在酸性介质中成功制备.采用拉曼光谱、X射线衍射、N2吸脱附、扫描电镜和透射电镜对制备的TiO2薄片进行表征.TiO2薄片的光催化活性通过罗丹明B光降解过程的光催化效果来进行评价.结果表明多级构造的大孔-介孔TiO2薄片为锐钛矿,且其三维有序的大孔孔壁均由有序的介孔所组成,其中,450℃煅烧后的TiO2样品表观反应速率常数k达到2.21×10-2 min-1,表现出最高的光催化活性.【期刊名称】《功能材料》【年(卷),期】2018(049)007【总页数】7页(P7001-7007)【关键词】玫瑰花瓣;P123;溶胶-凝胶法;大孔-介孔;TiO2;光催化【作者】赵健全;廖婵娟;陈霞;卢照;童华【作者单位】华中科技大学分析测试中心,武汉 430074;湖南农业大学资源环境学院,长沙 410128;华中科技大学分析测试中心,武汉 430074;华中科技大学分析测试中心,武汉 430074;武汉大学化学与分子科学学院,武汉 430074【正文语种】中文【中图分类】TB3210 引言在过去的几十年中，多孔材料由于其在催化，离子交换，吸附与分离等方面的广泛应用而受到了越来越多的关注[1-3]。

自从有序介孔氧化硅MCM-41成功合成后[4]，有序微孔(孔径<2 nm)，介孔(2～50 nm)和大孔(>50 nm)材料的合成取得了很大的进步[5]。

近期，多级大孔-介孔材料以其优异的结构特性和潜在的应用价值引起了科研工作者的极大兴趣[6]。

与单一孔径如微孔、介孔和大孔材料相比，多级构造的大孔-介孔材料结合了大孔结构和介孔结构的优点，无疑更具优势。

大孔结构能够有效提高反应物和产物的扩散性能，增大反应的有效面积；介孔结构则具有高的比表面积和孔容，能够提高更多的吸附容量，增加反应活性位点和反应中心[7-8]。

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Allen, Matthew B. Keddie and Alexander Star, Nanoscale , 2010DOI: 10.1039/c0nr00043dVisible light induced photobleaching of methylene blue over melamine-doped TiO 2 nanocatalyst Jurate Virkutyte, Babita Baruwati and Rajender S. Varma, Nanoscale , 2010 DOI: 10.1039/c0nr00089bSelective detection of trace amount of Cu 2+ using semiconductor nanoparticles in photoelectrochemical analysisGuang-Li Wang, Jing-Juan Xu and Hong-Yuan Chen, Nanoscale , 2010 DOI: 10.1039/c0nr00084aFlower-like TiO 2 nanosructures with exposed {001} facets: Facile synthesis and enhanced photocatalysis Min Liu, Lingyu Piao, Weiming Lu, Siting Ju, Lei Zhao, Chunlan Zhou, Hailing Li and Wenjing Wang, Nanoscale , 2010DOI: 10.1039/c0nr00050g PapersElectroconvection in nematic liquid crystals via nanoparticle dopingMartin Urbanski, Brandy Kinkead, Hao Qi, Torsten Hegmann and Heinz-S. Kitzerow, Nanoscale , 2010 DOI: 10.1039/c0nr00139bSuperhydrophilicity-assisted preparation oftransparent and visible light activated N-doped titania filmQing Chi Xu, Diana V. Wellia, Rose Amal, Dai Wei Liao, Say Chye Joachim Loo and Timothy Thatt Yang Tan, Nanoscale , 2010 DOI: 10.1039/c0nr00105hThe influence of doping on the device characteristics of In 0.5Ga 0.5As/GaAs/Al 0.2Ga 0.8As quantum dots-in-a-well infrared photodetectors G. Jolley, L. Fu, H. H. Tan and C. Jagadish, Nanoscale , 2010DOI: 10.1039/c0nr00128gStudy of concentration-dependent cobalt ion doping of TiO 2 and TiO 2-x N x at the nanoscaleJames L. Gole, Sharka M. Prokes, O. J. Glembocki, Junwei Wang, Xiaofeng Qiu and Clemens Burda, Nanoscale , 2010 DOI: 10.1039/c0nr00125bD o w n l o a d e d o n 26 O c t o b e r 2011P u b l i s h e d o n 17 M a r c h 2010 o n h t t p ://p u b s .r s c .o r g | d o i :10.1039/C 0N R 00050GView Online / Journal Homepage / Table of Contents for this issueMultifunctional nanocomposites ofsuperparamagnetic (Fe 3O 4) and NIR-responsive rare earth-doped up-conversion fluorescent (NaYF 4:Yb,Er) nanoparticles and their applications inbiolabeling and fluorescent imaging of cancer cells Congcong Mi, Jingpu Zhang, Huanyu Gao, Xianlong Wu, Meng Wang, Yingfan Wu, Yueqin Di, Zhangrun Xu, Chuanbin Mao and Shukun Xu, Nanoscale , 2010 DOI: 10.1039/c0nr00102cEffect of doping on the morphology and multiferroic properties of BiFeO 3 nanorodsDimple P. Dutta, O. D. Jayakumar, A. K. Tyagi, K. G. Girija, C. G. S. Pillai and G. Sharma, Nanoscale , 2010 DOI: 10.1039/c0nr00100gEffect of substrate temperature on implantation doping of Co in CdS nanocrystalline thin films S. Chandramohan, A. Kanjilal, S. N. Sarangi, S.Majumder, R. Sathyamoorthy, C.-H. Hong and T. Som, Nanoscale , 2010DOI: 10.1039/c0nr00123fModification of neodymium-doped ZnO hybrid nanoparticles under mild hydrothermal conditions Behzad Shahmoradi, K. Soga, S. Ananda, R. Somashekar and K. Byrappa, Nanoscale , 2010 DOI: 10.1039/c0nr00069hEx situ vapor phase boron doping of silicon nanowires using BBr 3Gregory S. Doerk, Gabriella Lestari, Fang Liu, Carlo Carraro and Roya Maboudian, Nanoscale , 2010 DOI: 10.1039/c0nr00127aChange in conformation of polymer PFO on addition of multiwall carbon nanotubesMalti Bansal, Ritu Srivastava, C. Lal, M. N. Kamalasanan and L. S. Tanwar, Nanoscale , 2010 DOI: 10.1039/c0nr00001aAmino acid-assisted one-pot assembly of Au, Pt nanoparticles onto one-dimensional ZnO microrods Xianghong Liu, Jun Zhang, Xianzhi Guo, Shihua Wu and Shurong Wang, Nanoscale , 2010 DOI: 10.1039/c0nr00015aLuminescence resonance energy transfer from an upconverting nanoparticle to a fluorescent phycobiliproteinFiorenzo Vetrone, Rafik Naccache, Christopher G. Morgan and John A. Capobianco, Nanoscale , 2010 DOI: 10.1039/c0nr00126kDoping single-walled carbon nanotubes through molecular charge-transfer: a theoretical studyArun K. Manna and Swapan K. Pati, Nanoscale , 2010 DOI: 10.1039/c0nr00124dEnergy transfer study between Ce 3+ and Tb 3+ ions in doped and core-shell sodium yttrium fluoride nanocrystalsPushpal Ghosh, Arik Kar and Amitava Patra, Nanoscale , 2010DOI: 10.1039/c0nr00019aPt surface modification of SnO 2 nanorod arrays forCO and H 2 sensorsHui Huang, C. Y. Ong, J. Guo, T. White, M. S. Tse and O. K. Tan, Nanoscale , 2010 DOI: 10.1039/c0nr00159gPoly (acrylic acid)-capped lanthanide-doped BaFCl nanocrystals: synthesis and optical properties Qiang Ju, Wenqin Luo, Yongsheng Liu, Haomiao Zhu, Renfu Li and Xueyuan Chen, Nanoscale , 2010 DOI: 10.1039/c0nr00116cEnhanced Cu emission in ZnS :Cu,Cl/ZnS core–shell nanocrystalsCarley Corrado, Morgan Hawker, Grant Livingston, Scott Medling, Frank Bridges and Jin Z. Zhang, Nanoscale , 2010DOI: 10.1039/c0nr00056fSynthesis and characterization of zirconium-doped mesoporous nano-crystalline TiO 2Kanattukara Vijayan Bineesh, Dong-Kyu Kim and Dae-Won Park, Nanoscale , 2010 DOI: 10.1039/c0nr00108bZn-doped nanocrystalline TiO 2 films for CdS quantum dot sensitized solar cellsGuang Zhu, Zujun Cheng, Tian Lv, Likun Pan, Qingfei Zhao and Zhuo Sun, Nanoscale , 2010 DOI: 10.1039/c0nr00087fEffect of synergy on the visible light activity of B, N and Fe co-doped TiO 2 for the degradation of MO Mingyang Xing, Yongmei Wu, Jinlong Zhang and Feng Chen, Nanoscale , 2010 DOI: 10.1039/c0nr00078gFacile synthesis of lanthanide nanoparticles with paramagnetic, down- and up-conversion properties Zhengquan Li and Yong Zhang, Nanoscale , 2010 DOI: 10.1039/c0nr00073fGlucose oxidase-doped magnetic silica nanostrutures as labels for localized signalamplification of electrochemical immunosensors Jingjing Ren, Dianping Tang, Biling Su, Juan Tang and Guonan Chen, Nanoscale , 2010 DOI: 10.1039/b9nr00416eThe role of ellipticity on the preferential binding site of Ce and La in C 78-D 3h —A density functional theory studyK. Muthukumar and J. A. Larsson, Nanoscale , 2010 DOI: 10.1039/c0nr00021cTuning the shape and thermoelectric property of PbTe nanocrystals by bismuth dopingQian Zhang, Ting Sun, Feng Cao, Ming Li, Minghui Hong, Jikang Yuan, Qingyu Yan, Huey Hoon Hng, Nianqiang Wu and Xiaogang Liu, Nanoscale , 2010 DOI: 10.1039/c0nr00115eD o w n l o a d e d o n 26 O c t o b e r 2011P u b l i s h e d o n 17 M a r c h 2010 o n h t t p ://p u b s .r s c .o r g | d o i :10.1039/C 0N R 00050GView OnlineFlower-like TiO 2nanostructures with exposed {001}facets:Facile synthesis and enhanced photocatalysis †Min Liu,a Lingyu Piao,*b Weiming Lu,ac Siting Ju,b Lei Zhao,a Chunlan Zhou,a Hailing Li a and Wenjing Wang *aReceived (in Gainesville,FL,USA)24th January 2010,Accepted 17th February 2010First published as an Advance Article on the web 17th March 2010DOI:10.1039/c0nr00050gFlower-like TiO 2nanostructures with exposed {001}facets were synthesized by a low-temperature hydrothermal process from Ti powders for the ﬁrst time,and they exhibited enhanced photo-catalytic degradation of methylene blue dye under ultraviolet light irradiation.Titanium oxide (TiO 2),as one of the most important oxides,has been widely investigated due to its numerous applications in photovoltaic cells,1photocatalysis,2,3Li-ion battery materials,4sensors 5and so on.These applications originate from the unique physical and chemical properties of TiO 2which depend not only on the crystal phase and particle size but also on the exposed facet.6–10For anatase TiO 2,both theoretical and experimental studies have found that the minority {001}facets in the equilibrium state are especially reactive.8–11However,it has been demonstrated that the average surface energies are g {001}(0.90J m À2)>g {100}(0.53J m À2)>g {101}(0.44J m À2).7,9,10Although the higher-surface-energy {001}facets have much higher chemical activities,almost all of anatase TiO 2micro-and nano-structures reported to date are usually dominated by less-reactive {101}facets,which are thermodynamically stable due to their lower surface energy.Therefore,anatase TiO 2nanostructures with exposed {001}facets are rarely observed.An important step forward in the preparation of anatase TiO 2single crystals with exposed {001}facets were achieved by Lu and co-workers.11They reported the synthesis of anatase TiO 2microcrystals with exposed {001}facets by using TiF 4as the raw material.Since then,several researchers have prepared anatase TiO 2single crystals with exposed {001}facets from different raw materials,such as titanium tetraﬂuorine,titanium chloride,tetrabutyl titanate,titanium tetraisopropoxide,and so on.12–16However,these materials have high hydrolytic reaction rates which make it difﬁcult to control their reaction processes.Very recently,anatase TiO 2sheets with a high percentage of {001}facets were prepared from titanium nitride by Lu and co-workers.17However,the price of titanium nitride is still very high.Moreover,all of the previously mentioned experimentalprocesses require high temperatures,11–18even as high as 1300 C,15which not only increases the production cost but also hinders scaled-up production.Furthermore,nanomaterials with hierarchical architectures have attracted much attention,since they can possess a number of attractive properties and have a wide range of applications in catal-ysis,solar cells,Li-ion batteries,and so on.19–24For example,rose-like ZnO nanostructures,which consist of many nanosheets,exhibit enhanced light conversion efﬁciency in dye-sensitized solar cells (DSSC).23Flower-like ZnMn 2O 4nanostructures,which are composed of numerous nanorods,showed enhanced electrochemical lithium storage.24However,it remains a great challenge to develop feasible methods for the synthesis of well-deﬁned hierarchical TiO 2nanostructures.Herein,we report a simple and facile route for the one-pot synthesis of ﬂower-like TiO 2nanostructures with exposed {001}facets by a low-temperature hydrothermal process from Ti powders.These ﬂower-like TiO 2nanostructures with exposed {001}facets have never been reported until now.In agreement with calculations,it can be conﬁrmed that these ﬂower-like TiO 2nano-structures contain about 10–30%exposed highly reactive {001}facets.Moreover,these ﬂower-like TiO 2nanostructures exhibited enhanced photocatalytic degradation of methylene blue (MB)dye under ultraviolet (UV)light irradiation,and they also have poten-tial applications in photonic and optoelectronic devices,solar cells,sensors,and so on.In a typical synthesis,0.1g Ti powder (200mesh,99.9%purity,see Fig.S1of the ESI†),40ml H 2O and 0.25ml hydroﬂuoric acid (40wt %)were added into a Teﬂon-lined autoclave.Then,the mixture was kept at 120 C for 10h.After completion of the reaction,the products were collected by centrifugation and thoroughly washed with high-purity water (18M U )until pH 7.0was reached.Finally,the products were dried at 80 C.Fig.1a and b show typical ﬁeld-emission scanning electron microscope (FE-SEM)images of the ﬂower-like TiO 2nanostructures.It can be seen that the TiO 2product contains numerous ﬂower-like aggregates,and almost all of them show the same morphology.These ﬂower-like TiO 2nanostructures have a size around 300–700nm,and they are composed of large numbers of truncated tetragonal pyra-midal TiO 2nanocrystals.The width of their top surface is ca.50–150nm.The length of the truncated tetragonal pyramidal TiO 2nanocrystals is ca.100–200nm.Fig.1c shows an X-ray diffraction (XRD)pattern of the ﬂower-like TiO 2nanostructures.All XRD peaks of the synthesized ﬂower-like TiO 2nanostructures can be indexed to the anatase TiO 2phase (JCPDS No.21-1272)and no residual Ti phase can be detected.Remarkably enhanced (101)andaKey Laboratory of Solar Thermal Energy and Photovoltaic System,Institute of Electrical Engineering,Chinese Academy of Sciences,No.6Beiertiao,Zhongguancun,100190Beijing,China.E-mail:wjwangwj@;Fax:(+86)10-82547041;Tel:(+86)10-82547042bNational Center for Nanoscience and Technology,No.11Beiyitiao,Zhongguancun,100190Beijing,China.E-mail:piaoly@;Fax:(+86)10-82545505;Tel:(+86)10-82545505cInstitute of Metal Research,Chinese Academy of Sciences,Shenyang,110016,China†Electronic supplementary information (ESI)available:Additional FE-SEM images.See DOI:10.1039/c0nr00050gThis journal is ªThe Royal Society of Chemistry 2010Nanoscale ,2010,2,1115–1117|1115COMMUNICATION /nanoscale |NanoscaleD o w n l o a d e d o n 26 O c t o b e r 2011P u b l i s h e d o n 17 M a r c h 2010 o n h t t p ://p u b s .r s c .o r g | d o i :10.1039/C 0N R 00050G(004)peaks indicate that the TiO 2nanostructures are dominant in {101}and {001}facets.Fig.2a shows a transmission electron microscopy (TEM,FEI F-20)image of the ﬂower-like TiO 2nanostructures.It conﬁrms that the ﬂower-like TiO 2nanostructures were composed of many truncated tetragonal pyramidal TiO 2nanocrystals.An angle of 68.3 Æ0.3 ,which is consistent with the interfacial angle between (001)and (101),11,14,15was observed on the truncated tetragonal pyramidal TiO 2nanocrystals.It suggests that the truncated tetragonal pyramidal TiO 2nanocrystals expose facets of {001}and {101}.Fig.2b gives a schematic illustration of the ﬂower-like TiO 2nanostructures.Fig.2c shows a high-resolution TEM (HRTEM)image of a truncated tetragonal pyramidal TiO 2nanocrystal with clear crystalline lattice fringes.The lattice spacing of 0.352nm corresponds to the {101}planes,while the lattice spacing of 0.237nm corresponds to the {004}planes.The angle labeled in the corresponding fast-Fourier transform (FFT)image (Fig.2d)is 68.3 Æ0.3 ,which is identical to the theoretical value for the angle between the {101}and {001}facets.On the basis of the above characterizations,it can be conﬁrm that the ﬂower-like TiO 2nanostructures have exposed {001}facets.It has been demonstrated that metal Ti could react with HF forming TiO 2,under hydrothermal conditions.25Due to their lowsurface energy,TiO 2crystals grow with exposed {101}facets mainly during the early stages of synthesis.However,ﬂuorine ions can markedly reduce the surface energy of {001}facets to a level lower than that of {101}facets.11As a result,{001}facets are exposed during growth,and ﬂower-like TiO 2nanostructures with exposed {001}facets are formed.Therefore,hydroﬂuoric acid is believed to have a triple role here:to dissolve the Ti powders,to retard the hydrolysis of the titanium precursor,and to reduce the surface energy.18The photocatalytic activity of the ﬂower-like TiO 2nanostructures was evaluated in terms of the decolorization of MB dye under UV light irradiation.For photocatalytic reaction,the surface ﬂuorine was removed using a heat treatment process at 600 C in O 2for 2h,without altering the morphology (see Fig.S2of the ESI†).After that,30mg ﬂower-like TiO 2nanostructures was dispersed in 100ml of aqueous solution containing 0.01M NaOH and 25ppm MB.12Before exposure to UV light irradiation,the suspension was stirred in the dark for 1h to allow it reach a complete adsorption–desorption equilibrium.Then the solution was irradiated with $0.5mW cm À2UV light (with a wavelength peak at 365nm)under continuous stirring.The concentration of MB was determined from the absor-bance at the wavelength of 665nm.For comparison,the same procedure was also done for P25TiO 2powders.As shown in Fig.3,the ﬂower-like TiO 2nanostructures exhibited higher activity than that of the commercial P25TiO 2powders.The linear relationship of ln C 0/C vs.time (inset of Fig.3)shows that the photocatalytic degradation of MB follows pseudo-ﬁrst-order kinetics,ln(C 0/C )¼kt ,where C /C 0is the normalized MB concentration,t is the reaction time,and k is the pseudo-ﬁrst-rate constant.The apparent photochemical degradation rate constant for the ﬂower-like TiO 2nanostructures is 1.23Â10À2min À1,which is almost two times of that for the P25TiO 2powders,6.73Â10À3min À1.This further conﬁrms that the ﬂower-like TiO 2nanostructures exhibit high photocatalytic efﬁciency.The enhanced photocatalytic activity of the ﬂower-like TiO 2nanostructures can be attributed totheirFig.1(a,b)FE-SEM images of the ﬂower-like TiO 2nanostructures at low and high magniﬁcations,respectively.(c)XRD pattern of the ﬂower-like TiO 2nanostructures.Vertical bars indicate peak position and intensity of anatase TiO 2(JCPDS No.21-1272).Fig.2(a)TEM image of the ﬂower-like TiO 2nanostructures.(b)Schematic diagram of the ﬂower-like TiO 2nanostructures.(c)HRTEM image of a truncated tetragonal pyramidal TiO 2nanocrystal.(d)The corresponding fast-Fourier transform (FFT)pattern.1116|Nanoscale ,2010,2,1115–1117This journal is ªThe Royal Society of Chemistry 2010D o w n l o a d e d o n 26 O c t o b e r 2011P u b l i s h e d o n 17 M a r c h 2010 o n h t t p ://p u b s .r s c .o r g | d o i :10.1039/C 0N R 00050Gthree-dimensional (3D)hierarchical nanostructures and exposed {001}facets.3D hierarchical nanostructures are regarded to have a greater number of active sites than either 1D or 0D architec-tures.26,27Furthermore,it has been demonstrated that the {001}facets are more reactive toward dissociative adsorption of reactant mole-cules compared with {101}facets.28–32Therefore,high photocatalytic efﬁciency is expected for the ﬂower-like TiO 2nanostructures with {001}facets.In conclusion,ﬂower-like TiO 2nanostructures with exposed {001}facets have been successfully synthesized by a low-temperature hydrothermal process from Ti powders for the ﬁrst time.Owing to their chemically active {001}facets,these TiO 2nanostructures exhibited enhanced photocatalytic efﬁciency,and they could possibly be further used in photovoltaic cells,photonic and optoelectronic devices,sensors and so on.AcknowledgementsThis work was supported by the National Natural Science Foun-dation of China under Grant Nos 60576065and 50602008,the Knowledge Innovation Program of the Chinese Academy of Sciences under Grant No.KGCXZ-YW-351,and the National High-Tech-nology 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