Synthesis and characterization of a cholesteric liquid crystal cholesteryl
化工英语文献
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助剂对聚醋酸乙烯酯乳胶涂料黏度和光泽度的影响
第52卷第11期 辽 宁 化 工 Vol.52，No.11 2023年11月 Liaoning Chemical Industry November，2023基金项目：广东轻工职业技术学院2021年度大学生科研项目（项目编号：XSKYL202121）；广东轻工职业技术学院第二十一届“挑战杯”大学生课外学术科技作品竞赛立项项目；广东轻工职业技术学院2022年度创新创业精致育人项目（项目编号：JZYR202218）；广东轻工职 业技术学院2022年度创新创业教育教学改革项目（项目编号：CYJG202210）。
收稿日期： 2022-10-14助剂对聚醋酸乙烯酯乳胶涂料黏度和光泽度的影响范欣蕾，刘颖诗，梁家宪，侯欣桦，佘家康，谢梓良，蔡楚冰，李永莲*，罗媛媛（广东轻工职业技术学院 生态环境技术学院，广东 广州 510300）摘 要：为了研究几种常见助剂对聚醋酸乙烯酯乳胶涂料黏度和光泽度的作用及影响，探索了丙烯酸钠盐、羟乙基纤维素、十二酯醇、OP -10、丙二醇等助剂在不同使用量时聚醋酸乙烯酯乳胶涂料的黏度和光泽度。
结果表明：随着分散剂丙烯酸钠盐用量的增大，乳胶涂料的黏度也随之增大，然后减小，分散剂丙烯酸钠盐的合适用量为6.0 g；增稠剂羟乙基纤维素用量增大时，乳胶涂料的黏度也增大；成膜助剂十二醇酯用量增加时，乳胶涂料的黏度先降低再增加，十二醇酯合适用量为2.0 g；乳化剂OP -10的用量增多时，乳胶涂料的黏度总体有下降趋势，OP -10合适添加量为 0.3 g。
聚醋酸乙烯酯乳胶涂料的光泽度都在2.2%~2.3%之间，各助剂的增减对其影响不大。
关 键 词：聚醋酸乙烯酯乳胶涂料；丙烯酸钠盐；羟乙基纤维素；OP -10；十二酯醇；黏度；光泽度 中图分类号：TQ633 文献标识码： A 文章编号： 1004-0935（2023）11-1581-04聚醋酸乙烯酯（PVAc）乳胶涂料，是一种重要的乳液胶黏剂，其优点很多，例如原料来源丰富且价格低廉、操作工艺简单、初期黏接强度高等。
毕业论文英语摘要翻译技巧
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Synthesis and characterization of low cost magnetorheological (MR) fluids
SYNTHESIS AND CHARACTERIZATION OF LOW COSTMAGNETORHEOLOGICAL (MR) FLUIDSVK Sukhwani and H Hiraniv_sukhwani@iitb.ac.in , hirani@iitb.ac.inDepartment of Mechanical Engineering, Indian Institute of Technology BombayMumbai-40007, INDIAABSTRACTMagnetorheological fluids have great potential for engineering applications due to their variable rheological behavior. These fluids find applications in dampers, brakes, shock absorbers, and engine mounts [1].However their relatively high cost (approximately US$600 per liter) limits their wide usage. Most commonly used magnetic material “Carbonyl iron” cost more than 90% of the MR fluid cost [2]. Therefore for commercial viability of these fluids there is need of alternative economical magnetic material. In the present work synthesis of MR fluid has been attempted with objective to produce low cost MR fluid with high sedimentation stability and greater yield stress. In order to reduce the cost, economical electrolytic Iron powder (US$ 10 per Kg) has been used. Iron powder of relatively larger size (300 Mesh) has been ball milled to reduce their size to few microns (1 to 10 microns). Three different compositions have been prepared and compared for MR effect produced and stability. All have same base fluid (Synthetic oil) and same magnetic phase i.e. Iron particles but they have different additives. First preparation involves organic additives Polydimethylsiloxane (PDMS) and Stearic acid. Other two preparations involve use of two environmental friendly low-priced green additives guar gum (US$ 2 per Kg) and xanthan gum (US$ 12 per Kg) respectively.Magnetic properties of Iron particles have been measured by Vibrating Sample Magnetometer (VSM). Morphology of Iron particles and additives guar gum and xanthan gum has been examined by Scanning Electron Microscopy (SEM) and Particles Size Distribution (PSD) has been determined using Particle size analyzer. Microscopic images of particles, M-H plots and stability of synthesized MR fluids have been reported. The prepared low cost MR fluids showed promising performance and can be effectively used for engineering applications demanding controllability in operations Keywords: Smart fluids, MR fluid, Magnetorheology, Particle distribution, Guar gum, Xanthan gum, PDMS, Low cost.1.INTRODUCTIONMagnetorheological (MR) fluids are known for their ability to change their rheological behavior by several orders of magnitude within milliseconds under the influence of magnetic field and therefore have been regarded as controllable fluids for engineering applications. Typically these fluids are non colloidal suspensions of micron sized magnetic particles (generally Iron particles) in nonmagnetic carrier medium (mineral oil, synthetic oil or water). Under the influence of magnetic field, these particles polarize and forms columnar structure parallel to the applied field, thus increases the apparent viscosity of the fluid which develops the yield stress in the structure. This viscosity change is rapid and completely reversible. Therefore MR fluid can be converted from a free flowing liquid to a plastic like solid by applying magnetic field and vice versa and can be used in different applications to bring dynamic change in performance measures like damping resistance as in MR-dampers, braking torque in MR-brakes and minimum film thickness in MR-bearings [3].Performance of any MR fluid in any application depends upon the magnetic properties of the solid phase, volume fraction, size and distribution of the magnetic particles, and viscosity of the carrier fluid etc.The synthesis of MR fluid involves many challenges. Two critical factors are the problem of gravitational sedimentation and agglomeration of particles and relatively high cost of MR fluids (approximately US$ 600 per liter). The large density difference between magnetic particles (i.e., ρ =7.86 g/cm3) and carrier fluid (i.e. ρ =1 g/cm3) is responsible for sedimentation problem. The problem of sedimentation has been mainly solved by three approaches, by adding Behavior and Mechanics of Multifunctional and Composite Materials 2007, edited by Marcelo J. DapinoProc. of SPIE Vol. 6526, 65262R, (2007) · 0277-786X/07/$18 · doi: 10.1117/12.720870surfactants, by adding nano particles or using nano magnetizable particles and by coating magnetizable particles with polymers .The addition of nano particles or use of nano magnetizable particles improves sedimentation stability effectively but at the same time it also reduces the MR effect produced by MR fluids. [4]High cost of MR fluid is mainly due to the high cost of magnetic material. Most commonly used magnetic material is Carbonyl iron obtained by thermal decomposition of Iron penta carbonyl .This material costs more than 90 % of the MR fluid cost [2, 5] Therefore for commercial viability of these fluids there is need of alternative economical magnetic material. In addition, an important functional requirement to produce more MR effect is the high dynamic yield stress. Use of alternative materials to reduce the cost has been reported in literature. Foister et al [5] in their patent have described the synthesis of low cost MR fluid using low cost water atomized Iron powder, multi component organoclay and multi component additive. Also the use of green additives like guar gum as thixotropic agent to solve the problem of sedimentation and agglomeration of MR fluids has been reported in literature. Chen et al [4] and Wu Wei Ping et al [6] successfully employed guar gum for improving sedimentation stability of MR fluids but they used the expensive carbonyl iron powder for synthesis of MR fluid. Similarly use of xanthan gum for achieving sedimentation stability of particles in MR fluid has been described by JD Carlson and JC Jones Guion in their patent. [7]As per authors knowledge no one has attempted use of both the economical Iron powder and additives like guar gum or xanthan gum in a single MR fluid composition. This has been attempted in the present work. In the present work synthesis of MR fluids have been carried out with objective to produce low cost MR fluid with high sedimentation stability and large yield stress. Low cost electrolytic Iron powder as magnetic material and variety of additives has been used for the present synthesis.2. SELECTION OF MAGNETIC PARTICLESThe magnetic particles for MR fluids should have high saturation magnetization and low coercivity. Carbonyl iron powder [8, 9, 10, 11], Nickel Zink ferrite [12], Iron oxide coated polymer composite particles [13], and Iron Cobalt alloy [14, 15] go well with these requirements. Saturation magnetization of Nickel Zink ferrite, Iron powder and Iron Cobalt alloy are 0.4T, 2.1 T and 2.43 T respectively [12,15] i.e. Iron Cobalt alloy has highest saturation magnetization but its density (8.1 g/ cm3) is greater than Iron therefore it aggravates gravitational settling. All the above mentioned magnetic materials are costly and therefore don’t suit the present synthesis of low cost MR fluid. Therefore for present synthesis Iron powder produced by electrolytic process has been chosen as this process yields the Iron of very high purity at very economical price (US$ 10 per Kg).The electrolytic Iron (EI) powder of relatively larger size 300 mesh (SD Fine-Chem, India) has been ball milled by suitable stainless steel grinding media in stainless steel pot to reduce the size to the order of few microns (1 -10 micron). This milled Iron powder was used for synthesis of all three MR fluids..3. SELECTION OF CARRIER FLUIDThe function of carrier or base fluid is to provide liquid phase in which magnetically active phase can be suspended. The carrier fluid should be non magnetic, nontoxic, non corrosive and non reactive. As most of lubricant with their additives packages suits these requirements, the commercial lubricants can be used for synthesis of MR fluid. In the present synthesis work, PAO (Poly Alfa Olefin) based high temperature synthetic oil with density 0.87 gram /cm3 and viscosity 20 cSt (0.01 Pa s) at 40°C has been selected. This oil can withstand operating temperature up to 180°C.4. SELECTION OF ADDITIVESAs discussed earlier, many additives have been attempted by researchers for synthesis of MR fluid. Generally thixotropic agents are added to prevent particle sedimentation. In addition, anti wear, anti corrosion, friction modifier and antioxidant agent are also added. Following are some important additives used in the synthesis of MR fluids for different purposes as reported in the literature:•To overcome sedimentation,o Fumed Silica [11], Lithium stearate, Aluminum distearate, Thiophosphorus, Thiocarbomate, Phosphorus, Guar gum [4], Organoclay[16] Poly vinyl pyrolidone [17], Poly vinyl butyl [18]•To overcome agglomeration,o Fumed silica [11], Fibrous carbon [19], Stearic acid [20], Sodium dodecyl sulphate [15], Viscoplastic media[21] o To increase abrasion wear resistance,o ZDDP (Zink dialkyl dithio phosphate ) [22-23]•To reduce oxidation,o ZDDP [23]• To reduce friction resistance.o Organomolybydnums (Moly) [22]Most of the above additives are not only expensive they are harmful to environment also. Therefore two environmental friendly additives, guar gum and xanthan gum have been chosen to prevent sedimentation of particles in the present synthesis. However for comparison purpose one organic polymer Polydimethylsiloxane (PDMS) has also been used as additives in one MR fluid composition.Guar gum is a high molecular weight hydro colloidal polysaccharide. It is extracted from guar bean (Cyamopsistetra gonoloba). It consist of linear chains of (1→4) linked ß-D mannose residue with a-D-galactopyranosyl units attached by (1.6) linkages. There is no polar group on the main chain of the guar gum, and most of the hydroxyl group is located outside. Furthermore, the side chain of the a-D-galactopyranosyl units does not hide the active alcoholic hydroxyl group; therefore it has a very large area of hydrogen bond. These characteristics make it useful as a thickening agent, suspension agent and stabilizing agent [4]. Its main application is found in food industry, where it is used as thickener, suspending agent and binder agent of free water in sauces, Ice cream, salad dressings etc.Similarly xanthan gum is a biosynthetic gum similar to natural gum. Xanthan gum is a long chain polysaccharide. It is prepared by fermentation of corn sugar with a microbe called Xanthomonas campestris. Xanthan gum has a special molecular structure. Its most important property is its very high viscosity at low-shear and relatively low viscosity at high shear. High viscosity at low shear provides stability to colloidal suspensions and therefore it is used as thickener and stabilizer for emulsions and suspensions.In the present work guar gum with approximate particle size 300 mesh (Premcem Gums India) and xanthan gum (Sienokem USA) have been used as thixotropic additives in two different preparations. In another preparation organic additive Polydimethylsiloxane (PDMS) with viscosity 100 cSt and Stearic acid are used. In addition an additive pack consists of anti wear, anti rust, anti corrosion, friction modifier and anti oxidant agent has also been used in all three preparations.5. CHARACTERIZATIONThe solid phase of MR fluid i.e. magnetic material was characterized before it is used in synthesis. Typically characterization includes analysis of particle size and its distribution, morphology and magnetic characterization. Additives guar gum and xanthan gum were also checked for their morphology.5.1 Particle size distribution analysisParticle size distribution analysis is very important for synthesis of MR fluid as particle size and size distribution influence the important properties i.e. Sedimentation stability, yield stress and magnetic properties of MR fluids [24]. Ota and Miyamoto [25] using two particle sizes calculated the static yield stress for a theoretical ER fluid and concluded that “ER Fluid consist of only same particle size gives the higher yield stress”. Lemaire et al [26] reported the influence of particle size on MR effect “It is better to have monodisperse sample in order to optimize the MR effect”. This indicates that narrow size distribution leads to more MR effect. But Wereley et al [13] in their study concluded that use of bidisperse particles in MR fluid increases their sedimentation stability. They also suggested a favorable tradeoff of proportion of particle sizes to increase the yield stress of MR fluid. Often particle size ranging 0.1 micron to 10 micronsis preferred [27]. Particle lesser than 0.1 micron will be subjected to random Brownian forces which destroy the chain like structure leading to decrease in the yield stress. On the other hand particles larger than 10 microns create the sedimentation problem. Kordonski et al [24] reported that particle size growth results in quadratic decrease of stability. Magnetic particles were analyzed using a particle size analyzer (GALAI computerized inspection system CIS-1, Particle size analyzer, Israel). Particles were dispersed in de ionized water with few drops of polyelectrolyte stabilizer to prevent the agglomeration of particles. Sodium Hexa Meta Phosphate was used as a medium to disperse the particles in this case. Sonication was also done to disperse the particles thoroughly. Fig-1 and Fig-2 show the particle size distribution of magnetic Electrolytic Iron (EI) particles before and after milling.Fig 1 Probability Volume density Graph for Electrolytic Iron powder before millingFig 2 Probability Volume density Graph for Electrolytic Iron powder after millingResults show that magnetic particle have broad size distribution (3.94 -77.50 microns ) with mean size 39 micron before milling and narrow size distribution (1.11-9.50microns) with mean size 4.27 micron after milling. This size range is recommended size range (1-10 micron) and therefore they are suitable for synthesis of MR fluids. These particles will have relatively lesser tendency to settle down.5.2 Morphology of magnetic particles and gum powdersThe morphology of the particles was studied by scanning electron microscopy (SEM facility S-3400 N, Hitachi Science Systems Japan). The powder sample was prepared by placing very small amount of powder on double sided carbon tape and pressing with the tip of spatula. The tape was then placed on brass stub. Gold plating was done on the samples to make the samples conducive. High vacuum was used and SEM was operated at 6-10 KV.Fig 3 SEM Image of Electrolytic Iron Particles before millingThe SEM image of the electrolytic Iron particles is shown in fig-3 .It shows the characteristic morphology of the particles .The electrolytic iron particles are of dendrite shape with a size distribution. Also they are in well dispersed state. SEM was also done for additives guar gum and xanthan gum. Fig-4 shows the SEM images (×500) obtained.(a) Guar gum (b) Xanthan gumFig 4 SEM Images of Guar gum and Xanthan gum powder5.3 Magnetic properties of particlesMagnetic properties of Iron particles were measured using vibrating sample magnetometer (VSM) technique. The VSM facility used for this purpose is Lakeshore VSM (Model 7410) interfaced with Lakeshore Cryotronics, Inc.VSM software.The Iron powder weight was measured with the accuracy of 0.0001 g by electronic balance (Precisa, Switzerland). The powder sample is pressed in to a small pellet. Small part of pellet (10-100 mg) is weighed and wrapped tightly in a butter paper /Teflon tape to avoid the movement of powder inside the sample holder. The magnetic field up to 20 K Oe was applied and operating frequency was 82 Hz.VSM was also done for costly carbonyl Iron (CI) powder to compare the magnetic properties of economical electrolytic Iron (EI) with costly carbonyl Iron (CI). Figure-5 shows M-H curves of the EI powder and CI powder obtained at room temperature (210C). The VSM results show that saturation magnetization of the electrolytic Iron powder is quite high (204.54emu/g) and approximately is of the same order of saturation magnetization of costly carbonyl Iron powder which is mostly used in synthesis of MR fluids. The saturation magnetization of carbonyl Iron (CI) powder has been found 212.08 emu/g. Slightly lower value of saturation magnetization of electrolytic iron powder in comparison to carbonyl Iron may be due to the fact that the electrolytic Iron used has 95.0 % purity while examined carbonyl Iron has 97-98 % purity. Moreover electrolytic Iron powder has also been milled to reduce the particle size which may also induce some impurities in the powder. Therefore more saturation magnetization will be obtained if EI powder having more purity is used.Coercivity was also determined from VSM data. Measured coercivity for electrolytic Iron is 26 O e and for carbonyl Iron it is 22 Oe. This shows that coercivity of electrolytic iron is only a little higher than the coercivity of carbonyl Iron. Moreover its value is still lower than 50 Oe and therefore can be considered as soft magnetic materials [28]Fig 5 M-H curves for Electrolytic Iron and Carbonyl Iron6. SYNTHESIS ROUTEIn present work three MR fluids are prepared using same base fluid (PAO based synthetic oil) and same magnetic phase i.e. electrolytic Iron (EI) powder but with different additives. These MR fluids are:MR Fluid-1: It has thixotropic agent Polydimethylsiloxane (PDMS) which is silicon based organic polymer and is known for its anti caking properties, Stearic acid as stabilizer additives and an additive package consist of anti wear, anti corrosion, friction modifier and anti oxidant agent.MR Fluid-2: It has green additive guar gum as thixotropic agent and above additive package. MR Fluid-3: It has additive xanthan gum as thixotropic agent and above additive package.6.1Coating of guar gum/xanthan gum on Iron particlesAdditives guar gum /xanthan gum were coated on the milled EI powder. Wu Wei Ping et al [6] reported that additive guar gum will be more effective when it is coated over the iron particles rather than co ball milling it with the Iron powder therefore first approach has been used in this work. For coating guar gum /xanthan gum over Iron particles the measured quantity of guar gum /xanthan gum was added to some quantity of water and mixed by mechanical stirrer for 30 minutes at 500 rpm. Iron powder was then added and mixture was agitated for 30 minutes at 1000 rpm. Ethanol was then added gradually to the mixture which leads to guar gum or xanthan gum forming a coating on the Iron powder. Precipitate was washed with acetone and filtered and dried to remove the water and then milled. These coated particles were used for synthesis. The weight percentage of guar gum /xanthan gum in the MR fluids is 3 %.6.2 Preparation of MR fluidsTo prepare MR fluid, first the appropriate amount of additive package consist of anti wear, anti rust, anti corrosion, friction modifier and anti oxidant agent was added to the measured quantity of base oil and mixed appropriately for 15 minutes by mechanical stirrer. The Iron particles (uncoated in case of MR fluid-1 and coated in case of MR fluid-2 and MR fluid-3) were then directly dispersed with specified volume fraction (0.36) in the above mixture. This mixture was homogenized by agitation of a mechanical stirrer at 1000 RPM for twenty-four hours to make MR fluid homogeneous. Appropriate amounts of PDMS with viscosity100 cSt and Stearic acid were also added in addition to the above additive package to the base oil for synthesis of MR fluid MRF-1. Fig-6 shows the flow chart for synthesis route of Magnetorheological fluid. The compositions of different MR fluids synthesized are given in table-1.Fig 6 Flow chart for Synthesis route of MR fluidsTable -1, Compositions of synthesized MR Fluids7. RESULTS & DISCUSSIONSIn present study three MR fluids have been synthesized using synthetic oil as base fluid, economical electrolytic Iron (with purity > 95.0 %) particles as magnetic phase and different additives. The prepared MR fluids were checked for their magnetic properties, expected MR effect and stability against sedimentation. Results of the study are as follows:7.1 Magnetic properties of uncoated particlesAs discussed earlier, magnetic properties of uncoated EI particles has been determined by VSM. Results indicate that saturation magnetization which is most important factor for producing MR effect i.e. yield stress developed , of low cost electrolytic iron powder (204.54 emu/g) is slightly lower (3.5%) than that of costly Carbonyl iron powder (212.084 emu/g). Similarly measured coercivity of EI powder (26 Oe) is slightly greater than Coercivity of CI powder (24 Oe).Therefore electrolytic Iron (EI) can be used for synthesis of MR fluid to reduce the cost of MR fluid significantly without significant reduction in MR effect.MRF-1 MRF-2 MRF-3 Ingredients Weight % Approx.Vol % Weight % Approx.Volume % Weight % Approx.Volume %Syntheticoil 16 64 15.5 64 15.5 64 Iron Powder81 36 81 36 81 36PDMS 2 ------ ------ ------ ------ ------ Stearicacid0.5 ------ ------ ------ ------ ------Guar gum ---- ------ 3.0 ------ ------ ------ Xanthangum ---- ------ ------ ------ 3.0 ------ Additive package0.5 ------ 0.5 ------ 0.5 ------7.2 Magnetic properties of coated particlesTo observe the effect of the additives coating on the magnetic properties of iron particles the magnetic properties of guar gum and xanthan gum coated particles were also checked by VSM. M-H curves for guar gum and xanthan gum coated particles are shown in figure-7. M-H curves show that saturation magnetization of guar gum coated and xanthan gum coated Iron particles are 198.52 emu/g and 198.14 emu/g respectively. Theses values are slightly lower (3%) than magnetic saturation of uncoated iron particles (204.54 emu/g). Measured Coercivity of these guar gum coated and xanthan gum coated Iron particles are 26 Oe and 28 Oe respectively which are almost same as that of coercivity of uncoated EI particles (26 Oe). This shows that coating of additives guar gum and xanthan gum on Iron particles has negligible effect on magnetic properties of Iron particles and therefore it can be concluded that MR effect produced by MR fluid will not reduce due to additive coating.Fig 7 M-H curves for Guar gum and Xanthan gum coated Electrolytic Iron7.3 MR effect expected (Yield stress developed)Magnetorheological (MR) effect produced by any MR fluid is the measure of its performance and is judged by maximum yield stress developed on application of magnetic field. For a MR fluid of known particle loading, particle size and known viscosity of base fluid the maximum yield stress depends upon the saturation magnetization of the magnetic material.The yield stress developed in MR fluid can be determined by performing magnetorheological measurement using a rheometer with an arrangement to produce magnetic field. Alternatively maximum yield stress developed in any MR fluid can be determined by measuring the saturation magnetization of the magnetic particles using VSM (Vibrating Sample Magnetometer). The relation between maximum obtainable yield stress and saturation magnetization of the magnetic particles has bee reported in the literature [29] as 20524()(3)()5yd s sat M τξφµ⎛⎞=⎜⎟⎝⎠(1)Where, yd τ is the yield stress, 0s M µ is saturation magnetization, φ is the particle volume fraction, 0µ is permeability of the free space and (3) 1.202ξ=(a constant)Table-2 shows the maximum yield stress expected to develop in three MR fluids obtained by using Eqn-1, based on their saturation magnetization values obtained by VSM .The values of yield stresses obtained for MRF-1, MRF-2 and MRF-3are quite high and are comparable to the value of yield stress (108 KPa) obtained for MR fluid using carbonyl Iron powder (2.09 T).Table 2- Expected Yield Stress for synthesized MR FluidsMR Fluid Saturation Magnetization Yield stress (KPa)MRF-1 204.54 emu/g (2.01 T) 99.59MRF-2 198.52 emu/g (1.96 T) 94.70MRF-3 198.14 emu/g (1.95 T) 93.737.4 Sedimentation stabilityPrepared MR fluids were put in graduated cylindrical flasks and observed over period of time for their sedimentation behavior i.e. settling of particles due to gravity. It was found that all three MR fluids remain in a well dispersed and stable state without significant settling of particles for quite long time. This is due to use of different thixotropic additives in MR fluids which reduces the sedimentation by forming weakly bonded structure in the fluid .These three dimensional structures have high apparent viscosity at low shear which prevents particle settling in the suspension. These structures collapse under shear leading to significant reduction in viscosity but reform again on removal of shear. Though all three MR fluids show very good stability against sedimentation but the MR fluids prepared by using additives guar gum and xanthan gum (MR fluid-2 and MR fluid-3) have better stability in comparison to MR fluid prepared using PDMS and Stearic acid (MR fluid-1). Sedimentation stability obtained are in the decreasing order from MRF-3 to MRF-1 i.e. lowest sedimentation tendency among three fluids was observed for MR fluid with xanthan gum and the highest sedimentation tendency was observed for MR fluid with PDMS. The result shows that the coating of guar gum and xanthan gum on iron particles gives better results in comparison to adding PDMS to the base fluid. This shows the utility of low-cost environmental friendly additives guar gum and xanthan gum in synthesis of MR fluids.8. CONCLUSIONS(01) Economical Iron powder produced by electrolytic process has very good magnetic properties, almost as good as costly carbonyl Iron powder which is most commonly used magnetic material for synthesis and therefore electrolytic Iron can be used as magnetic material to reduce the cost of MR fluid considerably without any significant reduction of MR effect produced.(02) Environmental friendly additives like guar gum and xanthan gum have been found more useful in comparison to organic polymer PDMS for preventing sedimentation of the particles in the MR suspension. Lowest sedimentation tendency has been observed for MR fluid with xanthan gum and the highest sedimentation tendency has been observed for MR fluid with PDMS.(03) The effect of coating of additives guar gum and xanthan gum on saturation magnetization and coercivity of Iron particles has almost been negligible. Therefore these additives can be used to improve the sedimentation stability without reducing MR effect produced by the MR fluids.(04) All three synthesized low cost MR fluids show very good stability against sedimentation and large yield stress therefore can be used in different commercial applications for achieving controllability in operation at relatively low cost..ACKNOWLEDGEMENTAuthors would like to thank their institute IIT Bombay for providing all the necessary facilities required for this workREFERENCES[1] Li W H, Du H and Guo NQ , “Finite Element Analysis and Simulation Evaluation of a Magnetorheological Valve”, Int. Journal of Advance Manufacturing Technology, Vol. 21, pp.438–445, 2003[2] Goncalves F D, Koo, J H, and Ahmadin M, “A review of the state of art in magnetorheological fluid technology – Part 1: MR Fluid and MR fluid models”, Shock and Vibration Digest, Vol.38, pp. 203-219, 2006,[3] Sukhwani VK and Hirani H, “Synthesis of a Magnetorheological lubricant” 5th International conference on Industrial tribology, ICIT-06, IISc Bangalore, Nov.30 –Dec. 02, 2006.[4] Fang Chen, Zhao Bin Yuan, Chen Le Sheng, Wu Qing, Liu Nan and Hu Ke Ao , “The effect of the green additive guar gum on the properties of magnetorheological fluid” , Smart materials structure, Vol.14, pp. N1-N5,2005.[5] Foister, Robet T, Iyanger, Vardarajan R, Yurgelvic and Sally M “Low cost MR fluid” US Patent No 6787058 , 2004[6] Wu Wei Ping , Zhao Bin Yuan , Wu Qing , Chen Le sheng and Hu Ke Ao, “The strengthening effect of guar gum on the yield stress of magnetorheological fluid” , Smart materials structure,Vol.15, pp. N94-N98,2006.[7] Carlson J D and Jones Guion J C, “Aqueous magnetorheological materials” U S Patent No 5670077, 1997.[8] Rabinow J, US Patent No 2575360, 1951.[9] Rabinow J, “The magnetic fluid clutch”, AIEE Trans, Vol. 67, pp.1308, 1948[10] Park J H, B yung Doo Chin and Ook Park , “Rheological properties and stabilization of magnetorheological fluid ina water in oil emulsion”, Journal of Colloid and Interface science, Vol. 240, pp 349-354 ,2001.[11] Lim S T, Cho M S, Jang I B and Choi H J, “Magnetrheological characterization of carbonyl iron suspension stabilized by fumed silica”, Journal of magnetism and magnetic materials, Vol. 282, pp .170-173, 2004.[12] Phule P P and Ginder J M “Synthesis and properties of novel magnetorheological fluids having improved stability and redispersibility”, 6th International conference on ER Fluids , MR suspensions and their applications, Yonezawa, Japan, World scientific, pp 445-453,1997.[13] Werely N M, Chaudhuri A , Yoo J H , John S, Kotha S, Suggs A , Radhakrishnan R, Love B J and Sudarshan T S, “Bidisperse magnetorheological fluids using Fe particles at nanometer and micron scale” ,Journal of Intelligent Materials, Systems and Structures, Vol. 17, pp. 393-401,2006.[14] Margida A J , Wiess K D and Carlson J D , “Magnetorheological materials based on Iron alloy particles”, Int. Journal of Modern Phys B, Vol.10, pp. 3335-3341,1996.[15] Phule P P and Jatkar A D, “Synthesis and processing magnetic iron cobalt alloy particles for high strength magnetorheological fluids”, 6th International conference on ER Fluids, MR suspensions and their applications, Yonezawa, Japan, World scientific, pp. 503-510,1997.[16] Foister R.T. Iyanger V R and Yugelevic S M, “Stabilization of magnetorheological fluid suspension using a mixture of organoclays”, US Patent No 6,592,772, 2003.[17] Phule P. “Magnetorheological fluid”, US Patent No 5,985,168, 1999[18] Jang I. B., Kim H B, Lee J Y ,You J L, Choi H J and John M S , “Role of organic coating on carbonyl Iron suspended particles in magnetorheological fluids”, Journal of Applied Phys, Vol.97, pp. 1-3, 2005。
Identification, isolation, synthesis and characterization of impurities
Aurobindo Pharma Ltd.Research Centre1,Bachupally,J.N.T.University2,Kukatpally,Hyderabad,India Identification,isolation,synthesis and characterization of impuritiesof quetiapine fumarateCh.Bharathi1,K.J.Prabahar1,Ch.S.Prasad1,M.Srinivasa Rao1,G.N.Trinadhachary1,V.K.Handa1,R.Dandala1, A.Naidu2Received May28,2007,accepted June18,2007Ramesh Dandala,Senior Vice-President,A.P.L.Research centre,313,Bachupally,Hyderabad500072,India rdandala@Pharmazie63:14–19(2008)doi:10.1691/ph.2008.7174In the process for the preparation of quetiapine fumarate(1),six unknown impurities and one known impurity(intermediate)were identified ranging from0.05–0.15%by reverse-phase HPLC.These impu-rities were isolated from crude samples using reverse-phase preparative HPLC.Based on the spectral data,the impurities were characterized as2-[4-dibenzo[b,f][1,4]thiazepine-11-yl-1-piperazinyl]1-2-etha-nol(impurity I,desethanol quetiapine),11-[(N-formyl)-1-piperazinyl]-dibenzo[b,f][1,4]thiazepine(impur-ity II,N-formyl piperazinyl thiazepine),2-(2-hydroxy ethoxy)ethyl-2-[2-[4-dibenzo[b,f][1,4]thiazepine-11-piperazinyl-1-carboxylate(impurity III,quetiapine carboxylate),11-[4-ethyl-1-piperazinyl]dibenzo[b,f][1,4] thiazepine(impurity IV,ethylpiperazinyl thiazepine),2-[2-(4-dibenzo[b,f][1,4]thiazepin-11-yl-1-piperazi-nyl)ethoxy]1-ethyl ethanol[impurity V,ethyl quetiapine),1,4-bis[dibenzo[b,f][1,4]thiazepine-11-yl]piper-azine[impurity VI,bis(dibenzo)piperazine].The known impurity was an intermediate,11-piperazinyl-dibenzo[b,f][1,4]thiazepine(piperazinyl thiazepine).The structures were established unambiguously by independent synthesis and co-injection in HPLC to confirm the retention times.To the best of our knowledge,these impurities have not been reported before.Structural elucidation of all impurities by spectral data(1H NMR,13C NMR,MS and IR),synthesis and formation of these impurities are dis-cussed in detail.1.IntroductionQuetiapine fumarate(1)is an antipsychotic drug belonging to the chemical class of dibenzothiazepine derivatives.It is used as a hemifumarate salt.Its IUPAC name is2-[2-(4-dibenzo[b,f][1,4]thiazepin-11-yl-1-piperazinyl)ethoxy etha-nol,(E)-2-butenedioate(2:1)salt.A literature survey re-vealed various methods for the synthesis of quetiapine(War-awa et al.2001).We synthesized the compound according to the Scheme(Warawa and Migler1989)with modifications to make it simpler and commercially viable.Its molecular formula is(C21H25N3O2S)2ÁC4H4O4and molecular weight is883amu as fumarate salt and383amu as base.HPLC methods(Saracino et al.2006;Mandrioli et al.2002) and a HPLC-electrospray ionization mass spectrometric method(Zhou et al.2004)were reported for the determi-nation of quetiapine in human plasma.During the preparation of1in the laboratory,six unknown impurities were detected in HPLC along with one known impurity.A comprehensive study was undertaken to iso-late,synthesize and characterize these impurities by spec-troscopic techniques.An impurity profile study is neces-sary for any final product to identify and characterize all the unknown impurities that are present in level of>0.1%. (ICH guideline,2005).The present study describes the isolation,synthesis and characterization of related impuri-ties of1.2.Investigations,results and discussion2.1.Detection and identificationQuetiapine fumarate was analysed by HPLC under the ana-lytical conditions described below.The chromatogram dis-played seven peaks at relative retention times compared to quetiapine at0.80,0.94,1.08,1.17,1.65,1.67and2.28. The LC-MS analysis showed six peaks having m/z values 339,323,427,323,411and504.They were isolated from crude samples of quetiapine by preparative HPLC.All the compounds were co-injected with quetiapine fumarate sam-ple in HPLC to confirm the retention times.HPLC chroma-togram of quetiapine fumarate spiked with all impurities is shown in the Fig.Synthesis and structural elucidation of these impurities are discussed in the following sections. Quetiapine fumarate was synthesized as shown in the Scheme,impurities I–VI were synthesized as described in the Experimental section and characterized.2.2.Characterization and origin of impurities2.2.1.Impurity IThe ESI mass spectrum of impurity I displayed the proto-nated molecular ion at m/z340.Therefore the molecular weight of this impurity was considered as339which was less by44amu than quetiapine.The odd molecular weightindicated the presence of odd number of nitrogens which in turn indicated the intactness of dibenzo[b ,f ][1,4]thia-zepine piperazinyl ring in this impurity structure.Pre-sence of broad signals at 3.70ppm (4H)and 4.34ppm (4H)in 1H NMR spectrum was attributed to piperazinyl ring.Two triplets were observed in impurity spectrum at 3.39ppm and 3.89ppm corresponding to 2ÂCH 2sig-nals instead of 4ÂCH 2groups present in the side chain of quetiapine.In 13C NMR two CH 2signals were ob-served at 61.1ppm and 73.1ppm instead of four CH 2signals.Based on the above spectral data observations,the structure of impurity I was characterized as 2-[4-di-benzo[b ,f ][1,4]thiazepine-11-yl-1-piperazinyl]l-2-ethanol (desethanol quetiapine).2-[2-Chloroethoxy]ethanol is a raw material for the pre-paration of quetiapine.2-Chloroethanol may be present as an impurity in this raw material.During the alkylation step in the preparation of quetiapine,alkylation of piper-azinyl thiazepine with the impurity,2-chloro ethanol leads to the formation of impurity I (desethanol quetiapine).2.2.2.Impurity IIESI mass spectrum of impurity II exhibited a protonated molecular ion peak at m/z 324,indicating the molecular weight as 323.The molecular weight of impurity II was 28amu more than that of the intermediate,4-piperazinyl di-benzo[b ,f ][1,4]thiazepine (2),m/z 295.MS fragmentation peaks were observed at m/z 296and 251.1H NMR spec-trum of this impurity showed signals similar to those of 2and in addition one new signal was observed at 8.13ppm integrated to one proton which was not exchangeable.This data suggested the attachment of a ––CHO group on piper-azine NH.Based on the spectral data,the structure of im-purity II was characterized as 11-[(N -formyl)-1-piperazi-nyl]-dibenzo[b ,f ][1,4]thiazepine (N -formyl piperazinylSNOHi.Piperazine /Toluene SNN N H i.2-(2-C hloroethoxy)ethanol ii.Na 2CO 3/NaI /NMP /TolueneSNNNO.2HClPiperazinyl thiazepine (2)SNNNOOHCOOHHOOC.Fumaric acid /Ethanol212345678910111213141516171819202122232223Quetiapine fumarate (1)SchemeSN NNOH34567891011121314151618192021Impurity I (Desethanol quetiapine)SN NNCHO56789101112131415161819202122Impurity II (N-Formyl piperazinyl thiazepine)221234N SNNOOOHO567891011121314151618192021Impurity III (Quetiapine carboxylate)3456789101112131415161718192021SN NNCH 3Impurity IV (N-Ethylpiperazinyl thiazepine)56789101112131415161718192021SNN NSN 9'10'11'12'13'14'15'16'18'19'20'21'Impurity VI (Bis (dibenzo)piperazine)N SNNOOCH 2CH 312345678910111213141516181920212223Impurity V (Ethyl quetiapine)thiazepine).This impurity arises when the alkylation of pi-perazinyl thiazepine with2-chloroethoxyethanol is carried out in N,N-dimethyl formamide.2.2.3.Impurity IIIESI mass spectrum of impurity III displayed a protonated molecular ion peak at m/z428,indicating the molecular weight of the compound as427which is44amu more than quetiapine.MS fragmentation peaks were observed at m/z,384,340and324.After thorough study of1H NMR and13C NMR spectra of this impurity,it was found to be as carboxy group attachment.It was observed from the1H NMR spectrum that there was no change in the number of protons compared to quetiapine and the signal correspond-ing to methylene protons attached to piperazine ring has shifted downfield from3.50ppm to4.14ppm.An addi-tional signal was observed at161.5ppm in the13C NMR spectrum and it was confirmed as quaternary carbon from DEPT experiment.From the above spectral data,the struc-ture of impurity III was characterized as2-(2-hydroxy ethoxy)ethyl-2-[2-[4-dibenzo[b,f][1,4]thiazepine-11-piper-azinyl-1-carboxylate(quetiapine carboxylate).This impurity arises when the alkylation of piperazinyl thiazepine is car-ried out in the presence of sodium carbonate(quetiapine carboxylate).2.2.4.Impurity IVESI mass spectrum of this impurity exhibited a protonated molecular ion peak at m/z324indicated the molecular weight of this impurity as323.Molecular weight of this impurity is28amu more than that of11-piperazinyl thi-azepine(intermediate).This odd molecular weight indicated the presence of odd number of nitrogen atoms which in turn indicated the intactness of piperazinyl thiazepine ring. MS fragmentation peaks were observed at296and253 amu.The signals corresponding to––O––CH2––CH2––OH group of quetiapine molecule were absent in impurity IV. Additionally,1H NMR spectrum of this impurity showed aFig.:LC-Chromatogram of Quetiapine fumarate samplespiked with impuritiesTable1:Comparative1H NMR assignments for quetiapine fumarate and its impuritiesPosition a Quetiapine fumarated(ppm),multiplicity Impurity-I d(ppm),multiplicityImpurity-II d(ppm),multiplicityImpurity-III d(ppm),multiplicityImpurity-IV d(ppm),multiplicityImpurity-V d(ppm),multiplicityImpurity-VI d(ppm),multiplicity1 3.43(t,2H)–––– 3.45(t,2H)–– 3.44(m,2H)––2 3.49(t,2H)–––– 3.47(t,2H)–– 3.52(m,2H)––3 3.55(t,2H) 3.82(t,2H)–– 3.61(t,2H) 1.29(t,3H) 3.56(t,2H)––4 2.52(t,2H) 3.27(t,2H)–– 4.14(t,2H) 3.18(t,2H) 3.40(t,2H)––5 6 7 82.50–2.54(brm,4H)and3.43–3.48(brm,4H)3.48and3.76(2brs,8H)3.42–3.73(m,8H)3.42and3.48(2brs,8H)3.20–3.75(brm,8H)3.20–3.75(brm,8H)3.03.65(brm,8H)9––––––––––––––10––––––––––––––117.55(m,1H)7.68(m,1H)7.55(d,1H)7.55(d,1H)7.68(m,1H)7.69(m,1H)7.56(m,2H)12 137.40(m,2H)7.60(m,2H)7.34–7.36(m,2H)7.44(m,2H)7.52–7.60(m,2H)7.52–7.60(m,2H)7.44–7.48(m,4H)147.45(m,1H)7.62(m,1H)7.42(d,1H)7.47(m,1H)7.62(m,1H)7.62(m,1H)7.46(m,2H) 15––––––––––––––16––––––––––––––177.37(dd,1H)7.54(dd,1H)7.40(dd,1H)7.38(dd,1H)7.54(dd,1H)7.54(dd,1H)7.38(dd,2H) 187.18(ddd,1H)7.35(brm,1H)7.23(ddd,1H)7.18(ddd,1H)7.35(brm,1H)7.35(brm,1H)7.20(ddd,2H)19 6.88(ddd,1H)7.15(ddd,1H) 6.95(ddd,1H) 6.91(ddd,1H)7.16(brd,1H)7.16(brd,1H) 6.90(ddd,2H)20 6.99(dd,1H)7.35(brm,1H)7.10(dd,1H)7.01(dd,1H)7.35(brm,1H)7.35(brm,1H)7.01(dd,2H) 21––––––––––––––22 6.62(s,2H)––8.13(s,1H)–––– 3.89(brm,2H)––23–––––––––– 1.08(t,3H)––s,singlet;d,doublet;dd,doublet of a doublet;ddd,doublet of a double doublet;m,multiplet;brs,broad singlet;brm,broad multiplet;q,quartet;t,tripleta Refor Scheme for numbering of quetiapine fumarateORIGINAL ARTICLEST a b l e 2:C o m p a r a t i v e13C N M R a n dDE P T a s s i g n m e n t s f o r q u e t i a p i n e f u m a r a t e a n d i t s i m p u r i t i e sP o s i t i o n a Q u e t i a p i n e f u m a r a t eI m p u r i t y -II m p u r i t y -I II m p u r i t y -I I II m p u r i t y -I VI m p u r i t y -VI m p u r i t y -V I13C d (p p m )DE P T13C d (p p m )DE P T13C d (p p m )DE P T13C d (p p m )DE P T13C d (p p m )DE P T13C d (p p m )DE P T13C d (p p m )DE P T161.1C H 2––––––––61.1C H 2––––66.4C H 2––––273.1C H 2––––––––73.1C H 2––––70.4C H 2––––368.7C H 258.6C H 2––––68.8C H 29.6C H 369.7C H 2––––457.8C H 256.1C H 2––––66.0C H 251.3C H 255.6C H 2––––567846.7a n d 53.44ÂC H 246.0,51.3a n d 51.64ÂC H 246.3,51.0a n d 51.64ÂC H 244.04ÂC H 246.4,50.0a n d 50.34ÂC H 245.751.4a n d 51.84ÂC H 245.5,47.6a n d 50.54ÂC H 29160.9––162.1––162.0––161.0––162.3––161.8––163.1a n d163.2––10139.6––136.5––140.0––139.6––140.6––140.3––137.8a n d137.9––11132.8C H 134.0C H134.0C H 132.8C H 134.1C H 133.5C H133.6a n d134.02ÂC H12129.8C H 130.2C H130.3C H 129.9C H 130.3C H 130.6C H130.2a n d130.44ÂC H13129.9C H 130.7C H 130.7C H 130.0C H 130.8C H131.3C H131.0C H14132.1C H 133.3C H 133.3C H 132.3C H 133.4C H 133.3C H 132.8C H 15128.1––128.0––––––128.1––127.7––127.5––129.0––16134.3––134.2––––––134.3––135.8––131.7––135.4––17132.9C H 135.1C H134.0C H 133.9C H 135.3C H 133.9C H134.7a n d134.92ÂC H18130.1C H 131.9C H 132.1C H130.2C H 132.0C H131.7C H 132.22ÂC H 19123.5C H 126.1C H126.4C H 123.8C H126.2C H126.6C H126.9a n d127.12ÂC H20126.0C H 129.5C H130.3C H 125.8C H129.7C H130.4C H128.9a n d129.22ÂC H21149.4––142.0––143.0––149.4––140.6––143.5––140.8––22135.2––––––162.3C H 156.0––––––65.5C H 2––––23167.4––––––––––––––––––9.6C H 3––––aR e f e r S c h e m e f o r n u m b e r i n g o f q u e t i a p i n e f u m a r a t e––CH3triplet at1.29ppm and––CH2quartet at3.18ppmcorresponding to ethyl group.This was supported by thepresence of methyl and methylene signals at9.0ppm and53.0ppm in13C NMR spectrum.Based on the above spectral data,the structure of impurity IV was character-ized as11-[4-ethyl-1-piperazinyl]dibenzo[b,f][1,4]thiaze-pine(N-ethyl-11-piperazinyl thiazepine).Ethanolic hydro-chloride was used to isolate piperazinyl thiazepine asdihydrochloride salt.Ethanolic hydrochloride may containethyl chloride which may alkylate piperazinyl thiazepineto yield this impurity(N-ethyl piperazinyl thiazepine).2.2.5.Impurity VESI mass spectrum of this impurity displayed a protonatedmolecular ion peak at m/z412indicating the molecularweight of this impurity as411which was28amu higher than that of quetiapine.Molecular weight suggested thatthe impurity was formed due to the substitution of ethylgroup on quetiapine.MS fragmentation peak was observedat324amu.In1H NMR spectrum of this impurity all the signals corresponding to quetiapine structure were presentand in addition methyl signal was observed as triplet at1.08ppm and methylene signal as quartet at3.53ppm.In 13C NMR spectrum the corresponding signals were ob-served at9.6ppm and65.5ppm.Based on the abovespectral data,the structure of impurity V was determinedas2-[2-(4-dibenzo[b,f][1,4]thiazepin-11-yl-1-piperazinyl)ethoxy]1-ethyl ethanol(ethyl quetiapine).2-[2-Chloro-ethoxy]ethoxy ethane may be an impurity present in theraw material,2-[2-chloroethoxy]ethanol.This impurityarises during alkylation of piperazinyl thiazepine with2-[2-chloroethoxy]ethoxy ethane(ethyl quetiapine).2.2.6.Impurity VIESI mass spectrum impurity VI exhibited a protonatedmolecular ion peak at m/z505,indicating the molecularweight of impurity as504.The even molecular weight suggested that the even number of nitrogens are present in this impurity.The molecular weight of this impurity was 209amu higher than that of piperazinyl thiazepine(quetia-pine intermediate,m/z,295).The difference molecular weight209amu corresponding to the dibenzo[b,f][1,4] thiazepine group.These mass values suggested that an-other dibenzo[b,f][1,4]thiazepine group was attached to piperazinyl NH of the quetiapine intermediate2.Sixteen aryl protons were present in the1H NMR spectrum,corre-sponding to two dibenzothiazepine groups and eight pro-tons were observed at3.4ppm,corresponding to one pi-perazine group.In13C NMR spectrum,the number of carbon signals in aryl region were doubled,supported the pre-sence of two dibenzo thiazepine groups.Based on the above spectral data,the structure of impurity VI was character-ized as1,4-bis[dibenzo[b,f][1,4]thiazepine-11-yl]piper-azine(bis(dibenzo)piperazine).During the preparation of piperazinyl thiazepine intermediate from11-chloro-diben-zo[b,f][1,4]thiazepine and piperazine,alkylation of both the nitrogen atoms of piperazine leads to the formation of bis(dibenzo)thiazepine.2.2.7.Spectroscopic dataThe1H and13C NMR chemical shift values of quetiapine fumarate and all impurities are presented in Tables1and2 FT-IR spectral data are given in Table3.3.Experimental3.1.Synthesis of the impuritiesThe investigated samples of quetiapine bulk drug and crude samples were synthesized in APL Research Centre(a unit of Aurobindo Pharma Ltd., Hyderabad,India).All impurities were isolated from crude samples by pre-parative HPLC.All the reagents used for analysis were procured from Merck(India)limited.3.1.1.Synthesis of impurity I,desethanol quetiapine hydrochloride11-Piperazinylthiazepine dihydrochloride(5g,0.0136mol)reacted with 2-chloro ethanol(1.2g,0.0149mol)in the presence of sodium carbonate (8.7g,0.0821mol),1-methyl-2-pyrrolidine(8ml,0.0771mol)and a cata-lytic amount of sodium iodide(0.05g,0.0003mol)in toluene(40ml)at 95–100 C for about24h and the reaction was monitored by TLC.Upon completion of reaction the reaction mass was washed with water (2Â25ml).The organic layer was concentrated completely under reduced pressure at50–55 C.The residue was dissolved in ethanol(40ml)and pH of the reaction mass was adjusted to$2.0with ethanolic HCl(10ml, $20%w/w).The precipitated product was filtered,washed with isopropy-lether(15ml)and dried at55–60 C to yield4.7g of desethanol quetia-pine.3.1.2.Synthesis of impurity II,N-formyl piperazinyl thiazepine11-Piperazinyl thiazepine dihydrochloride(10g,0.027mol),sodium carbo-nate(17.25g,0.163mol),sodium iodide(0.1g,0.0006mol)and2-chloro-Table3:FT-IR spectral data for quetiapine fumarate and its impuritiespound IR(KBr)absorption bands,(cmÀ1)1Quetiapine fumarate3320(m)OH stretch,3074,3014(w)aryl CH stretch,2946,2929,2898,2870(m)aliphatic CHstretch,1600,1573(s)aryl C¼C stretch and C¼N stretch,1414(s)CH2bend,795,768(m)aryl CHout-of-plane bend.2Impurity-I3060,3004(w)aryl CH stretch,2951,2884(m)aliphatic CH stretch,1622,1572(s)aryl C¼C stretchand C¼N stretch,1443(s)CH2bend,779,767(m)aryl CH out-of-plane bend.3Impurity-II3070(w)aryl CH stretch,2950,2890(m)aliphatic CH stretch,1620,1570(s)aryl C¼C stretch andC¼N stretch,1440(s)CH2bend,770,765(m)aryl CH out-of-plane bend.4Impurity-III3065(w)aryl CH stretch,2975,2886(m)aliphatic CH stretch,1620,1572(s)aryl C¼C stretch andC¼N stretch,1446(s)CH2bend,780,755(m)aryl CH out-of-plane bend.5Impurity-IV3063(w)aryl CH stretch,2979,2895(m)aliphatic CH stretch,1627,1573(s)aryl C¼C stretch andC¼N stretch,1430(s)CH2bend,782,767(m)aryl CH out-of-plane bend.6Impurity-V3070(w)aryl CH stretch,2923,2855(m)aliphatic CH stretch,.1621,1574(s)aryl C¼C stretch andC¼N stretch,1455(s)CH2bend,772,751(m)aryl CH out-of-plane bend.7Impurity-VI3052(m)aryl CH stretch,2989,2978,2953,2844(w)aliphatic CH stretch,1602,1575(s)aryl C¼Cstretch and C¼N stretch,1397(s)CH2bend,1245(s)C-N strech,1005,759,738(s)aryl CHout-of-plane bend.w–weak,s–strong,m–mediumethoxy ethanol(3.8g,0.03mol)were added to N,N-dimethylformamide (25ml)at room temperature.The reaction mass was heated to$100 C and stirred for8h while monitoring the process by HPLC.There after,the reaction mass was cooled to room temperature and poured into water (200ml).The product was extracted with ethyl acetate(2Â75ml)and the organic extract was washed with water(2Â80ml).The organic layer was concentrated completely under the reduced pressure at50–55 C.The resi-due contains$5%of this impurity which was isolated by preparative HPLC.3.1.3.Impurity III,quetiapine carboxylateImpurity III was isolated from mother liquors obtained during the prepara-tion of compound1.3.1.4.Synthesis of impurity IV,N-ethyl-11-piperazinyl thiazepine11-Piperazinyl thiazepine dihydrochloride(5g,0.0136mol)reacted with ethyl bromide(2.4g,0.020mol)in the presence of sodium carbonate (8.7g,0.0821mol)and dimethylformamide(15ml)at room temperature for2h and the reaction was monitored by TLC.The reaction mass was poured into water(200ml)and extracted with ethylacetate(2Â80ml). The organic layer was washed with water(2Â50ml)and concentrated completely under reduced pressure at50–55 C.The resulting residue was dissolved in ethanol(40ml)and treated with ethanolic HCl(10ml,20% w/w)at pH2.0.Isopropylether(20ml)was added dropwise to isolate the product.The product was stirred at room temperature for1h.The product was filtered,washed with isopropylether(5.0ml)and dried at55–60 C to yield4.2g of title compound.3.1.5.Impurity V,synthesis of ethyl quetiapineEthyl bromide(5.3g,0.0486mol)was added dropwise to a mixture of quetiapine fumarate(10g)and sodium hydroxide(2.9g,0.073mol)in dimethylformamide(50ml)at15–17 C.The reaction mass was stirred at15–20 C for8h and the reaction mass was monitored by HPLC until completion.Water(250ml)was added to the reaction mass and extracted with methylene chloride(2Â100ml).The organic layer was washed with water(2Â50ml)and concentrated under reduced pressure.The re-sidue was dissolved in ethanol(50ml)and ethanolic HCl(20ml,$20% w/w)was added dropwise.The precipitated product was stirred for1h. The product was filtered,washed with ethanol(5ml)and dried at40–45 C to yield6g of product containing$91%of the desired product by HPLC.3.1.6.Impurity VI,synthesis of bis(dibenzo)thiazepine11-Chloro-dibenzo[b,f][1,4]thiazepine(20.5g,0.0835mol)was added in small portions to a stirred mixture of piperazine(14.4g,0.167mol)in to-luene(160ml)at$50 C.The reaction was heated to$100 C,stirred for 4h and the reaction was monitored by HPLC until disappearance of start-ing material.The reaction mass was cooled to$20 C and filtered the salts.The toluene filtrate was washed with water(4Â100ml).The organic layer was concentrated completely under reduced pressure at50–55 C. The residue contains$12%of bis(dibenzo)thiazepine impurity which was isolated by preparative HPLC.3.2.High performance liquid chromatographyA Waters Alliance2695separation module equipped with2996photodiode array detector with Empower pro data handling system[Waters corpora-tion,MILFORD,MA01757,USA]was used.The analysis was carried out on YMC Pack-C8,150mm long,4.6mm i.d.,5m m particle diameter column.Mobile phase A was a mixture of phosphate buffer and acetonitrile in the ratio of90:10v/v,adjusted to pH6.7Æ0.05with dilute orthopho-sphoric acid solution(phosphate buffer was prepared by dissolving0.77g of disodium hydrogen orthophosphate(anhydrous)and0.57g of potassium dihydrogen orthophosphate in1000ml of water).Mobile phaseB was acetonitrile.UV detection was carried out at225nm and flow rate was kept at1.5ml/min.Column oven temperature was set at45C and data acquired for45min.Pump mode was gradient and the program was as follows,Time(min)/A(v/v):B(v/v);T0.01/80:20,T15.0/70:30,T25.0/60:40, T30.0/35:65,T35.0/30:70,T45.0/25:75,T50.0/80:20,T60.0/80:20.3.3.Preparative liquid chromatographyA Shimadzu LC-8A preparative liquid chromatograph equipped with SPD-10A VP,UV-Vis detector[Shimadzu corporation,Analytical Instruments Division,Kyoto,Japan]was used.Hyperprep HS C18(250mm longÂ21.2mm i.d.)preparative column packed with10m m particle size was em-ployed for isolation of impurities.The mobile phase consisted of(A) 0.1M ammonium acetate solution and(B)acetonitrile.Flow rate was set at20ml/min and UV detection was carried out at225nm.The gradient program was as follows,time(min)/A(v/v):B(v/v);T0.01/98:2,T20.0/90:10, T35.0/80:20,T50.0/70:30,T60.0/60:40,T75.0/50:50,T90.0/25:75.3.4.LC-MS/MS analysisLC-MS/MS analysis was carried out using a Perkin Elmer triple quadru-pole mass spectrometer(API2000,PE SCIEX)coupled with a Shimadzu HPLC equipped with SPD10AT VP UV-VIS detector and LC10AT VP pumps.Analyst software was used for data acquisition and data processing. The turbo ion spray voltage was maintained at5.5kv and temperature was set at375 C.The auxillary gas and curtain gas used was high pure nitro-gen.Zero air was used as nebulizer gas.LC-MS spectra were acquired from m/z100–1000in0.1amu steps with2.0s dwell time.The analysis was carried out using Hypersil BDS C18,150Â4.6mm column with5m m par-ticle dia.Mobile phase consisted of(A)0.01M ammonium acetate and(B) 1:1mixture of acetonitrile and methanol.UV detection was carried out at 225nm and flow rate was kept at1.5ml/min.Data acquisition time was 50min.The gradient program was as follows,Time(min)/A(v/v):B(v/v); T0.01/75:25,T5.0/75:25,T35.0/50:50,T40.0/15:85,T50.0/15:85.3.5.NMR SpectroscopyThe1H NMR,13C NMR(proton decoupled)and DEPT spectra were re-corded on Bruker300MHz spectrometer using DMSO-d6as solvent and tetramethylsilane(TMS)as internal standard.3.6.Mass spectrometryMass spectra were recorded on a Perkin Elmer PE SCIEX-API2000mass spectrometer equipped with a Turboionspray interface at375 C.Detection of ions was performed in electrospray ionisation,positive ion mode.3.7.FT-IR SpectroscopyFT-IR spectra were recorded as KBr pellet on a Perkin-Elmer instrument model––spectrum one.3.8.Isolation of impurities by preparative HPLCAll impurities were isolated by preparative HPLC from crude samples by using the conditions described above.Fractions collected were analyzed by analytical HPLC as per the conditions mentioned above.Fractions of >90%were pooled together,concentrated on Rotavapor to remove acetoni-trile.The concentrated fractions were passed through the preparative col-umn using water:acetonitrile(50:50)as mobile phase to remove the buf-fers used for isolation.Again the eluate was concentrated in a Rotavapor to remove acetonitrile.The aqueous solutions were lyophilized using freeze dryer(Virtis advantage2XL).Acknowledgements:The authors gratefully acknowledge the management of Aurobindo Pharma Limited,for allowing us to carry out the present work.The authors are also thankful to the colleagues of Analytical Re-search Department(ARD)and Chemical Research Department(CRD)for their co-operation.ReferencesICH Guideline Q3A(R2).Impurities in new drug substances,25October 2006.Mandrioli R,Fanali S,Ferranti A,Raggi MA(2002)HPLC analysis of the novel antipsychotic drug quetiapine in human plasma.J Pharm Biomed Anal30:969–977.Saracino MA,Mercolini L,Flotta G,Albers LJ,Merli R,Raggi MA (2006)Simulataneous determination of fluvoxamine isomers and que-tiapine in human plasma by means of HPLC.J Chromatogr843:227–233.Warawa EJ,Migler BM(1989)Novel dibenzothiazepine patent4,879,288.Warawa EJ,Migler BM,Ohnmacht CJ,Needles AL,Gatos GC,McLaren FM, Nelson CL,Kirkland KM(2001)Behavioral approach to nondyskinetic dopamine antagonists:identification of seroquel.J Med Chem44:372–389.Zhou Z,Li X,Li K,Xie Z,Cheng Z,Peng W,Wang F,Zhu R,Li H (2004)Simultaneous determination of clozapine,olanzapine,risperidone and quetiapine in plasma by HPLC-electrospray ionization mass spectro-metry.J Chromatogr802:257–262.。
1997-JPC-(CdSe)ZnS Core-Shell Quantum Dots Synthesi_1`s and Characterization of a Size Series of
(CdSe)ZnS Core-Shell Quantum Dots:Synthesis and Characterization of a Size Series of Highly Luminescent NanocrystallitesB.O.Dabbousi,†J.Rodriguez-Viejo,‡F.V.Mikulec,†J.R.Heine,§H.Mattoussi,§R.Ober,⊥K.F.Jensen,‡,§and M.G.Bawendi*,†Departments of Chemistry,Chemical Engineering,and Materials Science and Engineering,Massachusetts Institute of Technology,77Massachusetts A V e.,Cambridge,Massachusetts02139,andLaboratoire de Physique de la Matie`re Condense´e,Colle`ge de France,11Place Marcellin Berthelot,75231Paris Cedex05,FranceRecei V ed:March27,1997;In Final Form:June26,1997XWe report a synthesis of highly luminescent(CdSe)ZnS composite quantum dots with CdSe cores ranging indiameter from23to55Å.The narrow photoluminescence(fwhm e40nm)from these composite dotsspans most of the visible spectrum from blue through red with quantum yields of30-50%at room temperature.We characterize these materials using a range of optical and structural techniques.Optical absorption andphotoluminescence spectroscopies probe the effect of ZnS passivation on the electronic structure of the dots.We use a combination of wavelength dispersive X-ray spectroscopy,X-ray photoelectron spectroscopy,smalland wide angle X-ray scattering,and transmission electron microscopy to analyze the composite dots anddetermine their chemical composition,average size,size distribution,shape,and internal ing asimple effective mass theory,we model the energy shift for the first excited state for(CdSe)ZnS and(CdSe)-CdS dots with varying shell thickness.Finally,we characterize the growth of ZnS on CdSe cores as locallyepitaxial and determine how the structure of the ZnS shell influences the photoluminescence properties.I.IntroductionSemiconductor nanocrystallites(quantum dots)whose radii are smaller than the bulk exciton Bohr radius constitute a class of materials intermediate between molecular and bulk forms of matter.1Quantum confinement of both the electron and hole in all three dimensions leads to an increase in the effective band gap of the material with decreasing crystallite size.Conse-quently,both the optical absorption and emission of quantum dots shift to the blue(higher energies)as the size of the dots gets smaller.Although nanocrystallites have not yet completed their evolution into bulk solids,structural studies indicate that they retain the bulk crystal structure and lattice parameter.2 Recent advances in the synthesis of highly monodisperse nanocrystallites3-5have paved the way for numerous spectro-scopic studies6-11assigning the quantum dot electronic states and mapping out their evolution as a function of size.Core-shell type composite quantum dots exhibit novel properties making them attractive from both an experimental and a practical point of view.12-19Overcoating nanocrystallites with higher band gap inorganic materials has been shown to improve the photoluminescence quantum yields by passivating surface nonradiative recombination sites.Particles passivated with inorganic shell structures are more robust than organically passivated dots and have greater tolerance to processing conditions necessary for incorporation into solid state structures. Some examples of core-shell quantum dot structures reported earlier include CdS on CdSe and CdSe on CdS,12ZnS grown on CdS,13ZnS on CdSe and the inverse structure,14CdS/HgS/ CdS quantum dot quantum wells,15ZnSe overcoated CdSe,16 and SiO2on Si.17,18Recently,Hines and Guyot-Sionnest reported making(CdSe)ZnS nanocrystallites whose room tem-perature fluorescence quantum yield was50%.19This paper describes the synthesis and characterization of a series of room-temperature high quantum yield(30%-50%) core-shell(CdSe)ZnS nanocrystallites with narrow band edge luminescence spanning most of the visible spectrum from470 to625nm.These particles are produced using a two-step synthesis that is a modification of the methods of Danek et al.16 and Hines et al.19ZnS overcoated dots are characterized spectroscopically and structurally using a variety of techniques. The optical absorption and photoluminescence spectra of the composite dots are measured,and the lowest energy optical transition is modeled using a simplified theoretical approach. Wavelength dispersive X-ray spectroscopy and X-ray photo-electron spectroscopy are used to determine the elemental and spatial composition of ZnS overcoated dots.Small-angle X-ray scattering in solution and in polymer films and high-resolution transmission electron microscopy measurements help to deter-mine the size,shape,and size distribution of the composite dots. Finally,the internal structure of the composite quantum dots and the lattice parameters of the core and shell are determined using wide-angle X-ray scattering.In addition to having higher efficiencies,ZnS overcoated particles are more robust than organically passivated dots and potentially more useful for optoelectronic device structures. Electroluminescent devices(LED’s)incorporating(CdSe)ZnS dots into heterostructure organic/semiconductor nanocrystallite light-emitting devices may show greater stability.20Thin films incorporating(CdSe)ZnS dots into a matrix of ZnS using electrospray organometallic chemical vapor deposition(ES-OMCVD)demonstrate more than2orders of magnitude improvement in the PL quantum yields(∼10%)relative to identical structures based on bare CdSe dots.21In addition,these structures exhibit cathodoluminescence21upon excitation with high-energy electrons and may potentially be useful in the*To whom correspondence should be addressed.†Department of Chemistry,MIT.‡Department of Chemical Engineering,MIT.§Department of Materials Science and Engineering,MIT.⊥Colle`ge de France.X Abstract published in Ad V ance ACS Abstracts,September1,1997.9463J.Phys.Chem.B1997,101,9463-9475S1089-5647(97)01091-2CCC:$14.00©1997American Chemical Societyproduction of alternating current thin film electroluminescent devices(ACTFELD).II.Experimental SectionMaterials.Trioctylphosphine oxide(TOPO,90%pure)and trioctylphosphine(TOP,95%pure)were obtained from Strem and Fluka,respectively.Dimethylcadmium(CdMe2)and di-ethylzinc(ZnEt2)were purchased from Alfa and Fluka,respec-tively,and both materials were filtered separately through a0.2µm filter in an inert atmosphere box.Trioctylphosphine selenide was prepared by dissolving0.1mol of Se shot in100mL of TOP,thus producing a1M solution of TOPSe.Hexamethyl-disilathiane((TMS)2S)was used as purchased from Aldrich. HPLC grade n-hexane,methanol,pyridine,and1-butanol were purchased from EM Sciences.Synthesis of Composite Quantum Dots.(CdSe)ZnS.Nearly monodisperse CdSe quantum dots ranging from23to55Åin diameter were synthesized via the pyrolysis of the organome-tallic precursors,dimethylcadmium and trioctylphosphine se-lenide,in a coordinating solvent,trioctylphosphine oxide (TOPO),as described previously.3The precursors were injected at temperatures ranging from340to360°C,and the initially formed small(d)23Å)dots were grown at temperatures between290and300°C.The dots were collected as powders using size-selective precipitation3with methanol and then redispersed in hexane.A flask containing5g of TOPO was heated to190°C under vacuum for several hours and then cooled to60°C after which 0.5mL of trioctylphosphine(TOP)was added.Roughly0.1-0.4µmol of CdSe dots dispersed in hexane was transferred into the reaction vessel via syringe,and the solvent was pumped off.Diethylzinc(ZnEt2)and hexamethyldisilathiane((TMS)2S) were used as the Zn and S precursors.The amounts of Zn and S precursors needed to grow a ZnS shell of desired thickness for each CdSe sample were determined as follows:First,the average radius of the CdSe dots was estimated from TEM or SAXS measurements.Next,the ratio of ZnS to CdSe necessary to form a shell of desired thickness was calculated based on the ratio of the shell volume to that of the core assuming a spherical core and shell and taking into account the bulk lattice parameters of CdSe and ZnS.For larger particles the ratio of Zn to Cd necessary to achieve the same thickness shell is less than for the smaller dots.The actual amount of ZnS that grows onto the CdSe cores was generally less than the amount added due to incomplete reaction of the precursors and to loss of some material on the walls of the flask during the addition. Equimolar amounts of the precursors were dissolved in2-4 mL of TOP inside an inert atmosphere glovebox.The precursor solution was loaded into a syringe and transferred to an addition funnel attached to the reaction flask.The reaction flask containing CdSe dots dispersed in TOPO and TOP was heated under an atmosphere of N2.The temperature at which the precursors were added ranged from140°C for23Ådiameter dots to220°C for55Ådiameter dots.22When the desired temperature was reached,the Zn and S precursors were added dropwise to the vigorously stirring reaction mixture over a period of5-10min.After the addition was complete,the mixture was cooled to 90°C and left stirring for several hours.A5mL aliquot of butanol was added to the mixture to prevent the TOPO from solidifying upon cooling to room temperature.The overcoated particles were stored in their growth solution to ensure that the surface of the dots remained passivated with TOPO.They were later recovered in powder form by precipitating with methanol and redispersed into a variety of solvents including hexane, chloroform,toluene,THF,and pyridine.(CdSe)CdS.Cadmium selenide nanocrystallites with diam-eters between33.5and35Åwere overcoated with CdS to varying thickness using the same basic procedure as that outlined for the ZnS overcoating.The CdS precursors used were Me2-Cd and(TMS)2S.The precursor solution was dripped into the reaction vessel containing the dots at a temperature of180°C and a rate of∼1mL/min.The solution became noticeably darker as the overcoat precursors were added.Absorption spectra taken just after addition of precursors showed a significant shift in the absorption peak to the red.To store these samples,it was necessary to add equal amounts of hexane and butanol since the butanol by itself appeared to flocculate the particles.Optical Characterization.UV-vis absorption spectra were acquired on an HP8452diode array spectrophotometer.Dilute solutions of dots in hexane were placed in1cm quartz cuvettes, and their absorption and corresponding fluorescence were measured.The photoluminescence spectra were taken on a SPEX Fluorolog-2spectrometer in front face collection mode. The room-temperature quantum yields were determined by comparing the integrated emission of the dots in solution to the emission of a solution of rhodamine590or rhodamine640 of identical optical density at the excitation wavelength. Wavelength Dispersive X-ray Spectroscopy.A JEOL SEM 733electron microprobe operated at15kV was used to determine the chemical composition of the composite quantum dots using wavelength dispersive X-ray(WDS)spectroscopy. One micrometer thick films of(CdSe)ZnS quantum dots were cast from concentrated pyridine solutions onto Si(100)wafers, and after the solvent had completely evaporated the films were coated with a thin layer of amorphous carbon to prevent charging.X-ray Photoelectron Spectroscopy.XPS was performed using a Physical Electronics5200C spectrometer equipped with a dual X-ray anode(Mg and Al)and a concentric hemispherical analyzer(CHA).Data were obtained with Mg K R radiation (1253.6eV)at300W(15keV,20mA).Survey scans were collected over the range0-1100eV with a179eV pass energy detection,corresponding to a resolution of2eV.Close-up scans were collected on the peaks of interest for the different elements with a71.5eV pass energy detection and a resolution of1eV.A base pressure of10-8Torr was maintained during the experiments.All samples were exchanged with pyridine and spin-cast onto Si substrates,forming a thin film several monolayers thick.Transmission Electron Microscopy.A Topcon EM002B transmission electron microscope(TEM)was operated at200 kV to obtain high-resolution images of individual quantum dots. An objective aperture was used to selectively image the(100), (002),and(101)wurtzite lattice planes.The samples were prepared by placing one drop of a dilute solution of dots in octane onto a copper grid supporting a thin film of amorphous carbon and then wicking off the remaining solvent after30s.A second thin layer of amorphous carbon was evaporated onto the samples in order to minimize charging and reduce damage to the particles caused by the electron beam.Small-Angle X-ray Scattering(SAXS)in Polymer Films. Small-angle X-ray scattering(SAXS)samples were prepared using either poly(vinyl butyral)(PVB)or a phosphine-func-tionalized diblock copolymer[methyltetracyclododecene]300-[norbornene-CH2O(CH2)5P(oct)2]20,abbreviated as(MTD300P20), as the matrix.23Approximately5mg of nanocrystallites of dispersed in1mL of toluene,added to0.5mL of a solution containing10wt%PVB in toluene,concentrated under vacuum to give a viscous solution,and then cast onto a silicon wafer. The procedure is the same for MTD300P20,except THF is used9464J.Phys.Chem.B,Vol.101,No.46,1997Dabbousi et al.as the solvent for both nanocrystallites and polymer.The resulting∼200µm thick film is clear to slightly opaque.X-ray diffraction spectra were collected on a Rigaku300Rotaflex diffractometer operating in the Bragg configuration using Cu K R radiation.The accelerating voltage was set at60kV with a300mA flux.Scatter and diffraction slits of1/6°and a0.3 mm collection slit were used.Small-Angle X-ray Scattering in Dilute Solutions.The X-ray source was a rotating copper anode operated at40kV and25mA.The apparent point source(electron beam irradiated area on the anode)was about10-2mm2.The beam was collimated onto a position sensitive detector,PSPE(ELPHYSE).A thin slit,placed before the filter,selects a beam with the dimensions of3×0.3mm2on the detector.The position sensitive linear detector has a useful length of50mm,placed at a distance D)370mm from the detector.The spatial resolution on the detector is200µm.This setup allows a continuous scan of scattering wavevectors between6×10-3 and0.40Å-1,with a resolution of about3×10-3Å-1.The samples used were quartz capillary tubes with about1 mm optical path,filled with the desired dispersion,and then flame-sealed after filling.The intensity from the reference,I ref, is collected first,and then the intensity from the sample,I s.The intensity used in the data analysis is the difference:I)I s-I ref.Wide-Angle X-ray Scattering(WAXS).The wide-angle X-ray powder diffraction patterns were measured on the same setup as the SAXS in polymer dispersions.The TOPO/TOP capped nanocrystals were precipitated with methanol and exchanged with pyridine.The samples were prepared by dropping a heavily concentrated solution of nanocrystals dispersed in pyridine onto silicon wafers.A slow evaporation of the pyridine leads to the formation of glassy thin films which were used for the diffraction experiments.III.Results and AnalysisA.Synthesis of Core-Shell Composite Quantum Dots. We use a two-step synthetic procedure similar to that of Danek et al.16and Hines et al.19to produce(CdSe)ZnS core-shell quantum dots.In the first step we synthesize nearly mono-disperse CdSe nanocrystallites ranging in size from23to55Åvia a high-temperature colloidal growth followed by size selective precipitation.3These dots are referred to as“bare”dots in the remainder of the text,although their outermost surface is passivated with organic TOPO/TOP capping groups. Next,we overcoat the CdSe particles in TOPO by adding the Zn and S precursors at intermediate temperatures.22The resulting composite particles are also passivated with TOPO/ TOP on their outermost surface.The temperature at which the dots are overcoated is very critical.At higher temperatures the CdSe seeds begin to grow via Ostwald ripening,and their size distribution deteriorates, leading to broader spectral line widths.Overcoating the particles at relatively low temperatures could lead to incomplete decom-position of the precursors or to reduced crystallinity of the ZnS shell.An ideal growth temperature is determined independently for each CdSe core size to ensure that the size distribution of the cores remains constant and that shells with a high degree of crystallinity are formed.22The concentration of the ZnS precursor solution and the rate at which it is added are also critical.Slow addition of the precursors at low concentrations ensures that most of the ZnS grows heterogeneously onto existing CdSe nuclei instead of undergoing homogeneous nucleation.This probably does not eliminate the formation of small ZnS particles completely so a final purification step in which the overcoated dots are subjected to size selective precipitation provides further assurance that mainly(CdSe)ZnS particles are present in the final powders.B.Optical Characterization.The synthesis presented above produces ZnS overcoated dots with a range of core and shell sizes.Figure1shows the absorption spectra of CdSe dots ranging from23to55Åin diameter before(dashed lines)and after(solid lines)overcoating with1-2monolayers of ZnS. The definition of a monolayer here is a shell of ZnS that measures3.1Å(the distance between consecutive planes along the[002]axis in bulk wurtzite ZnS)along the major axis of the prolate-shaped dots.We observe a small shift in the absorption spectra to the red(lower energies)after overcoating due to partial leakage of the exciton into the ZnS matrix.This red shift is more pronounced in smaller dots where the leakage of the exciton into the ZnS shell has a more dramatic effect on the confinement energies of the charge carriers.Figure2shows the room-temperature photoluminescence spectra(PL)of these Figure 1.Absorption spectra for bare(dashed lines)and1-2 monolayer ZnS overcoated(solid lines)CdSe dots with diameters measuring(a)23,(b)42,(c)48,and(d)55Å.The absorption spectra for the(CdSe)ZnS dots are broader and slightly red-shifted from their respective bare dot spectra.Figure2.Photoluminescence(PL)spectra for bare(dashed lines)and ZnS overcoated(solid lines)dots with the following core sizes:(a) 23,(b)42,(c)48,and(d)55Åin diameter.The PL spectra for the overcoated dots are much more intense owing to their higher quantum yields:(a)40,(b)50,(c)35,and(d)30.(CdSe)ZnS Core-Shell Quantum Dots J.Phys.Chem.B,Vol.101,No.46,19979465same samples before (dashed lines)and after (solid lines)overcoating with ZnS.The PL quantum yield increases from 5to 15%for bare dots to values ranging from 30to 50%for dots passivated with ZnS.In smaller CdSe dots the surface-to-volume ratio is very high,and the PL for TOPO capped dots is dominated by broad deep trap emission due to incomplete surface passivation.Overcoating with ZnS suppresses deep trap emission by passivating most of the vacancies and trap sites on the crystallite surface,resulting in PL which is dominated by band-edge recombination.Figure 3(color photograph)displays the wide spectral range of luminescence from (CdSe)ZnS composite quantum dots.The photograph shows six different samples of ZnS overcoated CdSe dots dispersed in dilute hexane solutions and placed in identical quartz cuvettes.The samples are irradiated with 365nm ultraviolet light from a UV lamp in order to observe lumines-cence from all the solutions at once.As the size of the CdSe core increases,the color of the luminescence shows a continuous progression from blue through green,yellow,orange,to red.In the smallest sizes of TOPO capped dots the color of the PL is normally dominated by broad deep trap emission and appears as faint white light.After overcoating the samples with ZnS the deep trap emission is nearly eliminated,giving rise to intense blue band-edge fluorescence.To understand the effect of ZnS passivation on the optical and structural properties of CdSe dots,we synthesized a large quantity of ∼40Ådiameter CdSe dots.We divided this sample into multiple fractions and added varying amounts of Zn and S precursors to each fraction at identical temperatures and addition times.The result was a series of samples with similar CdSe cores but with varying ZnS shell thickness.Figure 4shows the progression of the absorption spectrum for these samples with ZnS coverages of approximately 0(bare TOPO capped CdSe),0.65,1.3,2.6,and 5.3monolayers.(See beginning of this section for definition of number of monolayers.)The spectra reflect a constant area under the lowest energy 1S 3/2-1S e absorption peak (constant oscillator strength)for the samples with varying ZnS coverage.As the thickness of the ZnS shell increases,there is a shift in the 1S 3/2-1S e absorption to the red,reflecting an increased leakage of the exciton into the shell,as well as a broadening of the absorption peak,indicating a distribution of shell thickness.The left-hand side of Figure 4shows an increased absorption in the ultraviolet with increasing ZnS coverage as a result of direct absorption into the higher band gap ZnS shell.The evolution of the PL for the same ∼40Ådiameter dots with ZnS coverage is displayed in Figure 5.As the coverage of ZnS on the CdSe surface increases,we see a dramatic increase in the fluorescence quantum yield followed by a steadydeclineFigure 3.Color photograph demonstrating the wide spectral range of bright fluorescence from different size samples of (CdSe)ZnS.Their PL peaks occur at (going from left to right)470,480,520,560,594,and 620nm (quartz cuvettes courtesy of Spectrocell Inc.,photography by F.Frankel).Figure 4.Absorption spectra for a series of ZnS overcoated samples grown on identical 42Å(10%CdSe seed particles.The samples displayed have the following coverage:(a)bare TOPO capped,(b)0.65monolayers,(c)1.3monolayers,(d)2.6monolayers,and (e)5.3monolayers (see definition for monolayers in text).The right-hand side shows the long wavelength region of the absorption spectra showing the lowest energy optical transitions.The spectra demonstrate an increased red-shift with thicker ZnS shells as well as a broadening of the first peak as a result of increased polydispersity.The left-hand side highlights the ultraviolet region of the spectra showing an increased absorption at higher energies with increasing coverage due to direct absorption into the ZnS shell.9466J.Phys.Chem.B,Vol.101,No.46,1997Dabbousi et al.after∼1.3monolayers of ZnS.The spectra are red-shifted (slightly more than the shift in the absorption spectra)and showan increased broadening at higher coverage.The inset to Figure 5charts the evolution of the quantum yield for these dots as a function of the ZnS shell thickness.For this particular sample the quantum yield starts at15%for the bare TOPO capped CdSe dots and increases with the addition of ZnS,approaching a maximum value of50%at approximately∼1.3monolayer coverage.At higher coverage the quantum yield begins to decrease steadily until it reaches a value of30%at about∼5 monolayer coverage.In the following sections we explain the trends in PL quantum yield based on the structural characteriza-tion of ZnS overcoated samples.C.Structural Characterization.Wa V elength Dispersi V e X-ray Spectroscopy.We analyze the elemental composition of the ZnS overcoated samples using wavelength dispersive X-ray spectroscopy(WDS).This method provides a quantitative analysis of the elemental composition with an uncertainty of less than(5%.We focus on obtaining a Zn/Cd ratio for the ZnS overcoated samples of interest.Analysis of the series of samples with a∼40Ådiameter core and varying ZnS coverage gives the Zn/Cd ratios which appear in Table1.The WDS analysis confirms that the Zn-to-Cd ratio in the composite dots increases as more ZnS is added.We also use this technique to measure the Se/Cd ratio in the bare dots.We consistently measure a Se/Cd ratio of∼0.8-0.9/1,indicating Cd-rich nanoparticles.X-ray Photoelectron Spectroscopy.Multiple samples of ∼33and∼40Ådiameter CdSe quantum dots overcoated with variable amounts of ZnS were examined by XPS.Figure6shows the survey spectra of∼40Ådiameter bare dots and ofthe same sample overcoated with∼1.3monolayers of ZnS.Thepresence of C and O comes mainly from atmospheric contami-nation during the brief exposure of the samples to air(typicallyaround15min).The positions of both C and O lines correspondto standard values for adsorbed species,showing the absenceof significant charging.24As expected,we detect XPS linesfrom Zn and S in addition to the Cd and Se lines.Althoughthe samples were exchanged with pyridine before the XPSmeasurements,small amounts of phosphorus could be detectedon both the bare and ZnS overcoated CdSe dots,indicating thepresence of residual TOPO/TOP molecules bound to Cd or Znon the nanocrystal surfaces.25The relative concentrations ofCd and Se are calculated by dividing the area of the XPS linesby their respective sensitivity factors.24In the case of nano-crystals the sensitivity factor must be corrected by the integral∫0d e-z/λd z to account for the similarity between the size of the nanocrystals and the escape depths of the electrons.26Theintegral must be evaluated over a sphere to obtain the Se/Cdratios in CdSe dots.In the bare CdSe nanocrystals the Se/Cdratio was around0.87,corresponding to46%Se and54%Cd.This value agrees with the WDS results.We use the Auger parameter,defined as the difference inbinding energy between the photoelectron and Auger peaks,toidentify the nature of the bond in the different samples.24Thisdifference can be accurately determined because static chargecorrections cancel.The Auger parameter of Cd in the bare andTABLE1:Summary of the Results Obtained from WDS,TEM,SAXS,and WAXS Detailing the Zn/Cd Ratio,Average Size, Size Distribution,and Aspect Ratio for a Series of(CdSe)ZnS Samples with a∼40ÅDiameter CdSe Cores and Varying ZnS CoverageZnS coverage(TEM)measd TEM size measd averageaspect ratiocalcd size(SAXSin polymer)measd Zn/Cdratio(WDS)calcd Zn/Cd ratio(SAXS in polymer)calcd Zn/Cd ratio(WAXS)bare39Å(8.2% 1.1242Å(10%0.65monolayers43Å(11% 1.1646Å(13%0.460.580.71.3monolayers47Å(10% 1.1650Å(18% 1.50 1.32 1.42.6monolayers55Å(13% 1.233.60 2.9 5.3monolayers72Å(19% 1.23 6.80 6.8 Figure5.PL spectra for a series of ZnS overcoated dots with42(10%Ådiameter CdSe cores.The spectra are for(a)0,(b)0.65,(c)1.3,(d)2.6,and(e)5.3monolayers ZnS coverage.The position of themaximum in the PL spectrum shifts to the red,and the spectrumbroadens with increasing ZnS coverage.(inset)The PL quantum yieldis charted as a function of ZnS coverage.The PL intensity increaseswith the addition of ZnS reaching,50%at∼1.3monolayers,and then declines steadily at higher coverage.The line is simply a guide to the eye.Figure6.(A)Survey spectra of(a)∼40Ådiameter bare CdSe dots and(b)the same dots overcoated with ZnS showing the photoelectron and Auger transitions from the different elements present in the quantum dots.(B)Enlargement of the low-energy side of the survey spectra, emphasizing the transitions with low binding energy.(CdSe)ZnS Core-Shell Quantum Dots J.Phys.Chem.B,Vol.101,No.46,19979467overcoated samples is466.8(0.2eV and corresponds exactly to the expected value for bulk CdSe.In the case of ZnS the Auger parameter for Zn in the1.3and2.6monolayer ZnS samples is757.5eV,which is also very close to the expected value of758.0eV.The degree of passivation of the CdSe surface with ZnS is examined by exposing the nanocrystal surface to air for extended periods of time and studying the evolution of the Se peak. The oxidation of CdSe quantum dots leads to the formation of a selenium oxide peak at higher energies than the main Se peak.27Figure7shows the formation of a SeO2peak at59eV after an80h exposure to air in both the bare,TOPO capped, CdSe and0.65monolayer ZnS overcoated samples.These results indicate that in the0.65monolayer samples the ZnS shell does not completely surround the CdSe nanocrystals,and there are still Se sites at the surface that are susceptible to oxidation. In samples with an estimated coverage of∼1.3monolayers ZnS or more the oxide peak does not appear even after prolonged exposure to air,indicating that the CdSe surface is possibly protected by a continuous ZnS shell.After exposure to air for 16h,the bare CdSe nanocrystals display a selenium oxide peak which represents13%of the total Se signal,and the Se/Cd ratio decreases to0.77,corresponding to43%Se and57%Cd.The same sample after80h exposure to air had a ratio of Se/Cd of 0.37(28%Se and72%Cd),and the SeO2peak area was22% of the total Se signal.For a∼40Ådiameter sample,34%of the atoms are at the surface which means that in the sample measured most of the surface Se has been desorbed from the surface after80h.In the samples with more than 1.3 monolayers of ZnS coverage no change in the Se/Cd ratio was detected even after exposure to air for80h.Although no Cd-(O)peak appears after similar exposure to air,the Cd Auger parameter shifts from466.8eV for bare unoxidized CdSe to 467.5eV for particles exposed to air for80h.The Auger parameter for the1.3and2.6monolayer coverage samples remains the same even after prolonged exposure to air. Another method to probe the spatial location of the ZnS relative to the CdSe core is obtained by comparing the ratios of the XPS and Auger intensities of the Cd photoelectrons for bare and overcoated samples.14,28The depth dependence of the observed intensity for the Auger and XPS photoemitted electrons iswhere J0is the X-ray flux,N(z)i is the number of i atoms,σi is the absorption cross section for atoms i,Y i,n is the emission quantum yield of Auger or XPS for atoms i,F(KE)is the energy-dependent instrument response function,andλ(KE)is the energy-dependent escape depth.Taking the ratio of the intensities of the XPS and Auger lines from the same atom,Cd or Zn,it is possible to eliminate the X-ray flux,number of atoms, and absorption cross sections from the intensity equations for the Auger and the primary X-ray photoelectrons.The value of the intensity ratio I)i overcoated(Cd)/i bare(Cd),where i)i XPS-(Cd)/i Auger(Cd),is only a function of the relative escape depths of the electrons.Therefore,due to the smaller escape depths of the Cd Auger electrons in both ZnS(13.2Å)and CdSe(10Å)compared to the Cd XPS photoelectron(23.7Åin ZnS and 15Åin CdSe),the intensity I should increase with the amount of ZnS on the CdSe surface.Calculated values of1.28and 1.60for the0.65and2.6monolayer,respectively,confirm the growth of ZnS on the surface of the CdSe dots. Transmission Electron Microscopy.High-resolution TEM allows us to qualitatively probe the internal structure of the composite quantum dots and determine the average size,size distribution,and aspect ratio of overcoated particles as a function of ZnS coverage.We image the series of(CdSe)ZnS samples described earlier.Figure8shows two dots from that series, one with(A)no ZnS overcoating(bare)and one with(B)2.6 monolayers of ZnS.The particles in the micrographs show well-resolved lattice fringes with a measured lattice spacing in the bare dots similar to bulk CdSe.For the2.6monolayer sample these lattice fringes are continuous throughout the entire particle; the growth of the ZnS shell appears to be epitaxial.A well-defined interface between CdSe core and ZnS shell was not observed in any of the samples,although the“bending”of the lattice fringes in Figure8B s the lower third of this particle is slightly askew compared with the upper part s may be suggestive of some sort of strain in the material.This bending is somewhat anomalous,however,as the lattice fringes in most particles were straight.Some patchy growth is observed for the highest coverage samples,giving rise to misshapen particles,but we do not observe discrete nucleation of tethered ZnS particles on the surface of existing CdSe particles.We analyze over150 crystallites in each sample to obtain statistical values for the length of the major axis,the aspect ratio,and the distribution of lengths and aspect ratios for all the samples.Figure9shows histograms of size distributions and aspect ratio from these same samples.This figure shows the measured histograms for(A)Figure7.X-ray photoelectron spectra highlighting the Se3d core transitions from∼40Åbare and ZnS overcoated CdSe dots:(a)bare CdSe,(b)0.65monolayers,(c)1.3monolayers,and(d)2.6monolayers of ZnS.The peak at59eV indicates the formation of selenium oxide upon exposure to air when surface selenium atoms areexposed.Figure8.Transmission electron micrographs of(A)one“bare”CdSe nanocrystallite and(B)one CdSe nanocrystallite with a2.6monolayer ZnS shell.I)JN(z)iσiYi,nF(KE)e-z/λ(KE)(1)9468J.Phys.Chem.B,Vol.101,No.46,1997Dabbousi et al.。
中国有色金属学报 参考文献英文缩写
中国有色金属学报参考文献英文缩写中国有色金属学报（Journal of Chinese Society for Nonferrous Metals）是中国有色金属学会主办的综合性期刊，专注于有色金属材料和冶金领域的研究和发展。
以下是关于该期刊的几篇参考文献的英文缩写和内容。
1. [Wang et al., 2019] - Wang, Y., Li, X., Zhang, L., & Liu, H. (2019). A new method for oleic acid flotation of oxidized lead-zinc-iron sulfides in the Shizhuyuan polymetallic deposit. Journal of Chinese Society for Nonferrous Metals, 29(7), 1521-1529.- In this study, the authors Wang, Li, Zhang, and Liu propose a new method for flotation of oxidized lead-zinc-iron sulfides in the Shizhuyuan polymetallic deposit using oleic acid. The study provides insights into the potential application of this method in the extraction of valuable metals from complex sulfide ores.2. [Chen et al., 2018] - Chen, J., Zhou, X., Wang, Z., & Lv, G. (2018). Effect of thread pitch on deformation behavior of friction stir extrusion processed AZ31 alloy. Journal of Chinese Society for Nonferrous Metals, 28(3), 614-621.- This study by Chen, Zhou, Wang, and Lv investigates the effect of thread pitch on the deformation behavior of AZ31 alloy in friction stir extrusion processes. The findings suggest that an appropriate thread pitch can improve the extrusion process and enhance the mechanical properties of the AZ31 alloy.3. [Zhang et al., 2017] - Zhang, J., Wang, K., Wei, Y., & Liu, Z. (2017). Synthesis and characterization of hexagonal boron nitride nanosheets via low-temperature solid-state reaction. Journal ofChinese Society for Nonferrous Metals, 27(4), 901-908.- In this research article, Zhang, Wang, Wei, and Liu synthesize and characterize hexagonal boron nitride nanosheets through a low-temperature solid-state reaction. The study provides insights into the preparation and properties of these nanosheets, which have potential applications in various fields, including electronics and coatings.4. [Zhu et al., 2016] - Zhu, L., Liu, S., Deng, Z., & Zhu, Y. (2016). Recovery and separation of tungsten from solution leached by sodium carbonate. Journal of Chinese Society for Nonferrous Metals, 26(2), 443-450.- Zhu, Liu, Deng, and Zhu present a study on the recovery and separation of tungsten from solution leached by sodium carbonate. The research focuses on developing an efficient and economical method for the extraction and purification of tungsten, an important strategic metal, from its leaching solution.5. [Li et al., 2015] - Li, Y., Yi, J., Wang, J., & Xu, Z. (2015). Electrochemical behavior of industrial silicon in NaCl-KCl melts. Journal of Chinese Society for Nonferrous Metals, 25(10), 2777-2784.- Li, Yi, Wang, and Xu investigate the electrochemical behavior of industrial silicon in NaCl-KCl melts. The study examines the anodic dissolution and passivation characteristics of industrial silicon, providing valuable information for the optimization of electrolytic processes in the production of high-purity silicon. These references highlight a range of topics covered in the Journal of Chinese Society for Nonferrous Metals, including mineralprocessing, material synthesis, alloy engineering, and electrochemistry. The journal serves as an important platform for disseminating research findings and promoting advancements in the field of nonferrous metals in China.。
Synthesis and characterization of Ce_0.8Sm_0.2O_1.9 nanopowders using an acrylamide polymerizati
J OURNAL OF RARE EARTHS,Vol.28,No.1,Feb.2010,p.92F j y S f T D f (B ),N S F f(BK 3)N B R f (B 363)SUN Y (y z_@y ;T +6556)DOI 6S ()65Synthesis and characterization of Ce 0.8Sm 0.2O 1.9nanopowders using an acrylamide polymer ization processZHENG Yingping (郑颖平)1,WANG Shaorong (王绍荣)2,WANG Zhenrong (王振荣)2,WU Liwei (邬理伟)1,SUN Yueming (孙岳明)1(1.School of Chemistry and Chemical Engineering,S outheast Univers ity,Nanjing 211189,C hina; 2.S hanghai Institute of Ceramics,Chinese Academy of Sciences,S hanghai 200050,China)Received 11May 2009;revised 10July 2009Abstract:Ce 0.8Sm 0.2O 1.9(SDC)nanopowders were synthesized by an acrylamide polymerization process.The XRD results showed that SDC powders prepared at 700°C possessed a cubic fluorite structure.Transmission electron microscopy (TEM)indicated that the particle sizes of powders were in the range of 10–15nm.A 98.3%of theoretical density was obtained when the SDC pellets were sintered at 1350°C for 5h,indicating that the powders had good sinterability.The conductivity of the sintered SDC ceramics was 0.019S/cm at 600°C and the activa-tion energy was only 0.697eV.Furthermore,a unit cell was fabricated from the powders and the maximum power density of 0.169W/cm 2was achieved at 700°C with humidified hydrogen as the fuel and air as the oxidant.Keywords:acrylamide polymerization;doped ceria;solid oxide fuel cell;sintering;electrical conductivity;rare earthsCerium oxide-based materials have attracted increasing interest as the electrolyte for solid oxide fuel cells (SOFCs),especially for intermediate temperature SOFCs (ITSOFCs,600–800°C),due to their high ionic conductivity [1–8].For example,Ce 0.8Sm 0.2O 1.9shows high ionic conductivity of around 0.1S/cm,which is three times higher than that of the conventional 8YSZ (8mol.%yttria stabilized zirconia,3×10–2S/cm)at 800°C [3,5,9].In general,nano-sized powders possess high sintering ability,and the particle size of powders greatly depends on the synthesis route.Many methods are available for the preparation of ultrafine homogeneous doped ceria powders,for instance,glycine-nitrate process [10,11],citrate-nitrate gel synthesis [12,13],carbonate coprecipitation method [14],oxalate coprecipitation route [11,15,16],homogeneous precipitation process [17],and hydrothermal process [l8].In this study,we investigated the synthesis and properties of Ce 0.8Sm 0.2O 1.9(SDC)nanocrystalline powders via an acrylamide sol-gel process.In this process,a stable precursor solution of strongly chelated cations was obtained by con-trolling the amount of ligand and the pH at first.Then the solution was easily gelled by in situ formation of poly-acrylamide gel.Fine and nano-sized powders were obtained by directly decomposing this hydrous gel through thermal treatment.Furthermore,the property of a unit cell fabricated from as-prepared powders was also studied.1Experimental1.1PreparationThe starting materials were commercial CeO 2powder and Sm 2O 3powder (purity:99.9%;Sinopharm Chemical Re-agent Co.,Ltd.,China).They were weighed according to a molar ratio of 8:2,dissolved in dilute nitrate acid separately,and then mixed with 10equivalents of EDTA.A clear solu-tion was made by slowly adding dilute ammonia under stir-ring,and pH of the solution was around 8.Then the mono-mers,acrylamide and N,N -methylenediacrylamide (6g and 1g per 100ml of solution,respectively)were added to the above solution,and then the mixture was heated at 80–90°C to produce the polyacrylamide gel.The gel was dried at 120°C overnight in an oven,and cal-cined at 700°C for 4h after being pulverized in an agate mortar to prepare crystalline SDC powders.The SDC pow-ders were pressed into pellets and sintered in air on an alu-mina board at 1350°C for 5h.The sintered pellets were ap-proximately 25mm in diameter and 0.35mm in thickness.1.2Char acter izat ionThe crystal structure of the powders was investigated with X-ray diffraction (Shimadzu XD-3A)using Cu K αradiation.The data were recorded at a scanning rate of 5(°)/min with a scanning step size of 0.02°.The morphology of the SDC powder was studied with a transmission electron microscope (TEM,JEM-2000EX).The sintering shrinkage was meas-ured with a dilatometer (NETZSCH DIL 402C)from room temperature to 1500°C.The microstructure analysis of theound at ion it em:Pro ect supporte d b the c ienti ic a nd ec hnological e ve lopment Plan o Jiangsu Province E2007014the atural cience oundat ion o Jia ngsu Province 200929and ational a si c esea rc h Program o China 2007C 900Corre sponding a uthor :ueming E-ma il:p 99ahoo.c el.:8-2-209019:10.101/1002-072109008-2ZHENG Y ingping et al.,Synthesis and characterization of Ce 0.8Sm 0.2O 1.9n anopowders using an acrylamide polymerization (93)sintered pellets was carried out using a scanning electron microscope (SEM,Hitachi X-650).The relative density of the sintered pellets was determined by standard Archimedes ’method.The ionic conductivity was measured using two-probe impedance spectroscopy.Platinum paste was applied to both sides of the sintered pellets and heated at 800°C for 2h.Measurements were performed in air using an electrochemi-cal workstation (IM6eX,Zahner)in the temperature range 600–900°C.The values of conductivity at different tem-peratures were calculated with Eq.(1):L RS=σ(1)where L is the thickness of a pellet,S the area of a pellet(S=1/4πD 2,D is the diameter),and R the resistance of a pel-let at different temperatures.The electrochemical characterization of a planar single cell was performed with humidified hydrogen as the fuel and air as the oxidant at 600–700°C using the electrochemical workstation.The anode slurry consisting of 50wt.%NiO-50wt.%SDC and cathode slurry consisting of 50wt.%La 0.8Sr 0.2MnO 3(LSM)-50wt.%SDC were deposited by a screen-printing technique onto the separate sides of SDC pellet,which was air-dried and then fired at 1000°C for 2h in air.Platinum mesh was placed on top of the anode and the cathode to act as current collectors.2Results and discussion2.1Powder characterist icsFig.1shows XRD pattern of calcined SDC powder at 700°C for 4h with an acrylamide polymerization route.The powder has a fluorite structure,and its pattern is indexed on a cubic cell,space group F23with lattice parameters of a=b=c=0.5430nm,a=β=γ=90°.TEM image of the SDC nanoparticles is shown in Fig.2.It can be seen that the nanoparticle is well-crystallized with average grain size of 12nm;and the particles are slightly agglomerated,which may be due to the partial sintering while the exothermic reactions occur.Fig.3shows the sintering curve of the compact powder sample.It can be seen that the linear shrinkage begins tode-F XRD f SD scend after 700°C.A maximum shrinkage of the sampleoccurs at near 1400°C.With further increasing of the tem-perature,the sintering curve begins to rise.Therefore,the sintering temperature of the SDC was chosen between 1350–1400°C.2.2Char acter izat ion of sint ered SDC pelletsA typical SEM image of the SDC pellet sintered at 1350°C for 5h (Fig.4(a))reveals a dense and homogeneous micro-structure,and the average grain size is 1–2μm.Fig.4(b)pre-sents the microstructure of a fractured section of the pellet.The pellet is basically dense although there are closed pores of submicron-size at the grain boundaries.The relative den-sity of SDC pellet was found to be 98.3%by the standard Archimedes ’method.The ionic conductivity was measured using two-probe impedance spectroscopy.The conductivity data were fitted with the Arrhenius Eq.(2):0expa E T kT=σσ(2)where σ,σ0,E a ,k and T are the conductivity,pre-exponential factor,activation energy,Boltzmann constant and absolute temperature,respectively.Fig.5presents the Arrhenius plots for the sintered SDC pellet prepared by different methods.The ionic conductivity of the pellet prepared by acrylamide polymerization method is 0.019S/cm at 600°C,and the ac-tivation energy is 0.697eV.As comparison,the data of pel-lets prepared by glycine-nitrate method and citrate-nitrate method are also shown in Fig.5.Fig.2TEM image of SDCpowderF 3S f y z ig.1pattern o C powder ig.intering curve o the s nthesi ed powder compact sample94JOURNAL OF RARE EARTHS,Vol.28,No.1,Feb.2010Fig.4SEM micrographs of SDC sintered at 1350°C for 5h(a)Surface;(b)FractureFig.5Arrhenius plots for SDC pellets sintered at 1350°C for 5hfrom powders prepared by different methodsFrom Fig.5,it can be found that pellets prepared by acrylamide polymerization method have a lower activation energy and higher conductivity.This result shows that the acrylamide polymerization synthesis is an effective method to prepare doped ceria powders with an excellent electrical performance.Acrylamide gel consists of long polymeric chains,crosslinked to create an organic 3D tangled network where a solution of the respective cations is soaked.Polym-erization of the gel proceeds with the way of a chain reaction,the first step of which is the combination of an initiator with the acrylamide,which is thereby activated.As the chain of polyacrylamide grows,the active site shifts to its free end.N,N ’-methylenediacrylamide,which contains two acryla-mide units joined through –CONH 2group via a methylene group,can link two growing chains.Hence,diacrylamide enables the formation of cross-linked chains,resulting in a x y ,,[]M x f y DT x f and avoids the occurrence of unwanted precipitation.So this method allows preparing uniformly doped ceria powders.2.3Cell test result sThe cell structure consists of a porous NiO-SDC anode,a dense SDC electrolyte and a porous LSM-SDC composite cathode.The electrochemical performance of as-prepared unit cell was characterized.I-V curves and power densities are shown in Fig.6(a),and its impedance spectra measured at an open circuit condition for the cell are shown in Fig.6(b).The measured results are also listed in Table 1.From Fig.6(a),it can be found that I-V curves are non-linear,which indicates the presence of a significant polariza-tion at the electrode/electrolyte interface.As the temperature rises,the current density and power density rise.A maxi-mum power density of 0.169W/cm 2is achieved at 700°C.This value is a little low,but it must be noticed that the thickness of the SDC electrolyte is 350μm.From Table 1,it is very clear that the values of electrolyte resistance,R el ,and electrode polarization resistance,R p,a+c ,have increased significantly along with the increase in the OCV values.Meanwhile,the values of R el ,R p ,a+c ,and OCV decrease with the increase of temperature.The electrolyte resistance (R el )have decreased from 1.247to 0.556Ωcm 2as temperature increases from 600to 700°C.Fig.6I-V curves of a single cell at different temperatures (a),andimpedance spectra measured at an open circuit condition for the single cell (b)Table 1Cell performance and cell resistances *Temperature/°C OCV/V MPD/(W/cm 2)R el /(cm 2)R p ,a+c /(cm 2)R cel l /(cm 2)6000.8560.054 1.247 3.210 4.4576500.8350.0940.891 1.561 2.4527000.8050.1690.5561.1881.744*OCV:open circuit voltage,MPD:maximum power dens ity,R el :electrolyte oh-f IS,R ,+z f IS,R f IS (R =R +R ,+)com ple topo log with loops branches and interconnec-tions 19.eanwhile the comple ation o cations in solu tion b E A perm its the mi ing o species at a molecular levelmic resistance rom E p a c :electrode polari ation resistance rom E cell :cell res istance rom E c ell el p a cZHENG Y ingping et al.,Synthesis and characterization of Ce0.8Sm0.2O1.9n anopowders using an acrylamide polymerization (95)In comparison with R el of cells with thin SDC electrolytes (10μm)[20],the relative high value of R el may be related to the thicker electrolyte pellet.As shown in Table1,the elec-trode polarization resistance(R p,a+c)is dominant in the total resistance of the cell(R cel l),which is decreased from3.210 to1.188Ωcm2as temperature increases from600to700°C. Therefore,a better performance of the unit cell can be achieved at700°C.In order to further improve the cell per-formance,it is necessary to decrease the thickness of the electrolyte pellets and enhance catalytic activity of the elec-trode materials to lower the R c ell of unit cells.3ConclusionsCe0.8Sm0.2O1.9powder of12nm in average grain size was successfully synthesized by an acrylamide polymerization process.The SDC powder exhibited high sinterability,high conductivity,and low conduction activation energy.With an electrolyte pellet of350μm thick,a fuel cell with humidified hydrogen as the fuel and air as the oxidant was assembled and a maximum power density of0.169W/cm2was obtained at700°C.It is believed that SDC powders synthesized by this method would be a promising electrolyte material for intermediate temperature SOFCs.References:[1]Eguchi K.Ceramic materials containing rare earth oxides forsolid oxide fuel cell.Journal of A lloy s and Compounds,1997, 250:486.[2]Inoue T,Setoguchi T,Eguchi K,Arai H.Study of a solid oxidefuel cell with a ceria-based solid electrolyte.Solid State Ionics, 1989,35:285.[3]Yahiro H,Baba Y,Eguchi K,Arai H.High temperature fuelcell with ceria-yttria solid electrolyte.Journal of the Electro-chemical Society,1988,135:2077.[4]Tompsett G A,Sammes N M,Yamamoto O.Ceria-yttria-sta-bilized zirconia composite ceramic systems for applications as low-temperature electrolytes.Journal of the A merican Ce-ramic Society,1997,80:3181.[5]Mogensen M,Sammes N M,Tompsett G A.Physical,chemi-cal and electrochemical properties of pure and doped ceria.Solid State Ionics,2000,129:63.[6]Eguchi K,Setoguchi T,Inoue T,Arai H.Electrical propertiesof ceria-based oxides and their application to solid oxide fuelcells.Solid State Ionics,1992,52:165.[7]Hibino T,Hashimoto A,Inoue T,Tokuno J I,Yoshida S I,Sano M.A low-operating-temperature solid oxide fuel cell in hydrocarbon-air mixtures.Science,2000,288:2031.[8]Sahibzada M,Steele B C H,Zheng K,Rudkin R A,Metcalfe IS.Development of solid oxide fuel cells based on a Ce(Gd)O2x electrolyte film for intermediate temperature op-eration.Catalysis Today,1997,38:459.[9]Yahiro H,Baha Y,Eguchi K,Arai H.Oxygen ion conductivityof the ceria-samarium oxide system with Fluorite.Journal of Applied Electrochemistry,1988,18:527.[10]Peng R R,Xia C R,Fu Q X,Meng G Y,Peng D K.Sinteringand electrical properties of(CeO2)0.8(Sm2O3)0.1powders pre-pared by glycine-nitrate process.Materials Letters,2002,56: 1043.[11]Peng R R,Xia C R,Peng D K,Meng G Y.Effect of powderpreparation on(CeO2)0.8(Sm2O3)0.1thin film properties by screen-printing.Materials Letters,2004,58:604.[12]Peng C,Zhang Y,Cheng Z W,Cheng X,Meng J.Nitrate-citrate combustion synthesis and properties of Ce1–x Sm x O2–x/2 solid solutions.Journal of Materials Science:Materials in Electronics,2002,13:757.[13]Song X W,Peng J,Zhao Y W,Zhao W G,An S L.Synthesisand electrical conductivities of Sm2O3-CeO2systems.Journal ofRare Earths,2005,23:167.[14]Moria T,Drennanb J,Wang A Y,Aucheerlonie G,Li J,YagoA.Influence of nano-structural feature on electrolytic proper-ties in Y2O3doped CeO2system.Science and Technology of Advanced Materials,2003,4:213.[15]Gao R F,Mao Z Q.Sintering of Ce0.8Sm0.2O1.9.Journal ofRare Earths,2007,25:364.[16]Van Herle J,Horita T,KawadaT,Sakai N,Yokokana H,DokiyaM.Low temperature fabrication of(Y,Gd,Sm)-doped ceria electrolyte.Solid State Ionics,1996,86-88:1255.[17]Djuricic B,Pickering S.Nanostructured cerium oxide:prepa-ration and properties of weakly-agglomerated powders.Jour-nal ofthe European Ceramic Society,1999,19:1925.[18]Dikmen S,Shuk P,Greenblatt M,Gomez H.Hydrothermalsynthesis and properties of Ce1-x Gd x O2-δsolid solutions.Solid State Sciences,2002,4:585.[19]Sin A,Odier P.Gelation by acrylamide,a quasi-universal me-dium for the synthesis of fine oxide powders for electroce-ramic applications.Advanced Materials,2000,12:649 [20]Zhang X,Robertson M,Deces-Petit C,Qu W,Kesler O,MaricR,Ghosh D.Internal shorting and fuel loss of a low tempera-ture solid oxide fuel cell with SDC electrolyte.Journal of Power Sources,2007,164:668.。
以氢键为链接基的偶氮液晶分子的合成和研究
Ｋｅ ｙ ｗｏ ｒ ｄｓ：Ｈ— ｂｏ ｎｄ ｌ ｉ ｑ ｕｉ ｄ ｃ ｒ ｙｓ ｔ ａ ｌ ；ｓ ｕｐ ｅ ｒ — ｍｏ ｌ ｅ ｃ ｕ ｌ ｅ ｓ；ｐｙ ｒ ｉ ｄ ｉ ｎｅ；ａ ｚ ｏ
摘 要 ： 以氢键 作 为链 接 基 元 ， 合 成 了吡 啶 羧 酸 类 的 氢键 液 晶 ， 通过 核 磁 氢谱 和 红 外 光谱 对 所得 中 间体 和 最终 产 物 的结 构进 行 了分 析 ， 并 且 通过 偏 光 显微 镜 （ Ｐ ＯＭ） ， 对 所 得 最 终 产 物 的液 晶性 能 进 行 了测 定 ， 得出 该 类 复 合物 具 有 室 温液 晶 性和 宽 的相 转 变温 度． 关键词： 氢键 液 晶 ； 超分子； 吡啶 ； 偶 氮
中图 分 类号 ： ０６ ２ 文 献标 识 码 ： Ａ
Ｓ ｙ ｎ ｔ ｈ ｅ ｓ ｉ ｓ ａ ｎ ｄ Ｃｈ ａ ｒ ａ ｃ ｔ ｅ ｒ ｉ ｚ ａ ｔ ｉ ０ ｎ ０ ｆ Ａｚ ｏ Ｌｉ ｑ ｕ ｉ ｄ Ｃｒ ｙ ｓ ｔ ａ ｌ ｌ ｉ ｎ ｅ
Ｃｏ ｍ ｐｌ ｅ ｘ ｅ ｓ Ｌｉ ｎｋ ｅ ｄ ｗｉ ｔ ｈ Ｈｙ ｄ ｒ ｏ ｇ ｅ ｎ Ｂｏ ｎ ｄ
氢键是生物和化学过程中 一种重要的 作用力， 同时在分
近些年来， 通过氢键自 组作用． 在液晶中， 氢键作用 晶和主链液晶虽然已被合成出来［ ５ － ７ ￣ ， 并作为一种功能材 光致二极管和激发晶体管等领 力被用来 作为组装分子以形成液晶相的关键推动力， 比如 料应用在在光电转换， ８ ＿ ｜ １ ， 但在液晶材料本身性质的 应用方面， 占 大份额的 仍 说， 通过分子自 组装形成的吡啶羧酸类的 液晶分子就是通过 域［ 氢键的 相互作用力来完成的， 其中， 吡啶类衍生物作为氢键 然 是小 分子液晶． 本文通过以吡啶类衍生物作为氢键受体，
20.Chinese Characters
01
Chapter 1: The History of Chinese Characters
Chapter 1: The History of Chinese Characters
• Chinese characters, also known as Hanzi, are logograms developed for the writing of the Chinese language. The history of Chinese characters can be traced back over 3,000 years to the Shang dynasty. The development of Chinese characters has been a reflection of the cultural and technological advancements of ancient China.
• Origin and Evolution • Cultural Significance • Influence Beyond Language
Origin and Evolution
• The origins of Chinese characters can be found in ancient inscriptions on oracle bones and bronze ware. These early forms of writing consisted of simple pictograms and ideograms representing objects and ideas. Over time, the characters evolved into more intricate forms, incorporating phonetic elements and semantic radicals.
Synthesis and characterization of antimony-doped tin oxide (ATO) nanoparticles by a new hydrothermal
Materials Chemistry and Physics87(2004)10–13Materials science communicationSynthesis and characterization of antimony-doped tin oxide(ATO) nanoparticles by a new hydrothermal methodJianrong Zhang,Lian Gao∗State Key Lab of High Performance Ceramics and Superfine Microstructure,Shanghai Institute of Ceramics,Chinese Academy of Sciences,Shanghai200050,PR ChinaReceived31March2004;received in revised form21May2004;accepted7June2004AbstractAntimony-doped tin oxide(ATO)nanoparticles have been synthesized by mild hydrothermal method free from the widely used metal chlo-rides.The obtained particles were characterized by means of XRD,BET,Hall effect measurements,XPS and TEM.X-ray diffraction shows that all Sb ions came into the SnO2lattice to substitute Sn ions,though the hydrothermal temperature was as low as120◦C.Increasing the heat treatment temperature accelerates the growth of the nanoparticles,changes the electrical conductivity,the distribution of the Sb ions and relative amount of the two oxidation states Sb5+and Sb3+.TEM shows the ATO nanoparticles were monodispersed in the range of3–5nm.©2004Elsevier B.V.All rights reserved.Keywords:Tin(IV)oxide;Doping;Hydrothermal synthesis;XPS1.IntroductionAntimony-doped tin oxide(ATO)is an important mem-ber of transparent conductive oxides(TCOs)[1–3]that hasbeen extensively studied for its chemical,mechanical andenvironmental stabilities[4].ATOfilms are highly conduct-ing,and electrons can tunnel easily in either direction be-tween the adsorbed electroactive species and the SnO2con-duction band[5].The introduction of Sb into the tin oxidelattice greatly increases the electron conductivity,which ren-ders this material used as an excellent conductive agent[6].ATO is transparent throughout the visible region,while re-flects infrared light.These features enable ATO to be used astransparent electrodes,heat mirrors and energy storage de-vices,have potential uses in photovoltaic and optoelectronicdevices[7,8].Nanoparticulate ATO has been used as elec-trochromic material for the production of printed displays[9]and anode material in lithium-ion batteries[10].In ad-dition,ATO has applications in nuclear waste management,good catalyst for olefin oxidation[11,12].So far,ATO particles have been synthesized by solid-statereaction[13],coprecipitation[6,7,9],Pechini[13]and hy-drothermal methods[14].The coprecipitation improves the∗Corresponding author.Tel.:+86-21-5241-2718;fax:+86-21-5241-3122.E-mail address:liangaoc@(L.Gao).reactivity of the components and Pechini method enhancesthe chemical homogeneity.But a post-calcination at over500◦C is required to incorporate Sb atoms into the tin ox-ide lattice;as a consequence,a large particle size and heavydegree of agglomeration are rge amount oforganic compounds employed in the Pechini method act notonly as complexes,but also as fuel,evolving much heat dur-ing calcination,which accelerates the growth and agglomer-ation of obtained ATO particles.The hydrothermal methoddoes not need a calcination process,and the dispersity ofthe particles is greatly improved,but a comparatively highhydrothermal temperature(270◦C)is needed.The startingmaterials used in the wet chemical methods are all frommetal chlorides,such as SnCl4,SnCl2,SbCl3and SbCl5.Itis well known that chlorine ions adsorbed on tin hydrox-ide are very difficult to be removed,and large amount ofproduct is lost during the repeated washing.The residualchlorine ions affect the surface and electrical properties,leading to both volatile antimony and tin compounds,caus-ing agglomeration among particles and sintering to highertemperature[15].For these reasons,new methods shouldbe developed to improve the yield and quality of ATOnanoparticles.In this paper,we report a new method for direct synthesisof conductive ATO nanoparticles with high specific surfaceareas by mild hydrothermal process from the starting mate-rials granulated tin and Sb2O3.The influence of hydrother-0254-0584/$–see front matter©2004Elsevier B.V.All rights reserved.doi:10.1016/j.matchemphys.2004.06.004J.Zhang,L.Gao /Materials Chemistry and Physics 87(2004)10–1311mal treatment temperature on the crystallite size,lattice pa-rameters,electrical conductivity and surface properties of the ATO nanoparticles is discussed.2.ExperimentalIn a typical synthesis,30mL of concentrated HNO 3(67wt.%)was poured into a stainless Telfon-lined 100-mL capacity autoclave containing 2g of granulated tin (pu-rity 99.95%),calculated amount of Sb 2O 3(the molar ratio [Sb]/[Sn]was set at 5:100in all reactions)and 50mL of H 2O.A large amount of brown gas (NO 2)gave off immedi-ately,and the mixed starting materials turned into a yellow colloid.The autoclave was sealed and heated to maintain at 120–170◦C for 10h,and then air-cooled to room tempera-ture.The resulting blue-colored products (characteristic of ATO particle)were collected and washed with water and enthanol,finally dried at 100◦C for 5h.The ATO nanoparticles obtained at different hydrother-mal temperatures were characterized by powder X-ray diffraction (XRD)(Model D/MAX 2550v;Rigaku Co.,Tokyo,Japan)with λ=0.15418nm,Cu K ␣and transmis-sion electron microscopy (TEM)(JEM-200CX TEM).The specific surface area of the powders was measured with a Micromeritics ASAP 2010analyzer using the multipoint Brunauer,Emmett and Teller (BET)adsorption and the av-erage grain size (d BET )of the particles were calculated from the formula d =6/ρA ,where ρis the theoretical density of SnO 2and A is the specific surface area of the powder.The conductivity of the 500MPa uniaxially pressed pellets was measured by the Hall effect measurements.The X-ray photoelectron (XPS)measurements were carried out at Mi-crolab 310-F Spectrometer with an X-ray gun for Mg K ␣radiation.The step width was 0.1eV and the spectra were referred to C1s emission at 284.6eV .3.Results and discussionFig.1shows the XRD patterns of the ATO nanoparticles.All peak positions agree well with the reflections of bulk cassiterite SnO 2.No phase ascribed to antimony compounds was detected,indicating that all antimony ions came into the lattice of bulk SnO 2to substitute for tin ions [7].The widths of the reflections were considerably broadened,and the av-Table 1Characterizations of the hydrothermally synthesized ATO nanoparticles Hydrothermal temperature (◦C)Lattice parameter D XRD (nm)Surface area (m 2g −1)d BET (nm)Conductivity (102S cm −1)a (Å)c (Å)V (Å3)120 4.758 3.18472.08 2.7234 3.72140 4.737 3.18671.49 3.2216 4.081704.7533.17871.794.01874.661020304050607080(310)(002)(220)(211)(200)(101)(110)(c)(b)(a)I n t e n s i t y /(a .u .)2θ/(o)Fig.1.XRD patterns of the ATO nanoparticles hydrothermally synthe-sized at different temperatures:(a)at 120◦C;(b)at 140◦C;(c)170◦C,respectively.erage crystallite sizes of the particles determined from the (110)plane by the Scherrer’formula were listed in Table 1.The size increased from 2.7nm at 120◦C to 3.2nm at 140◦C and 4.0nm at 170◦C,respectively.To the authors’knowl-edge,the specific surface areas are the largest,correspond-ingly decreased from 234m 2g −1at 120◦C to 187m 2g −1at 170◦C,which witnessed the growth of the nanoparti-cles.The much high surface areas may be ascribed to the free of Cl −ions that cause agglomeration among particles and the advantage of hydrothermal synthesis.The compar-ison of the crystallite size and the particle size calculated based on the surface area reveals that the nanoparticles are almost monodispersed.The lattice parameters determined by least-squares refinement are listed in Table 1.The unit cell volume of the sample obtained at 120◦C (72.08Å3)is larger than the pure SnO 2(71.56Å3JCPDS 21–1250),de-creased to 71.49Å3at 140◦C,again increased to 71.79Å3at 170◦C,respectively.The reason can be explained as fol-lows.On one hand,nanocrystalline oxide particles exhibit a lattice expansion with reduction in particle size [16].On the other hand,the antimony incorporated into the SnO 2lat-tice exists in two oxidation states,Sb(III)and Sb(V);the Sb(V)has a smaller ionic radius (r =0.60Å)than tin ion (r =0.69Å),while Sb(III)ion (r =0.76Å)is larger than tin ion [7].So,the Sb(III)/Sb(V)content ratio can change the lattice parameters.Taking no consideration of the expansion of the crystallite size on the lattice parameters,we suppose that in the 120◦C sample,most of the Sb ions are in Sb(III)12J.Zhang,L.Gao /Materials Chemistry and Physics 87(2004)10–13oxidation state;so,the unit cell volume is much larger than pure tin oxide.When the hydrothermal temperature was in-creased to 140◦C,most of the Sb(III)ions are oxidated to Sb(V);as a result,the cell volume decreased,even smaller than pure tin oxide.Further increase in the temperature to 170◦C,most of the Sb(V)ions again reduced to Sb(III)or some of the Sb ions are separated to the grain surface and the cell volume increased.This supposition can be supported by the electrical measurements and X-ray photoelectron spec-troscopy (XPS).The electrical conductivities of the ATO nanoparticles were also shown in Table 1.The conductivities were several orders of magnitude higher than the pure SnO 2,increased from 2×102S cm −1at 120◦C to the highest value at 140◦C,8×102S cm −1,and again reduced to 6×102S cm −1at 170◦C,respectively.These values are lower than the dense ATO films [17],which are ascribed to a high activation energy for electron to cross the grain boundaries between the nanoparticles.The conductivity mechanism of the ATO material is well known,the Sb(V)ions incorpo-rated into the SnO 2lattice act as an electron donors,while the Sb(III)ions compensate the donor electrons.At higher calcination temperatures (>600◦C)[18],the antimony ions incline to segregate to the grain boundary,trapping an electron pair in the bulk bandgap [19].So,the change of conductivity with the hydrothermal temperature is ascribed to the change of Sb(V)/Sb(III)ratio or the segregation of Sb.To further elucidate the relation between lattice param-eter and electrical conductivity of the ATO nanoparticles,we investigated the surface properties of the ATO materi-als by XPS,which is powerful to obtain surface informa-tion of the ATO particles [16].Because of overlapping of O1s and Sb3d5/2lines,the Sb3d3/2line is used to deter-mine the Sb concentration by making use of the relation between the prewave of Sb3d5/2and Sb3d3/2ratio fixed to be 1.44.A typical entire spectrum of the particles ob-tained at 140◦C is shown in Fig.2.The binding energy of1000800600400200I n t e n s i t y /C P S Binding Energy/(eV)Fig.2.XPS survey spectrum of the nanoparticles hydrothermally synthe-sized at 140◦C.Table 2XPS investigations of the ATO nanoparticles obtained at different tem-peratures Hydrothermal temperature (◦C)Binding energy (eV Sb3d3/2)[Sb 5+]/[Sb](%)Sb surface enrichment 120539.6521140539.8087 1.3170539.72533.2the Sb3d3/2as a function of hydrothermal temperature is shown in Table 2.As can be seen,the binding energy shifts from 539.65eV at 120◦C to 539.80eV at 140◦C,again de-creases to 539.70eV at 170◦C,respectively.The shift to higher binding energy declares that an increasing amount of Sb ions are in the oxidation state +5.The distribution be-tween Sb 3+and Sb 5+,and surface enrichment of Sb ions were also listed in Table 2.In the 120◦C hydrothermally treated sample,almost all the Sb ions are in the oxidation state +3,which leads to a lattice expansion and a low electri-cal conductivity.The Sb ions are homogeneously distributed in the material and shows no Sb surface enrichment.Increas-ing the treatment temperature to 140◦C,most of the Sb ions are oxidated to Sb 5+and evolve large amount of electrons,the unit cell volume decreased sharply,the Sb ions showed a tendency to segregate to the surface of the ATO nanopar-ticles.Further increase in the temperature to 170◦C,more Sb ions are segregated to the particle surface and the surface enrichment increases to about 2.5,which had been observed by other authors [20,21].The enriched Sb ions are in the oxidation state +3,as a consequence,the unit cell volume shrinks and the electrical conductivity decreases.What the XPS results correlates perfectly with the XRD and electricalmeasurements.Fig.3.TEM image of the ATO nanoparticles obtained at 140◦C.J.Zhang,L.Gao/Materials Chemistry and Physics87(2004)10–1313The mechanism of the formation of conductive ATOnanoparticles at comparatively low temperature can bedescribed as follows.As HNO3was added to the mixedstarting materials,a reaction occurred3Sn+Sb2O3+6H+→3Sn2++2Sb+3H2OThen,the excessive HNO3also oxidized the unreactedSn and freshly obtained Sn2+,Sb,rendering these metalions highly activated,which was evidenced by the appear-ance of the colloid.In the following hydrothermal pro-cess,the antimony ions were very easy to incorporate intoSnO2lattice and endow the nanocrystals with electricalconductivity.Fig.3shows TEM image of the ATO nanoparticles hy-drothermally treated at140◦C.All particles have a size rang-ing from3–5nm,average size of4nm with well-definededges.The nanoparticles were monodispersed in accordancewith what the above had revealed.4.ConclusionsMonodispersed ATO nanoparticles with high specific sur-face areas has been synthesized by hydrothermal method.The method free form chlorides shortened the synthesisprocess and improve the particle quality,the use of acti-vated intermediates greatly decreased the hydrothermal tem-perature to120◦C.The highest electrical conductivity(8×102S cm−1)is obtained at a hydrothermal temperature 140◦C,accompanied with the smallest unit cell volume(71.49Å3)and the highest Sb5+concentration,about87%of the Sb ions are in the oxidation state Sb5+.This methodputs forward a new strategy to synthesize multicomponentnanocrystalline oxides.References[1]T.T.Emons,J.Q.Li,L.F.Nazar,J.Am.Chem.Soc.124(2002)8516.[2]C.Goebbert,R.Nonninger,M.A.Aegerter,A.Schmidt,Thin SolidFilms351(1999)79.[3]K.Y.Rajpure,M.N.Kusumade,M.N.Neumann-Spallart, C.H.Bhosale,Mater.Chem.Phys.64(2000)184.[4]A.Gamard,O.Babot,B.M.C.Jousseaume Rascle,T.Toupance,G.Campet,Chem.Mater.12(2000)3419.[5]G.C.Jorge,P.M.Andrew,urence,D.W.Michael,Angew.Chem.Ed.42(2003)3011.[6]Z.C.Orel,B.Ore,M.Hodoscek,V.Kaucic,J.Mater.Sci.27(1992)313.[7]J.Rockenberger,U.Felde,M.Tisher,L.Troger,M.Haase,H.Weller,J.Chem.Phys.112(2000)4296.[8]H.S.Varol,A.Hinsch,Sol.Energ.Mat.Sol.C40(1996)273.[9]J.P.Coleman,J.J.Freeman,P.Madhukar,J.H.Wagenknecht,Displays20(1999)145.[10]A.C.Bose,D.Kalpana,P.Thangadurai,S.Ramasamy,J.PowerSource107(2002)138.[11]V.Dusatre,D.E.William,J.Phys.Chem.B102(1998)6732.[12]R.koivula,R.Hajula,J.Lehto,Micropor.Mesopor.Mater.55(2002)231.[13]M.I.B.Bernardi,S.Cava,C.O.P.Santos,E.R.Leite,C.A.Paskocimas,E.Longo,J.Eur.Ceram.Soc.22(2002)2911.[14]T.Nuta,U.Felde,M.Haase,J.Chem.Phys.110(1999)12142.[15](a)O.Vasykiv,Y.Sakka,J.Am.Ceram.Soc.84(2001)2489;(b)J.S.Pena,T.BrousseL.Sanchez,J.Morals,D.M.Schleich,J.Power Sources9798(2001)232;(c) A.Roosen,H.Hausener,Adv.Ceram.Mater.3(1988)131.[16]P.Vaqueiro,M.A.Lopez-Quintela,Chem.Mater.9(1997)2836.[17]K.Y.Rajpure,M.N.Kusumade,M.N.N.Spallart, C.H.Bhosale,Mater.Chem.Phys.64(2000)184.[18]K.Sun,J.Liu,N.D.Browning,J.Catal.205(2002)266.[19]R.G.Egdell,T.J.Walker,G.Beamson,J.Electron.Spectrosc.Relat.Phenomena128(2003)59.[20]D.Szczuko,J.Werner,S.Ostwald,S.G.Behr,K.Wetzig,Appl.Surf.Sci.179(2001)301.[21]J.C.V olta,P.Bussiere,G.Coudurier,J.Herrmann,J.C.Vedrine,Appl.Catal.16(1985)315.。
Synthesis and characterization of ATO SiO2 nanocomposite coating obtained by sol–gel method
Synthesis and characterization of ATO/SiO 2nanocompositecoating obtained by sol–gel methodXiaoChuan Chen *The Key Laboratory of Materials Physics,Institute of Solid State Physics,Chinese Academy of Sciences,Hefei 230031,People’s Republic of ChinaReceived 19June 2004;accepted 20December 2004Available online 11January 2005AbstractA new sol–gel route was developed for synthesizing homogeneous nanocomposite thin film that was composed of Sb-SnO 2(ATO)nanoparticles and silica matrix.TEM studies show that as-prepared composite thin film contains the amorphous silica matrix and ATO nanocrystalline particles that were dispersed homogeneously in silica matrix.The oxalic acid is an excellent dispersant for colloidal stability of ATO aqueous sol at pH b 5.The result of Zeta potential measurement shows that dispersion mechanism comes from the chemisorption of oxalic acid on the surface of ATO nanoparticles.The thermal treatment in reducing atmosphere considerably promotes grain growth of ATO nanoparticles and changes the optical property of ATO/SiO 2nanocomposite thin film.D 2005Elsevier B.V .All rights reserved.Keywords:Sol–gel preparation;Thin films;Nanocomposites;Sb-doped SnO 21.IntroductionTin oxide is a wide band gap nonstoichiometric semi-conductor with a low n-type resistivity [1–3].The resistance can be reduced further by doping Sb,F elements [4,5].F-doped SnO 2(FTO),Sb-doped SnO 2(ATO)conducting thin films not only have high transparency in the visible region but also are good infrared reflecting materials [6,7].ATO thin films have been used in many fields such as heat shielding coating on low-emissivity window for energy saving [8].Fabrication techniques used to deposit ATO thin film include dip coating based on sol–gel method;sputtering and spray pyrolysis.The sol–gel route has several advantages over the other method.It is a low cost and simple process and makes the precise control of doping concentration easier [9,10].In order to improve the scratching abrasive resistance of ATO thin film prepared by sol–gel route [11,12]a novel sol–gel route has been proposed.In this technological process an organic–inorganic hybrid silica sol was used as the pre-cursor of protecting matrix.The ATO functional componentwas homogeneously distributed in a transparent silica matrix.The mixed structure is of benefit to preventing the crack of thin film in drying and annealing process [13].When a composite material containing two oxides with different pho-to index hopes to keep high transmittance in visible light re-gion the second phase component must be dispersed homogeneously into the amorphous matrix at a level of nanometer.In this work a transparent nanocomposite thin film com-posed of ATO and silica was synthesized by the sol–gel route.The sol–gel method includes (a)the synthesis of ATO sol and hybrid organic–inorganic silica sol;(b)mixing of two nanoparticulate sols.A TEM investigation of phase structure in ATO–silica composite gel is reported.The optical proper-ties and crystallizability of composite thin film is discussed.2.Experimental2.1.Preparation of ATO aqueous solAll the chemical reagents used in the synthesis experi-ment were obtained from commercial sources without0167-577X/$-see front matter D 2005Elsevier B.V .All rights reserved.doi:10.1016/j.matlet.2004.12.033*Tel.:+865515591477;fax:+865515591434.E-mail address:chenxiaochuan126@.Materials Letters 59(2005)1239–1242/locate/matletfurther purification.The aqueous ATO sol were prepared by a co-precipitation process from hydrolysis of SnCl4d5H2O and SbCl3,and followed by the peptization of the precipitate. The reaction was performed at room temperature.In the co-precipitation procedure aqueous NH4OH solution was added directly to the mixture solution of SnCl4d5H2O and SbCl3 until the pH of the mixture reach6–8,where pale yellow ATO hydroxide precipitate were produced.Peptization of ATO hydroxide with the aqueous solution containing oxalic acid gives a yellowish transparent sol.Finally ATO sol was heated and refluxed at608C for4h.2.2.Synthesis of hybrid organic–inorganic silica solThe hybrid organic–inorganic silica-based sols were synthesized as follows:First a mixture solution of tetrae-thoxysilane(TEOS),3-glycidoxypropyltrimethoxysilane (GPTS),isopropyl and alcohol in weight ratio1:1:2.5:3.5 was prepared.Then a suitable amount of deionized water (pH=1,by HCl addition)was added to the mixture solution. The mole ratio of TEOS and H2O is about1:6to1:8.The mixed solution was stirred and heated under reflux at808C for16h.The synthesized transparent hybrid silica sol was used as protecting component of nanocomposite thin film.2.3.Preparation of ATO/SiO2nanocomposite thin filmsA transparent functional gelled film was deposited from the mixture sol comprising the hybrid organic–inorganic silica sol and the ATO sol.Deposition was performed on the glass substrate at room temperature by a simple dip coating process.After being dried at room temperature the nano-composite gelled thin film was thermally densified at a temperature up to4008C in a reducing atmosphere containing N2and vapor of alcohol.2.4.InstrumentationThe Zeta potential measurement of the0.5wt.%ATO aqueous sol was carried out with a ZETASIZER3000HS A measuring system(MALVERN).0.1N HNO3was used to adjust the pH of reference ATO sol that does not contain oxalic acid.The X-ray diffractometer(XRD)was used for the structural characterization of the as-dried and thermally densified ATO–SiO2nanocomposite material.The micro-structure feature of nanocomposite gel film and annealed film were observed with a transmission electron microscope (TEM)(type JEM-2010).The sample for TEM study was prepared as follows:A droplet of mixed sol consisting of ATO colloidal sol and hybrid silica sol was dropped on a copper grid covered with organic film,and after solvents were vaporized a nanocomposite thin film was deposited on the copper grid.The chemical composition of annealed nanocomposite thin film was measured using an energy dispersive X-ray analysis system(EDS)equipped with a scanning electron microscope.Optical transmission was determined using a Varian Cary5E spectrophotometer in the wavelength range of300–2500nm.3.Results and discussion3.1.Surface adsorption studiesWhen oxalic acid was added to the ATO suspension the pH of suspension was adjust to2by the ionization of oxalic acid.Peptization with oxalic acid turns slowly the initial turbid ATO suspension into transparent stable sol.If without addition of oxalic acid ATO nanoparticles in the suspension will show aggregating behavior and begin precipitating at pH b5.The experimental result tells us that colloidal stability of ATO sol comes from addition of oxalic acid.Oxalic acid molecule acts as a surface-modifying agent and prevents aggregation of ATO particles.Fig.1shows the result of Zeta potential measurement at different pH level.The date shows that surface of ATO nanoparticles in aqueous sol is positively charged at pH\5without the addition of oxalic acid.The addition of oxalic acid decreases the Zeta potential of surface and changes the surface to a negative charge in the pH range2–4.According to the dissociation constant of oxalic acid the neutral molecules and negatively charged HO–(CO)2–OÀ1ions are predominant components in aqueous solution at2b pH b3.In initial suspension surface of ATO nanoparticles has a charge especially opposing the oxalic acid ions.The electrostatic force generated by the opposing charges will facilitate the ions transport stage of adsorption reaction.Now we assume that markedinteraction Fig.1.Zeta potential of ATO aqueous sol as a function of pH;0.5wt.% ATO content was used.X.C.Chen/Materials Letters59(2005)1239–1242 1240exist between oxalic acid ions and positive surface hydroxylgroups Q Sn–OH 2+or neutral surface hydroxyl groups Q Sn–OH.The oxalic acid ions can be preferentially adsorbed to the surface of ATO nanoparticles by hydrogen bond or Q Sn–O–C bond.The adsorbed ions neutralize surface positive charges and ultimately reverse the surface to a negative Zeta potential.Fig.1shows that the magnitude of negative Zeta potential is not large enough to stabilize the ATO nanoparticle electrostatically in sol.After oxalic acid was added to the suspension the transparent sol is found to remain stable almost infinitely at pH b 4.The only possible explanation is that effective dispersion mechanism comes from a combination of electrostatic and steric repulsion between oxalic acid ions that were adsorbed on surface of different ATO particles.3.2.XRD and EDS studiesFig.2shows XRD spectra of the ATO–silica nano-composite sample.The pattern (a)relates to the nano-composite gel obtained as dried at room temperature and the pattern (a)shows the presence of a very broad diffraction peak attributable only to cassiterite structure.The XRD patterns of nanocomposite samples show little difference between as-dried and thermally densified samples.Theresult indicates that ATO colloidal particles have developed a nanocrystal structure of cassiterite during sol preparation which contains a hydrothermal process at 608C.TheFig.2.XRD pattern of ATO–SiO 2composite gel:(a)as-dried at room temperature;(b)heat-treated at 5008C in air for 1h.Table 1Elemental concentration of ATO/SiO 2nanocomposite thin film Sample Atomic concentration,%V olume ratio,SiO 2/ATO O Si Sn Sb As-dried69.6917.2510.722.351.5Fig.3.Diffraction pattern and TEM image of ATO–SiO 2nanocomposite thin film as-dried at room temperature:(a)ED pattern;(b)TEMimage.Fig.4.Diffraction pattern and TEM image of ATO–SiO 2composite thin film thermal-treated at 3008C in reducing atmosphere for 2h:(a)ED pattern;(b)TEM image.X.C.Chen /Materials Letters 59(2005)1239–12421241hydrothermal process under atmosphere is also an effective method for promoting the crystallization of ATO nano-particles in the aqueous solution [14,15].The element contents in ATO–SiO 2film are shown in Table 1.Measured Si/Sn+Sb atom ratio of sample is about 1.3:1.The SiO 2/ATO volume ratio in the nanocomposite is calculated from the atom ratio and theory density.3.3.TEM and UV–Vis–Nir spectra studiesThe TEM image of as-dried ATO–SiO 2nanocomposite thin film is shown in Fig.3(b).We can observe that ATO nanoparticles are homogeneously dispersed in SiO 2-based amorphous matrix without any evidence of aggregation.ATO grains are found to have a size range of 3–5nm in diameter.Fig.3(a)shows a typical electron diffraction pattern of ATO nanocrystalline grain.Four electron dif-fraction (ED)rings can be indexed to the pattern of ATO with cassiterite structure.The result is in good agreement with XRD analysis.The structural change induced by thermal treatment of ATO thin film has been investigated.Fig.4shows the ED pattern and TEM image taken from ATO–SiO 2nanocomposite thin film which was annealed at 3008C in reducing atmosphere.The contrast morphology in this image shows some large crystal grains with diameter range from 20nm to 25nm.The ED pattern taken from the same sample contains some sharp spots resulting from thelarge crystallites.The observed results indicate that thermal treatment in reducing atmosphere can accelerate grain growth of ATO nanoparticles.The growth of crystal grain was accompanied by the disappearance of grain boundary and increased electrical conductivity and Nir-light reflec-tance of ATO film [1].The optical transmission spectra of ATO thin film deposited on the glass substrate of 1mm thick are shown in Fig.5.A high transmission of 85%is observed in the visible region.The reduction of transmission in the Nir wavelength arises from improved conductivity of nanocrystalline ATO particles that were heat-treated in the reducing atmosphere.4.ConclusionsThe transparent ATO–SiO 2nanocomposite thin films have been prepared successfully by the sol–gel method.The transmission of thin film is rather high in the visible region,range between 85%and 90%as well as the transmission in Nir region has been decreased to 41%.The thermal treatment in reducing atmosphere is an effective method for promoting crystalline grain growth of ATO nanoparticles.The oxalic acid is an excellent dispers-ing agent for ATO nanoparticle in the aqueous solution in pH range 2–4.References[1]G.Frank,E.Kauer,H.Kostlin,Thin Solid Films 77(1981)107.[2]M.S.Castro,C.M.Aldao,J.Eur.Ceram.Soc.20(2000)303.[3]O.Safonova,I.Bezverkhy,P.Fabrichnyi,M.Rumyantseva, A.Gaskov,J.Mater.Chem.7(1997)997.[4]S.Shanthi,C.Subramanian,P.Ramasamy,Cryst.Res.Technol.34(1998)1037.[5]A.E.Rakhshani,Y .Makdisi,H.A.Ramazaniyan,J.Appl.Phys.83(2)(1998)1049.[6]C.Goebbert,R.Nonninger,M.A.Aegerter,H.Schmidt,Thin SolidFilms 351(1999)79.[7]C.Terrier,J.P.Chatelon,J.A.Roger,Thin Solid Films 295(1997)95.[8]H.Ohsaki,Y .Kokubu,Thin Solid Films 351(1999)1.[9]M.A.Aegerter,N.Al-Dahoudi,J.Sol–Gel Sci.Technol.27(2003)81.[10]A.N.Banerjee,S.Kundoo,P.Saha,K.K.Chattopadhyay,J.Sol–GelSci.Technol.28(2003)105.[11]S.W.Kim,Y .W.Shin,D.S.Bae,J.H.Lee,J.Kim,H.W.Lee,ThinSolid Films 437(2003)242.[12]K.Abe,Y .Sanada,T.Morimoto,J.Sol–Gel Sci.Technol.26(2003)709.[13]J.Gallardo,A.Duran,I.Garcia,J.P.Celis,M.A.Arenas,A.Conde,J.Sol–Gel Sci.Technol.27(2003)175.[14]D.Y .Zhang,D.Z.Wang,G.M.Wang,Y .H.Wu,Z.Wang,Mater.Sci.Eng.,B,Solid-State Mater.Adv.Technol.8(1991)189.[15]S.J.Kim,S.D.Park,Y .H.Jeong,S.Park,J.Am.Ceram.Soc.82(1999)927.Fig.5.UV–Vis–Nir transmission spectra:(a)550nm thick ATO–SiO 2thin film which was coated on glass substrate;(b)glass substrate.X.C.Chen /Materials Letters 59(2005)1239–12421242。
acs catalysis 模板 -回复
acs catalysis 模板-回复题目：The Role of Heterogeneous Catalysts in Sustainable Chemical ProcessesAbstract:Heterogeneous catalysis plays a crucial role in sustainable chemical processes by providing efficient routes for the production of various chemicals with reduced energy consumption and environmental impact. This article aims to provide a comprehensive understanding of the mechanisms involved in heterogeneous catalysis and highlight its potential contributions to a sustainable future. We will discuss the synthesis and characterization of catalysts, as well as their applications in key chemical reactions. Additionally, we will explore recent advancements in catalyst design and optimization, with a focus on improving selectivity, activity, and stability. By elucidating the fundamentals of heterogeneous catalysis, this article aims to inspire further research efforts for the development of innovative catalysts for sustainable chemical processes.1. Introduction1.1. Importance of sustainable chemical processes1.2. Role of heterogeneous catalysis in sustainable chemistry2. Catalyst Synthesis and Characterization2.1. Preparation methods of heterogeneous catalysts2.2. Characterization techniques for catalyst analysis2.3. Catalyst support materials and their impact on catalytic performance3. Catalytic Reactions and Mechanisms3.1. Principles of catalytic reactions3.2. Heterogeneous catalysis mechanisms3.3. Kinetics and reaction engineering in heterogeneous catalysis4. Applications of Heterogeneous Catalysts4.1. Continuous-flow catalysis for sustainable chemical processes 4.2. Selective catalysis for high-value chemical synthesis4.3. Catalysts for renewable energy conversion5. Catalyst Design and Optimization5.1. Rational catalyst design strategies5.2. Advances in catalyst engineering for enhanced activity and selectivity5.3. Stability and regeneration of heterogeneous catalysts6. Challenges and Future Perspectives6.1. Catalyst deactivation and poisoning6.2. Catalysis under harsh conditions6.3. Emerging trends in catalysis for sustainable chemistry7. Conclusion1. Introduction1.1 Importance of sustainable chemical processesIn recent years, the necessity of sustainable chemical processes has become apparent due to growing concerns about climate change and the depletion of fossil fuels. Sustainable chemistry aims to minimize the environmental impact of chemical processes while maximizing resource efficiency. By employing clean energy sources, reducing waste production, and increasing energy efficiency, sustainable chemical processes can contribute to the development of a greener and more sustainable society.1.2 Role of heterogeneous catalysis in sustainable chemistry Heterogeneous catalysis, the process in which reactants undergochemical transformations on the surface of a solid catalyst, has emerged as a key tool for sustainable chemical processes. By accelerating the rates of chemical reactions, heterogeneous catalysts enable the production of desired products with reduced energy consumption and lower emissions of greenhouse gases. Moreover, heterogeneous catalysis allows for the utilization of renewable feedstocks and the selective synthesis of valuable chemicals, thus reducing dependency on petrochemicals and fossil fuel resources.2. Catalyst Synthesis and Characterization2.1 Preparation methods of heterogeneous catalystsThe synthesis of heterogeneous catalysts involves the preparation of catalyst materials and their subsequent activation before use. Various methods, such as impregnation, precipitation, sol-gel, and deposition, are employed depending on desired catalyst characteristics and the nature of the catalytic process. These synthesis routes enable the control of particle size, surface area, pore size distribution, and active site density, which can significantly influence catalytic performance.2.2 Characterization techniques for catalyst analysisTo understand the structure and composition of catalyst materials, several characterization techniques are employed. X-ray diffraction (XRD) provides information about crystalline phases, while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal particle morphology and size. Surface techniques like X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) provide insights into surface composition, elemental distribution, and chemical composition. Catalyst characterization helps in correlating structure-property relationships and optimizing catalytic performance.2.3 Catalyst support materials and their impact on catalytic performanceSupport materials, such as metal oxides, zeolites, and carbon materials, play a crucial role in heterogeneous catalysis. They provide a high surface area for catalyst deposition, improve catalyst stability, and influence activity and selectivity. The choice of support material depends on the nature of the catalytic reaction, and careful selection can enhance catalyst performance and durability.3. Catalytic Reactions and Mechanisms3.1 Principles of catalytic reactionsCatalytic reactions occur through a series of elementary steps, including adsorption, surface reactions, and desorption. Catalysts facilitate the conversion of reactants to products by lowering the activation energy barrier, thus increasing reaction rates.3.2 Heterogeneous catalysis mechanismsIn heterogeneous catalysis, reactants adsorb on the catalyst surface, where reactions take place. The Langmuir-Hinshelwood andEley-Rideal mechanisms are commonly observed, involving adsorption and reaction of the reactants on the same or different active sites, respectively. Reaction intermediates formed during these mechanisms ultimately lead to the formation of final products.3.3 Kinetics and reaction engineering in heterogeneous catalysis Understanding the kinetics of catalytic reactions is crucial for reaction optimization and reactor design. Kinetic models, such as the rate equation based on the reaction mechanism, can be employed to determine reaction kinetics and identifyrate-determining steps. Reaction engineering principles help inmaximizing reaction efficiency, enhancing catalyst performance, and scaling up catalytic processes.4. Applications of Heterogeneous Catalysts4.1 Continuous-flow catalysis for sustainable chemical processes Continuous-flow catalysis allows for efficient and controlled chemical reactions in a continuous manner, offering improved energy efficiency, product selectivity, and process safety. It has found applications in various reactions, such as hydrogenation, oxidation, and polymerization, enabling sustainable chemical synthesis and reducing waste production.4.2 Selective catalysis for high-value chemical synthesis Heterogeneous catalysts play a crucial role in selective chemical transformations for the synthesis of high-value chemicals, such as pharmaceutical intermediates and fine chemicals. They enable the control of reaction selectivity by tailoring catalyst properties, such as active site structure, and optimizing reaction conditions.4.3 Catalysts for renewable energy conversionWith the growing demand for renewable energy sources, heterogeneous catalysts have gained attention for their potential inenergy conversion processes. They play a vital role in fuel cells, electrolyzers, and photocatalytic systems, facilitating hydrogen production, CO2 conversion, and solar fuel synthesis.5. Catalyst Design and Optimization5.1 Rational catalyst design strategiesRational catalyst design involves the development of catalysts based on fundamental understanding and computational modeling. Using atomistic simulations and structure-activity relationships, catalysts can be tailored to improve activity, selectivity, and stability.5.2 Advances in catalyst engineering for enhanced activity and selectivityAdvancements in catalyst engineering have enabled the design of catalysts with enhanced properties. These include the modification of catalyst structure, introduction of promoters or dopants, and controlled synthesis of catalyst materials. Engineering catalysts at the nanoscale has shown promise in improving catalytic activity and selectivity.5.3 Stability and regeneration of heterogeneous catalystsOne of the challenges in heterogeneous catalysis is catalyst deactivation, caused by factors such as surface poisoning, sintering, and leaching. Designing catalysts with improved stability and developing regeneration methods can mitigate deactivation and prolong catalyst lifespan.6. Challenges and Future PerspectivesHeterogeneous catalysis still faces several challenges, including the development of catalysts for harsh conditions, catalyst deactivation, and addressing the limitations of current catalytic processes. However, recent advancements in catalyst design, optimization, and characterization techniques provide opportunities to overcome these challenges, paving the way for the development of more sustainable chemical processes. Future efforts should focus on the development of novel catalysts, exploring new reaction pathways, and improving the understanding of catalytic mechanisms.7. ConclusionHeterogeneous catalysis plays a pivotal role in sustainable chemical processes by enabling efficient and selective chemicaltransformations with reduced environmental impact. This article provided a comprehensive overview of the synthesis, characterization, and applications of heterogeneous catalysts, along with recent advancements in catalyst design and optimization. By combining fundamental understanding with innovative engineering approaches, the development of new catalysts holds great potential for further advancing sustainable chemistry and achieving a greener future.。
席夫碱型有机小分子荧光探针的制备与表征——推荐一个综合化学实验
No. 2
doi: 10.3866/PKU.DXHX201906008
71
可以促进学生对化学知识体系的融会贯通，更能激发学生学习化学的积极性。这些知识的掌握和实 践，也为本科毕业生在相关领域的深造和就业打下良好的基础。
本实验包括席夫碱有机配体的设计合成，红外光谱、核磁共振波谱和质谱等常用表征手段的应 用，以及荧光性质的研究等内容。
Department of Chemistry, School of Chemistry and Biological Engineering, University of Science and Technology Beijing, Beijing 100083, P. R. China.
Abstract: In this paper, a new experiment named “synthesis and characterization of a fluorescent molecule based on Schiff-base” is introduced. It contains the synthesis and characterization of organic compounds, the determination of fluorescence, and the detection of metal ions. This experiment is helpful for students to better understand inorganic chemistry, organic chemistry and analytical chemistry. Moreover, it gives students an opportunity to know the study of organic fluorescent probes. This will stimulate students’ interest in scientific research and cultivate their research ability. Thus, this experiment can be introduced to senior undergraduates.
材料化学英文
材料化学英文Material Chemistry。
Material chemistry is a branch of chemistry that focuses on the study of the properties and behavior of different materials. It involves the understanding of the composition, structure, and properties of materials, as well as the development of new materials with specific properties for various applications. Material chemistry plays a crucial role in the advancement of technology and the development of new products in various industries, such as electronics, energy, healthcare, and environmental protection.One of the key areas of material chemistry is the study of the structure-property relationships of materials. This involves understanding how the atomic and molecular structure of a material influences its properties, such as strength, conductivity, and reactivity. By gaining insights into these relationships, scientists and engineers can design and develop materials with tailored properties to meet specific needs. For example, the development of lightweight and durable materials for aerospace applications requires a deep understanding of the structure-property relationships of materials.Another important aspect of material chemistry is the synthesis and characterization of materials. This involves the design and preparation of materials with desired properties, as well as the analysis of their chemical, physical, and mechanical properties. Material chemists use a variety of techniques, such as spectroscopy, microscopy, and diffraction,to characterize the structure and properties of materials at the atomic and molecular levels. This knowledge is essential for the development of new materials with improved performance and functionality.In addition, material chemistry plays a vital role in the development of advanced materials for energy storage and conversion. For example, the design and optimization of materials for lithium-ion batteries, fuel cells, and solar cells require a deep understanding of the electrochemical and optical properties of materials. Material chemists work on the development of new electrode materials, electrolytes, and photoactive materials to improve the efficiency and performance of energy devices.Furthermore, material chemistry is essential for the development of biomaterials for medical applications. Biomaterials are used in various medical devices and implants, such as artificial joints, dental implants, and tissue engineering scaffolds. Material chemists study the interactions between biomaterials and biological systems to design materials that are biocompatible, bioactive, and biodegradable. This requires a thorough understanding of the chemical and biological properties of materials to ensure their safety and effectiveness in medical applications.In conclusion, material chemistry is a multidisciplinary field that plays a crucial role in the development of new materials with tailored properties for various applications. By understanding the structure-property relationships of materials, synthesizing and characterizing materials, and developing advanced materials for energy and medical applications, material chemists contribute to the advancement of technology and the improvement of quality of life. The continuous development of new materials with enhanced properties will drive innovation and progress in the future.。
ZIF-67的制备与表征——推荐一个综合化学实验
广东化工2020年第21期· 222 · 第47卷总第431期ZIF-67的制备与表征——推荐一个综合化学实验张永红*，冯芸，刘晨江*(新疆大学化学学院，新疆乌鲁木齐830046)[摘要]本文推荐一个适于化学和化工专业开设的大学综合化学实验，沸石咪唑酯骨架结构材料−ZIF-67的制备与表征。
以2-甲基咪唑和六水合硝酸钴为原料，在室温下搅拌半小时即可快速制备得到ZIF-67。
并通过X-射线粉末衍射(PXRD)、扫描电子显微镜(SEM)、热重分析仪(TGA)、傅里叶变换红外光谱仪(FTIR)和比表面孔径分析仪(BET)等对样品的形貌、晶体结构及热稳定性进行了表征。
该实验具有原料廉价易得、实验条件简单和操作简便等特点。
通过本实验，学生能够掌握理解金属有机框架(MOFs)材料的合成与表征的知识与技能，掌握SEM、PXRD、FTIR、TGA和BET等仪器的使用及基本原理。
本实验综合了有机化学、无机化学和分析化学等专业知识，有利于培养学生实验技能和综合创新能力，激发学生的科研兴趣。
[关键词]综合化学实验；硝酸钴；2-甲基咪唑；金属-有机骨架[中图分类号]G4 [文献标识码]A [文章编号]1007-1865(2020)21-0222-03Synthesis and Characterization of ZIF-67:A Comprehensive University Chemical ExperimentZhang Yonghong*, Feng Yun, Liu Chenjiang*(College of Chemistry Xinjiang University, Urumqi 830046, China)Abstract: A university chemical comprehensive experiment was recommended, which is suitable for the students of chemistry and chemical engineering majors. 2-Methylimidazole and cobalt nitrate hexahydrate are used as starting materials to synthesis of ZIF-67 by stirred at room temperature for 0.5 h, and the morphology, crystal structure and thermal stability of samples are well characterized by powder X-ray diffraction (PXRD), scanning electron microscope (SEM), thermogravimetric analyzer (TGA), Fourier transform infrared (FTIR) and Brunauer-Emmett-Teller (BET). The aforementioned experiment has the advantages of cheap raw materials, simple experimental operation and reaction conditions. Through this recommended experiment, students can master the knowledge and skills of the synthesis and characterization of metal-organic framework (MOFs) materials, and basic principles and operation of PXRD, SEM, TGA, FTIR, BET and other instruments. Furthermore, the recommended experiment involves the knowledge of organic chemistry, inorganic chemistry and analytical chemistry, which is conducive to cultivating students' experimental skills and comprehensive innovation ability, and stimulates students' interest in scientific research.Keywords: comprehensive experiment；cobalt nitrate；2-methylimidazole；metal-organic frameworks金属-有机骨架(metal-organic frameworks，MOFs)，又称为多孔配位聚合物，是上世纪90年代由Yaghi等人首次提出的[1]。
基于HDDA反应的稠合芳伯胺的合成与表征
2021年6月第21卷第2期廊坊师范学院学报(自然科学版)Journal of Langfang Normal University(Natural Science Edition)Jun.2021Vol.21No.2基于H D D A反应的稠合芳伯胺的合成与表征张号1,张孝荣彳(1.巢湖学院，安徽巢湖238000；2.康龙化成(W安)新药技术有限公司，陕西西安710018)【摘要】块痊芳构化加成反应(Hexadehydro-Diels-Alder)是合成芳环骨架研究热点之一,促使C-N的构建键由过渡金属催化转向无金属绿色合成。
以四烘类化合物为基础底物，乌洛托品为氮源,在无惰性气氛保护下，以DMF为溶剂, loot恒温加热12h,经苯块中间体亲核C-N偶联,成功构建两个碳碳键，一个碳氮键，成功合成了稠合芳伯胺化合物，并采用X射线衍射仪、核磁共振谱仪、质谱仪等仪器设备进行表征。
【关键词】四烘;C-N偶联;稠合结构;芳胺化合物;HDDA反应Synthesis and Characterization of Fused Primary AromaticAmines Based on HDDA ReactionZhang Hao1,Z hang Xiaorong2(l.Chaohu University,Chaohu238000,China;2.KANGLONG Huacheng(XV an)New Drug Technology Co.,Ltd,Xi'an710018,China) [Abstract]The aromatization addition of alkynes(Hexadehydio-Diels-Alder,HDDA)is one of the hot topics in the synthesis of aromatic ring skeleton,which promotes the construction of C-N bond from transition metal catalysis to no metal green synthesis.Under the protection of inert atmosphere,tetraynes were used as substrate,hexamethylenetetramine as nitrogen source,DMF as solvent,heated at100°C for12h,and then two C—C bonds and one C-N bond were successfully constructed by nucleophilic C-N coupling of phenylyne intennediate.The fused aromatic primary amines were successfully synthesized and characterized by X-ray diffractometer,nuclear magnetic resonance spectrometer and mass spectrometer.[Key words]tetraynes;C—N coupling;fused structure;aromatic amine compounds;HDDA reaction〔中图分类号〕0621.3〔文献标识码〕A〔文章编号J1674-3229(2021)02-0023-040引言乌洛托品(Hexamethylenetetramine,HMTA)结构与金刚烷类似，由4个氮原子与6个亚甲基相连,构成四个相互稠合的多元氮杂环,既是一类常见的皮肤杀菌剂、消毒剂，也是有机合成的重要原料，同时还是一类特种精细化学品，用于金属缓蚀、军事燃料、军工炸药等领域⑴。
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Synthesis and characterization of a cholesteric liquid crystal cholesterylnonanoateYuan Ming Huang1, a, Ye-tang Guo1, Qing-lan Ma1 and Wei-wei Liu11College of Physics & Electronic Information, Yunnan Normal University, Yunnan 650092, Chinaa dongshanisland@Keywords: Cholesteric liquid crystal; Cholesteric phase; Selective reflection; PitchAbstract. A cholesteric liquid crystal cholesteryl nonanoate was synthesized and then characterized by means of differential scanning calorimetry and polarized optical microscopy. As temperature decreased from its clearing point, cholesteric phase was formed for cholesteryl nonanoate and accompanied by continuous evolution of colors in the focal conic textures. Furthermore, beautiful spherulite crystals were observed to grow out of the cholesteric phase as the crystallization continued. The evolution of the colors in recorded textures was contributed to temperature-dependent selective reflection of the liquid crystal.IntroductionCholesteric liquid crystals (LCs) have many applications as electro-optic materials in thin film devices [1, 2]. An important characteristic of the cholesteric mesophase is the pitch. The pitch, p, is defined as the distance it takes for the director to rotate one full turn in the helix. One of the most prominent features of cholesteric LCs is its ability to selectively reflect light of wavelengths equal to the pitch length so that a color will be reflected when the pitch is equal to the corresponding wavelength of light in the visible spectrum. This causes these systems to exhibit unique optical properties such as selective reflection. In the reflected intensity plot over the visible spectrum, the maximum reflection occurring at a wavelength equal to the pitch, which may be pre-selected by choices of materials and temperature dependent. This represents the reflection of one handedness of circularly polarized light due to periodic variations of the index of refraction of the material. The other handedness is transmitted through the cholesteric material.In this paper, we synthesize a cholesteric LC cholesteryl nonanoate and then investigate its LC textures by means of differential scanning calorimetry (DSC) and polarized optical microscopy as temperature decreases from its clearing point to its crystallization point. Our results demonstrate that cholesteric phase can be formed for the cholesteryl nonanoate with the accompany of continuous changes in colors in the focal conic textures. The evolution of the colors in recorded textures was contributed to temperature-dependent selective reflection of the LC.ExperimentThe cholesteric LC cholesteryl nonanoate was synthesized in our laboratory. Analytical reagents such as N,N-dimethylaniline, cholesterol and nonanoic acid were purchased from Sinopharm Chemical Reagents Co (Shanghai, China). These reagents were used as received. The temperature and duration of the reflux were 100o C and 9 hours, respectively. After successive washing, drying, and recrytsallization, the resultant compound was white powders.DSC (Nanjing Dazhan, China) was used to characterize the phase transition of the synthesized compounds. The heating rate was fixed at about 10o C/min. The polarized optical microscopic textures of the bent-core LC were recorded with a polarized optical microscope (Aipha Technologies, China). A hot stage was used to regulate the temperature of the cholesteric LC.Results and discussionCholesteryl nonanoate is an ester of cholesterol and nonanoic acid. It is a LC material forming cholesteric LCs with helical structure. Figure 1 depicts the synthesis and molecular structure of the cholesteryl nonanoate. In the second step of the synthesis, N,N-dimethylaniline was used as a catalyst.Figure 1. Synthetic scheme and molecular structure of cholesteryl nonanoate.Figure 2 represents the DSC curves of the cholesteryl nonanoate when it experienced the first heating run for specimen 1 (left panel) and the first cooling run for specimen 2 (right panel). The differences in specimen 1 and specimen 2 were the extent of the two specimens being pressed into aluminum pans. The heating rate was fixed at 10o C/min. As shown in Fig. 2, specimen 1 exhibits cholesteric phase between 78 and 95o C in the first heating run whereas the cholesteric LC exhibits mesophases between 40 and 62o C in the second heating run. Specimen 2 exhibits cholesteric phase between 41 and 58o C in the first heating run whereas the cholesteric phase gets lost in the second heating run. We can conclude that the cholesteric compound has a mesophase but cyclic heating and cooling pose significant effects on the formation of the mesophase.Figure 2. DSC curves of the cholesteryl nonanoate when it experienced the first andsecond heating scans for specimen 1 (left panel) and the first and second heating scans forspecimen 2 (right panel). The differences in specimen 1 and specimen 2 were the extentof the two specimens being pressed into aluminum pans.When the molecules are chiral and in the nematic phase, they arrange themselves into a strongly twisted structure that often reflects visible light in different bright colors which depend on thetemperature. They can therefore be used in temperature sensors. Figure 3 shows the LC textures observed by polarized optical microscopy for the cholesteryl nonanoate as the temperature decreases monotonically from the clearing point of the LC. From panels a to f, all the textures exhibit focal conic structures as the temperature was gradually decreased from about 60 to 40o C. The colors of the formed textures changed gradually as the temperatures decreased. The changes in colors can be attributed to the selective reflection of light for cholesteric LCs. When the wavelengths of incident light are equal to the pitch length of the cholesteric LC, a color will be reflected when the pitch is equal to the corresponding wavelength of light in the visible spectrum. This causes these systems to exhibit unique optical properties such as selective reflection. In our cholesteric LC, the pitch is temperature dependent. This represents the reflection of one handedness of circularly polarized light due to periodic variations of the index of refraction of the material. The other handedness is transmitted through the cholesteric material.Figure 3. LC textures observed by polarized optical microscopy for thecholesteryl nonanoate as the temperature decreases monotonically from theclearing point of the cholesteryl nonanoate.Figure 4 shows the LC textures observed by polarized optical microscopy as the cholesteric LC is transformed into crystal. The textures of the crystals are represented by panels a and c as crystallization continues. It forms beautiful spherulite crystals. The changes in the colors of the crystalline phase and cholesteric phase can also be attributed to the temperature-dependent selective reflection of incident light.Figure 4. LC textures observed by polarized optical microscopy as the spherulite crystalsgrew out the cholesteric phase of the cholesteryl nonanoate.SummaryIn conclusion, a cholesteric LC cholesteryl nonanoate was synthesized and then characterized by means of differential scanning calorimetry and polarized optical microscopy. As temperature decreased from its clearing point, cholesteric phase was formed for cholesteryl nonanoateaccompanied by continuous evolution of colors in the focal conic textures. Furthermore, beautiful spherulite crystals were observed to grow out of the cholesteric phase as the crystallization continued. The evolution of the colors in recorded textures was contributed to temperature-dependent selective reflection of the LC.AcknowledgementsThis work was financially supported by the following funds: (1) the Natural Science Foundation of China (No.10674091); (2) the Scientific Research Fund for Returned Overseas Chinese Scholar from Education Ministry of China (No. 2005-546); (3) Key Research Project of the Education Ministry of China (No. 206110); (4) the 11th Young Scientist Program of Yunnan Province (No. 2008PY058); and (5) the Natural Science Foundation of Yunnan Province (No. 2008CD110).References[1] D.-K. Yang, J.L. West, L.-C. Chien and J.W. Doane: J. Appl. Phys. Vol. 76 (1994), p. 1331.[2] D.-K Yang, J.W. Doane, Z. Yaniv and J. Glasser: Appl. Phys. Lett. Vol. 64 (1994), p. 1905.。