纳米CeO2粉体制备方法的研究进展

综述了近年来国内外纳米CeO2粉体的几种主要制备方法及它们的研究进展,其中重点介绍了液相法及其特点,对纳米CeO2的制备技术和发展趋势进行了展望,并指出了今后应重点研究和解决的主要问题.     

喷雾热分解法制备纳米CeO2粉末的研究进展

用喷雾热分解法(Spray Pyrolysis,简称sP)制备超细或纳米粉末具有产品纯度高、成分均匀、成分间的化学计量比易控制等优点,而且制备过程连续,操作简单,成本低.目前纳米CeO2被广泛用于催化剂、燃料电池、微电子等领域,颗粒的粒度与形貌是影响CeO2粉末特性的重要因素.该文作者从控制纳米CeO2粒度与形貌的角度,总结分析近年来国内外新型或改进的SP技术及其工艺特点,介绍纳米CeO2粒子在SP过程中的形成机制和影响因素,并指出现存的问题和今后的发展趋势.     

十二烷基磺酸钠改性纳米CeO2的研究

采用十二烷基磺酸钠(SDS)对纳米CeO2粉体进行表面改性以提高其在有机材料中的分散性,以活化指数表征改性效果,并用IR、TG-DSC、TEM和LPSA表征了改性纳米CeO2的效果和结构。结果表明,最佳改性工艺条件为:十二烷基磺酸钠用量4%,反应温度70℃,反应时间6h,pH=7。SDS以化学键合的方式吸附在纳米CeO2的表面,并形成了有机包覆层,经SDS改性过的纳米CeO2的分散性明显提高,粒度降低44%。     

电化学法和沉淀法制备的纳米结构CeO_2的微观结构比较

利用X射线衍射、X射线小角散射、扫描电子显微镜、透射电子显微镜等分析手段对电化学法、沉淀法制备的纳米结构的CeO2 的微观结构进行了比较 ,发现电化学法制备CeO2 是由分散的纳米颗粒组成 ,而沉淀法制备的CeO2 则是由粗大片状颗粒组成 ,而该片状颗粒具有纳米的结构。电化学法的CeO2 比沉淀法CeO2 具有更细的纳米结构     

水相介质中纳米CeO2的分散行为

通过测定悬浮液体系润湿性、表面电性及分散性研究了纳米CeO2在不同条件下水相介质中的分散行为.结果表明 纳米CeO2 在水相介质中的润湿与分散受体系pH值的影响很大, 与Zeta电位有相当好的一致关系, 其分散机理主要是双电层静电排斥作用; 纳米CeO2的等电点(pHPZC)为6.8左右; 纳米CeO2颗粒在酸性水介质中表面带正电, 在碱性水介质中表面带负电, Zeta电位分别在pH值为4和11左右时较高, 相应润湿性和分散性较好; 随机械搅拌速率和时间的增加, 纳米CeO2的分散性增强; 超声波对纳米CeO2的分散作用明显优于机械搅拌, 20 kHz频率下超声波分散1 min便能显著改善纳米CeO2的分散状态; 加入六偏磷酸钠(SHP)作为分散剂将改变纳米CeO2颗粒表面电性, 使其带负电, Zeta电位随SHP浓度增加而增大, 起增强双电层的静电排斥作用; 当SHP浓度达225 mg·L-1时, Zeta电位趋于稳定, 并使纳米CeO2在广泛的pH值范围内获得较高的Zeta电位和很好的分散效果, 从而降低了体系pH值的影响.     

纳米氧化铈颗粒的粒度分析研究

针对自制的纳米CeO2进行了一系列粒度分析研究,包括XRD、SEM、TEM、动态光散射法、比表面分析法、X射线衍射法和X射线小角度散射法(SAXS).不同的研究手段得到的纳米CeO2的粒径不尽相同,并阐述了各种研究手段的优缺点及适用范围.     

表面修饰纳米CeO2的摩擦学研究

研究了表面修饰的纳米CeO2的摩擦学性能。以溶胶-凝胶法制得纳米CeO2,并使用本实验室制得的苯并三氮唑乙酸对其进行表面修饰。采用多种测试技术对表面修饰的CeO2颗粒进行表征,并在MRS-10A四球极压抗磨损试验机上测试了其抗磨性能。结果表明,表面修饰的纳米CeO2颗粒可很好地分散于菜籽油中,作为添加剂,具有较好的抗磨效果,在392 N载荷下磨斑直径减小了11.1%,较高载荷摩擦环境更适合其抗磨性能的发挥,具有重要的推广应用前景。     

CeO2纳米晶的制备及其光催化活性的研究

以硝酸稀土为原料，碳酸氢铵作沉淀剂，乙二醇、丙三醇、聚乙二醇1000和PVA为分散剂，通过控制一定的反应条件，制得易沉降、过滤的水合碳酸铈，此前驱物在一定温度下焙烧即可得到CeO2纳米晶。通过X射线衍射、扫描电镜、紫外可见分光光度计等分析测试方法研究了CeO2纳米晶的形成过程、微观形貌、粒度及光吸收特性。结果表明：此前驱物在400℃以上焙烧，即可得到立方相CeO2纳米晶，分散剂的种类和焙烧温度对CeO2纳米晶的粒度、分散性及光催化活性均有一定的影响。在适宜条件下，CeO2纳米晶可使染料酸性黑10B的脱色率达98％以上。     

高温溶液法制备CeO_2纳米晶体及其紫外吸收性能研究

采用高温溶液法分解硝酸铈制备了不同形貌的CeO2纳米晶体。采用XRD、TEM和FTIR研究了表面活性剂和分解温度对纳米晶体尺寸、形貌和物相结构的影响。实验结果表明,控制表面活性剂的种类(如油胺、油酸、二甲基硅油)和数量,可以得到具有球形、线形、"四叶草"形和类四边形的纳米晶体。随着分解温度的提高,CeO2纳米晶体的形貌趋于完整,粒径逐渐变大。分解温度达到300℃时可以得到线形的CeO2纳米晶体,温度达到320℃得到的线形粒子的长径比可以达到45左右。通过紫外-可见光吸收光谱可知,所得不同形貌的CeO2纳米晶体均具有较好的紫外吸收性能和可见光的透过性能,所有样品对紫外光的吸收均达到90%以上,可以有效的用作紫外屏蔽材料。     

电化学法和沉淀法制备的纳米结构CeO2的微观结构比较

利用X射线衍射、X射线小角散射、扫描电子显微镜、透射电子显微镜等分析手段对电化学法、沉淀法制备的纳米结构的C eO2的微观结构进行了比较，发现电化学法制备CeO2是由分散的纳米颗粒组成，而沉淀法制备的Coeh则是由粗大片状颗粒组成，而该片状颗粒具有纳米的结构。电化学法的CeO2比沉淀法CeO2具有更细的纳米结构。     

Preparation and performance of CeO_2 hollow spheres and nanoparticles

CeO_2 hollow spheres were synthesized by polystryrene sphere(PS) templates and CeO_2 nanoparticles were prepared by a facile method. The as-obtained products were characterized by scanning electron microscopy(SEM), N_2 adsorption-desorption, X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR) and UV-vis diffuse reflectance spectra. The results showed that the structure of the obtained CeO_2 hollow spheres was hollow microsphere with a diameter of 380 nm and the average particle size of CeO_2 nanoparticles was about 1700 nm. The two samples' Brunauer-Emmett-Teller(BET) surface area was 67.1 and 37.2 m~2/g. The CeO_2 hollow spheres had a better performance than nanoparticles at UV-shielding because of higher surface area and the structure of hollow sphere.     

From nanoparticles to single atoms for Pt/CeO_2:Synthetic strategies,characterizations and applications

Pt/CeO_2 catalysts with unitary Pt species,nanoparticles,clusters or single atoms,often exhibit excellent activity and unique selectivity in many catalytic reactions benefiting from their small size,abundant unsaturated active sites,and unique electro nic structure.In recent years,a tre mendous number of related articles have provided great inspiration to future research and development of Pt/CeO_2 catalysts.In this review,the state-of-the-art evolution of Pt nanoparticles to Pt single atoms on CeO_2 is reviewed with the emphasis on synthetic strategies,advanced characterization techniques(allowing one to clarify the single atoms from clusters),the catalytic applications and mechanisms from the viewpoint of theoretical calculation.Finally,the critical outlooks and the challenges faced in developing the single-atom Pt/CeO_2 catalysts are highlighted.     

Effect of CeO_2-ZrO_2 on Pt/C electrocatalysts for alcohols oxidation

The electrocatalytic activity and stability of Pt/C catalyst modified by using CeO_2-ZrO_2 mixed oxides for the alcohols electrochemical oxidation as probes were investigated. The catalyst samples were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM). The electrochemical properties were measured by a three electrode system on electrochemical workstation(IVIUM). The results showed that the presence of CeO_2-ZrO_2 might be associated with the presence of Pt, which indicated that possibly there was synergistic effect between CeO_2-ZrO_2 and Pt nanoparticles. The electrocatalytic activity and stability of Pt-MO_x/C(M=Ce, Zr) for methanol and ethanol oxidation was better than that of Pt-CeO_2/C, which was attributed to that CeO_2-ZrO_2 composited oxides enhanced oxygen mobility and promoted oxygen storage capacity(OSC). Furthermore, the best performance was found when the molar ratio of CeO_2 to ZrO_2 was 2:1 for the oxidation of methanol and ethanol. The forward peak current density of Pt-MO_x/C(M=Ce, Zr, Ce:Zr=2:1) towards the methanol electrooxidation was about 3.8 times that of Pt-CeO_2/C. Pt-MO_x/C(M=Ce, Zr) appeared to be a promising and less expensive methanol oxidation anode catalyst.     

CeO2with diverse morphologies-supported IrOx nanocatalysts for efficient oxygen evolution reaction—Commemorating the 100th anniversary of the birth of Academician Guangxian Xu

IrOx-based catalysts are considered the most promising candidates for oxygen evolution reaction(OER)due to their high efficiency.However,improving their intrinsic catalytic activity is essential for practical application.In this work,CeO₂with three different morphologies(rod,cube,octahedron)and supported IrOx nanoparticles were fabricated,and they display morphology-dependent OER activity.The IrOx/CeO₂-rod shows the highest activity;the catalysts have a catalytic activity sequence of rod>cube>octahedron.A plausible mechanism was proposed:the CeO₂support with different morphologies modulates the electronic structure of IrOx by the synergistic interaction promoted by oxygen vacancies between the active component and the support,thereby altering the catalytic activity of the IrOx/CeO₂catalyst.     

Oxygen vacancy enhanced biomimetic superoxide dismutase activity of CeO_2-Gd nanozymes

Cerium oxide-based nanozymes have recently drawn much attention in the field of biomedical and antioxidant applications,because of their unique regenerative or autocatalytic properties.Herein,we studied the biomimetic superoxide dismutase(SOD) nanozymes CeO_2-Gd that combines the fluorescence properties of rare earth Gd with the antioxidant properties of CeO_2 nanoparticles,which was prepared via facile route.The structure and composition of the CeO_2-Gd were measured and verified by X-ray powder diffraction(XRD),Raman spectroscopy,transmission electron microscopy(TEM),energydispersive X-ray spectroscopy(EDX),and X-ray electron spectroscopy(XPS).Confocal microscopy was used to image cells.Antioxidant performance and cell viability of these nanozymes were measured in vitro using BGC-803 cell.CeO_2-Gd nanozymes with a higher Ce~(3+)/Ce~(4+) ratio show higher superoxide dismutase(SOD) mimetic activity.Their antioxidant activity and fluorescence properties of CeO_2-Gd in BGC-803 cancer cells are enhanced by oxygen vacancies generated by doping rare-earth elements Gd.This work may guide the future design of CeO~2-Gd-based biomimetic nanozymes for anticancer and antioxidant applications.     

Rare-Earth Functional Films Prepared by Ion Beam Epitaxy

Rare-Earth Functional Films Prepared by Ion Beam Epitaxy     

High activity of CeO_2-TiO_2 composites for deep oxidation of 1,2-dichloroethane

CeO_2-TiO_2 catalysts prepared by different methods were investigated for deep oxidation of 1,2-dichloroethane(DCE),as a typical representative of the chlorinated volatile organic compounds(CVOCs).Characterization analysis reveals that CeO_2-TiO_2 catalysts prepared by sol-gel and coprecipitation methods exhibit higher specific area,CeO_2 and TiO_2 particles are highly dispersed into each other and the reducibility and mobility of active oxygen species are obviously promoted due to the strong interaction between the two catalysts CeO_2 and TiO_2,resulting in higher catalytic activity for DCE oxidation to and less chlorinated byproduct.The high calcination temperature would lead to the formation of a new monoclinic phase Ce_(0.3)Ti_(0.7)O_2 and sintering,which is the main reason for the catalytic activity for DCE oxidation markedly decreases.     

The variation of microstructures,spectral characteristics and catalysis effects of Fe~(3+) and Zn~(2+) co-doped CeO_2 solid solutions

Fe~(3+)and Zn~(2+)ions were doped into the lattice of CeO_2 via the hydrothermal method.The micro structure and spectra features were analyzed systemically.XRD results show that the solid solubility of Fe~(3+)and Zn~(2+)ions in Ce_(1-x)(Fe_(0.5)Zn_(0.5))_xO_2 can be identified as x=0.16.The cell volumes are decreased by increasing the doped content.The TEM graphs prove that the grain size of the sample is about 10 nm,and the EDS result indicates that the doped contents are in accordance with that of the theory concentrations.Meanwhile,the doping also causes the increasing concentrations of the defects and oxygen vacancies which are supported by the XPS,Raman,UV and PL characterizations.The samples exhibit better catalytic activities for improving the hydrogen storage properties and the electrochemical kinetics of the ball milled Mg_2Ni based composites.Further,the catalysis effects are improved by increasing the doped contents,which can be ascribed to the increasing contents of the oxygen vacancies,defects,the special electron transition states and the nature of the doped ions in CeO_2-based solid solutions.     

Mesoporous CeO_2-C hybrid spheres as efficient support for platinum nanoparticles towards methanol electrocatalytic oxidation

The development of direct methanol fuel cells(DMFCs) is partially limited by the poor kinetics of methanol oxidation reaction(MOR) at the anode side.It was reported that the interaction between Pt and CeO_2 enhances the electrocatalytic performance of Pt catalyst for MOR.In this work,a hybrid material(CeO_2-C) composed of CeO_2 and carbon was successfully prepared by a simple hydrothermal method followed by calcination in inert atmosphere.The hierarchically porous nanostructure and especially good electronic conductivity of CeO_2-C make it an excellent support for Pt particles for application in electrocatalytic process.TEM investigation reveals that triple-phase interface of Pt,carbon and CeO_2 forms in Pt/CeO_2-C catalyst.Performance of the as-prepared catalyst for MOR was studied in alkaline medium.The Pt/CeO_2-C catalyst shows superior catalytic performance for MOR compared with Pt/CeO_2 and the physical mixture of Pt/CeO_2 and acetylene black(Pt/CeO_2+C).The significantly improved performance can be attributed to the synergetic effect between Pt particles and CeO_2-C support,and the better conductivity of CeO_2-C.This study provides a possible method to expand the application potential of CeO_2 materials in MOR,and may also be used in other electrocatalytic process.     

CeO_2/CuO catalysts using different template agent for preferential CO oxidation in H_2-rich stream

The CeO_2/CuO catalysts using different template agent(F68 L64, F127 and P123) were synthesized by the simple template and impregnation method. They were characterized by FESEM, XRD, N2 physisorption and H2-TPR techniques. It is found that the CeO_2/CuO catalysts are double pore distribution, and CeO_2 can enter into the gap of CuO supports and form the contact interface of copper and cerium. Among the asprepared catalysts, the CeO_2/CuO-F127 catalyst displays better activity at lower temperature and the CeO_2/CuO-P123 catalyst presents higher activity at higher temperature. The CeO_2/CuO-P123 catalyst has the smallest crystallite sizes of CuO and CeO_2 as well as the largest size of cubes, which may improve the interaction of copper and cerium and enhance the performance of CO oxidation.