纳米级PbCO3制备方法的改进

对沉淀法制备的PbCO3 结构和形貌的表征发现PbCO3 晶体生长速度很快 ,沉淀法很难制备纳米级PbCO3 。采用 80 0 0r/min高速条件下的沉淀法 ,制备了纳米级PbCO3 。同时对原料和反应物浓度影响的实验表明 ,Pb(CH3 COO) 2 ·3H2 O取代Pb(NO3 ) 2 时 ,所制备PbCO3 的粒度分布集中 ,粒子尺寸为 10 30nm ,并且粒子粒径随着Pb(CH3 COO) 2 ·3H2 O浓度的增大而减小     

纳米复合氧化物CuO·SnO2的制备与结构表征

0引言由于纳米材料在热学、电学、磁学、光学等方面具有的独特性能,使其在新功能材料、催化、光电能转换等许多领域引起了人们浓厚的研究兴趣[1]。近年来,纳米催化剂对固体推进剂的燃烧性能影响研究已成为热点[2～9]。但是由于固体推进剂燃烧的特殊性,要求不仅提高燃速,而且降低压力指数,因此并非所有的纳米催化剂都是有效的。大量实践已证明[10],多种催化剂的复合使用,将可获得远远优于单一催化剂的效果。研究已发现[11],纳米复合氧化物是由多种元素复合而成,使其在结构和性能上得到互补和叠加,加上纳米粒子所具有的各种效应,从而产生独特…     

盐助溶液燃烧法制备高比表面氧化铈纳米粉体

提出了一种新颖的快速制备高比表面氧化铈纳米粉体的方法———盐助溶液燃烧法,通过XRD、TEM和比表面积分析,研究了燃料/氧化剂的比率、不同盐的种类和用量对产物性质的影响。研究发现,在传统的溶液燃烧法中简单的引入KCl导致产物比表面积由14.10 m2.g-1剧增到156.74 m2.g-1,得到了4~6 nm高分散性的纳米氧化铈粒子。通过示意图初步讨论了盐助溶液燃烧合成过程高分散纳米氧化铈粒子形成的可能机制,认为由于自蔓延溶液燃烧反应快速释放出大量的热量,使反应体系产生瞬间高温,盐会迅速在新形成的纳米晶的表面原位析出形成薄盐层,当快速冷却后,氧化铈纳米晶就被镶嵌在凝固的盐基质中,阻止了新生成纳米粒子的重新团聚和烧结,从而得到氧化铈单分散粒子。     

金属纳米粒子/聚合物体系的稳定性及其机理

金属纳米粒子由于其小的尺寸和大的比表面积等特点,使其具有独特的热性能、电性能、磁性能和光性能,以及很强的团聚趋势.因此金属纳米粒子是否被稳定在纳米尺度内,是它们能否表现出独特性能的关键.本文综述了非离子聚合物、聚电解质、两亲聚合物、双亲水聚合物、树状聚合物对金属纳米粒子的稳定作用及其稳定机理的研究进展.     

金属纳米粒子/聚合物体系的稳定性及其机理

金属纳米粒子由于其小的尺寸和大的比表面积等特点,使其具有独特的热性能、电性能、磁性能和光性能,以及很强的团聚趋势。因此金属纳米粒子是否被稳定在纳米尺度内,是它们能否表现出独特性能的关键。本文综述了非离子聚合物、聚电解质、两亲聚合物、双亲水聚合物、树状聚合物对金属纳米粒子的稳定作用及其稳定机理的研究进展。     

金属纳米粒子/聚合物体系的稳定性及其机理

金属纳米粒子由于其小的尺寸和大的比表面积等特点,使其具有独特的热性能、电性能、磁性能和光性能,以及很强的团聚趋势。因此金属纳米粒子是否被稳定在纳米尺度内,是它们能否表现出独特性能的关键。本文综述了非离子聚合物、聚电解质、两亲聚合物、双亲水聚合物、树状聚合物对金属纳米粒子的稳定作用及其稳定机理的研究进展。     

氯化铵对TiO2纳米晶的形成、 结构及性能的影响

以四氯化钛为原料, 通过氯化铵诱导晶化和热挥发分解法制备了二氧化钛纳米晶, 经粉末XRD, TEM, IR和比表面积及热重分析等手段进行了表征. 通过对粒子生长动力学分析, 在700 ℃以下存在两种生长势, 400 ℃时出现转折, 400 ℃以下粒子生长所需活化能为8.23 kJ/mol; 400 ℃以上粒子生长需活化能为45.71 kJ/mol. 于200 ℃时灼烧样品的表面积最大, 对甲基橙光催化降解活性最高.     

氧化硅对金红石相纳米TiO2微结构的影响

通过硅酸钠水解生成的无定形氧化硅对金红石相纳米TiO₂进行修饰,利用红外光谱、紫外-可见漫反射光谱、X射线衍射、透射电镜和比表面仪对纳米TiO₂进行了表征。结果表明,氧化硅沉积在纳米TiO₂的表面和颗粒之间形成一个空间网络体系,有效地抑制了TiO₂晶粒尺寸和原始粒径的长大。当热处理温度低于700 ℃时,经氧化硅处理的纳米TiO₂的晶粒尺寸、原始粒径和比表面积几乎不变;当热处理温度高于700 ℃时,经氧化硅处理的纳米TiO₂的晶粒尺寸和原始粒径开始缓慢变大,比表面积快速下降,在900 ℃下煅烧2 h,经氧化硅处理的纳米TiO₂原始粒径仍为20～40 nm。氧化硅的存在使纳米TiO₂吸收紫外线的能力增强并使其平均孔径变小。     

纳米TiO2-SiO2复合氧化物的制备与性质

采用溶胶-凝胶结合CO2超临界干燥方法制备了比表面积大、热稳定性好的纳米TiO2-SiO2复合氧化物.考察了原料组成和焙烧温度对复合氧化物比表面积、热稳定性和酸性的影响,通过加氢脱硫反应考察了该复合氧化物作为加氢精制催化剂载体的可行性.结果表明,采用该方法制备的复合氧化物为纳米颗粒,在n(Ti)/n(Si)=1时,其比表面积和孔容最大;与纯TiO2相比,引入SiO2明显提高了复合氧化物的热稳定性和晶型稳定性;以此复合氧化物为载体的加氢精制催化剂具有很好的低温脱硫活性,TiO2-SiO2复合氧化物载体的酸性特征影响了催化剂的加氢脱硫活性.     

pH值调节方式对LAB辅助合成纳米Cu2O微球的影响与组装机理

以Cu(Ac)2为原料,两性表面活性剂月桂酰胺丙基甜菜碱(LAB)为模板,采用两种不同的调节pH值方式制备了Cu_2O纳米材料。表征结果表明两种调节pH值方式均可获得Cu_2O纳米微球,并都呈立方晶相,而且样品的红外吸收峰、固体紫外吸收峰都不同程度的发生了蓝移;第一种Cu_2O纳米微球由针状纳米粒子积聚而成,针状纳米粒子间空隙孔径主要分布在25~50 nm之间,比表面积为22 m~2·g~(-1),禁带宽度为2.15 eV;第二种Cu_2O纳米微球由小的纳米球状体堆积而成,球状体间孔道直径集中在25~50 nm和50~125 nm两个区域,比表面积为9 m~2·g~(-1),禁带宽度为2.46 eV。两种不同的调节pH值方式获得的Cu_2O纳米微球,其反应历程和自组装机理存在不同。     

Preparation of Forsterite (Mg2SiO4) Powders Via an Aqueous Route Using Magnesium Salts and Silicon Tetrachloride (SiCl4)

Forsterite (Mg₂SiO₄) powders were prepared by mixing SiCl₄ with aqueous solutions of either Mg(CH₃COO)₂·4H₂O or Mg(NO₃)₂·6H₂O and heating the powdered gel. The powders were characterised using thermal analysis (DTA and TGA), X-ray diffraction (XRD), nitrogen adsorption surface area analysis (BET) and transmission electron microscopy (TEM). On heating, MgO and enstatite (MgSiO₃) were observed in addition to forsterite. On heating to 1200°C, forsterite was the dominant phase in the powders produced from Mg(NO₃)₂·6H₂O, and MgO was the dominant phase in the powders produced from Mg(CH₃COO)₂·4H₂O. The primary particle sizes of these powders were between 100 and 500 nm, which remained the same on heat treatment. However, higher temperatures gave rise to an increase in the size and densities of the agglomerates of primary particles.     

Three-dimensional hybrid networks based on aspartic acid

Three-dimensional achiral coordination polymers of the general formula M₂(D, l-NHCH (COO)CH₂COO)₂·C₄H₄N₂ where M = Ni and Co and pyrazine acts as the linker molecule have been prepared under hydrothermal conditions starting with [M(L-NHCH(COO)CH₂COO)·3H₂O] possessing a helical chain structure. A three-dimensional hybrid compound of the formula Pb_2.5[N{CH(COO) CH₂COO}₂2H₂O] has also been prepared hydrothermally starting with aspartic acid and Pb(NO₃)₂. In this lead compound, where a secondary amine formed by the dimerisation of aspartic acid acts as the ligand, there is two-dimensional inorganic connectivity and one-dimensional organic connectivity.     

Syntheses,crystal structures,and magnetic properties of a series of Fe2Ln complexes

A family of phenoxo-bridged heterometallic Schiff base trinuclear complexes, [Fe₂LnL₂(C₃H₇COO)(H₂O)]·CH₃OH·CH₃CN·H₂O (Ln = Sm, 1; Gd, 2; Tb, 3; Dy, 4) is reported. Those complexes were afforded by “one-pot” reaction of a polydentate Schiff base ligand 2-hydroxy-3-methoxy-phenylsalicylaldimine (H₂L) with Fe(NO₃)₃·9H₂O, Ln(NO₃)₃·6H₂O and sodium butyrate (C₃H₇COONa) in a mixture of methanol and acetonitrile in the presence of triethylamine as a base. Single-crystal X-ray diffraction analysis reveals that the structures of the four complexes are isomorphic. In each complex, two anionic [FeL₂]^? units coordinate to the central lanthanide ion as a tetradentate ligand using its four phenoxo oxygens, forming a two-blade propeller-like molecular shape. Magnetic properties of 1–4 were investigated using variable temperature magnetic susceptibility, and weak ferromagnetic exchange between the Fe^III and Ln^III ions has been established for the Gd derivative. The Tb and Dy complexes show no evidence of slow relaxation behavior above 2.0 K.     

Preparation and Optical Properties of Gold-Dispersed BaTiO3, PGO (Pb5Ge3O11) and PLT (Pb1-1.5xLaxTiO3) Thin Films by Sol-Gel Process

Gold-dispersed BaTiO₃, PGO and PLT thin films, which will be used for third-order nonlinear optical devices, were prepared by sol-gel process with spin-coating using HAuCl₄4H₂O, Ba(CH₃COO)₂, Ti[O(CH₂)₃CH₃]₄, Pb(CH₃COO)₂3H₂O, Ge[O-n-C₄H₉]₄, La(CH₃COO)₃1.5 H₂O as starting materials. The thin films were heat-treated in air at temperatures ranging from 400 to 800 for 1 h. The nonlinear optical property of these thin films was measured by the degenerate four-wave mixing (DFWM) method using a frequency-doubled Nd: YAG laser with 20 ps pulse duration. Third-order nonlinear susceptibility χ⁽³⁾ of gold-dispersed BaTiO₃, PGO and PLT thin films with 5 vol% of gold were 1.410⁻⁶ esu, 3.510⁻⁷ esu respectively. The large χ⁽³⁾ may be ascribed to the high dielectric constant of the films.     

Thermal stability of new zinc acetate-based complex compounds

New zinc acetate based complex compounds (of general formula Zn(CH₃COO)₂·1?2L·nH₂O) containing one or two molecules of urea, thiourea, coffeine and phenazone were prepared namely: Zn(CH₃COO)₂·2.5H₂O, Zn(CH₃COO)₂·2u·0.5H₂O, Zn(CH₃COO)₂·tu·0.5H₂O, Zn(CH₃COO)₂·2tu, Zn(CH₃COO)₂·cof·2.5H₂O, Zn(CH₃COO)₂·2cof·3.5H₂O, Zn(CH₃COO)₂·2phen·1.5H₂O. The compounds were characterized by IR spectroscopy, chemical analysis and thermal analysis. Thermal analysis showed that no changes in crystallographic modifications of the compounds take place during (heating in nitrogen before) the thermal decompositions. The temperature interval of the stability of the prepared compounds were determined. It was found that the thermal decomposition of hydrated compounds starts by the release of water molecules. During the thermal decomposition of anhydrous compounds in nitrogen the release of organic ligands take place followed by the decomposition of the acetate anion. Zinc oxide and metallic zinc were found as final products of the thermal decomposition of the zinc acetate based complex compounds studied. Carbon dioxide and acetone were detected in the gaseous products of the decomposition of the compounds if ZnO is formed. Carbon monoxide and acetaldehyde were detected in the gaseous products of the decomposition, if metallic Zn is formed. It is supposed that ZnO and Zn resulting from Zn acetate complex compounds here studied, possess different degree of structural disorder. Annealing takes place by further heating above 600°C.     

Influence of the precursor salts in the synthesis of CaSnO<Subscript>3</Subscript> by the polymeric precursor method

CaSnO₃ was synthesized by the polymeric precursor method, using different precursor salts as (CH₃COO)₂Ca·H₂O, Ca(NO₃)₂·4H₂O, CaCl₂·2H₂O and CaCO₃, leading to different results. Powder precursor was characterized using thermal analysis. Depending on the precursor different thermal behaviors were obtained. Results also indicate the formation of carbonates, confirmed by IR spectra. After calcination and characterization by XRD, the formation of perovskite as single phase was only identified when calcium acetate was used as precursor. For other precursors, tin oxide was observed as secondary phase.     

Redox reactions between metal nitrates and polyols with the formation of nanopowders

The reduction of metal nitrates (Cu(NO₃)₂ · 6H₂O, AgNO₃, and Ni(NO₃)₂ · 6H₂O) by polyols under hydrothermal conditions at temperatures of 150–250°C was studied. The possibility of synthesizing copper, silver, and nickel powders with average particle sizes of 10 to 150 nm depending on the concentration of initial reagents, the temperature, and the nature of a reducer was established using X-ray diffraction analysis and atomic force microscopy. Lanthanide and alkali-earth nitrates were shown to form highly dispersed powders of metal carbonates with an average particle size of ～23 nm under similar conditions.     

Fabrication of lead titanate nanocrystals via gas-bubbling sol–gel process

With Pb(CH₃COO)₂ · 3H₂O and Ti(C₄H₉O)₄ as precursor materials, (CH₃)₂CHOH and ammonium tartrate as solvent and surfactant, respectively, the ferroelectric lead titanate (PT) nanocrystals of tailorable sizes were successfully prepared via a novel gas-bubbling sol–gel process, in which water and ammonia were carried into the solution by nitrogen gas through a bundle of stainless steel needle-like tubes, and a subsequent heating treatment in an oxygen-free atmosphere. It has been found that the dimensions of resulting nanocrystals are strongly affected by the internal diameter of tubes for gas-bubbling, while the velocity of carrier gas flowing in the tubes mainly controls the bubbling rate or the yield of nanocrystals. The possible mechanism for the formation of size-tailorable nanocrystals via such a gas-bubling sol–gel process is discussed in this paper.     

Synthesis of Quantum-Size Cadmium-Zinc Sulfide Particle-Doped Glasses by the Sol-Gel Method

The optical properties of extremely small particles of semiconductor materials provide a sensitive probe of the band structure in the materials. The Sol-Gel process has been applied successfully to the preparation of small particle-size CdS-doped silica glasses such that quantum size effects are significant. Transparent and colorless gels were prepared through the hydrolysis of a complex solution of Si(OC₂H₅)₄, (CH₃)₂SO, Zn(CH₃COO)₂·2H₂O and Cd(CH₃COO)₂·2H₂O. These gels were heated at 350, 500 and 750°C. The thermal treatments of samples were established by TDA/TGA analysis. By means of shift in optical absorption spectra, quantum size effects could be inferred in glasses containing these calcogenide microcrystals.     

片状Co9S8/ZnS/C复合材料的制备及电催化产氧性能

以六水合硝酸钴[Co(NO_3)_2·6H_2O]为钴源、六水合硝酸锌[Zn(NO_3)_2·6H_2O]为锌源、2,2′-硫代二乙酸(C4H6O4S)为硫源,采用溶剂热法制备出了片状的Co_9S_8/ZnS/C复合材料。采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和N_2吸附/脱附测试等手段对于片状Co_9S_8/ZnS/C复合材料结构和形貌等进行表征,同时对片状Co_9S_8/ZnS/C复合材料进行了电催化产氧性能测试。结果表明:片状Co_9S_8/ZnS/C复合材料的起始过电位为390 mV,塔菲尔斜率为144 mV·dec~(-1),具有高的电催化产氧性能。