Rational Fabrication of Size Tunable SnO2 Hollow Microspheres

A designed solution route was developed to fabricate size tunable SnO₂ hollow microspheres based on the sol-gel theory. The hydrolysis of SnSO₄ released protons to form SnO₂ particulates and induced the decrease of pH value. To minimize the high surface energy, the SnO₂ particulates tended to assemble into large particles, the size of which was affected by the electrolyte concentration or pH value. Elevating SnSO₄ content aroused the decrease of the pH value that directed to the shrinkage of the aggregated particle size of SnO₂. Size tunable SnO₂ hollow microspheres were then rationally fabricated under solvothermal conditions via Ostwald ripening by simply adjusting the SnSO₄ concentration. The in situ pH decrease directed to the shrinkage of the particle size from 270 nm to 112 nm. The formation mechanism was confirmed and rationally elucidated by the time dependant morphology evolution. Charge-discharge tests revealed that the reduced particle size aroused an improved lithium ion battery performance.     

Mechanism of influence of reaction parameters on the particle preparation by reverse micelle method

In this paper, particles of calcium tungstate as a model compound were prepared by a reverse micelle??s method. The morphology of particles was tuned from rod to spindle-like and spherical by altering the temperature and concentration of reactants. A volume per single particle and a total number of particles were calculated to explain quantitatively the mechanism of influence of reaction conditions on the process. It was found that the reactant concentration had no effect on the number of particles. With increasing temperature or reaction time, the number of particles decreased, whereas the particle volume increased. The bulk water in the micelles seemed actually affect the size of particles.     

Fabrication and characterization of ZnO particles with different morphologies for photocatalytic degradation of pentachlorophenol

In this work, ZnO particles with different morphologies were successfully prepared by a simple solution route at low temperature. The products were characterized by SEM, EDS, XRD, TEM, HRTEM, SAED, TG–DTA and UV–Vis DRS. To further understand the formation processes of these ZnO particles, XRD analyses of the intermediates and concentration measurements of Zn(II) remaining in the reaction solution were made at regular intervals throughout the reactions. A possible formation mechanism is discussed. Photocatalytic activity of the as-prepared ZnO powders, evaluated by degradation of pentachlorophenol under UV irradiation, is found to be closely related to the particle morphology.     

Facile chemical approach to ZnO submicrometer particles with controllable morphologies

We have developed a simple wet-chemistry approach to fabricating ZnO submicrometer particles with unique morphologies including rings, bowls, hemispheres, and disks. The size and morphology of the particles can be conveniently tailored by varying the concentrations of the zinc precursor. The reaction temperature, pH, and concentration of ammonia are also found to play critical roles in directing the formation of these particle morphologies. These submicrometer particles exhibit strong white-light emission upon UV excitation as a result of the presence of surface defect states resulting from the fabrication method and synthesis conditions.     

Template-free polyoxometalate-assisted synthesis for ZnO hollow spheres

ZnO hollow spheres with diameters ranging from 400 to 600 nm and the thickness of shell approximate 80 nm were synthesized by a simple polyoxometalate-assisted solvothermal route without using any templates. The effect of polyoxometalate concentration, reaction time and temperature on the formation of the hollow spheres was investigated. The results indicated that the hollow spheres were composed of porous shells with nanoparticles and polyoxometalate play a key role in controlling morphology of ZnO. A possible growth mechanism based on polyoxometalate-assisted assembly and slow Ostwald ripening dissolution in ethanol solution is tentatively proposed. In addition, the room temperature photoluminescence spectrum showed that the ZnO hollow spheres exhibit exciting emission features with wide band covering nearly all the visible region.     

Preparation of Disperse Silver Particles by Chemical Reduction

Mastery over the microscopic shape and size of a nanoparticle enables accurate control of its properties for some strict application. The mechanism of shape-controlled synthesis was discussed by investigating the formation of silver nanospheres prepared by chemical reduction method using Ag(NH₃)₂⁺ as metal source, ascorbic acid as reducing agent and polyvinylpyrrolidone (K-30) as dispersant. The effects of temperature, PVP/AgNO₃ mass ratio, pH value and the interaction between PVP and silver on the shape and particle size were studied by XRD and SEM. The results show that the morphology of silver particles could transform from branched to spherical and the particle size gradually decrease with the increase of PVP/AgNO₃ mass ratio. The particles size can also be significantly influenced by pH value and temperature. The key point for preparing high dispersity spherical silver powder is that the growth rate of each plane of the particle must be uniform and synchronous. Silver powders with spherical particles with mean size of 0.2 μm were synthesized under the optimum conditions (PVP/AgNO₃ mass ratio 0.6, pH 7, reaction temperature of 40°C).     

氧化锌空心微球的制备及其催化性能

以乙二醇为溶剂,聚乙二醇-10000为表面活性剂,硝酸锌和醋酸钠为原料,利用溶剂热法,合成了氧化锌空心微球。 并用X射线衍射、扫描电子显微镜、热重、比表面和孔径分布等对其进行了表征。 考察了硝酸锌用量、聚乙二醇-10000用量、反应时间和反应温度等对氧化锌空心微球形貌和大小的影响。 考察了氧化锌空心微球催化分解高氯酸铵的性能,结果表明,由于氧化锌空心微球的加入,高氯酸铵的分解温度由442 ℃降低至280 ℃左右。     

均分散氧化钛粒子的制备研究

用升温水解法制备了组成为TiO2的球形和椭球形均分散粒子。系统地研究了制备条件对粒子大小和形状的影响,用电子显微镜和红外光谱对粒子的形态和组成进行了分析。跟踪测定了均分散粒子形成过程中体系电导率的变化,探讨了均分散粒子的形成机制。     

Formation of nanocrystalline ZnO particles into bacterial cellulose pellicle by ultrasonic-assisted in situ synthesis

Nanocrystalline zinc oxide particles were synthesized and simultaneously incorporated into a three-dimensional nanofibrous matrix of bacterial cellulose (BC) pellicles by a newly created method called “ultrasonic-assisted in situ synthesis”. The BC pellicles were first immersed in a zinc acetate solution. Then the Zn²⁺-absorbed BC pellicle was further immersed in ammonium hydroxide solution with simultaneous ultrasonic treatment. The effect of immersion time of the BC pellicles in zinc acetate solution and ultrasonic treatment time on crystalline size and percent incorporation of ZnO into the BC pellicles were determined. The crystalline size of ZnO incorporated in BC pellicles was in the range of ~54–63 nm that were similar to the diameter of BC nanofibrils. The amount of ZnO into the BC pellicles was found to increase with increasing immersion time. A longer ultrasonic treatment time resulted in smaller crystalline size of the incorporated ZnO. The particle size, morphology and dispersion of the synthesized ZnO in the BC matrix were examined by transmission electron microscope and scanning electron microscope with inbuilt energy dispersive X-ray analysis. The mechanism of the formation of the nanocrystalline ZnO particles onto the BC nanofibrils was discussed. Moreover, the antibacterial activity of the nanocrystalline ZnO particle-incorporated BC sheet against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) was also evaluated.     

纳米片状ZnO的室温制备及其胶状前体的稳定性分析

以醋酸锌和氢氧化钠为原料,采用室温直接沉淀法得到了ZnO的前体胶状醋酸锌碱式盐,通过控制pH值,在室温下分别制备了碱式盐Zn5(OH)8(Ac)2·2H2O和六方晶系纤锌矿ZnO,并利用X射线衍射、扫描电子显微镜和能谱(EDS)等测试技术对产物进行表征。 结果表明,采用直接沉淀法在pH值为7的环境下得到了具有{n{[Zn5(OH)8(H2O)2]2+}·(2n-x)Ac-}x+·xAc-胶团结构的稳定胶体体系,室温下干燥后的产物的成分为碱式盐Zn5(OH)8(Ac)2·2H2O;而在pH值为14时,胶状前体发生聚沉生成白色沉淀,室温干燥后得到纳米片状ZnO。 还考察了pH值对胶状前体稳定性的影响,并探讨了ZnO的生成机理。     

Simple solvothermal route to synthesize ZnO nanosheets, nanonails, and well-aligned nanorod arrays

ZnO nanosheets, nanonails, and well-aligned nanorods were fabricated on Zn foils by a solvothermal approach using ethanol as the solvent. A lower synthesis temperature and a shorter time period favor the formation of nanosheets. By optimizing the synthesis temperature and time period, ZnO nanonails with a hexagonal cap and a long stem could be produced. A higher temperature was not favorable to produce uniform and smooth nanorods. Well-aligned ZnO nanorod arrays were produced with diameters within 100-250 nm and lengths up to approximately 6 microm when NaOH was added to the solvent. By optimizing the reaction parameters, the morphology, size, and orientation of the nanoforms could be tailored. The ZnO nanorods exhibit an excitonic strong UV emission and a defect-related broad green emission at room temperature. The defect-related green emission band decreased with the improvement of the degree of alignment of the nanorods.     

INFLUENCES OF ACID POST-TREATMENT ON THE MORPHOLOGY OF SOAPFREE P（MMA-EA-MAA） PARTICLES PREPARED BY SEEDED EMULSION POLYMERIZATION

Soap-free poly（methyl methacrylate-ethyl acrylate-methacrylic acid） latex particles with narrow size distribution were synthesized by seeded emulsion polymerization, and the porous particles were created by a stepwise alkali/acid treatment method. Effects of acid treatment conditions on the particle morphology were investigated. Results show that one to three pores were formed inside most of particles after post-treatment. At pH 7.0, when the treatment temperature was lower than 70℃, the size of particles and the volume of pores remained almost unchanged, and these two values increased significantly when the temperature was higher than 70℃. Both the particle size and the pore volume decreased with the increase of initial pH value and treatment time in the acid treatment. As the pH was below 4.0 and the treatment time was longer than 180 min, the particles shrunk in size.     

The generation of void morphology inside soap-free P(MMA-EA-MAA) particles prepared by seeded emulsion polymerization

Monodisperse soap-free P(MMA-EA-MAA) latex particles were synthesized by seeded emulsion polymerization of methyl methacrylate (MMA), ethyl acrylate (EA) and methacrylic acid (MAA), and the particles with void morphology were obtained after undergoing alkali post-treatment. Effects of treatment conditions on particle morphology were investigated. Results showed that the void particles can be obtained under the conditions of the temperature >60 degrees C, initial pH >10.0, treatment time >20 min and 2-butanone amount >2.0 ml. The particle volume and the void size increased to the maximum and then decreased with the increases of initial pH and the treatment time, and these two values increased monotonously with the treatment temperature or 2-butanone amount increased. When the treatment temperature was elevated to 90 degrees C, the treatment time was longer than 180 min, or the 2-butanone amount was more than 8.0 ml, the relatively small voids inside most of the particles combined together to form a large one. The void structure disappeared completely as the initial pH was higher than 12.0. The generation mechanism of the void morphology was discussed.     

不同形貌的Fe3O4微-纳米粒子的溶剂热合成

以FeCl3?6H2O为铁源,用乙二醇或1,2丙二醇为溶剂,PEG为表面活性剂,以及NaOH或KOH为碱源,采用溶剂热法,制备出具有亲水性、分散性较好、超顺磁性和形貌各异的Fe3O4微、纳米颗粒,并对其形貌、结构和磁性进行了表征. 结果表明,产物是均为立方晶系Fe3O4,其颗粒尺寸从20nm-600nm可调. 我们观察到碱源的种类和用量、反应时间、溶剂等对产物形貌的影响,其中碱的用量影响最大. 本文对不同形貌Fe3O4的形成过程进行了探讨,并提出了合理的解释. 所得到的室温下呈现超顺磁性的Fe3O4粒子可以初步满足了生物医学中的应用.     

纳米氢氧化镁的合成及其形貌控制

用乙醇和水的混合溶剂热法合成氢氧化镁纳米材料,并用透射电镜(TEM)和X射线衍射(XRD)表征其形貌和结构,同时考察了镁源、温度、反应时间、反应物浓度和溶剂热体系对氢氧化镁纳米材料形貌的影响,探索其生长机理。镁源通过改变氢氧化镁纳米粒子的结晶习性从而影响形貌,温度和反应时间受热力学和动力学的控制使氢氧化镁纳米材料的生长从六个等价面的取向生长向各向同性生长转变,从而导致形貌由六边形片状结构向圆形变化,反应物浓度和溶剂热体系影响成核快慢,从而影响氢氧化镁纳米材料的晶型。     

聚合物基ZnO纳米线的制备和生长机理研究

采用独特的高分子溶液自组装生长方法, 在经化学镀预处理的基底上利用高分子溶液的网络络合效应制备了ZnO纳米线. 通过场发射扫描电子显微镜(FE-SEM), X射线能谱仪(EDS)等对样品的表面形貌及组成进行了观测表征. 结果显示, 纳米线直径约50 nm, 长度达到了数微米; 产物Zn、O化学计量比接近1∶1. 通过Si基底经化学镀工艺预处理和未经化学镀预处理对ZnO纳米结构、紫外吸收和PL性能影响的分析比较, 发现了化学镀Ni对于纳米线长度和直径尺寸的控制更为有效; 在PL图谱中, 经化学镀预处理的样品在中心波长385 nm出现了由激子碰撞复合所形成的近紫外发光峰. 进一步还分析了在不同的pH值和反应时间下样品的紫外吸收和光致发光性能. 通过以上实验, 讨论并提出了ZnO纳米线的生长机理及过程, 认为纳米线的生长是在化学镀催化剂和高分子双重作用下进行的.     

氧化锌纳米棒微结构光电极的制备

通过两步法,即首先热分解醋酸锌制备氧化锌晶种层,在晶种的诱导下,再采用低温水热法在氟掺杂的SnO₂导电玻璃(fluorine-doped tin oxide, FTO)基底导电面上成功制备出高取向性的氧化锌纳米棒阵列光电极。系统研究了前驱液浓度、溶液pH值、反应时间等实验条件对光电极微结构的影响。实验结果表明在一定变化范围内,随着前驱液浓度和溶液pH值的增大,纳米棒的直径增大;随着反应时间的延长,纳米棒的长度增长。将氧化锌纳米棒阵列薄膜制作成染料敏化太阳电池(dye-sensitized solar cell, DSSC)的光电极,并对电池的I-V特性进行了表征。     

Temperature- and pH-dependent morphology and FT-IR analysis of magnesium carbonate hydrates

Various morphologies of magnesium carbonate hydrates have been synthesized by carefully adjusting the reaction temperature and pH value of the initial reaction solution in the precipitation process. At lower temperatures (from room temperature to 328 K) and lower pH values (variation with the reaction temperature), magnesium carbonate hydrates are prone to display needlelike morphology, and the axis diameter of the particles decreases with the increase of reaction temperature and pH value. With the further increase of the reaction temperature (333-368 K) and pH value, the sheetlike crystallites become the preferred morphology, and at higher temperatures and pH values, these crystallites tend to assemble into layerlike structures with diverse morphologies, such as spherical-like particles with rosette-like structure and cakelike particles built from sheetlike structure. Fourier transform infrared (FT-IR) spectra show that these various morphologies are closely related to their compositions. The needlelike magnesium carbonate hydrate has a formula of MgCO3.xH2O, in which the value x is greatly affected by the experimental conditions, whereas with the morphological transformation from needlelike to sheetlike structure, their corresponding compositions also change from MgCO3.xH2O to Mg5(CO3)4(OH)2.4H2O in the interval of 328-333 K.     

Synthesis of nanosized chitosan-poly(acrylic acid) particles by a dropping method

Deoxyribonucleic acid (DNA) vaccines are being investigated extensively because of their excellent potential over conventional protein ones. A suitable DNA carrier, consisting of uniformly dispersed chitosan-poly(acrylic acid) particles with an average size of 30 nm, was successfully synthesized by a dropping method with a ratio of chitosan solution to poly(acrylic acid) solution of 1:1 and was incubated in a buffer solution with a pH value of 3.0. The particle size increased from 35.76 to 45.90 nm when the pH value of the buffer solution was increased from 3.0 to 7.4. After freeze-drying, the non-incubated mixed solution showed a membranous morphology. A powdered product was formed from the mixed solution as incubated in buffer solution with pH values of 3.0 and 5.3. However, when the mixed solution was incubated in a buffer solution of pH 7.4, a mixture of membrane and powder was obtained.     

纳米ZnO的制备及其光催化性能研究

本文以羟丙基纤维素(HPC)作为分散剂,运用沉淀法制备出了粒径均匀的ZnO颗粒.通过透射电子显微镜(TEM),X射线衍射(XRD),紫外可见光吸收光谱,光致发光谱(PL)对ZnO进行了性能表征,并探讨了其形成机理及制备中的影响因素.利用纳米ZnO作为光催化剂对有机染料罗丹明B进行了光降解实验,实验结果表明,此方法制备的ZnO具有良好的光催化性能,有望在治理环境污染等领域具有良好的应用.