Preparation of cellulose-ZnO hybrid films by a wet chemical method and their characterization

Zinc oxide (ZnO) nanoparticles were immobilized on the surface of regenerated cellulose films by a wet chemical method in which the controlled hydrolysis of a Zn(II)-amine complex leads to the formation of ZnO nanoparticles. Cellulose-ZnO materials were characterized by spectral, thermal and optical methods. Scanning electron microscope and atomic force microscope analyses confirmed the formation of ZnO nanoparticles on the surface of the regenerated cellulose film and X-ray diffraction patterns showed the ZnO had the wurtzite structure. The reported method is very simple, and can immobilize the nanoparticles without the aid of a binder or dendritic side group and without high temperature treatments like calcination. ZnO immobilized on biopolymers like cellulose has many potential applications such as strain sensors, biomedical sensors, flexible display devices and optoelectronics.     

LB技术制备FePt纳米粒子单层膜

FePt纳米粒子由于具有高的矫顽力而成为高密度垂直磁记录材料的研究热点之一,均匀有序排布的FePt纳米粒子薄膜将有利于提高磁记录介质的记录密度,因此,如何使FePt纳米颗粒均匀有序地排布是当前需要解决的关键问题之一,很多研究小组利用磁控溅射、自组装和电沉积等方法对FePt纳米颗粒的均匀分布进行了详细的研究,     

X-ray diffraction analysis of ultradisperse systems: The Debye formula

Problems of X-ray diffraction analysis of ultradisperse systems with the particle size up to 5 nm are discussed in the review. A method for calculating X-ray diffraction patterns using the Debye formula within the kinematic theory of X-ray scattering (Debye Function Analysis-DFA) is presented. The DFA method makes it possible to obtain information on the atomic structure, shape and size of nanoparticles, and verify hypotheses on the presence of deformations, stacking faults and other structural features of ultradisperse and nanostructured systems. The method is applicable for modeling the diffraction patterns of objects with an arbitrary (not necessarily crystal) structure. Applications of the method for examining the structure of various objects are discussed.     

Synthesis and characterization of heat-stabilized albumin magnetic microspheres

Human serum albumin magnetic microspheres containing 30% iron oxide particles were synthesized by a heat-stabilization process. The average diameter, the size distribution and the morphology were characterized by scanning electron microscopy, atomic force microscopy and transmission electron microscopy. The distribution of the iron oxide nanoparticles within the microspheres was confirmed by the contrast obtained in the morphology by backscattered electron imaging in scanning electron microscopy. Energy-dispersive X-ray spectroscopy showed the presence of iron in the microspheres. The cabbage like surface structure in some of the microspheres obtained in scanning electron microscopy can be better understood by atomic force microscopy. This peculiar surface structure in the microsphere may be due to the cross-linking in the protein molecule by heat. The amount of iron oxide in the microsphere was analyzed by atomic absorption spectroscopy. The magnetic properties of the particles were measured in a superconducting quantum interference device magnetometer. Received: 12 September 2000 Accepted: 5 February 2001     

Composition-dependent sintering behaviour of chemically synthesised CuNi nanoparticles and their application in aerosol printing for preparation of conductive microstructures

Copper, nickel and copper–nickel nanoparticles were prepared by solution combustion method for use in direct write printing. Structural (X-ray diffraction) and morphological (transmission electron microscope) investigations showed that pure metal (Cu and Ni) and CuNi alloy particles with face-centred cubic crystal structure were formed. Atomic absorption spectrometer studies confirmed that the nanoparticle compositions corresponded to the initial Cu/Ni molar ratios selected for synthesis. Particle size and morphology were significantly influenced by composition, with high Cu content coinciding with small, spherical particles as opposed to larger, irregular shapes observed at high Ni concentrations. X-ray photoelectron spectroscopy measurements revealed that after the reduction process the surface of the alloy nanoparticles was partially oxidised in air and the amount of metallic surface species decreased, while the concentration of oxidic surface species and hydroxides increased with increasing Cu concentration (i.e. decreasing particle size). Dispersions of CuNi nanoparticles have been deposited by use of AerosolJet? and sintered under reducing atmosphere at 300–800?°C in order to prepare conductive structures. Resistivity measurements and microscopical studies (SEM-FIB) of printed and sintered CuNi structures showed that the sintering properties of nanoparticles were dependent on their chemical composition.     

Structure determination of CdS and ZnS nanoparticles: direct modeling of synchrotron-radiation diffraction data

We introduce a modified method of powder-diffraction data analysis to obtain precise structural information on freestanding ZnS and CdS nanoparticles with diameters well below 5 nm, i.e., in a range where common bulk-derived approaches fail. The method is based on the Debye equation and allows us to access the crystal structure and the size of the particles with high precision. Detailed information on strain, relaxation effects, stacking faults, and the shape of the particles becomes available. We find significant size differences between our new results and those obtained by established methods, and conclude that a mixed zinc-blende/wurtzite stacking and significant lattice distortions occur in our CdS nanoparticles. Our approach should have direct impact on the understanding and modeling of quantum size effects in nanoparticles.     

The effect of surface properties on visible luminescence of nanosized colloidal ZnO membranes

Luminescence properties of nanosized zinc oxide (ZnO) colloids depend greatly on their surface properties, which are in turn largely determined by the method of preparation. ZnO nanoparticles in the size range from 3 to 9 nm were prepared by addition of tetramethylammonium hydroxide ((CH3)4NOH) to an ethanolic zinc acetate solution. X-ray diffraction (XRD) indicates nanocrystalline ZnO membranes with polycrystalline hexagonal wurtzite structure. The ZnO membranes have a strong visible-emission intensity and the intensity depends upon hydrolysis time. The infrared spectra imply a variety of forms of zinc acetate complexes present on the surface of ZnO particles. The effect of the ZnO membrane surface properties on photoluminescence is discussed.     

Production and structural characterization of crystalline silver nanoparticles from Bacillus cereus isolate

To date, biosynthesis of metal nanoparticles has been intensively studied using bacteria and fungi. We have isolated and identified metal resistant bacterial strains from electroplating industries, they produce silver nanoparticles. The reduction reaction of aqueous silver nitrate with bacterial biomass was carried out for 120 h. Bacteria produced metallic nanoparticles showed a strong absorbance at surface plasmon resonance wavelength around 420 nm. The size and morphology of these nanoparticles were typically imaged using high resolution transmission electron microscopy, the particles size ranges between 4 and 5 nm and are spherical in shape. The crystal structure of the particles was characterized by X-ray diffraction pattern. The full width half maxima from X-ray diffraction measurements indicated that the particles exhibited face-centered cubic phase.     

Structural organization of gold nanoparticles onto the ITO surface and its optical properties as a function of ensemble size

Self-assembly of citrate-stabilized gold nanoparticles (AuNPs) onto an optically transparent indium tin oxide (ITO) surface followed by neutralization of these particles using dodecanethiol as a surfactant have been demonstrated. X-ray photoelectron spectroscopic (XPS) studies revealed the partial removal of citrate ions from the immobilized AuNPs, which advances the dilution of electrostatic attraction between AuNPs and the APS (amino-terminated monolayer)-functionalized ITO surface. The resultant AuNPs restore their mobility to some extent and form small ensembles. Some of the immobilized AuNPs were completely removed from the surface due to neutralization, as confirmed by XPS studies. Interparticle distance and size of ensembles were manipulated by consecutive cycles of immobilization and neutralization of AuNPs. Controlled nanostructural fabrication progression, which leads to two-dimensional lateral growth of AuNPs, provides a method for systematically shifting the surface plasmon resonance band based on the increase in plasmon coupling among the closely placed AuNPs of an ensemble. The magnitude of shift increases with the size of ensemble. This manipulated chemical strategy offers a convenient and simple method to tune the optical properties of materials on a nanoscale.     

Nanosilica-supported polyethoxyamines as low-cost, reversible carbon dioxide sorbents

Nanoparticles capped with amine ligands with different steric properties, dodecylamine and oleylamine, respectively, are investigated in the solid state as well as in solution. A combined X-ray diffraction, small angle X-ray scattering and electron microscopy investigation showed that the nanoparticles exhibit the sphalerite modification of ZnS as crystal phase with a diameter of 3-5 nm. A close packing of the monocrystalline nanoparticles in the solid state is observed. However, in the dodecylamine sample, besides spherical particles, a fraction of the nanoparticles is elongated. The nanoparticles are readily resoluble in apolar solvents like hexane. Dynamic light scattering (DLS) and SAXS investigations of the solutions reveal that the nanoparticles are dissolved as singular particles. In the case of oleylamine-capped ZnS, a defined core-shell structure with a ZnS core with a diameter of 4 nm and an organic shell with a thickness of approximately 2 nm have been found. Dodecylamine-capped nanoparticles slightly tend to form agglomerates with a diameter of approximately 40 nm.     

Characterization of titanium dioxide nanoparticles using molecular dynamics simulations

Molecular dynamics simulations of titanium dioxide nanoparticles in the three commonly occurring phases (anatase, brookite, and rutile) are reported. The structural properties inferred by simulated X-ray diffraction patterns of the nanoparticles were investigated. The titanium-oxygen bond length as a function of size, phase, and temperature was determined and was found to be dependent on the coordination environment of the titanium and independent of phase and size. The equilibrium Ti-O bond length is 1.86 A for a four-coordinated titanium ion, 1.92 A for a five-coordinated titanium ion, and 1.94 A for an octahedral titanium ion. Smaller nanoparticles are characterized by a higher fraction of titanium ions that are four and five coordinated, due to the larger surface area-to-volume ratios. The surface energies for anatase, rutile, and brookite particles were reported. The surface energy of the nanoparticle increases and approaches a constant value as the particle gets bigger. The surface energies of small rutile particles are higher than that for anatase particles of a similar size, consistent with anatase being the more stable phase of nanocrystalline titanium dioxide.     

氧化锆改性的Ni/LaAl11O18用于CO甲烷化反应:催化剂结构对催化性能的影响

对于煤制天然气,CO甲烷化技术起着重要作用,其研究核心之一是高效催化剂的开发.目前,CO甲烷化催化剂主要采用金属Ni作为活性组分,但存在高温易烧结和易积炭等问题.因此,如何使其同时具有较高的催化活性和高温稳定性是亟待解决的问题.针对这些问题,本文以高热稳定性的六铝酸镧(LaAl11O18)为载体,采用浸渍法担载金属镍,制备了Ni/LaAl11O18催化剂;以高化学惰性的ZrO2为包覆层,采用改进的连续吸附反应法,将ZrO2前驱体液相沉积在Ni/LaAl11O18表面进行改性,制备了具有包覆结构的Ni/LaAl11O18@ZrO2甲烷化催化剂.探讨了ZrO2在Ni/LaAl11O18表面的分布形式以及不同沉积包覆量对催化剂结构、CO甲烷化催化剂活性和稳定性的影响.分别采用氮气物理吸附、X射线衍射、透射电镜、扫描电镜、氢气程序升温还原、氢气程序升温脱附、X射线光电子能谱、热重分析和电感耦合等离子体原子发射光谱法等手段对催化剂进行了系统表征.结果表明,ZrO2纳米粒子能够同时分布在催化剂活性组分和载体表面,增加了金属?载体间相互作用力,高温还原时可以有效抑制活性金属Ni的烧结,成功构筑了具有显著限域结构的包覆型催化剂.同时,ZrO2的包覆不利于金属的氢气化学吸附.在常压,260?600 oC和120 L g?1h?1条件下对催化剂进行了催化活性测试.结果显示,与未改性的催化剂相比,包覆后催化剂上CO转化率略有降低,但是其CH4选择性明显提高,适量的ZrO2包覆对CH4得率有较好的促进作用,但是过量的ZrO2包覆会因占据过多的金属镍表面使得CO转化率显著降低.在常压,550 oC和120 L g?1h?1空速的操作条件下所进行的107 h稳定性测试结果表明,包覆型Ni/LaAl11O18@ZrO2催化剂展示了良好的高温稳定性,具有优异的抗烧结和抗积碳性能.这主要是因为包覆型催化剂具有良好的"限域"效应,从而显著改善了催化剂的抗烧结性能;同时较强的金属?载体相互作用以及ZrO2助剂对CO2的活化提升了催化剂的消碳能力,增强了Ni/LaAl11O18@ZrO2催化剂的抗积碳能力.总之,本文构筑了一种高稳定性的包覆型催化剂Ni/LaAl11O18@ZrO2,可广泛应用到其他多种高温反应中.     

Composites based on SiO2 micrograins and cobalt-containing nanoparticles: Synthesis, structure, and magnetic properties

Cobalt-containing particles are synthesized on the surface of silicon dioxide micrograins prepared by the Stöber-Fink method. The composition and structure of nanoparticles are determined by transmission electron microscopy, X-ray diffraction analysis, and EXAFS. The average size of cobalt nanoparticles in the samples is found to be 14 ± 5 nm. The resulting composites are shown to be ferromagnetics with low specific magnetization values.     

ZnO Nanoparticle Functionalization by Organosilanes Catalyzed with Ethylene Diamine for Production of Stable Nanodispersions in Water

A simple method that was used to obtain stabilized ZnO nanoparticles and their dispersions in water is presented. It yields anisotropic (trigonal prismatic) nanocrystals with dimensions below 50 nm. The Partial Profile Relaxation (PPR) technique was applied in the analysis of X-ray diffraction data with complex anisotropic broadening. Ethylene diamine catalyzed silanization was utilized for the covalent surface functionalization, which allowed us to obtain stable waterborne dispersions when aminosilanes were used. The difference in the surface structure of ZnO nanoparticles for different variants of functionalization was investigated by ²⁹Si NMR spectroscopy. The combination of X-ray diffraction and dynamic light scattering data indicates minimal degree of particle agglomeration in the dispersions.     

乳液聚合法制备纳米金/聚苯乙烯复合粒子

以氯金酸为前驱体,十二烷基硫醇和硼氢化钠分别作为稳定剂和还原剂,采用相转移法制备了单分散的金纳米粒子.将金纳米粒子通过乳液聚合的方法制备了纳米金/聚苯乙烯复合粒子.通过紫外-可见吸收光谱(UV-Vis)研究了纳米金和纳米金/聚苯乙烯复合粒子的光吸收特性,使用傅立叶变换红外光谱(FT-IR)、X射线衍射(XRD)、透射电子显微镜(TEM)和动态光散射(DLS)对产物的组成、晶体结构、形貌、以及粒径进行了表征.结果表明,复合粒子为粒径分布较窄的球形,其中的金纳米粒子为面心立方结构.热失重分析(TGA)说明制备的纳米金/聚苯乙烯复合粒子具有很好的热稳定性.     

退火温度对CdSe纳米薄膜的形成及光电性能影响

在室温下,采用循环伏安法在ITO上沉积CdSe纳米薄膜。利用X射线衍射仪(XRD)、场发射扫描电镜(FESEM)、原子力显微镜(AFM)、X射线光电子能谱分析(XPS)、紫外-可见(UV-VIS)分光光度计以及电化学工作站对不同温度退火后的CdSe纳米薄膜的晶体结构、形貌、光学性能、光电化学性能进行表征和测试。结果表明,退火温度对CdSe纳米薄膜的形貌和性能起到关键性作用。薄膜表面平整、厚度均匀,且由呈纳米颗粒状的立方相CdSe构成;经退火后,CdSe纳米颗粒出现不同程度的长大现象,Se含量随退火温度的升高而减少。紫外-可见吸收光谱表明随着退火温度的升高,CdSe纳米薄膜对可见光的吸收发生红移,表明禁带宽度逐渐减小,表现出量子尺寸效应。通过光电流测试表明随着退火温度的升高,CdSe薄膜的光电响应效应显著提高。     

退火温度对CdSe纳米薄膜的形成及光电性能影响

在室温下,采用循环伏安法在ITO上沉积CdSe纳米薄膜。利用X射线衍射仪(XRD)、场发射扫描电镜(FESEM)、原子力显微镜(AFM)、X射线光电子能谱分析(XPS)、紫外-可见(UV-VIS)分光光度计以及电化学工作站对不同温度退火后的CdSe纳米薄膜的晶体结构、形貌、光学性能、光电化学性能进行表征和测试。结果表明,退火温度对CdSe纳米薄膜的形貌和性能起到关键性作用。薄膜表面平整、厚度均匀,且由呈纳米颗粒状的立方相CdSe构成;经退火后,CdSe纳米颗粒出现不同程度的长大现象,Se含量随退火温度的升高而减少。紫外-可见吸收光谱表明随着退火温度的升高,CdSe纳米薄膜对可见光的吸收发生红移,表明禁带宽度逐渐减小,表现出量子尺寸效应。通过光电流测试表明随着退火温度的升高,CdSe薄膜的光电响应效应显著提高。     

Non-aqueous synthesis of AuCu@ZnO alloy-semiconductor heteroparticles for photocatalytical degradation of organic dyes

Heteroparticles with anisotropic structure have emerged as a focus of research. They contain two distinct sides with different composition, structures, ionization potential and surface chemistry. The asymmetric structure allows a tuning of chemical, optical, electrical, magnetic, mechanical and thermodynamic properties within a single particle by controlling composition, size, shape and organization at the nanoscale. Here we report the preparation of AuCu@ZnO heteroparticles using non-aqueous solution chemistry by in situ alloying of the metal domains of AuCu@ZnO nanoparticles. The size, shape and optical properties of the AuCu@ZnO hybrid nanoparticles were characterized by transmission electron microscopy and UV–visible spectroscopy. The nanocrystals have a multipod-like morphology with ZnO domains connected to an AuCu alloy core. The AuCu@ZnO nanoparticles showed a pronounced red-shift of the plasmon band compared to Au@ZnO heteroparticles. The crystal structure and phase purity were confirmed by X-ray powder diffraction. Surface-functionalization with imidazole-type ligands rendered the AuCu@ZnO nanoparticles water soluble. The AuCu@ZnO alloy heteroparticles showed an enhanced activity compared to Au@ZnO for the photocatalytic degradation of organic pollutants, as demonstrated with the model compound rhodamine B.     

Fabrication of zinc ferrite nanocrystals by sonochemical emulsification and evaporation: observation of magnetization and its relaxation at low temperature

A new ultrasound assisted emulsion (consisting of rapeseed oil and aqueous solution of Zn(2+) and Fe(2+) acetates) and evaporation protocol has been developed for the synthesis of zinc ferrite (ZnFe(2)O(4)) nanoparticles with narrow size distribution. The as-synthesized sample consisted of crystalline zinc ferrite particles with an average diameter of approximately 4 nm, whereas the average size of the heat-treated ferrite particles increases to approximately 12 nm. To remove the small amount of oil present on the surface of the as-synthesized ferrite sample, heat treatment was carried out at 350 degrees C for 3 h. The as-synthesized and heat-treated ferrites were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), TGA/DTA, transmission electron microscopy (TEM), and energy dispersion X-ray spectroscopy (EDS) techniques. Magnetic measurements show that the nanocrystalline ZnFe(2)O(4), prepared through this technique, is either at par with those obtained in other cases or even more improved. Both the as-synthesized and heat-treated samples reveal relaxation of magnetization. Our study also shows that one can tailor the magnetization and relaxation pattern by suitably controlling the particle size of the nanocrystalline ZnFe(2)O(4). The key features of this method are avoiding (a) the cumbersome conditions that exist in the conventional methods, (b) the usage of necessary additive components (stabilizers or surfactants, precipitants), and (c) calcination requirements. In addition, rapeseed oil has replaced organic nonpolar solvents used in earlier studies. As a whole, this simple straightforward sonochemical approach results in a better pure phase system of nanoferrite with improved magnetic properties.