贵金属/WO3复合纳米晶的气敏与光催化研究进展

WO3作为新型的气敏材料和光催化剂具有广阔的应用前景,通过贵金属纳米簇修饰后的WO3复合纳米晶比WO3基体材料在性能上大幅提高。本文综述了贵金属修饰对WO3基体气敏和光催化性能的影响,其中气敏性能以不同敏感气体(如NOx、H2S、H2等)为分类依据,而光催化性能以不同贵金属(Au、Ag、Pt等)添加剂为分类依据,系统综述了贵金属/WO3复合纳米晶的气敏和光催化性能研究最新进展,并总结了常见贵金属/WO3的气敏和光催化机理模型,提出了贵金属/WO3在气敏和光催化应用过程中存在的问题及前景展望。     

氯代硝基苯催化加氢合成氯代苯胺的催化剂研究进展

综述了近期氯代硝基苯催化加氢合成氯代苯胺的催化剂研究进展,对贵金属(包括贵金属纳米簇催化剂及负载型贵金属催化剂)、骨架镍及非晶态合金等催化剂的结构和性能特点进行了分析和比较。贵金属催化剂活性高,选择性好,反应条件温和。雷尼镍催化剂具有价格较低的优势,但其加氢脱氯的副反应较为严重,多需要采用具有毒性的助催化剂来提高产物的选择性。非晶态合金作为一种新型催化材料具有很好的催化反应性能,其热稳定性还有待进一步提高。     

松香歧化新型催化剂的研究

本研究用非贵金属A、B、D为活性组分,采用醇盐水解法制备氧化物负载非贵金属纳米粒子催化剂。考察了单一组分及它们的混合物催化松香歧化反应的催化性能,初步探讨了松香歧化反应机理。     

松香歧化新型催化剂的研究

本研究用非贵金属A、B、D为活性组分，采用醉盐水解法制备氧化物负载非贵金属纳米粒子催化剂。考察了单一组分及它们的混合物催化松香歧化反应的催化性能，初步探讨了松香歧化反应机理。     

金属纳米簇催化剂的稳定化方法研究进展

液相化学还原法制备的金属纳米簇具有优良的催化性能,但纳米粒子不稳定,容易团聚。本文对金属纳米簇的多种稳定化研究方法,如采用有机配体稳定、表面活性剂稳定、高分子聚合物稳定、离子液体稳定、生物质稳定等进行了综述,总结了载体对金属纳米簇的分散固定作用,并对如何开展金属纳米簇催化剂的研究提出了一些建议和看法。     

沸石分子筛封装纳米金属催化材料的研究进展

综述了近几年国内外沸石分子筛封装纳米金属催化材料的研究进展。重点介绍了在沸石晶体中固定活性金属位置,有效地将纳米粒子的高活性和沸石选择性、稳定性的优点结合,在一系列反应中提高催化性能。在沸石晶体中固定独立的金属位点、金属团簇的合成策略、催化性能和机理研究等。特别是金属纳米粒子被高比表面积沸石分子筛封装后解决了金属纳米粒子的聚集和烧结问题。并介绍了沸石分子筛封装纳米金属催化材料目前的局限性和未来的发展前景。     

沸石分子筛封装纳米金属催化材料的研究进展

综述了近几年国内外沸石分子筛封装纳米金属催化材料的研究进展。重点介绍了在沸石晶体中固定活性金属位置,有效地将纳米粒子的高活性和沸石选择性、稳定性的优点结合,在一系列反应中提高催化性能。在沸石晶体中固定独立的金属位点、金属团簇的合成策略、催化性能和机理研究等。特别是金属纳米粒子被高比表面积沸石分子筛封装后解决了金属纳米粒子的聚集和烧结问题。并介绍了沸石分子筛封装纳米金属催化材料目前的局限性和未来的发展前景。     

贵金属纳米粒子/无机复合材料的制备及性能

介绍了贵金属纳米粒子／无机复合材料的制备方法,陈述了这类材料在光、电、磁、催化等方面的性能,并对今后的发展趋势进行了展望。     

生物质还原制备贵金属纳米颗粒的研究进展

纳米尺度的贵金属材料,因其独特的催化、电、磁和光学性能而受到广泛关注,已经成为当今纳米技术领域的一个研究热点。利用植物、微生物、动植物蛋白质、纤维素等具有还原能力的生物质还原制备贵金属纳米材料已成为一种环境友好型的制备方法。针对近年来利用不同生物质还原制备贵金属纳米颗粒的研究进展进行了综述。     

铂纳米簇/壳聚糖杂化膜催化苯部分加氢制备环己烯

研究了铂纳米簇/壳聚糖杂化膜(Pt/CS)对液相苯部分加氢反应的催化性能.通过微波加热还原氯铂酸的方法制备了单分散铂纳米簇,并将其与壳聚糖(CS)进行杂化后得到铂纳米簇/壳聚糖杂化膜.利用,ITEM、Frr-IR、XRD和XPS等对铂纳米簇以及杂化膜的结构进行了表征,透射电镜表明,铂纳米颗粒平均粒径为3.7 mm.XP...     

Partikelform und Porosität von biogenen Pyrolysekoksen

Char particles from pyrolyzed biomass vary in particle size and shape. On average, the particles are more elongated the larger their size. The average size‐specific elongation is almost alike for all investigated samples, i.e. independent from their source material and process. The particle collectives cannot be characterized accurately with classical particle size distributions, which assume spherical particle shape. Accounting for their shape, they can be described more accurately with particle size distributions that are based on an ellipsoid model. The high bulk porosity is mainly attributed to the spaces between particles.     

超细粉在声场导向管喷流床中的聚团尺寸预测模型

超细粉的流化性能与聚团尺寸密切相关。通过分析超细粉聚团在声场导向管喷流床中的形成过程,提出了高速射流的剪切作用和聚团间的碰撞作用是决定聚团尺寸的主要原因。在此基础上,结合聚团在射流剪切过程和聚团间碰撞过程中的力平衡分析,建立了声场导向管喷流床中聚团尺寸分布的预测模型;并运用这一模型成功预测了不同射流气速下,超细TiO₂颗粒在声场导向管喷流床中的聚团平均直径和聚团尺寸分布。     

溶剂与添加剂对溶剂沉淀法制备PA12粉体的影响

通过改变溶剂沉淀法中复合溶剂中乙醇的浓度或添加剂（SiO₂）的含量制备PA12粉体,并使用激光粒度分析仪、霍尔流速计等对PA12粉体的性能进行了测试与分析。研究发现,乙醇的浓度与添加剂的含量均对PA12粉体的性能存在密切的关联;随乙醇浓度的提高,PA12粉体平均粒径先减后增、粒径分布均匀性提高与流动速率提高、密度降低;随着SiO₂含量的增加,PA12粉体的流动速率与粒径分布均匀性提高,平均粒径与密度呈现先减后增的趋势。     

New fast integrated mobility spectrometer for real-time measurement of aerosol size distribution—I: Concept and theory

A new instrument capable of measuring aerosol size distribution with high time and size resolution, and high signal-to-noise ratios is described. The instrument, referred to as Fast Integrated Mobility Spectrometer (FIMS), separates charged particles based on their electrical mobility into different trajectories in a uniform electric field. The particles are then grown into super-micrometer droplets, and their locations on the trajectories are recorded by a fast charge-coupled device (CCD) imaging system. Images captured by the CCD reveal mobility-dependent particle positions and their numbers, which are then used to derive a particle size distribution spectrum. By eliminating the need to scan over a range of voltages, FIMS significantly improves the measurement speed and counting statistics. A theoretical framework has been developed to quantify the measurement range, mobility resolution, and transfer function of FIMS. It is shown that FIMS is capable of measuring aerosol size distributions with high-time and size resolution.     

Analysis of polymer blend morphologies from transmission electron micrographs

Thermomechanical properties of polymer blends seem to depend on their morphology on microscales and in particular on the size of the dispersed phase particles and/or their distances (ligament thickness). Precise characterization of morphologies by few simple geometrical parameters is often a quite delicate task, in particular because of the strong polydispersity of these systems. We present here a simple method based on image analysis of transmission electron micrographs (TEM) to estimate both distributions in particle size and ligament thickness. We first reconstruct three-dimensional distributions in particle size from two-dimensional measurements and show in particular that corrections from section thickness become significant when thickness is comparable to particle size. Knowing the distribution in particle size, we extend the model initially proposed by Wu to estimate the distribution in ligament thickness. This method provides a more detailed relation between the distribution in particle size and the distribution in ligament thickness. Advantages and limitations of the method are illustrated by practical examples on polyamide-12 systems filled with various particle dispersions.     

Intraspecific Competition, Growth, Chemistry, and Susceptibility to Voles in Seedlings of Betula pendula

We studied the effects of the intensity of intraspecific competition, as indicated by seedling density, and competitive success within populations, as indicated by seedling size, on the secondary chemistry of the stems of silver birch seedlings and their palatability to field voles. We found that the size of seedlings and their total phenolic concentrations were inversely related to stand density. Voles, however, did not discriminate between seedlings grown at the densities studied. Variation in competitive success was associated with several phenomena. Seedling size was positively related to the concentrations of several secondary compounds and to vole preferences, but negatively related to nitrogen concentration. We suggest that the ecological consequences of variation in seedling size cannot be predicted without knowledge of the mechanism behind the variation.     

Some interesting properties of metals confined in time and nanometer space of different shapes

The properties of a material depend on the type of motion its electrons can execute, which depends on the space available for them (i.e., on the degree of their spatial confinement). Thus, the properties of each material are characterized by a specific length scale, usually on the nanometer dimension. If the physical size of the material is reduced below this length scale, its properties change and become sensitive to its size and shape. In this Account we describe some of the observed new chemical, optical, and thermal properties of metallic nanocrystals when their size is confined to the nanometer length scale and their dynamical processes are observed on the femto- to picosecond time scale.     

Recent progress in the pore size control of silicon carbide ceramic membranes

The demand for separation and purification applications under harsh conditions has grown strongly in recent years. Silicon carbide (SiC) ceramic membranes have broad prospects in this aspect due to their unique characteristics, but its pore size control is a crucial problem. Therefore, it is of great significance to develop simple and feasible methods for precise control of the pore size of SiC membranes to improve membrane selectivity and expand their application range. This review describes the pore formation process in the preparation of SiC membranes, focusing on the selection of SiC particles, sintering temperature, sacrificial template, sintering aids, oxidation process and other factors affecting the pore size and analysis. Finally, the control of SiC membrane pore size is summarized and the outlook is proposed.     

DISTRIBUTION PATTERNS DUE TO DIFFUSION IN A COAGULATION-FRAGMENTATION PROCESS WITH CLUSTER-WALL INTERACTIONS

The chemical reactivity of metal nanoclusters is determined mainly by their size and their oxidation state. The control of metal particle size is essential in order to manipulate their reactivity and interfacial behavior. Uniformity of size and spatial distribution of the metal nanoclusters is essential in the study of their properties and can be achieved primarily by conducting their synthesis in the presence of stabilizers. These materials, such as surfactants or polymers, adsorb onto the surfaces of growing clusters and create a “shielding effect,” a chemical barrier that prevents the effects of van der Waals interactions between particles, thus inhibiting particle aggregation. Polymers are frequently used as stabilizers for metal clusters because they are transparent, permeable, and nonconductive, and as such, do not interfere with and/or mask the potential optical, electrical, and catalytic properties of these clusters. When the concentration of the polymer in the reaction solution is above its critical coil overlap, entanglements occur, and hence the polymer may be viewed as a dynamically cross-linked network. Since the metal precursors can interact with the polymer via weak polar interactions, the metal cluster formation will therefore occur within the confines of these closed polymeric domains. In this work we will show, both theoretically and experimentally, the consequences of these interactions in the confines of the polymeric domains on metal particle size and particle size distribution.     

Determination of the characteristics of agglomerates in aqueous suspensions using nonlinear optimization

Measurement of characteristics of particles in suspensions without dilution has a practical interest in formulation, mineral processing, material sciences and environmental technologies.These characteristics are the size, shape, and surface properties of the primary particles, and also the size, structure and the number of primary particles in the agglomerates.In this work, the multiple light-scattering model through the optical analyzer, Turbiscan MA 2000 is used to determine the mean settling velocities of monodisperse glass beads and two polydisperse samples of powders, kaolin D and alumina, differing by their particle size distribution, their shape and their surface properties.Beyond the experimental validation of theoretical and empirical predictions, the nonlinear adjustment of experimental settling data gives the number of primary particles per agglomerate and the agglomerate size. These two characteristics lead to the determination of the fractal dimension of the agglomerates. The latter was found in the range of 2.5-2.7 for all suspensions examined. The calculation of permeability and spherical factor reveals the nonspherical impermeable agglomerates.