CHARACTERIZATION OF NANOSTRUCTURES:TOOLS AND CHALLENGES G.Cox,W.Wohlleben and W.Schrepp

Apart from long-known and applied nanostructures like carbon black for tyres or pigments for coatings nanotechnoiogy has created highly sophisticated structures used for nano/molecular electronics,diagnostics,drug delivery,UV-absorbers etc.Often the main question to be solved analytically is the local determination of tiny amounts of chemicals resulting in an ever increasing need for highly sensitive as well as locally resolved techniques.Applications of techniques like mass spectroscopy,transmission electron microscopy as well as ultracentrifugation to problems arising from nanotechnology in the chemical industry will be described.     

CHARACTERIZATION OF NANOSTRUCTURES:TOOLS AND CHALLENGES

Apart from long-known and applied nanostructures like carbon black for tyres or pigments for coatings nanotechnology has created highly sophisticated structures used for nano/molecular electronics,diagnostics,drug delivery, UV-absorbers etc.Often the main question to be solved analytically is the local determination of tiny amounts of chemicals resulting in an ever increasing need for highly sensitive as well as locally resolved techniques.Applications of techniques like mass spectroscopy,transmission el...     

Analytical ultracentrifugation of gels

Analytical ultracentrifugation is a powerful tool for the determination of thermodynamic, elastic and molecular parameters and structural properties of gels. Although gelling systems are an important class of mixtures, only a few researchers have studied their properties by means of analytical ultracentrifugation. This might be due to the extreme experimental difficulties concerning the detection of the polymer concentration in turbid gels, adhesion problems, etc. Nevertheless, the potential benefit of such experiments has led to several investigations in this field during recent years. These resulted in the introduction of a theoretical treatment of the sedimentation of even multicomponent gels and an improved experimental set-up which allows the characterization of a gel/solvent system in a limited concentration range in a single sedimentation equilibrium experiment. For microgels prepared and crosslinked in emulsions, an interesting rapid sedimentation velocity technique is available for their characterization. This review article describes the capabilities of the experimental method and what has been achieved with it in the past. Furthermore, it gives an outlook on applications which may be possible in the future.Dedicated to Prof. Dr. W. Borchard on occasion of his 60th birthday     

Synthesis, characterization and optical band gap of NiO nanoparticles derived from anthranilic acid precursors via a thermal decomposition route

This study focuses on the preparation and characterization of single phase NiO nano particles. Four nickel anthranilic acid complexes were synthesized by the semi-solid phase reaction method as precursors for the preparation of NiO nanoparticles via a solid-state decomposition procedure at 700 °C. Thermogravimetric analysis (TGA) was applied to determine the thermal behavior of the precursors and the temperature at which the precursors decompose leaving the oxide. The crystalline structures of the products were investigated by X-ray diffraction (XRD), the morphology of particles by SEM and TEM. The particles size was determined by STM, and the average particle size was found to be 8 nm. Electronic spectra were used to clarify qualitatively the change in absorption band positions on changing the particle size of NiO. The optical band gap of the NiO nanoparticles was calculated and indicated a direct transition. The values of the optical band gap of NiO nanoparticles increase as the particle size decreases.     

The preparative dynamic density gradient method

In this work the development of a new ultracentrifugation method is described. The preparative density gradient method (PDDG) allows the fractionation of colloidal systems according to the density of their components. The fractions—collected separately—can be subjected to further investigations with any appropriate physical or analytical method. The particle density of a colloidal system is a very valuable information that can be used in many ways. Here for the first time a method is presented that could make the access to that information much easier for laboratories throughout the world. The preparative dynamic density gradient is performed in a preparative ultracentrifugation tube by layering heavy water under a sample that is dispersed or dissolved in water. The water and heavy water molecules undergo a fast diffusion process finally leading to a homogeneous solvent mixture. While reaching this equilibrium the water–heavy water concentration varies over the cell radius. Thus a density gradient is built up. Fractions of the sample will move to the radial position where their densities are matched. They can then be collected separately. In this work basic experiments and results that lead to the development of the PDDG will be presented. Calculations based on basic ultracentrifugation theory confirm the described experimental findings. An example will demonstrate the problem solving capability of this new method.     

无机卤化物钙钛矿纳米结构的带隙可调制备及光电应用研究

在半导体领域,通过合金化集成两种以上半导体的单纳米结构近年来相继问世,随着纳米材料的成分变化,可以灵活实现半导体的带隙调控,在光通信以及集成光电器件领域有着广泛的应用。然而,传统半导体纳米结构因不同成分之间存在晶格失配,其带隙调节的范围受到了很大限制。因此,钙钛矿作为对晶格失配具有高容忍度的半导体材料,在半导体带隙调控及器件研究领域显示出了巨大的潜力。本文综述了无机卤化物钙钛矿一维合金纳米材料的合成方法以及近年来的研究进展,总结了可调带隙钙钛矿一维合金纳米材料在光电子器件领域中的应用,包括波长可调谐纳米激光器、光电探测器、白光发光二极管、全光开关、太阳能电池等。实现单纳米结构带隙工程将对未来集成器件的发展产生深远的影响。     

无机纳米粒子填充聚合物的研究进展

对纳米粒子的历史、结构及特性作了简要介绍，着重介绍了纳米粒子的表面处理及其在填充了聚合物方面的应用开发。     

Understanding of surface tension?

The importance of the molar dimensions for surface properties of not too large molecules is stressed. The understanding of surface properties of pure liquids is described in molar units with a simple model of normal liquids. The increasing knowledge makes it necessary to use idealized models. A hypothesis is given for the temperature constancy of the surface energy of small molecules without H-bonds, and a model is developed for the free energy σ_m and its temperature dependency. This seldom example of the direct measurement of the isothermic work or the free energy could help to illustrate the difference between energy and free energy. Received: 24 July 2000 Accepted: 26 October 2000     

Thermogravimetric analysis of SPEEK membranes: Thermal stability, degree of sulfonation and cross-linking reaction

Thermal degradation of SPEEK membranes is studied by coupling thermogravimetric analysis (TGA) and mass spectrometry (MS). Main mass losses can be attributed to water evaporation, desulfonation and oxidative pyrolysis of polymer main chain. The analysis can be used to determine the degree of sulfonation (DS) and the degree of cross-linking (DCL) between macromolecular chains. Furthermore, the thermogravimetric curves can be modelled using non-isothermal chemical kinetics, allowing determination of activation energies during thermal degradation of SPEEK membranes.     

Janus颗粒表面活性剂的研究进展

Janus颗粒（JPs）是一类新型的具有微米或纳米尺寸、2个半球具有不同化学特性的胶体粒子。 其中,两亲性JPs在其2个半球上分别表现出亲水和疏水的特性,作为一种新型表面活性剂受到广泛的关注。 本文综述了近几年来两亲性JPs的制备方法、表面活性理论、两亲性表征方法及其在乳液聚合中的应用,并探讨了今后的研究方向。     

SARS 3CL蛋白酶同源二聚化与底物结合互为别构调控因素

研究了严重急性呼吸系统综合症(SARS)冠状病毒3C-Like蛋白酶(3CLpro)在存在底物或抑制剂时的二聚体形成情况. 通过测定酶活性随酶浓度的变化, 拟合出在底物存在下酶二聚体的解离常数约为0.94 μmol·L-1, 小于纯蛋白酶的二聚体解离常数(14.0 μmol·L-1), 表明底物对二聚体的形成具有增强作用. 选用与底物具有类似结合方式的靛红类抑制剂N-萘甲基靛红-5-甲酰胺(5f), 利用超速离心沉降速率方法定量测定了SARS 3CL蛋白酶单体和二聚体在不同浓度5f时的含量, 发现5f同样具有诱导二聚体形成的能力. 在3 μmol·L-1蛋白酶浓度下测定得到诱导二聚的EC50 值(半数有效浓度)约为1 μmol·L-1, 说明二聚体中只有一个单体与抑制剂结合. 研究结果表明, 随着底物浓度的升高, SARS 3CL蛋白酶会形成更多的二聚体, 而二聚体含量的提高又反过来提高酶的活性, 这种双向别构调控机制有可能是病毒用来调控多聚蛋白水解速率和组装时机的一种方法.     

Ion-exchange behavior of stannic selenoiodate and stannic selenosilicate: analytical application of stannic selenoiodate

Two new inorganic ion exchangers, stannic selenoiodate and stannic selenosilicate have been synthesized. The ion-exchange capacity of stannic selenoiodate and stannic selenosilicate for K⁺ was found to be 1.84 and 1.23 meq g^–1, respectively. pH titration studies reveal monofunctional and bifunctional behavior for stannic selenosilicate and stannic selenoiodate, respectively. Distribution coefficients of metal ions in dimethylformamide–HCl and formamide–HCl systems have been determined. Some important and analytically difficult quantitative binary and ternary separations, and selective separations of Ag⁺, Sn⁴⁺, Zr⁴⁺, Co²⁺, and Ni²⁺ have been achieved on stannic selenoiodate columns. The practical utility of the material has been demonstrated by analyzing the metal ion content of electroplating waste.     

Assessment of doped ceria as electrolyte

A model describing the performance of a fuel cell based on 10 mol% gadolinia-doped ceria, Ce_0.9Gd_0.1O_1.95−x (CG10), was formulated. The total electrical conductivity of CG10 was measured under very reducing conditions in the temperature range of 753 K to 948 K. Oxygen permeation experiments were carried out to measure the leak current through a ceria electrolyte. The results of the measurements are compared with predictions of the formulated model. Furthermore, the response of a fuel cell to changing operating conditions such as external load, temperature, electrode polarization resistances, and defect chemistry is investigated using the model. It is found that the maximum achievable efficiency of a CG10-based fuel cell is increased when (1) the temperature is decreased, when (2) the electrolyte thickness is increased, or when (3) the cathode polarization resistance is decreased. The efficiency can also in certain circumstances be increased by an increase of anode polarization resistance. Finally, the efficiency is reduced if the vacancy formation enthalpy is decreased to the level of fine-grained CG10. The performance of a CG10-based cell is evaluated by comparing it with a state-of-the-art zirconia-based cell. At 873 K, the efficiency of a fuel cell with a 10-μm CG10 electrolyte was limited to 0.74, whereas a cell with a perfect electrolyte would have an efficiency of 1. The power output of the CG10 cell at this efficiency is, however, four times larger than the zirconia-based cell at the same efficiency. This is due to the much lower cathode polarization resistance of -CG10 cathodes on CG10 compared to the (La_0.75Sr_0.25)_0.95MnO₃ cathodes on stabilized zirconia.