A Comparison of Chemical Activity at Ordered and Disordered Tetrahedrally Coordinated Semiconductor Surfaces

This paper discusses the surface order-dependent adsorptive activity at the surfaces of tetrahedrally coordinated semiconductors. It stresses the differences between elemental (e.g., Si) and compound materials (e.g., Gas, CdS, and ZnO) as well as the differences between ordered and disordered nonpolar compound semiconductor surfaces. Several examples will be presented that compare oxygen adsorption on ordered and disordered surfaces. It will be shown that adsorption on ordered nonpolar compound semiconductor surfaces is weak in comparison to adsorption on ordered elemental semiconductor surfaces, that among the compound semiconductors the ordered nonpolar surfaces of the II-VI materials (e.g.,) are much weaker adsorbents than the similar surfaces of the III-V materials (e.g., GaAs), and that adsorption on nonpolar compound semiconductor surfaces is much enhanced by surface disorder. It will be argued that these phenomena can collectively be attributed to bonding ionicity. Finally, an attempt will be made to establish a connection between the order/disorder phenomena described here and the collective electronic and active site models of surfaceactive catalysis.     

Hydrogen Adsorption on Ordered and Disordered Pt-Ni Alloys

Topics in Catalysis - The bulk properties and chemical reactivity of disordered Pt-Ni alloys in the A1 (fcc) structure are investigated using different methods: Virtual Crystal Approximation (VCA),...     

Spatial Variations in the Sintering Rate of Ordered and Disordered Particle Structures

Local sintering rates were measured in two-dimensional, ordered and disordered structures constructed from glass spheres. In ordered arrays, made from monosized spheres, the local sintering rates varied from 1/2 to 2 times the average sintering rate. In contrast, disordered arrays, made from bimodal particle sizes, sintered more homogeneously, the local sintering rate deviating less than 15% from the average. The total average densification strain was also greater for the disordered structures. As a result, for the same time and temperature cycle, the disordered structures sintered to near full density while the ordered structures did not. Poor densification in the ordered structure was attributed to packing defects such as domain walls and dislocations. Some evidence was obtained for a correlation between densification and the average coordination number of particles.     

Ordered Mesoporous Materials with Improved Stability and Catalytic Activity

Microporous crystals of zeolites such as Y, Beta, and ZSM-5 are widely used commercial catalysts, but their applications are strongly limited by their small pore sizes. Recent progress in solving this is used to ordered mesoporous materials such as MCM-41, HMS, and SBA-15. These mesoporous materials have pore diameters of 2.0–30 nm and exhibit good catalytic properties for the catalytic conversion of bulky reactants. However, when compared with microporous crystals of zeolites, the catalytic activity and hydrothermal stability are relatively low, which severely hinders their practical applications in industrial catalytic reactions such as petroleum cracking. The relatively low catalytic activity and hydrothermal stability can be attributed to the amorphous nature of the mesoporous walls. In this account, we systemically review the routes for improving catalytic activity and hydrothermal stability of mesoporous materials, which include (1) acidic sulfated zirconia supported in mesoporous materials; (2) strongly acidic and thermally stable mesostructured sulfated zirconia with tetragonal crystalline phase; (3) strongly acidic and hydrothermally stable mesoporous aluminosilicates synthesized in alkaline media; (4) strongly acidic and hydrothermally stable mesoporous aluminosilicates synthesized in strongly acidic media; (5) hydrothermally stable mesoporous titanosilicates with catalytically active titanium species in oxidations; (6) high-temperature generalized synthesis of ultrastable ordered mesoporous silica-based materials by using fluorocarbonhydrocarbon surfactant mixtures.     

Molecular Dynamics Simulations of Phosphorylated Intrinsically Disordered Proteins: A Force Field Comparison

Phosphorylation is a common post-translational modification among intrinsically disordered proteins and regions, which helps regulate function by changing the protein conformations, dynamics, and interactions with binding partners. To fully comprehend the effects of phosphorylation, computer simulations are a helpful tool, although they are dependent on the accuracy of the force field used. Here, we compared the conformational ensembles produced by Amber ff99SB-ILDN+TIP4P-D and CHARMM36m, for four phosphorylated disordered peptides ranging in length from 14–43 residues. CHARMM36m consistently produced more compact conformations with a higher content of bends, mainly due to more stable salt bridges. Based on comparisons with experimental size estimates for the shortest and longest peptide, CHARMM36m appeared to overestimate the compactness. The difference between the force fields was largest for the peptide showing the greatest separation between positively charged and phosphorylated residues, in line with the importance of charge distribution. For this peptide, the conformational ensemble did not change significantly upon increasing the ionic strength from 0 mM to 150 mM, despite a reduction of the salt-bridging probability in the CHARMM36m simulations, implying that salt concentration has negligible effects in this study.     

超声波辅助磷酸铝镁有序介孔材料低热固相合成及其形貌自组装

在超声波的辅助下,以十六烷基三甲基溴化铵为模板,通过六水氯化铝、十二水磷酸氢二钠与六水氯化镁的低热固相反应合成了磷酸铝镁(MgAlPO)有序介孔材料,对材料进行了性能表征,探讨了磷酸铝镁介孔材料的自组装机理. 结果表明,镁以同晶取代的方式进入磷酸铝骨架,并形成有序的介孔材料;有序介孔孔道呈平行四边形排列,其微观形貌为球形,球体曲面由不同粒径的纳米粒子自组装而成,其BET比表面积为502.7 m2/g,孔容为0.3378 cm3/g,孔半径分布中心为1.21 nm.     

Assessing the Antimicrobial Activity of Polyisoprene Based Surfaces

There has been an intense research effort in the last decades in the field of biofouling prevention as it concerns many aspects of everyday life and causes problems to devices, the environment, and human health. Many different antifouling and antimicrobial materials have been developed to struggle against bacteria and other micro- and macro-organism attachment to different surfaces. However the “miracle solution” has still to be found. The research presented here concerns the synthesis of bio-based polymeric materials and the biological tests that showed their antifouling and, at the same time, antibacterial activity. The raw material used for the coating synthesis was natural rubber. The polyisoprene chains were fragmented to obtain oligomers, which had reactive chemical groups at their chain ends, therefore they could be modified to insert polymerizable and biocidal groups. Films were obtained by radical photopolymerization of the natural rubber derived oligomers and their structure was altered, in order to understand the mechanism of attachment inhibition and to increase the efficiency of the anti-biofouling action. The adhesion of three species of pathogenic bacteria and six strains of marine bacteria was studied. The coatings were able to inhibit bacterial attachment by contact, as it was verified that no detectable leaching of toxic molecules occurred.     

A New Chemical Probe for Phosphatidylinositol Kinase Activity

Phosphatidylinositol kinases (PIKs) are key enzymatic regulators of membrane phospholipids and membrane environments that control many aspects of cellular function, from signal transduction to secretion, through the Golgi apparatus. Here, we have developed a photoreactive “clickable” probe, PIK‐BPyne, to report the activity of PIKs. We investigated the selectivity and efficiency of the probe to both inhibit and label PIKs, and we compared PIK‐BPyne to a wortmannin activity‐based probe also known to target PIKs. We found that PIK‐BPyne can act as an effective in situ activity‐based probe, and for the first time, report changes in PI4K‐IIIβ activity induced by the hepatitis C virus. These results establish the utility of PIK‐BPyne for activity‐based protein profiling studies of PIK function in native biological systems.     

国内外化工厂水消防系统设计比较

在总结国外投资的大中型化工厂项目水消防设计的基础上,对国内外化工厂水消防系统设计,在消防系统、电源保障、水泵的启动方式、管网和消防水池的形式等方面进行了比较。     

Plasma Chemical Modification of Polycarbonate Surfaces for Electroless Plating

The preliminary steps of the “electroless” metallization of polycarbonate are investigated by XPS. They consist of the chemisorption of a catalyst (Pd) on the surface to be metallized. The corresponding surface can be activated either by chemical etching or by reactive or non-reactive gas plasma treatment. Therefore, the surface treatment of polycarbonate determines the palladium adsorption. It is shown here that a surface carrying oxygenated functions adsorbs palladium through Sn²⁺ ions which are themselves bonded to oxygen atoms. On the other hand, a surface on which nitrogenated groups have been grafted (by NH₃ or N₂ plasma treatment) chemisorbs palladium directly on these nitrogen atoms. Reaction mechanisms are proposed in both cases and a new and simplified process for making the surfaces catalytic is proposed.     

Plasma Chemical Modification of Polycarbonate Surfaces for Electroless Plating

The preliminary steps of the “electroless” metallization of polycarbonate are investigated by XPS. They consist of the chemisorption of a catalyst (Pd) on the surface to be metallized. The corresponding surface can be activated either by chemical etching or by reactive or non-reactive gas plasma treatment. Therefore, the surface treatment of polycarbonate determines the palladium adsorption. It is shown here that a surface carrying oxygenated functions adsorbs palladium through Sn²⁺ ions which are themselves bonded to oxygen atoms. On the other hand, a surface on which nitrogenated groups have been grafted (by NH₃ or N₂ plasma treatment) chemisorbs palladium directly on these nitrogen atoms. Reaction mechanisms are proposed in both cases and a new and simplified process for making the surfaces catalytic is proposed.     

Comparison Between FT-IR and XPS Characterization of Carbon Fiber Surfaces

Fourier transform infrared internal reflection spectroscopy and X-ray photoelectron spectroscopy XPS have been applied to investigate the surface of polyacrylonitrile-based carbon fibers treated by chemical oxidation and electrochemical oxidation. We have found that infrared spectroscopy has comparable sensitivity to XPS and that the amount of the functionality introduced at the fiber surface depends on the oxidation time in the case of chemical oxidation and on the electrolyte used in the case of electrochemical oxidation.     

Recent Studies of Chemical Interactions on Surfaces Using Molecular Beams

In 1970 Merrill reviewed the application of molecular beams to studies of gas-surface interactions related to catalysis [1]. Since that time there has been a rather impressive increase in the number of experimental studies in this area. More recently, Saltsburg has reviewed the dynamical aspects of gas-surface collisions, with some emphasis on beam experiments [2]. The latest advances in experimental techniques in molecular beam studies of reactive scattering and heterogeneous catalysis have been reviewed by Smith [3] and most recently by Madix [4]. The purpose of this review is to present both a comprehensive survey of the experimental work that has been reported subsequent to the review by Merrill and to focus critical attention on what is felt to be the more significant features of this work. While our first intent can be carried out rather objectively, we have chosen to focus on those aspects of the work that relate more closely to our own research.     

植物资源化学实验国内外教学比较与改革初探

介绍了国内外植物资源化学实验教学中的差别,试以改革国内实验教学内容及方式,强化学生对基础理论知识的理解、吸收和对基本实验技能、技巧的掌握。试图通过增加影像教学的手段增强教师示范性环节以提高学生动手能力和激发实验兴趣。     

Recent Studies of Chemical Interactions on Surfaces Using Molecular Beams

In 1970 Merrill reviewed the application of molecular beams to studies of gas-surface interactions related to catalysis [1]. Since that time there has been a rather impressive increase in the number of experimental studies in this area. More recently, Saltsburg has reviewed the dynamical aspects of gas-surface collisions, with some emphasis on beam experiments [2]. The latest advances in experimental techniques in molecular beam studies of reactive scattering and heterogeneous catalysis have been reviewed by Smith [3] and most recently by Madix [4]. The purpose of this review is to present both a comprehensive survey of the experimental work that has been reported subsequent to the review by Merrill and to focus critical attention on what is felt to be the more significant features of this work. While our first intent can be carried out rather objectively, we have chosen to focus on those aspects of the work that relate more closely to our own research.     

纳米TiO2半导体光催化性能的影响因素

TiO2以具有安全、廉价、无污染、适用范围广等优点而成为最有开发前途的绿色环保型光催化剂。以TiO2半导体为光催化剂的多相光催化氧化技术是几十年发展起来的一项污染治理新技术,具有良好的应用前景。文中主要从晶体结构、粒径、比表面积、表面羟基及载流子俘获剂5个方面,详细分析了这些因素对纳米TiO2光催化性能的影响。     

Segregation Isotherms at the Surfaces of Oxides

A non-Arrhenius segregation isotherm is derived which includes the change in the heat of segregation with surface coverage due to impurity—impurity interactions. It is shown that a linear dependence of log ( X_s ) on the reciprocal temperature, where X_s is the surface atomic ratio, can derive either from a constant heat of segregation, i.e., Arrhenius behavior, or from a heat of segregation that varies as X⁻¹_s . This isotherm is then used to calculate the equilibrium surface coverages of Ca at the {001} surface of MgO₁ Mg at the {0001} surface of α-Al₂O₃, γ at the {1012} and {1120} surfaces of α-Al₂O₃, and Na at the {111} and {110} surfaces of Li₂O from the calculated heats of segregation. Where possible, comparisons are made with experiment. The more useful operational definition of the heat of segregation, namely, that derived from the measured coverage or that defined atomistically and obtained by calculation, is discussed.