Pulsed laser deposition of nanostructured Ag films

Ultra-thin (0.5-5 nm) films of Ag have been prepared by pulsed laser deposition in vacuum using a 26 ns KrF excimer laser at 1 J cm⁻². The deposition was controlled using a Langmuir ion probe and a quartz crystal thickness monitor. Transmission electron microscopy showed that the films are not continuous, but are structured on nanometer size scales. Optical absorption spectra showed the expected surface plasmon resonance feature, which shifted to longer wavelength and increased in strength as the equivalent film thickness was increased. It is shown that Maxwell Garnett effective medium theory can be used to calculate the main features of optical absorption spectra.     

Interaction of metals with an organic semiconductor: Ag and In on PTCDA

The interaction of Ag and In with a thin film of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) was studied by near-edge X-ray absorption fine structure (NEXAFS). Upon Ag deposition on a PTCDA film of 20 nm thickness the relative intensities and lineshapes, as well as the angular dependence of the spectra remains unchanged, illustrating the formation of a chemically unreactive Ag/PTCDA interface. On the other hand, the adsorption of 0.3 nm In strongly decreases the intensity of the π^* resonances in C and O K-edge NEXAFS spectra. This is attributed to a strong charge transfer between In and PTCDA, leading to a redistribution of the charge in the molecule. However, the absence of a strong shift or new features and negligible dependence of peak intensities corresponding to π^* resonances on the In thickness indicate that the interaction between In and PTCDA is not accompanied by a covalent bond formation.     

天然气和氧偶联制环氧乙烷催化剂的反应性能

研制了天然气和氧经偶联反应制环氧乙烷的Ａｇ－Ｂａ－Ｃｓ／Ａｌ２Ｏ３催化剂（ＮＥＯ－１）。用Ｎ２＋Ｏ２＋Ｃ２Ｈ４和偶联产物气加氧作原料气，在２５０℃，空速２５００ｈ＾－１时，乙烯转化率和ＥＯ选择性分别达到了３０％和８０％，ＮＥＯ－１催化具有适宜的比表面和孔结构，用ＸＰＳ分析发现，与新鲜的催化相比，经活化和反应后的催化剂表面的Ｂａ，Ｃｓ原子浓度增高，并具有较多的吸附氧物种。     

ZnO对Ag/SiO2催化剂银的分散作用及对吲哚合成稳定性的影响

将ZnO助剂加到由苯胺和乙二醇一步合成吲哚的Ag/SiO2催化剂中,发现ZnO助剂能大大提高催化剂的稳定性.XRD和TEM表征首次得到:ZnO是结构型助剂,它能使银很好地分散在SiO2表面上,并可有效地抑制反应过程中银粒子的烧结.     

Magnetic phase transitions in nanostructures induced by shear stress under high pressure

Magnetic phase transitions of the first and second order were revealed by Mössbauer spectroscopy in nanosystems of - and -ferric oxides and metallic europium subjected to shear stress (240°) under high pressure (20 kbar). For - and -ferric oxide nanoclusters, the Curie (Neel) points decreased to 300 K, whereas for nanostructured europium the Neel point increased from 90 to 100 K. The thermodynamic model of magnetic phase transitions predicting a change in the character of magnetic phase transitions and a decrease (increase) in the critical Neel (Curie) points in nanoclusters was developed. The type of magnetic phase transitions and the change in the critical points were caused by defects in nanoclusters, whose maximum concentration was observed for the clusters with the 20—50 nm size range.     

New palladium nanoclusters. Synthesis,structure, and catalytic properties

The reduction of palladium(ii) carboxylates Pd₃(OCOR)₆ (R = Me, Et, CHMe₂, CMe₃) with hydrogen in alcohol solutions containing 1,10-phenanthroline (phen) and subsequent oxidation with oxygen gave new palladium nanoclusters, mainly particles with a nearly spherical metal core and an average size of 18 . Based on elemental analysis, NMR, X-ray photoelectron spectroscopy, and EXAFS, nanoclusters were described by the idealized formula Pd₁₄₇phen₃₂O₆₀(OCOR)₃₀. The specimens contained up to 25% smaller 55-atomic Pd clusters with a 10 metal core. New nanoclusters catalyze hydrogenation of alkynes and alkenes, reduction of nitriles with formic acid, oxidation of aliphatic and benzylic alcohols, oxidative esterification of ethylene and propylene, and disproportionation of benzyl alcohol into toluene and benzaldehyde.     

二(氢过碘酸)合银(III)配离子氧化愈创甘油醚的反应动力学及机理

在碱性介质中,用传统的分光光度法研究了Ag(III)配离子,即[Ag(HIO6)2]5-,氧化药物分子愈创甘油醚的动力学及其机理.用质谱鉴定了氧化产物;反应对Ag(III)和愈创甘油醚均为一级;在温度25.0-40.0℃范围内,通过分析[OH-]和[IO4-]tot对反应速率的影响,二级速率常数有以下表达式:k′=(ka kb[OH-])K1/｛f([OH-])[IO4-]tot K1｝,在25.0℃及离子强度0.30mol·L-1时,对此反应有ka=(2.6±1.2)×10-2mol-1·L·s-1,kb=(2.8±0.1)mol-2·L2·s-1,及K1=(4.1±0.4)×10-4mol·L-1,求出了涉及ka,kb的活化参数,并据此推出反应机理为反应体系中的[Ag(HIO6)2]5-配离子在前期平衡后,反应活性中心与药物分子形成Ag(III)-过碘酸-愈创甘油醚分子三元配合物,配位甘油醚分子通过两个平行途径将两电子传递给中心原子Ag:一个途径无OH-离子参与,另一途径有OH-参与完成.     

Ag核Au壳双金属复合纳米线的制备及其表面增强拉曼光谱研究

采用氧化铝模板结合交流电沉积技术制备纯银纳米线, 然后通过化学还原方法, 并控制加入的金盐的量, 在已制备好的银线表面包裹不同厚度的金壳层, 得到具有核壳结构的Ag_核Au_壳复合纳米线. 采用电子显微镜(SEM, TEM)和表面增强拉曼光谱对该复合结构纳米线进行相关表征, 纳米线的表面形貌与加入的金盐的量有关. 以苯硫酚(TP)和对巯基苯胺(PATP)为探针分子, 研究了此类复合纳米线的表面增强拉曼散射效应. 并以PATP在金银纳米线表面吸附的表面增强拉曼光谱的差别为探针, 表征了复合纳米线表面金的包裹程度, 结果表明一定厚度的包裹程度可制备无针孔效应的核壳结构金银复合纳米线.     

Electrochemical characteristics of a platinum electrode modified with a matrix of polyvinyl butyral and colloidal Ag containing immobilized horseradish peroxidase

A new hydrogen peroxide biosensor was constructed, which consisted of a platinum electrode modified by a matrix of polyvinyl butyral (PVB) and nanometer-sized Ag colloid containing immobilized horseradish peroxidase (HRP), and using Co(bpy)₃³⁺ as mediator in the hydrogen peroxide solution. The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The modified process was characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The HRP immobilized on colloidal Ag was stable and retained its biological activity. The sensor displays excellent electrocatalytic response to the reduction of H₂O₂. Analytical parameters such as pH and temperature were also studied. Linear calibration for H₂O₂ was obtained in the range of 1×10^–5 to 1×10^–2 M under optimized conditions. The sensor was highly sensitive to H₂O₂, with a detection limit of 2×10^–6 M, and the sensor achieved 95% of steady-state current within 10 s. The sensor exhibited high sensitivity, selectivity and stability.     

Ab initio and DFT studies on tautomerism of indazole in gaseous and aqueous phases

Electronic structure of optimized Ge₅, Ge₁₇, Ge₅–O and Ge₅ embedded in SiO₂ nanoparticles have been studied by density functional theory to find out the effect of cluster size and Ge–O bond(s) on the optical energy gap between LUMO and HOMO. It was found that the optical energy gap depends on both cluster size and the number of Ge–O bonds nonlinearly. The optical energy gap was found to be in visible light range when the Ge₅ nanoparticle has been embedded in SiO₂ matrix.