Chemistry and Physics of Alkali Metals on MoS2 Surfaces

The interaction of alkali metal with surfaces has been of great interest to the community of catalysis since alkali metal can play an important role as a promoter. On alkali-doped MoS₂, such a promotion effect of alkali metal has been exemplified in the direct synthesis of linear alcohols from CO and H₂, where the alkali-doping switches the catalyst selectivity from methanation to alcohol synthesis. This paper reviews recent high-resolution X-ray photoelectron spectroscopy experiments that have provided direct observation of electron transfer from alkali metals to a model single crystal MoS₂ and the capture of the supra-valence electrons in the subsequent oxidation reactions.     

Pt–Ba–Al2O3 for NOx storage and reduction: Characterization of the dispersed species

Pt–Ba–Al₂O₃ active and selective for NO_x storage and selective reduction to N₂ has been prepared and tested. Characterization of the parent Al₂O₃, Pt–Al₂O₃ and Ba–Al₂O₃ materials, as well as of Pt–Ba–Al₂O₃ catalyst in the oxidized, reduced and sulphated state has been performed by FT-IR spectroscopy of low-temperature adsorbed carbon monoxide and of adsorbed acetonitrile. XRD, TEM and XPS analyses have also been performed. Evidence for the predominance of Ba species, which are highly dispersed on the alumina support surface, and may be carbonated or sulphated, has been provided. Competitive interaction of Pt and Ba species with the surface sites of alumina has also been found.     

退火温度对掺氮ZnO薄膜结构和光电特性的影响

采用Zn3N2热氧化法在直流磁控溅射设备上制备了掺氮Zn0薄膜(ZnO:N),研究了不同退火温度对样品结构和光电特性的影响.X射线衍射谱(XRD)结果表明,Zn3N2在600℃以上退火即可转变为Zn0:N薄膜.X射线光电子能谱(XPS)发现,在热氧化法制备的ZnO:N薄膜中,存在两种与N相关的结构,分别是N原子替代O(受主)和N2分子替代O(施主),这两种结构分别于不同的退火温度下存在,并且700℃下退火的样品在理论上具有最高的空穴浓度,这一点也由霍尔测量结果得到证实.同时,从低温PL光谱中观察到了与N.受主有关的导带到受主(FA)和施主-受主对(DAP)的跃迁,并由此计算出热氧化法制备的ZnO:N薄膜中的N.受主能级位置.     

硅橡胶泡沫伽马辐照后结构和元素分布研究

在密闭的氮气气氛下,用伽马射线辐照聚二甲基硅橡胶泡沫,采用全反射红外光谱(ATR)和X射线光电子能谱(XPS)对辐照后的化学结构和元素含量变化进行了表征.结果表明:化学结构单元Si-CH3最容易受到伽马射线的影响,在低的辐照剂量下表面Si-CH3成分随着辐照剂量增加而减小;高剂量下材料的元素分布发生了变化,近表面C元素含量要比泡沫体中部的C元素含量高.因此,在密闭环境下辐照老化后的硅橡胶泡沫的表面性能和体内性能存在差异.     

Influence of Additives in Adhesion of UV Radiation Surface-Treated SBS Rubber

In this study, the effect of additives (oils, lubricants) included in the formulations of different block styrene-butadiene-styrene (SBS) rubbers on the effectiveness of the ultraviolet (UV) radiation treatment to improve adhesion to polyurethane adhesive was analyzed. The modifications on the UV-treated rubber surfaces for different lengths of treatment have been characterized by contact-angle measurements (ethylene glycol, 25°C), Attenuated Total Reflectance-Infrared (ATR-IR) spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscopy (SEM). The adhesion properties have been evaluated from T-peel strengths of treated rubber/polyurethane adhesive/leather joints. The UV-radiation treatment on all rubber surfaces produced an increase in wettability, carbon-oxygen polar moieties, and ablation. The oxidation degree produced on the rubber surface treated with UV radiation was less when oils and lubricants were included in the formulation, likely due to competition of the oxidation process with the migration of low-molecular-weight additives to the rubber surface. On the SBS2 rubber surface (rubber containing carbon black and calcium carbonate fillers), the migration of oils and lubricants was also produced during the UV-radiation treatment, but a decrease in adhesion occured likely due to the lower tensile strength and higher extent of oxidation produced by the UV radiation treatment.     

掺Al的Ge-SiO_2薄膜的结构和光致发光性质

采用射频磁控溅射复合靶技术制备了掺Al的Ge SiO2 薄膜。薄膜在N2 保护下进行了不同温度的退火处理。采用FTIR ,XRD ,XPS分析了样品的结构。样品的PL谱结果表明退火温度、沉积温度以及样品中的Al含量对Al Ge SiO2 薄膜的光致发光的峰位和峰强有一定的影响。     

Performance of natural‐fiber–plastic composites under stress for outdoor applications: Effect of moisture,temperature, and ultraviolet light exposure

The effects of moisture, temperature, and ultraviolet (UV) light on performance of natural‐fiber–plastic composites (NFPC) were assessed. We conducted short‐term tests in the laboratory and long‐term tests under natural exposure and measured changes in mechanical properties and color in samples of the composite. Chemical changes of the composite's materials were measured by X‐ray photoelectron spectroscopy to elucidate the mechanisms of chemical transformations on the material surface. Relative humidity highly affected the modulus of rupture (MOR) and the modulus of elasticity (MOE), and had a greater effect than temperature and UV exposure on performance of the composite. The lightness of the composite was increased by the UV effect in the short‐ and the long‐term tests. The X‐ray photoelectron spectroscopy (XPS) analysis suggested that the composite was protected by the UV absorber. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2570–2577, 2006     

Photocatalytic hydrogen production by biomimetic indium sulfide using Mimosa pudica leaves as template

Biomimetic sulfur-deficient indium sulfide (In_2.77S₄) was synthesized by a template-assisted hydrothermal method using leaves of Mimosa pudica as a template for the first time. The effect of this template in modifying the morphology of the semiconductor particles was determined by physicochemical characterization, revealing an increase in surface area, decrease in microsphere size and pore size and an increase in pore volume density in samples synthesized with the template. X-ray photoelectron spectroscopy (XPS) analysis showed the presence of organic sulfur (SO/SC/SH) and sulfur oxide species (SO₂, SO₃²⁻, SO₄²⁻) at the surface of the indium sulfide in samples synthesized with the template. Biomimetic indium sulfide also showed significant amounts of Fe introduced as a contaminant present on the Mimosa pudica leaves. The presence of these sulfur and iron species favors the photocatalytic activity for hydrogen production by their acting as a sacrificial reagent and promoting water oxidation on the surface of the templated particles, respectively. The photocatalytic hydrogen production rates over optimally-prepared biomimetic indium sulfide and indium sulfide synthesized without the organic template were 73 and 22 μmol g⁻¹, respectively, indicating an improvement by a factor of three in the templated sample.     

Absorption of acrylates and polysilazanes in the far UVC and the VUV regions

A simple but reliable method was developed for the determination of wavelength-dependent absorption coefficients in the vacuum-UV (VUV) spectral range 160 nm < λ < 195 nm.