石墨烯涂层在甲苯低温催化燃烧用堇青石负载Pd整体式催化剂中的作用（英文）

对于传统整体催化剂而言,堇青石等基体比表面积低,往往需先涂覆活性氧化铝等高比表面涂层,此外低温催化燃烧反应生成的水和周围空气中的水分会大量吸附于亲水性氧化物涂层表面,导致贵金属催化活性降低,同时,贵金属的分散度也是影响催化剂活性的主要因素.我们利用石墨烯高疏水性、二维平面结构、对苯环强吸附及对贵金属颗粒的高分散与锚定作用等独特性能,发展基于石墨烯涂层的高活性纳米Pd整体催化剂,以改善上述问题.所制备的Pd/石墨烯/堇青石(Pd/Gr/Cor)复合材料作为整体催化剂用于甲苯低温燃烧反应,通过考察催化性能和吸附行为,重点研究了石墨烯涂层的作用.催化性能结果表明,与无石墨烯涂层的传统Pd/Cor催化剂相比,Pd/Gr/Cor催化剂对甲苯的起燃温度从175℃降至132℃,且在水蒸气存在的情况下表现出更好的稳定性.TEM和吸水速率表征表明,石墨烯涂层可显著提高Pd纳米粒子的分散性,提高堇青石载体的疏水性.动力学研究表明,Pd/Gr/Cor催化剂上甲苯催化燃烧符合一级反应动力学规律,活化能为60.93 k J/mol.此外,研究了其吸附行为,包括吸附等温线,吸附动力学和吸附热力学.模拟结果表明,Pd/Gr/Cor催化剂对甲苯具有优异的吸附性能,对甲苯的吸附符合Freundlich模型,为化学吸附.FLm双点位吸附模型表明,石墨烯表面吸附了大量的甲苯,而Pd粒子表面吸附的甲苯相对较少,但亲和力较强.吸附热力学计算表明,石墨烯对甲苯的吸附是一个自发的放热反应,是一个熵减小的过程,表明甲苯分子可在石墨烯上高度有序组装.石墨烯与Pd之间的显著浓度差和亲和力的差距确保了反应过程中甲苯在石墨烯上的快速转移.吸附动力学研究表明,催化剂对甲苯的吸附为快速过程,催化反应为控速步骤.综上,石墨烯涂层不仅可以提高Pd纳米粒子的分散性,提高催化剂的疏水性,在催化反应过程中,还可利用其强吸附能力提高催化剂表面的甲苯浓度,而显著的浓度差和亲和力的差距可作为驱动力为Pd粒子提供甲苯,从而发挥吸附-催化协同作用优势,进一步提高催化性能.     

Generation of tightly focused twin Bessel beams using circular Dammann gratings under radial polarization incidence

Generation of longitudinally polarized focusing twin Bessel beams in focal region of a high numerical aperture (NA) objective is described based on circular Dammann gratings for radially polarized Bessel–Gauss input fields. Numerical simulations show that, under focusing of an objective of NA=0.95, the depth of focus (DOF) of the focused twin Bessel beams can reach as long as tens or even ～10² of wavelengths while its average transverse spot over the whole range of the DOF is kept subdiffration-limited. At the same time, the longitudinal polarization purity in focus volume is higher than 90% for the central lobe. Therefore, this tightly focused non-diffracting field should be of great interest for applications in numerous areas, such as particle acceleration and manipulation, micromachining, second-harmonic generation, Raman spectroscopy, etc.     

Adsorption stripping voltammetry of phenol at Nafion-modified glassy carbon electrode in the presence of surfactants

In this paper, a new voltammetric method for the determination of phenol is described. In pH 8.00 phosphate buffer and in the presence of long-chain cationic surfactant—cetyltrimethylammonium bromide—phenol has a very sensitive oxidation peak at 0.47 V (vs. SCE) on the Nafion-modified glassy carbon electrode (GCE). The experimental parameters, such as supporting electrolyte and pH values, amounts of Nafion, varieties and concentration of surfactants, accumulation potential and time, as well as scan rate were optimized. The peak current is linear with the concentration of phenol in the range from 8×10⁻⁹ to 1×10⁻⁵ M, and the detection limit is 1×10⁻⁹ M after being accumulated at −0.50 V (vs. SCE) for 3 min. Trace levels of phenol in water samples were determined by using this voltammetric method, the average recovery was calculated to be 99.56%.     

Application of ultrasonic surface waves in the detection of microcracks using the scanning heating laser source technique

This letter reports the application of the scanning heating laser source technique to detect microcracks that may be undetected by conventional methods.In the proposed approach,we monitor changes in the transmitted surface acoustic waves(SAWs) as a heating source is scanned over the crack.The experimental system for microcrack detection by a scanning heating laser source is obtained by exploiting the strong dependence of the transmission efficiency of acoustic pulses on the state of the contacts,whether open or closed,between the crack faces.Microcracks can be detected successfully by confirming the heating position at the point of maximal improvement of the transmission efficiency of the SAWs.     

30m望远镜三镜系统运动学接口设计及分析

光学系统中,为防止像差的引入造成成像质量下降,光学元件的准直与间距必须严格保证。所以,在光学仪器接口设计过程中,提高接口的重复性定位能力和降低接口的接触应力水平是非常重要的。在30 m望远镜(TMT)三镜系统设计过程中,三镜作为Ritchey-Chirtien(R-C)式光学系统中重要的光学元件,需严格保证其位置和姿态。三镜系统寿命周期中,由于清洗、镀膜的要求,需要多次拆装,为保证装配精度,需设计了一套定位用运动学接口。从运动学定位原理出发,使用赫兹接触理论以及IBM磨损理论对运动学接口进行了相应校核,并分析了影响运动学接口重复性定位精度的相应误差源,使用蒙特卡罗方法进行了相应仿真。另外,以三镜面形作为评指标,使用Ansys软件模拟了运动学接口,研究了接口参数对于三镜面形的影响。分析结果显示,在现有的设计及精度下,接口的接触应力水平满足使用要求,三个方向的重复性定位精度以及支撑效果能够达到设计指标。     

Zirconium-catalyzed Nagata reaction for the synthesis of 2-aryl-1,3,2-aryldioxaborins via a mild three-component condensation of phenols, aldehydes, and boronic acid

An efficient ZrCl₄-catalyzed ortho-hydroxyalkylation of phenols with aldehydes promoted by 3,5-bis(trifluoromethyl)phenyl boronic acid, leading to the formation of 2-aryl-1,3,2-aryldioxaborins, was investigated and optimized. The reaction afforded the desired aryldioxaborins in good to excellent yields under mild conditions at room temperature. The electron-deficient boronic acid promoter was essential. Electron-rich phenols react faster, and both alkyl and aryl aldehydes are suitable substrates. The resulting aryldioxaborins can be further elaborated to produce substituted saligenols, 2-ethoxy chromans, and 2-substituted phenols.     

On the calculation of highly oscillatory integrals with an algebraic singularity

In this paper we explore the evaluation of highly oscillatory integrals containing an algebraic singularity based on the change of variable t = x^−r, where r is a positive real number, and the analytical continuation. Robust numerical results demonstrate the accuracy and effectiveness of the proposed approach.     

红外波长标准物质的研制

选择聚苯乙烯薄膜作为红外光谱仪波长标准物质。采用挤出拉伸工艺制备了聚苯乙烯薄膜,考察了聚苯乙烯薄膜的均匀性和稳定性,确定了聚苯乙烯薄膜波长的特性量值。     

A mono-TTF-annulated porphyrin as a fluorescence switch

Annulation of one TTF unit directly to the porphyrin chromophore produces an almost nonfluorescent species which can be transformed into a fluorescent species by oxidation of the TTF unit.     

Voltammetric determination of ciprofloxacin based on the enhancement effect of cetyltrimethylammonium bromide (CTAB) at carbon paste electrode

Herein, an electrochemical method was developed for the determination of ciprofloxacin based on the enhancement effect of cetyltrimethylammonium bromide (CTAB). In pH 7.0 phosphate buffer, a poorly-defined oxidation peak is observed at carbon paste electrode (CPE) for ciprofloxacin. However, the oxidation peak current remarkably increases in the presence of low concentration of CTAB, suggesting that CTAB exhibits obvious enhancement effect to the determination of ciprofloxacin. All the experimental parameters, such as supporting electrolyte, pH value, concentration of CTAB, and accumulation time, were optimized for ciprofloxacin analysis. This new method possesses high sensitivity (detection limit is 5.0 × 10⁻⁸ mol l⁻¹), wide linearity (1.0 × 10⁻⁷−2.0 × 10⁻⁵ mol l⁻¹), rapid response, low cost and simplicity. Finally, this method was successfully employed to detect ciprofloxacin in drugs. The text was submitted by the authors in English.