Molecular beam studies on inelastic collision processes of methane molecules at a Pt(1 1 1) surface

Inelastic collision processes of CH₄ at a Pt(1 1 1) surface have been analyzed by means of super-sonic molecular beam technique. Obtained results of the angular intensity distribution of the reflected CH₄ with the incident kinetic energy ranging from 190 to 350 meV are found to qualitatively agree with the prediction from the classical collision model. Surface temperature dependence of the speed distributions of the reflected CH₄ qualitatively follows the prediction at the surface temperature below 500 K, but deviates from the prediction as the surface temperature increases under the irradiation of CH₄ with higher kinetic energies, where decomposition of CH₄ takes place. The discrepancy of data from the model can be understood by introducing into the model decreased effective surface mass and increased surface “roughness”.     

The cavity-microelectrode as a tip for scanning electrochemical microscopy

In this work, we present and discuss the use of cavity-microelectrodes (C-MEs) used as tip for the scanning electrochemical microscopy (SECM). Cavity-microelectrodes can be filled with a desired finely dispersed material thus compensating for the limited commercial availability of microwires. After discussing the possibility of filling and emptying a cavity-microelectrode with a desired tip shape, the consistency of negative and positive feedback approach curves obtained after filling a Au C-ME was verified. In addition, the tip/C-ME was tested under gas (oxygen) evolution condition, in order to demonstrate that the filling is stable in a wide range of gas fluxes thus extending the possible applications to tip generation/substrate collection mode. Finally, we introduce the use of the proposed system to quantify the rates of parallel reactions occurring at the material inserted in the tip under the tip generation/substrate collection mode.     

Melamine sponge derived porous carbon monoliths with NiMn oxides for high performance supercapacitor

Supercapacitors with good electrochemical performance and flexibility are in great demand. In this paper, the concept of preparing 3D porous carbon monoliths via direct calcination of melamine sponge is presented. This preparation method is simple and has good control of the structure. Porous carbon composite nickel-manganese oxides can be obtained by hydrothermal method followed with calcination. The electrochemical performances were tested and porous carbon monoliths with NiMn oxides exhibited a specific capacitance of 870 F/g in 1 mol/L KOH at a charge/discharge current density of 0.5 A/g and a capacity retention of 89.9% after 5000 times charge and discharge     

A prerequisite to achieving high performance polymer/inorganic thin film diodes

An alternative approach to high performance polymeric rectifiers based on p-type polymer poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) and an n-type zinc oxide (ZnO) films is demonstrated. It is evident that nanoscale grain compatibility at an interface does not ensure that the device has the highest performance, but only a prerequisite for the two materials to exhibit the interaction. Being a non-invasive probe, Raman spectroscopy is used to monitor the degree of interaction between PEDOT:PSS and ZnO films. High performance of devices is achieved by the control of grain matching and more essentially, by the strong interaction of molecules at the interface. The developed PEDOT:PSS/ZnO diode can rectify an incoming a.c. voltage signal at frequencies up to 18 MHz. Operating with a low turn-on voltage, the diode has a current density of 220 mA/cm² and a rectification ratio of 4000 in the open atmosphere which are higher than previously reported polymer/inorganic vertical diodes.     

双道原子荧光光谱法测定土壤中汞

采用沸水浴消解,用硝酸(3+1)对土壤中样品进行前处理,并用硼氢化钾(0.5g/L)作还原剂,硝酸(1%)作载液进行测定,建立了双道原子荧光光谱法测定土壤中汞的方法。对灯电流、负高压等参数进行优化。结果表明:经多个土壤成分分析标准物质验证,方法的检出限为0.000 7mg/kg,相对标准偏差为3.9%,加标回收率为95.4%~101%,方法简单、准确度高,适合于土壤中微量汞的测定。     

Formation of Pd dimers at regular and defect sites of the MgO(1 0 0) surface: cluster model calculations

The formation of Pd dimers on the surface of MgO has been studied by means of density functional theory (DFT) cluster model calculations. The following surface sites have been considered: regular five-coordinated anions at the (1 0 0) terraces, monoatomic steps, OH groups, and neutral vacancies (F centers). We discuss the energy balance of forming a dimer at a given site with respect to two isolated Pd atoms, one adsorbed at the defect and one on a regular terrace site. We found that all the defects considered lead to an energy gain when the dimer is formed, suggesting that they can be involved in nucleation and growth processes of metal clusters on the MgO surface. The dimerization energy is moderate for steps (≈0.8 eV), large for OH groups (≈1.3 eV) and rather small (<0.5 eV) for F centers.     

Synthesis of single crystalline (NH4)2V6O16·1.5H2O nest-like structures

Novel nest-like (NH₄)₂V₆O₁₆·1.5H₂O structures made of nanobelts have been synthesized by a facile hydrothermal approach. The powder X-ray diffraction pattern of the sample reveals the monoclinic crystalline phase of (NH₄)₂V₆O₁₆·1.5H₂O. The scanning electron microscopy images of the sample obtained at 130 °C for 3 days exhibit nest-like morphology. The transmission electron microscopy result reveals that the nanobelts have a smooth surface. The selected area electron diffraction pattern of the nanobelts indicates single crystalline nature. The two major weight losses occur in thermogravimetric analysis which correspond to the removal of water and ammonia molecules. Further, calcination of the (NH₄)₂V₆O₁₆·1.5H₂O product results in the formation of orthorhombic phase of shcherbianite V₂O₅.     

高活性耐硫MoO3改性NiO-Al2O3催化剂用于焦炉煤气甲烷化

采用双水解共沉淀法结合浸渍法合成了系列的MoO₃改性的xMoO₃/NiO-Al₂O₃催化剂(x%为MoO₃的质量分数),利用固定床装置对催化剂的甲烷化反应活性和耐硫性能进行评价,并对失活前后催化剂进行详细表征。结果表明,随着MoO₃含量的升高MoO₃改性后的催化剂甲烷化活性有所下降,但MoO₃的掺杂显著提升了催化剂的耐硫性能。催化剂低温甲烷化活性降低的原因在于MoO₃负载量的增加降低了催化剂的活性比表面积,但MoO₃的引入也为硫化物提供了一个竞争吸附位点,进而延缓了活性位点的硫中毒过程。当 MoO₃负载量(质量分数)为 12.5% 时,12.5MoO₃/NiO-Al₂O₃催化剂在 143 mg·m^-3 H₂S/H₂气氛下运行时间长达7 h,远高于其他催化剂。12.5MoO₃/NiO-Al₂O₃催化剂吸收硫的量(质量分数)达到0.71%,是NiO-Al₂O₃催化剂硫吸附量的1.48倍。XPS表征进一步发现12.5MoO₃/NiO-Al₂O₃催化剂表面生成的MoS₂最多,这说明在此负载量下Mo优先吸附了更多的硫而保护了活性位点。此外,MoO₃负载量为12.5%时,MoO₃在催化剂表面接近单层分散阀值,当竞争吸附发生时,为硫化物提供更多的吸附位点。