Reactivity of Pt/Al2O3 and Pt/CeO2/Al2O3 catalysts for partial oxidation of methane to syngas

The ceria modified Pt/CeO2/Al2O3 and Pt/Al2O3 catalysts were studied in the partial oxidation of methane to syngas. The SEM, XRD, TPR and TPD techniques were used for the catalyst characterization. The addition of ceria could enhance the Pt dispersion and decrease the Pt crystallise size; the activity and selectivity of catalyst for partial oxidation were improved significantly, and the methane total oxidation was suppressed sharply. The ceria effect was also discussed in a detailed way.

Electrocatalytic oxidation of hydrazines at a 4-pyridyl hydroquinone self-assembled platinum electrode and its application to amperometric detection in capillary electrophoresis

4-Pyridyl hydroquinone on a platinum electrode adsorbs through the pyridine nitrogen forming stable self-assembled layers. The electrocatalytical oxidation of hydrazines was performed by the modified electrode. The overpotential of hydrazines was decreased markedly at the self-assembled monolayer (SAM) electrode. The mechanism of hydrazine oxidation was also investigated. Amperometric detection of hydrazine under zero potential (vs Ag\AgCI\sat. KCl) was exhibited by the SAM electrode used as an electrochemical detector in a flow system. (C) 1998 Elsevier Science S.A. All rights reserved.

CATALYTIC-OXIDATION AND FLOW DETECTION OF ACETAMINOPHEN AT A DICYANOBIS(1,10-PHENANTHROLINE)IRON(II)-MODIFIED ELECTRODE

Dicyanobis(1,10-phenanthroline)iron(II)-modified glassy carbon electrodes were shown to exhibit an electrocatalytic response for the oxidation of acetaminophen with a decrease of 100 mV in the potential required. It can also inhibit the oxidation of ascor

The study of oxygen spillover and back spillover on Pt/TiO2 by a potential dynamic sweep method

Oxygen spillover and back spillover on Pt/TiO2 catalysts have been studied by a potential dynamic sweep method. The characteristics of I-V profiles of Pt/TiO2 electrodes in the three potential sweep regions are different from those of Pt and TiO2 electrodes. The catalytic role of Pt/TiO2 in oxygen spillover and back spillover is identified. It decreases, and the electrochemical oxygen adsorption (or desorption) increases with elevating temperature of hydrogen post-treatment of Pt/TiO2; to a certain extent (hydrogen post-treatment of Pt/TiO2 at 700 degrees C), the control step of oxygen electrode process (anodic oxidation or cathodic reduction) changes from oxygen diffusion to electrochemical oxygen adsorption or desorption, respectively. Increasing the amount of Pt supported on TiO2 enhances the processes of oxygen spillover and back spillover. (C) 1999 Elsevier Science B.V. All rights reserved.

化学修饰铋膜电极检测重金属镉

随着我国工业的快速发展，环境污染日益严重，其中重金属已经成为最主要的污染物 之一。重金属具有分布广泛、半衰期长等特点，因而对人们的生产生活危害巨大。镉作为 一种常见的重金属污染物，它能够引发废用性萎缩、肾功能衰竭和感染等疾病，因此对环 境中存在的痕量镉的进行检测显得极为重要。传统的痕量分析方法包括光谱分析法和色谱 分析法，但这两方法所使用的仪器比较笨重，操作过程复杂，因而不适于在线分析。电化 学分析方法因其快速、便携、价格低廉、灵敏度高等特点而受到了人们的广泛关注，其中 较为常用的阳极溶出伏安法已经在镉离子等重金属离子的现场快速高灵敏检测中发挥了 重要作用。然而传统阳极溶出法中使用的汞电极因具有毒性而被许多国家禁止使用，所以 寻找汞电极的替代电极成为近年来的阳极溶出技术的研究热点。铋膜电极因具有类似汞电 极的分析性能且环境友好而受到了广泛重视，特别是各种化学修饰方法使得铋膜电极的性 能得到了显著提高。但是目前铋膜电极仍存在稳定性低、抗干扰能力差等问题，这些不足 严重制约了该类电极在重金属的阳极溶出分析中的应用。本文旨在通过新的化学修饰方法 解决铋膜电极应用中的瓶颈问题，发展具有优异分析性能的化学修饰铋膜电极应用于镉离 子等重金属离子的阳极溶出分析。本文的主要研究内容包括： l）以阳极溶出法测定镉离子为例，研究了化学修饰铋膜电极的响应特性，考察了富 集时间、富集电位、铋离子浓度、离子载体浓度和Nafion 浓度等实验条件对检测灵敏度的 影响。 2）将离子载体引入铋膜电极与Nafion 结合使用，研究了镉离子在该电极上的阳极溶 出响应，并探讨了铜、铅、铟三种金属离子对镉离子检测选择性的影响。将这种改良后的 化学修饰铋膜电极用于实际海水样品的检测，所得结果与ICP-MS 的测量结果基本一致。 3）将四氟硼酸钠引入铋膜电极与离子载体、碳纳米管结合使用，研究了镉离子在该 电极上的阳极溶出响应，考察了铜、铅、铟离子对镉离子测定的影响。 4）考察了电解富集和开路电位富集两种富集方式对电极灵敏度和选择性的影响。 实验表明：通过预富集，在未除氧的溶液中即可得到显著的镉离子溶出电流峰，且背 景噪音低；加入离子载体后，电极对目标金属有良好的选择性，可以在复杂基体条件下测 定重金属离子镉；电解富集条件下电极的的灵敏度较高，而开路电位富集条件下电极的选 择性较好。这种环保的无汞化学修饰电极为海水中重金属污染物的检测提供了新的手段。

新型纳米材料及离子载体化学修饰电极的制备及其在痕量重金属检测中的应用

随着工农业生产的迅速发展，重金属污染问题越来越严重。由于重金属能 够在土壤、水体等环境中不断积累，并且通过食物链而进入人体内蓄积，因此对 人类健康构成潜在的危害。当人体内重金属含量过量时，会导致各种疾病的发生。 所以对痕量重金属污染物进行监测和分析，在食品安全、临床诊断和环境监测等 方面具有重要的现实意义。因此，研究快速、准确、灵敏、方便的检测重金属的 新方法十分必要。 近年来，化学修饰电极由于能够赋予电极新的、特定的功能，在提高电化 学选择性和灵敏度方面有着独特的优越性，因而成为电分析化学领域研究的热 点，并且被广泛应用于重金属元素的测定。但是，由于电极材料的限制，灵敏度 虽然有所改进，却始终很难达到一个新的高度。要提高化学修饰电极对重金属检 测的灵敏度，必须加入一些辅助的方法。 最近，纳米材料在很多分析方法中得到广泛应用，这些材料表现出很多它 们在常规尺度时所没有的独特的性质，如量子尺寸效应、表面效应、小尺寸效应、 量子隧道效应以及介电限域效应等。因此，作为一种新型的电极材料在电化学检 测和分析方面受到人们的日益关注。由于纳米材料本身具有大的比表面积和高的 表面自由能，这种纳米材料修饰电极的灵敏度得到大幅度提高。 离子载体是一类具有一个特定空腔的大环分子，能够从溶液中实现对某一 特定离子的萃取使之进入到有机相中。离子载体是电位型传感器敏感膜中的核心 成分，尽管它具有很高的选择性，但是除了电位分析外，在其它方面的用途却很 少被关注，可能是由于其本身的非导电性能所致。本论文采用纳米材料所特有的 对重金属离子强大的吸附性能和离子载体优良的选择性，制备了纳米材料及离子 载体修饰玻碳电极并用来对实际水样中痕量的重金属进行检测。主要内容包括以 下几个方面： 1.制备新型碳纳米管/铋膜复合修饰电极，研究了重金属钴在电极上的电化 学性能。结果表明，这种新型复合修饰电极的灵敏度得到显著提高，能实现最低 检测限为8´10-11 M的钴的吸附富集溶出。 2.利用羟基磷灰石的强吸附能力和碳纳米管的优异电化学性能，制备了新型 新型纳米材料及离子载体化学修饰电极的制备及其在痕量重金属污染物检测中的应用 II 的碳纳米管-纳米羟基磷灰石的双纳米复合材料，并将其用于金属镉的富集溶出。 结果表明，双纳米复合材料具有比单一材料更优异的性能，更有助于金属镉的富 集溶出。采用碳纳米管-纳米羟基磷灰石的双纳米复合材料修饰电极，能实现最 低检测限为4´10-9 M的镉的富集溶出，灵敏度得到明显提高。 3. 将导电性好、抗氧干扰能力强的铋膜与对重金属具有良好选择性的离子 载体相结合，制备了基于铋膜/离子载体的新型修饰电极，研究了金属铅在其表 面的富集溶出。结果表明，这种新型修饰电极的灵敏度和选择性都大为提高，具 有更高的溶出峰电流和更好的抗干扰能力，可以实现最低检测限为4.4´10-11 M 的铅的富集溶出。 4. 利用羟基磷灰石的强吸附能力和其三维多孔结构、离子载体对重金属离 子优异的选择性以及Nafion 膜良好的离子交换作用和化学稳定性，制备了基于 纳米材料和离子载体的新型化学修饰电极。这种方法不仅有助于提高对金属铅的 选择性和灵敏度，而且大大提高了富集效率。采用该新型化学修饰电极，能够实 现最低检测限为1´10-9 M的铅的富集溶出。

Dendrimers as "controllers" for modulation of electrodeposited silver nanostructures

Electrodeposition of silver nanostructures on a polyamidoamine (PAMAM) dendrimers-modified surface has been reported. The assembled PAMAM monolayer film was used as a substrate for electrodeposition. We found that the PAMAM dendrimers obviously affected nucleation growth and silver nanostructures (spherical, dendritic and "fish bone" shapes) were obtained, which were different from those deposited on unmodified surfaces. It was attributed to the unique structures and properties of PAMAM dendrimers compared with linear polymers.

Nanocomposite multilayer film of preyssler-type polyoxometalates with fine tunable electrocatalytic activities

Through layer-by-layer (LBL) assembly technique, iron oxide (Fe3O4) nanoparticles coated by poly (diallyldimethylammonium chloride) (PDDA) and Preyssler-type polyoxometalates (NH4)(14)NaP5W30O110.31H(2)O (P5W30) were alternately deposited on quartz and ITO substrates, and 4-aminobenzoic acid modified glassy carbon electrodes. Thus-prepared multilayer films were characterized by UV-visible spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. It was proved that the multilayer films are uniform and stable. And the electrocatalytic activities of the multilayer films can be fine-tuned by adjusting the assembly conditions in the LBL assembly process, such as the pH of the assembly solution. The multilayer films fabricated from P5W30 solutions dissolved in 0.1 M H2SO4 exhibit high electrocatalytic response and sensitivity toward the reduction of two substrates of important analytical interests, HNO2 and IO3- whereas the films assembled with P5W30 solutions dissolved in 1.0 M H2SO4 show remarkable electrocatalytic activity for the hydrogen evolution reaction (HER). Furthermore, the electrocatalytic properties of the HER of the latter film can be obtained from the former film upon exposure to 1.0 M H2SO4 for several hours.

Simultaneous determination of both the calibration constant in an electrochemical quartz crystal microbalance and the active surface area of a polycrystalline gold electrode

A novel method is employed for the simultaneous determination of both the calibration constant of an electrochemical quartz crystal microbalance (EQCM) and the active surface area of a polycrystalline gold electrode. A gold electrode: is immersed into a 1 mM KI/1 M H2SO4 solution and on which forms a neutral monolayer. The adsorbed iodine can then be completely oxidized into IO3-. The active surface area of a gold electrode can be obtained from the net electrolytic charge of the oxidation process, and the calibration constant in the EQCM can be calculated from the corresponding frequency shift. The result shows that this method is simple, convenient and valid. (C) 2000 Elsevier Science S.A. All rights reserved.

Simple preparation method of multilayer polymer films containing Pd nanoparticles

A simple route to the fabrication of multilayer films containing Pd nanoparticles is described. Following layer-by-layer assembly of PdCl42- and polycation, QPVP-Os (a quaternized poly(4-vinylpyridine) complexed with [Os(bpy)(2)Cl](2+/+)), on 4-aminobenzoic acid-modified glassy carbon electrodes, the three-dimensional Pd nanoparticle multilayer films are directly formed on electrode surfaces via electrochemical reduction of PdCl42- sandwiched between polymers. The growth of PdCl42- is easy on electrode surfaces by electrostatic interaction, and the assembly processes are monitored by cyclic voltammetry and UV-vis spectroscopy. The depth profile analyses by X-ray photoelectron spectroscopy verify the constant composition of the Pd nanoparticle multilayer films. Atomic force microscopy proves that the as-prepared Pd nanoparticles are uniformly distributed with an average particle diameter of 3-7 mn. The resulting Pd nanoparticle multilayer-modified electrode possesses high catalytic activity for the reduction of dissolved oxygen and oxidation of hydrazine compounds in aqueous solution.

ELECTROLYTE EFFECTS ON THE ELECTROCHEMICAL POLYMERIZATION OF N-BENZYLANILINE

The electrochemical behaviour of N-benzylaniline polymerization is determined by the nature of the electrolyte. The voltammograms for a poly-N-benzylaniline modified Pt electrode prepared in 1 M HCl (abbreviated to PBAn(HCl)), and 1 M H2SO4 (PBAn(H2SO4)) tested in 1 M hydrochloric, sulfuric, and perchloric acid were almost superimposable. The polymer film electrode prepared in 1 M HClO4 (abbreviated to PBAn(HClO4)) is electroinactive, and exhibits only charging behaviour in 1 M HClO4 solution and can be activated in hydrochloric or other acid electrolytes with a smaller anion. These interesting phenomena are explained in terms of the anions catalyzing the loss of benzyl groups.

Electrocatalytic oxidation of methanol at the titanium oxide electrode modified with Pt microparticles

The electrocatalytic oxidation of methanol at the Titanium oxide (TiOx, x<2) film modified with Pt microparticles has been studied. The results show that the modified electrodes exhibit a significant electrocatalytic activity and good stability for the oxidation of methanol. Under the optimal conditions, the peak current density at 0.58 V for the oxidation of methanol in the positive-going sweep is about 526 mA/cm(2) at the scan rate of 5 mV/s in 0.5 mol/L CH3OH and 0.5 mol/L H2SO4 solution and the over potential of the methanol oxidation at the modified electrode increases about 30 similar to 40 mV after 70 minutes at the current density of 100 mA/cm(2) and 50 mA/cm(2). The enhanced electrocatalytic activity and good stability are ascribed to the high dispersion of Pt microparticles in and on the TiOx film and the synergistic effect between Pt microparticles and TiOx.

Electrocatalytic Oxidation of Methanol on Polythionine Film Modified with Pt Microparticles

The electrocatalytic oxidation of methanol on polythionine(PTn) film modified with Pt microparticles has been studied by means of cyclic voltammetry and in-situ FTIR spectroscopy. The Pt microparticles produced by cyclic voltammetry were highly dispersed in and on the PTn film. The modified electrodes exhibit significant electrocatalytic activity for the oxidation of methano and the catalytic activity was found in dependence on the Pt loading. The linearly adsorbed CO species is the only intermediate in the oxidation of methanol and the abnormal IR spectra for adsorbed CO were observed. On such modified electrodes, adsorbed CO species derived from methanol can be readily oxidized. The enhanced electrocatalytic activity may be ascribed to the high dispersion of Pt microparticles in and on the PTn film and the synergestic effect between Pt microparticles and the polymer. From the above results, a possible reaction mechanism was proposed.

Macroporous Pt modified glassy carbon electrode: preparation and electrocatalytic activity for methanol oxidation

Three-dimensional (3D) macroporous Pt (MPPt) with highly open porous walls has been successfully synthesized using the hydrogen bubble dynamic template synthesis and galvanic replacement reaction. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical methods were adopted to characterize their structures and properties.