薄层伏安法液/液界面电子转移速率理论的研究进展

由于液/液界面可以看作是模拟生物膜或人造膜的简单模型,研究在此其上的电子转移过程对理解生物体复杂的生理变化过程具有重要意义。薄层伏安法因其简单、易操作等优点成为研究液/液界面电子转移过程的有力手段,因此对该方法的定量分析理论研究显得尤为重要。本文综述了薄层伏安法液/液界面电子转移速率理论近年来的研究进展,并对其可能的影响因素进行了分析。     

液/液界面电化学及其进展

液/液界面电化学及电分析化学与研究萃取和化学传感机理、相转移催化、药物释放、模拟生物膜等密切相关,近年来备受到关注. 文中结合作者课题组工作,介绍、综述该领域近十几年、尤其在液/液界面微观结构、电荷（离子与电子）转移反应及界面功能化的新进展.     

三相电极法研究液/液界面离子转移的进展

三相电极法作为研究液/液界面离子转移的一种新方法,具有简单、快速、经济的特点。文章回顾了液/液界面离子转移的发展历史,介绍了三相电极法的实验原理,并对其在电化学中的研究进展和应用进行了评述,引用文献48篇。     

线性电流扫描过程中的液/液界面离子转移动力学

本文从理论上推导了在线性电流扫描过程中,离子在液/液界面转移的电位-电流方程。提出了利用线性电流扫描方法获取离子转移动力学参数的方法。并对液/液界面电化学中常用的基本电解质离子(TPAs~+)在水/硝基苯界面的转移进行了实际研究。     

分立式悬液四电极微液／液界面电解池的研制

本文研究了一种适用于液/液界面电化学研究的悬液电解池及其性能,它能产生3～20mm~2的球形界面和0.025mm~2的微盘界面。通过微量注射器调节,界面易更新,且液滴稳定时间长达1h。介绍了一种耐强极性有机溶剂接触的玻璃表面疏水处理方法,经处理后的电解池可连续使用14天。以典型的四乙基铵离子的转移特征来验证本电解池的性能,获得满意的结果。     

固/液界面现场光谱电化学

固/液界面现场光谱电化学的方法包括各种电磁波透射和反射谱(紫外可见、拉曼、红外、X-光等)、磁共振谱(ESR、NMR)以及80年代发展起来的扫描显微谱(STM等)和非线性反射光谱(SHG)等等。固/液界面现场光谱电化学已渗透到固/液界面和电极表面结构,分子水平上的吸脱附和反应机理,电催化和反应动力学等许多研究领域。本文结合文献对上述几个方面以及固/液界面现场光谱电化学的发展方向进行综述。     

液/液界面电分析化学研究进展

本文对液/液界面电分析化学近年来的进展进行了综述,特别是结合我们自己的工作,对探讨液/液界面微观结构和构筑新型液/液界面方面的进展进行了重点介绍。目前通过理论模拟和各种实验技术的应用,液/液界面微观结构已初具轮廓;可供选择的有机相也得到了一定的拓展。这些进展为该领域今后的发展打下了基础并指明了方向。     

应用扫描电化学显微镜研究极化液/液界面上的电子转移反应

将含有氧化还原电对的水溶液滴涂在铂盘电极表面, 然后将该电极插入到1,2-二氯乙烷溶液中, 形成稳定的油/水界面. 液滴中的K3Fe(CN)6和K4Fe(CN)6氧化还原电对既可以作为水相中的参比电对参与控制液/液界面上的电势差, 同时又可以作为水相的电子授受体参与界面上的电子转移反应. 结合扫描电化学显微镜电化学系统的特点, 利用其双恒电位仪分别控制界面电势差和现场扫描的优点, 通过扫描电化学显微镜的渐进曲线得到了不同界面电势差控制的电子转移反应速率常数. 实验结果表明, 应用此方法获得的液/液界面可以被外加电位极化, 在一定的电势差范围内, 反应速率常数与界面电势差的关系遵守Butler-Volmer公式.     

液／液界面电化学研究中的控制电流脉冲技术

恒流脉冲技术是液/液界面电化学研究的有效手段之一,它能直接、迅速地提供界面双电层的信息并给出溶液电阻引起的欧姆降。V.Mare(?)ek 和 Z.Samec 首次利用微处理机和信号发生器等装置进行了这方面的研究,之后又用 D/A 转换线路取代了信号发生器,使这一技术的优点得到进一步的发挥。在本论文中,     

双通道微米管支撑的微-液/液界面上电荷转移反应的研究

将有机相和水相分别灌入双通道玻璃微米管θ管中的一个管中,利用θ管表面的亲水特征,在灌有有机相的微米管口附近形成微-液/液界面.利用循环伏安法研究了电荷在这种微-液/液界面上的转移反应,包括简单离子(四甲基铵离子TMA⁺)转移、加速离子转移(DB18C6加速K⁺离子)和电子转移(二茂铁/铁氰化钾+亚铁氰化钾体系)反应过程.结果表明,这种双通道微米管所得到的微-液/液界面具有不对称扩散场的特性.此装置是目前最简单的可用于研究液/液界面上的电荷转移反应的装置之一,即所谓的可进行"无溶液"液/液界面电化学及电分析化学研究的装置.     

薄层法研究十二烷基苯磺酸钠对硝基苯/水界面电子转移的影响

用薄层法研究了阴离子表面活性剂十二烷基苯磺酸钠(SDBS)对硝基苯/水界面电子转移的影响. 实验结果表明, 随着水相中十二烷基苯磺酸钠浓度的增加, 有机相中十甲基二茂铁(DMFc)和水相中Fe(CN)₆^3-发生的界面双分子反应的阴极平台电流呈现递减趋势, 但是界面双分子反应速率常数却呈递增趋势. 这是由于阴离子表面活性剂十二烷基苯磺酸钠在硝基苯/水界面形成了修饰层, 影响了界面双电层结构. SDBS在液/液界面的吸附为Langmuir吸附.     

Amperometric proton selective sensors utilizing ion transfer reactions across a microhole liquid/gel interface

A new cost-effective amperometric proton selective sensor utilizing a single microhole interface between two immiscible electrolyte solutions (ITIES) is developed. The sensing methodology is based on measuring currents associated with proton transfer across the interface assisted by a proton selective ionophore. The ellipse shaped micro-interface was first fabricated by simple mechanical punching with a sharp needle on a thin PVC film (12 μm thick) commercially available as a food wrapping material. The microhole was then filled up with a gellified polyvinylchloride (PVC)-2-nitrophenyloctylether (NPOE) to create a single microhole liquid/liquid interface. Direct ion transfer reactions across the polarized interface serving as ion sensing platforms were studied using cyclic voltammetry. In order to enhance the selectivity of proton sensing, a proton selective ionophore, octadecyl isonicotinate (ETH1778), was incorporated into the organic gel layer and their electrochemical sensing characteristics were investigated using cyclic voltammetry and differential pulse stripping voltammetry. As an example, we employed the proton selective sensor for the determination of glucose concentrations. The detection scheme involves two steps: (i) protons are first generated by the oxidation of glucose with glucose oxidase in the aqueous phase; and (ii) the current associated with the proton transfer across the interface is then measured for correlating the concentration of glucose.     

A comparative study of the anion transfer kinetics across a water/nitrobenzene interface by means of electrochemical impedance spectroscopy and square-wave voltammetry at thin organic film-modified electrodes

The kinetics of the transfer of a series of hydrophilic monovalent anions across the water/nitrobenzene (W/NB) interface has been studied by means of thin organic film-modified electrodes in combination with electrochemical impedance spectroscopy and square-wave voltammetry. The studied ions are Cl-, Br-, I-, ClO4-, NO3-, SCN-, and CH3COO-. The electrode assembly comprises a graphite electrode (GE) covered with a thin NB film containing a neutral strongly hydrophobic redox probe (decamethylferrocene or lutetium bis(tetra-tert-butylphthalocyaninato)) and an organic supporting electrolyte. The modified electrode is immersed in an aqueous solution containing a supporting electrolyte and transferring ions, and used in a conventional three-electrode configuration. Upon oxidation of the redox probe, the overall electrochemical process proceeds as an electron-ion charge-transfer reaction coupling the electron transfer at the GE/NB interface and compensates ion transfer across the W/NB interface. The rate of the ion transfer across the W/NB interface is the limiting step in the kinetics of the overall coupled electron-ion transfer reaction. Moreover, the transferring ion that is initially present in the aqueous phase only at a concentration lower than the redox probe, controls the mass transfer regime in the overall reaction. A rate equation describing the kinetics of the ion transfer that is valid for the conditions at thin organic film-modified electrodes is derived. Kinetic data measured with two electrochemical techniques are in very good agreement.     

Static electrification of solid oxide in liquid metal and electrical double layer at the interface

Static electrification of a solid oxide, say a semiconducting oxide in liquid metal, is mainly due to electron transfer between two phases. Excess electrons in the liquid metal phase provided by the oxide give rise to an electrical double layer at the interface. The electrical double layer may be divided into three parts, an immobile inner layer, a compressed diffuse layer, and a flat layer extending into the bulk liquid metal. Differential potential analysis and the induced emf method were used to measure the potential of the compressed diffuse layer and the excess electron density of the flat layer, respectively. Results show that most oxides in liquid metals carry positive charges on their surfaces and the potentials of the compressed diffuse layer are in the range of 3 to 42 microV. Such a low potential implies that the diffuse layer is considerably compressed. The excess electron densities of the flat layer are on the order of 10(22) electrons/m(3) of Hg and their contributions to surface charges of oxide are in the range of 10(17) to 10(18) charges/m(2) for the oxide/mercury systems with a solid density of 0.3 wt% at room temperature.     

Electroneutrality coupling of electron transfer at an electrode surface and ion transfer across the interface between thin-layer of 1-octyl-3-methylimidazolium bis(perfluoroalkylsulfonyl)imide covering the electrode surface and an outer electrolyte solution.

The electrode reaction of decamethylferrocene (DMFc) dissolved in a thin layer of a room-temperature molten salt (RTMS), 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C8mimC1C1N) or 1-octyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide (C8mimC2C2N), on a self-assembled monolayer-modified gold electrode is coupled with the ion transfer across the interface between the RTMS and the outer aqueous solution (W) to give a voltammogram whose shape resembles a voltammogram of a simple one-electron transfer process. The electroneutrality of the RTMS layer during the oxidation of DMFc to decamethylferricenium ion is maintained by the concomitant dissolution of C8mim+ ion from the RTMS phase to the W phase, and the reduction of decamethylferricenium ion to DMFc is accompanied by the transfer of either C1C1N- or C2C2N- from RTMS to W. The midpoint potential of the voltammogram varies with the concentration of the salt in the aqueous phase, C8mimCl or LiCnCnN (n = 1 or 2), in a Nernstian manner, showing that the phase-boundary potential between the RTMS and the W is controlled by the partition of these ions. Although the phase-boundary potential across the RTMS / W interface is Nernstian with respect to the ions common to both phases at the equilibrium, the polarization at the RTMS / W interface under current flow distorts the shape of the voltammograms, resulting in a wider peak separation in the voltammogram.     

Electron-conductor separating oil–water (ECSOW) system: a new strategy for characterizing electron-transfer processes at the oil/water interface

A new electrochemical method for studying the electron transfer (ET) at the oil (O)/water (W) interface (or the liquid/liquid) interface has been devised, in which the O- and W-phases are separated by an electron conductor (EC; e.g. Pt). For the EC separating O–W (ECSOW) system, the ET across the EC phase can be observed voltammetrically in a similar manner to the O/W interface, however, no ion-transfer (IT) process can be taken place. Although the ECSOW system is thermodynamically equivalent to the corresponding O/W interface, they may be different from a kinetic viewpoint. In practice, the cyclic voltammograms obtained with the nitrobenzene NB/W interface and the ECSOW system in the presence of ferrocene in NB and hexacyanoferrate in W have shown quite different features, when the concentrations of both redox species are lower. The voltammograms for the NB/W interface have strongly supported the IT mechanism which involves an interfacial transfer of ferricenium ion. Also, the ECSOW system has been shown to be promising for clarification of complicated charge-transfer processes involving biological compounds such as l-ascorbic acid.     

Effect of SDBS on interfacial electron transfer at the liquid/liquid interface by thin layer method

The effect of an adsorbed anionic surfactant sodium dodecyl benzene sulfonate(SDBS) on electron transfer(ET) reaction between ferricyanide aqueous solution and decamethylferrocene(DMFc) located on the adjacent organic phase was investigated for the first time by thin layer method.The adsorption of SDBS at the interface resulted in a decay in the cathodic plateau current of bimolecular reaction with increasing concentrations of SDBS in aqueous phase.However,the rate constant of electron transfer(k_(et)) i...     

Surface-interface investigations of an ultrathin pulsed laser deposited NiO/ZnO bilayer structure

We hereby report detailed structural and morphological studies for an ultrathin NiO/ZnO bilayer structure grown on sapphire (001) substrate using pulsed laser deposition technique. The combined X-ray reflectivity (XRR) and grazing incidence X-ray fluorescence (GIXRF) studies revealed formation of a low-density defective ZnO interfacial layer of thickness ~32 Å at the ZnO/sapphire interface prior to growth of main ZnO layer. Our results further indicate that the variation of electron density across the NiO/ZnO bilayer structure is smooth and we do not observe presence of any interface layer between them. X-ray diffraction measurements show that deposited ZnO layer is epitaxial in nature whereas NiO is highly oriented along (100) direction. The angle dependent X-ray absorption near edge fine structure (XANES) measurements at Ni–K edge has been utilized to determine depth-resolved oxidation state of Ni and the results have been correlated with the depth-resolved electron density of NiO layer. The method described here offers nondestructive determination of the microstructural parameters as well as depth-resolved mapping of oxidation state of a thin film-based heterojunction device. It extends several advantages over destructive methods which are abundantly reported in literature.     

Comparative study of the thermodynamics and kinetics of the ion transfer across the liquid/liquid interface by means of three-phase electrodes

A comparative study of the behavior of different sorts of three-phase electrodes applied for assessing the thermodynamics and kinetics of the ion transfer across the liquid/liquid (L/L) interface is presented. Two types of three-phase electrodes are compared, that is, a paraffin-impregnated graphite electrode at the surface of which a macroscopic droplet of an organic solvent is attached and an edge pyrolytic graphite electrode partly covered with a very thin film of the organic solvent. The organic solvent contains either decamethylferrocene or lutetium bis(tetra-tert-butylphthalocyaninato) as a redox probe. The role of the redox probe, the type of the electrode material, the mass transfer regime, and the effect of the uncompensated resistance are discussed. The overall electrochemical process at both three-phase electrodes proceeds as a coupled electron-ion transfer reaction. The ion transfer across the L/L interface, driven by the electrode reaction of the redox compound at the electrode/organic solvent interface, is independent of the type of redox probe. The ion transfer proceeds without involving any chemical coupling between the transferring ion and the redox probe. Both types of three-phase electrodes provide consistent results when applied for measuring the energy of the ion transfer. Under conditions of square-wave voltammetry, the coupled electron-ion transfer at the three-phase electrode is a quasireversible process, exhibiting the property known as "quasireversible maximum". The overall electron-ion transfer process at the three-phase electrode is controlled by the rate of the ion transfer. It is demonstrated for the first time that the three-phase electrode in combination with the quasireversible maximum is a new tool for assessing the kinetics of the ion transfer across the L/L interface.