三相电极法及其在液/液界面铬(Ⅵ)离子转移研究中的应用

将含有氧化还原探针的硝基苯溶液滴到边平面热解石墨(EPPG)电极上,然后将该电极插入到电解质水溶液中,从而使硝基苯、石墨表面以及水溶液形成一个三相接界线,即形成了EPPG三相电极。利用循环伏安法对EPPG三相电极法的原理进行了研究,得到了比文献报道更理想的液/液界面离子转移热力学数据。本研究还观察到铬(Ⅵ)离子在水相/硝基苯相界面上的转移反应,并测定了铬(Ⅵ)的离子转移热力学数据;同时还分别利用方波伏安法和傅里叶变换-方波伏安法结合"准可逆最大"现象对铬(Ⅵ)在水相/硝基苯相界面上的离子转移动力学进行了比较研究。     

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。     

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.     

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.     

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。     

液/液界面的电化学阻抗谱测量 Ⅱ: 液/液界面上离子传递的研究

本文成功地运用四电极系统阻抗谱技术来研究液/液界面上的离子传递。提出了从表观阻抗曲线获取真实界面阻抗曲线的方法。并用此方法对四甲铵离子在水/硝基苯界面上的传递进行了实际的动力学研究, 证实了四甲铵离子在水/硝基苯界面上的传递是可逆离子传递。     

液/液界面的电化学阻抗谱测量 Ⅱ: 液/液界面上离子传递的研究

本文成功地运用四电极系统阻抗谱技术来研究液/液界面上的离子传递.提出了从表观阻抗曲线获取真实界面阻抗曲线的方法.并用此方法对四甲铵离子在水/硝基苯界面上的传递进行了实际的动力学研究,证实了四甲铵离子在水/硝基苯界面上的传递是可逆离子传递     

四乙基铵阳离子在微液/液界面上转移的研究

用循环伏安法对简单离子四乙基铵阳离子（TEA^ ）转移进行了研究。结果表明：TEA^ 随微玻管内径减小（小于3μm),电流逐渐呈现拟稳态。随TEA^*浓度减小,ip值也减小。峰电流与扫描速度的平方根成正比,并且符合Randles-Sevcik关系。同时讨论了微液/液界面TEA^*体系简单离子的转移机理。     

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。     

铬天青S的液/液界面离子转移过程

本文研究了酸性染料显色剂铬天青S的液/液界面离子转移行为, 用循环伏安法和电流扫描计时电位法研究了铬天青S在水/硝基苯和水/1,2-二氯乙烷两种界面上的离子转移过程, 根据铬在青S在溶液中的离解平衡和电化学性质, 讨论了界面离子转移机理,研究了基础电解质和溶剂对铬天青S转移性能的影响, 在Britton-Robinson缓冲溶液中测得半波电位PH曲线与理论公式相一致, 由本法所得离解常数与文献值接近, 计算了转移离子的标准转移电位和标准吉布斯转移能。     

Carbon ceramic electrode modified with redox liquid

A carbon ceramic electrode modified with a redox liquid, butylferrocene, exhibiting in aqueous salt solution electrochemical behaviour resulting from the redox process of the modifier and ion transfer across the liquid-liquid interface has been prepared.     

Electrochemical determination of lead and lead ion transfer at liquid-liquid interfaces

The transfer behavior of lead (II) ion at a liquid-liquid interface, facilitated by neutral carriers (polyethylene glycols), is studied by an electrochemical method. The transfer process is discussed in terms of the formation of complexes in two phases and attributed to the transfer of a complex ion across the interface. The apparent standard transfer potential, ΔwoφPbL2+o, apparent standard Gibbs energy of transfer, ΔwoGPbL2+o, and the dissociation constant of the complex, KPbL2+, in the aqueous phase are obtained from the experimental data. The results suggest a new electrochemical method for the determination of lead.     

Determination of the ammonium ion by voltammetry at the liquid-liquid interface using calixarenes as neutral carriers

The transfer of alkali and alkaline earth metal ions and ammonium ions facilitated by the calixarenes 5,11,17,23-tetra(tert-butyl)-26,28-dihydroxycalix[4]-25,27-crown-5-ether, 5,11,17,23-tetra(tert-butyl)-26,28-di(ethoxycarbonylmethoxy)calix[4]-25,27-crown-5-ether, and 5,11,17,23-tetra(tert-butyl)-25,26,27,28-tetra(ethoxycarbonylmethoxy)-calix[4]arene was studied by voltammetry at the interface between two immiscible electrolyte solutions. The formal energies, transfer potentials, stoichiometry, and stability constants of the complexes were determined. The optimum conditions for determining the ammonium ion by voltammetry at the liquid-liquid interface were selected on the basis of these studies (the detection limit was 3.5 × 10^?6 M). The ammonium ion determination showed selectivity relative to the sodium ion.     

Second harmonic generation monitoring of nitric acid extraction by a monoamide at the water-dodecane interface

The interface dynamic properties of a monoamide extractant with potential for application to the front end of the nuclear cycle and to waste treatment are examined by second harmonic generation. The results are compared with bulk nitric ion titration and surface pressure measurements. SH static studies show the extractant reaching the interface and accurately match the IFT measurements. The main feature of the SH dynamic studies is a chaotic fluctuation period, strongly related to intense extraction. Fluctuations are a signature of the interface behaviour during the extraction process. Vertical development of the interface, often called protrusion, remains the most probable origin of the measured fluctuation. Additionally, interfacial measurements show a non-monotonic lag time during extraction, probably related to cooperative effects not observed in the bulk at the working concentration. Such mutual behaviour could be a supplementary prerequisite for the ion transfer across this liquid-liquid interface.     

Melittin adsorption and lipid monolayer disruption at liquid-liquid interfaces

Melittin, a membrane-active peptide with antimicrobial activity, was investigated at the interface formed between two immiscible electrolyte solutions (ITIES) supported on a metallic electrode. Ion-transfer voltammetry showed well-defined semi-reversible transfer peaks along with adsorptive peaks. The reversible adsorption of melittin at the liquid-liquid interface is qualitatively discussed from voltammetric data and experimentally confirmed by real-time image analysis of video snapshots. It is also demonstrated that polarization of the water/1,2-DCE interface results in drastic drop shape variations caused by large variations of the interfacial tension. The experimental data also confirmed that maximum adsorption occurs near the ion transfer potential. Finally, the interaction of melittin with a monolayer of L-α-dipalmitoyl phosphatidylcholine (DPPC) was also investigated showing that melittin destabilizes the lipidic monolayer facilitating its desorption. The non-covalent complex formation between melittin and DPPC was confirmed by mass spectrometry.     

Simple electrochemical method for deposition and voltammetric inspection of silver particles at the liquid-liquid interface of a thin-film electrode

A novel experimental methodology for depositing and voltammetric study of Ag nanoparticles at the water-nitrobenzene (W-NB) interface is proposed by means of thin-film electrodes. The electrode assembly consists of a graphite electrode modified with a thin NB film containing decamethylferrocene (DMFC) as a redox probe. In contact with an aqueous electrolyte containing Ag(+) ions, a heterogeneous electron-transfer reaction between DMFC((NB)) and Ag(+)((W)) takes place to form DMFC(+)((NB)) and Ag deposit at the W-NB interface. Based on this interfacial reaction, two different deposition strategies have been applied. In the uncontrolled potential deposition protocol, the electrode is immersed into an AgNO(3) aqueous solution for a certain period under open circuit conditions. Following the deposition step, the Ag-modified thin-film electrode is transferred into an aqueous electrolyte free of Ag(+) ions and voltammetrically inspected. In the second protocol the deposition was carried out under controlled potential conditions, i.e., in an aqueous electrolyte solution containing Ag(+) ions by permanent cycling of the electrode potential. In this procedure, DMFC((NB)) is electrochemically regenerated at the electrode surface, hence enabling continuation and voltammetric control of the Ag deposition. Hence, the overall electrochemical process can be regarded as an electrochemical reduction of Ag(+)((W)) at the W-NB interface, where the redox couple DMFC(+)/DMFC acts as a mediator for shuttling electrons from the electrode to the W-NB interface. Ag-particles deposited at the W-NB interface affect the ion transfer across the interface, which provides the basis for voltammetric inspection of the metal deposit at the liquid-liquid interface with thin-film electrodes. Voltammetric properties of thin-film electrodes are particularly sensitive to the deposition procedure, reflecting differences in the properties of the Ag deposit. Moreover, this methodology is particularly suited to inspect catalytic activities of metal particles deposited at the liquid-liquid interface toward heterogeneous electron-transfer reactions occurring at the at the liquid-liquid interface.     

Cyclic voltammetry of highly hydrophilic ions at a supported liquid membrane

Cyclic voltammetry has been used to study the coupling of ion transfer reactions at a liquid membrane. The liquids are either supported by a porous hydrophobic membrane (polyvinylidene difluoride, PVDF) when the organic solvent is non-volatile (o-nitrophenyloctylether) or are merely a free standing organic solvent layer such as 1,2-dichloroethane comprised between two hydrophilic dialysis membranes supporting the adjacent aqueous phases. The passage of current across the liquid membrane is associated with two ion transfer reactions across the two polarised liquid liquid interfaces in series. It is shown that it is possible to study the transfer of highly hydrophilic ions at one interface by limiting the mass transfer of the other ion transfer reaction at the other interface. Indeed, for systems comprising an ion M in one aqueous phase and a reference ion R partitioned between the membrane and the other aqueous phase, the observed and simulated cyclic voltammograms have a half-wave potential determined by the Gibbs energy of transfer of M transferring at one interface and by the limiting mass transfer of R at the other interface. This new methodology opens a way to measure the Gibbs energy of transfer of highly hydrophilic or hydrophobic ions, which usually limits the potential window at single liquid liquid interfaces (ITIES).     

Effect of gramicidin on phospholipid-modified monolayers and on ion transfer at a liquid-liquid interface.

The interaction of hybrid lipid/gramicidin A (gA) monolayers with dextran sulfate (DS) and the effect of this interaction on ion transfer at a liquid-liquid interface is reported. The interfacial and physicochemical properties are studied with Langmuir-Blodgett (LB) and electrochemical techniques. The results obtained from compression isotherms demonstrate that the interactions between the different species in the hybrid monolayer vary according to the chemical nature of the lipid (hydrocarbon region and charge of the head group). Interfacial capacitance measured with AC voltammetry indicates that the DS chains form a rather flat and compact layer when adsorbed to either zwitterionic or negatively charged phospholipid monolayers, and that calcium, even at low concentrations, interacts with the monolayers. These results are successfully described by a model based on the solution of the Poisson-Boltzmann equation in the interfacial region. Ion transfer and interactions with the lipid/gA/DS-modified monolayers were also studied with electrochemical techniques. Admittance data show that although the studied ions are not using gA channels for the transfer through the lipid membranes, the incorporation of gA in the lipid domain and the adsorption of DS at the interface have a significant effect on ion transfer across the monolayers. This effect can be explained as a consequence of the modified surface charge and of the compactness of the lipid domain due to its interaction with gA and to calcium and DS adsorption at the interface. The ion-transfer rate, therefore, depends on the composition of the monolayer and the chemical nature of the ion.     

Finite-element simulations of the influence of pore wall adsorption on cyclic voltammetry of ion transfer across a liquid-liquid interface formed at a micropore

Adsorption onto the walls of micropores was explored by computational simulations involving cyclic voltammetry of ion transfer across an interface between aqueous and organic phases located at the micropore. Micro-interfaces between two immiscible electrolyte solutions (micro-ITIES) have been of particular research interest in recent years and show promise for biosensor and biomedical applications. The simulation model combines diffusion to and within the micropore, Butler-Volmer kinetics for ion transfer at the liquid-liquid interface, and Langmuir-style adsorption on the pore wall. Effects due to pore radius, adsorption and desorption rates, surface adsorption site density, and scan rates were examined. It was found that the magnitude of the reverse peak current decreased due to adsorption of the transferring ion on the pore wall; this decrease was more marked as the scan rate was increased. There was also a shift in the half-wave potential to lower values following adsorption, consistent with a wall adsorption process which provides a further driving force to transfer ions across the ITIES. Of particular interest was the disappearance of the reverse peak from the cyclic voltammogram at higher scan rates, compared to the increase in the reverse peak size in the absence of wall adsorption. This occurred for scan rates of 50 mV s(-1) and above and may be useful in biosensor applications using micropore-based ITIES.     

Reversible electrochemical monitoring of surface confined reactions at liquid-liquid interfaces by modulation of ion transfer fluxes

The adsorption of the neutral surfactant Brij35 at a liquid-liquid interface is reversibly monitored via its disturbance of an electrochemically imposed ion flux across the interface, forming a promising experimental tool for the detection of surface confined reactions at such liquids and polymers.