The modification of platinum electrodes with commercial filtration membranes is used to study the interplay between solution and membrane mass-transport in non-aqueous solution. Two types of commercial membrane, “track-etched” polyethylene terephthalate and γ-Al2O3, are employed. Voltammetric and amperometric data is obtained under both hydrodynamic (rotating-disc) and stationary conditions, which is interpreted in terms of a pinhole model. Contrasting behaviour is seen for the different membranes, which can be understood by consideration of the membrane thickness relative to the diffusion layer established in solution. In particular, overlapping diffusion behaviour is observed for the much thinner polymer membranes under hydrodynamic conditions.

The modification of the liquid/liquid interface with membranes of silicalite, a neutral framework zeolite, is used to extend the potential window. This feature allows the observation of the transfer of extremely hydrophilic ions, due to the size-exclusion of organic ions from the interior of the zeolitic framework. Similarly, volume exclusion effects are shown to affect facilitated ion transfer processes involving alkali metal cations. In contrast, proton transfer is largely unaffected by the presence of the zeolite, which is suggestive of more rapid diffusion processes within the interior of the framework. The technique of liquid/liquid electrochemistry should allow the measurement of solution phase transport parameters for ions within microporous hosts.

The potentiometric behaviour of films of zeolite toward aqueous phase cations is described. The stability of the potentiometric responses toward various analytes is used to diagnose the applicability of these materials for electroanalysis. Size selective behaviour with regard to cationic species is observed: cations with a crystallographic diameter exceeding that of the zeolite pores gave no measurable potential response. The zeolite films were formed using three distinct preparation routes: pressing discs of zeolite powder (for zeolite Y, zeolite A and mordenite), growing a free-standing membrane of zeolite (for sodalite) and using a secondary growth step to heal defects in pressed zeolite A discs. The approach presented is the first report of the use of coherent polycrystalline films, consisting solely of zeolite, in a potentiometric study.

We present the first reported characterisation by x-ray diffraction and high resolution transmission electron microscopy of metals electrodeposited at the bare and templated liquid/liquid interfaces. Additional structural information is also obtained using ion transfer voltammetry as an in situ characterisation tool. In particular, the metallic deposits are shown to consist of aggregates of discrete nanoparticles, predominantly between 3 and 5nm in diameter. Deposition of platinum at the liquid/liquid interface is reported for the first time, which enables a preliminary comparison to be made between the growth mechanism of this metal and the growth of palladium, previously reported at this interface.

The deposition of metal nanostructures (wires and particles) on a graphite surface from an aqueous electrolyte solution was induced by galvanic displacement, via the oxidation of insoluble crystals of a ferrocene derivative (either n-butyl ferrocene or decamethyl ferrocene) present on the same substrate. Micron-to-millimetre-scale crystallites of decamethyl ferrocene were deposited on the graphite surface by evaporation from a solution of a nonpolar solvent (1,2-dichloroethane). Immersion of this modified surface into a dilute solution of a metal ion (e.g., CuII, AgI, PdII, PtII and others) caused the deposition of metal nanoparticles at step edges present on the graphite surface. The reducing equivalents required for the metal deposition process are provided by oxidation of the ferrocene derivative on the surface, as directly evidenced by elemental analysis and chronoamperometric experimental data presented here.

The modification of the water/organic interface with size-selective membranes is presented as a means to elucidate the mechanism of facilitated ion transfer processes. In particular, an interfacial or organic phase complexation reaction is observed for the transfer of Cu2+ ions facilitated by dibenzo-18-crown-6, whereas the complexation process for the 1,4,7,10-tetrathiacyclododecane facilitated transfer of the same ion is suggested to occur within the aqueous phase. The contrasting transfer mechanism is discussed in terms of the solution phase behaviour of the thio-ether ligand.

The strength of binding between a cholapod receptor and halide anions is quantified using voltammetry at the liquid/liquid interface, revealing very high affinities and size-selectivity peaking at chloride.

This work aims to develop a novel technology to treat produced water with the intent to reuse it for crop irrigation. The concentration of boron in produced water is relatively high — 4–5 ppm, which gives rise to poisoning of the plants if used for irrigation. Therefore, boron concentration must be reduced to safe levels between 0.3 and 0.5 ppm. A process based on liquid-liquid electrochemistry has been investigated to transfer selectively borate anions present in produced water to an immiscible phase. Experiments have been carried out at laboratory scale under stationary conditions in an ITIES cell (Interface between Two Immiscible Electrolytic Solutions) to determine the suitability of borate receptors, which facilitate transfer from the aqueous phase to the immiscible phase. These measurements allow the determination of the equilibrium conditions for the system and important parameters such as Gibbs energy of transfer for the borate anion. Simulations have been carried out using a finite element method to validate experimental results. The simulations and experimental results are used as a basis for further model development in both static and continuous operation regimes.

Recently reported studies on the transfer of silver ions across the aqueous I 1,2-dichloroethane interface using cyclic voltammetry (CV), facilitated by organic phase electrolyte anions, have been augmented by square-wave voltammetry (SWV) and square-wave stripping voltammetry (SWSV) studies and by consideration of the possible transfers of additional metal cations. Using SWV and SWSV, detection limits have been improved, from the 0.02 mM obtained by CV, to 1.4 muM (SWV) and 2 nM (SWSV). Additional studies show that mercury(I and II) ions, platinum(II) ions and gold(III) ions are also transferable across this interface, to differing extents. Of these three ions studied, highest sensitivity is achieved for the gold species.

The removal of colour from a crystal violet dye solution using a non-porous, electrically conducting carbon-based adsorbent was systematically investigated under different operating conditions. Whilst the adsorptive process was very quick (up to 88% of equilibrium capacity could be achieved within 2min), the adsorptive capacity of the adsorbent was very low (2mgg−1) compared with activated carbons. This was due to its low surface area. The conductivity of the adsorbent/electrolyte mixture within the anodic compartment of the electrochemical cell was found to be over 13 times greater with the new adsorbent compared with powdered activated carbon. One hundred percent could be achieved in a simple divided electrochemical cell using treatment times as low as 10min by passing a charge of 25Cg−1 at a current density of 20mAcm−2. The efficiency of electrochemical regeneration depends on a range of variables including charge passed, current density, treatment time, electrolyte type and concentration and the adsorbent bed thickness. Multiple adsorption and regeneration cycles indicate that there is little or no loss in adsorbent capacity on regeneration.

A simple, electroless approach to metallize the liquid/liquid interface is reported. The method is illustrated with the deposition of Pd at the bare water/1,2-dichloroethane interface, and for the "templated" deposition of Pd within the 100 nm diameter pores of gamma-alumina membranes.

A new approach to the voltammetric investigation of facilitated ion transfer processes is reported. The technique uses a rotating diffusion cell approach to induce laminar flow in the organic phase of a liquid|liquid electrochemical cell. The interface between two immiscible electrolyte solutions (ITIES) was stabilised against rotation with either γ-alumina or a track-etched polyester membrane. The resultant voltammetry is shown to be consistent with the Koutecký–Levich equation enabling kinetic parameters associated with facilitated transfer of sodium by dibenzo-18-crown-6 across the water|1,2-dichloroethane interface to be evaluated. In particular, the use of the more hydrophilic alumina membrane permits the uncertainties regarding the use of the membrane-stabilised ITIES, namely the interfacial position, to be eliminated.

The boundary element method is presented as an efficient and powerful method for the analysis of time-dependent electrochemical processes occurring at immiscible liquid/liquid interfaces. This paper outlines the theory and numerical details required for the development and application of two-dimensional transient diffusion models for the simulation of cyclic voltammetry behaviour at a range externally polarised immiscible liquid/liquid interfaces of differing topography. The benefits of the BEM approach are discussed, including the reduction in dimensionality brought about by the formulation procedure and complete elimination of the need for domain discretisation with the time-domain convolution approach. The versatility and efficiency of the numerical procedures are examined with respect to a number of liquid/liquid interface geometries and a series of working curves established to quantify the influence of interface topography on the observed voltammetric behaviour.

Transfer of silver ions across the water/1,2-dichloroethane interface was studied by cyclic voltammetry (CV). In the absence of added neutral ionophore, Ag+ transferred across the interface when the organic phase contained either tetraphenylborate or tetrakis(4-chloro)phenylborate anions, but this transfer was not possible in the presence of organic phase hexafluorophosphate or perchlorate anions. The ion transfer processes observed were independent of the nature of the organic phase cation. The CV in the presence of tetraphenylborate exhibited a shape consistent with an ion transfer followed by chemical reaction; the rate constant for the following chemical reaction was 0.016 s(-1). In the presence of tetrakis(4-chloro)phenylborate, a return peak equivalent in magnitude to the forward peak was observed, indicative of a simple ion transfer reaction uncomplicated by accompanying chemical reactions. The selectivity of the transfer was assessed with respect to other metal cations: no transfers for copper, cadmium, lead, bismuth, cobalt, nickel, palladium or zinc were observed. The selectivity of the transfer suggests this can form the basis of a selective voltammetric methodology for the determination of silver ions.

A simple nondestructive method is presented to characterize the physical properties of ultrafiltration membranes. The technique utilizes voltammetry at the interface between two immiscible electrolyte solutions (ITIES) and has been applied to commercially available gamma-alumina membranes. Upon the application of a potential difference across the ITIES, the voltammetric response resulting from an ion transfer is a direct measure of the membrane porosity. The technique has been applied to the measurement of the fractional porous area (porosity) and the membrane thickness. The reported technique offers advantages over existing methods such as being easy to use, reproducible, inexpensive, and nondestructive. Furthermore, unlike many optical techniques, this method is not limited by a minimum nominal pore size and has thus been used to make measurements when the reported nominal pore diameter is as small as 20 nm.

A hydrodynamic system based on the channel flow cell for voltammetric detection of ions at the liquid/liquid interface is reported. The current response for tetraethylammonium ion transfer across a membrane-supported liquid/liquid interface is shown to be consistent with existing theory for both the flow rate and voltage scan rate dependence of such processes, with no calibration factors or other adjustable parameters required. The analytical utility of such a device is discussed with specific regard to in situ measurements in flow systems.

Alumina membranes, with mean pore diameters of 100 nm, have been used as templates to control the electrodeposition of palladium. Deposition occurs at the polarised water–organic interface, leading to the formation of nanoparticles. The particles are formed at the mouth of the alumina pores, the locus of their formation being dictated by the position of the organic–water interface. It is shown that the relative position of the liquid phases with respect to the alumina is controlled by the surface wetting properties of the liquids, rather than gravity. This in turn controls the interfacial position and hence the size of the particles deposited. The presence of the alumina membrane prevents agglomeration. Electrochemical and electron microscopy data are presented in support of this proposed deposition mechanism.