Effect of silver particles deposited at the water∣nitrobenzene interface on the voltammetric response of thin-film electrodes

A novel experimental methodology for studying silver particles deposited at the water∣nitrobenzene (W∣NB) interface is proposed by means of thin-film electrodes. The electrode assembly consists of a graphite electrode (GE) covered with a thin NB film containing decamethylferrocene (DMFC) as a redox probe. The W∣NB interface was modified with silver particles in an AgNO3 aqueous solution, where a heterogeneous electron transfer reaction between DMFC(NB) and Ag(W)+ takes place to form a Ag-deposit at the W∣NB interface, and DMFC+ and NO3- in the organic phase. The Ag-modified thin-film electrode was inspected by voltammetry in a contact with an aqueous electrolyte free of Ag(W)+. The overall reaction at the thin-film electrode proceeds as a coupled electron–ion transfer reaction. Ag-particles deposited at the W∣NB interface affect significantly the ionic transfer, which provides the basis for a voltammetric inspection of the metal deposition at the W∣NB interface. When the concentration AgNO3(W) is close to the concentration of DMFC(NB), a dense Ag-film is formed that prevents completely the ionic transport, hence resulting in a complete vanishing of the voltammetric response. In a presence of [Fe(CN)6](W)3-, the response of the electrode is restored, having properties of a reductive catalytic electrode mechanism. The overall mechanism couples two simultaneous electron transfer reactions undergoing at separate interfaces, i.e. the reduction of DMFC(NB)+ to DMFC(NB) at the GE∣NB interface and the heterogeneous redox reaction between DMFC(NB) and [Fe(CN)6](W)3- to form DMFC(NB)+ and [Fe(CN)6](W)4- at the Ag-modified W∣NB interface. Under these conditions the Ag-film acts as an effective conductive medium for fast electron exchange between DMFC(NB) and [Fe(CN)6](W)3-. The methodology proposed is particularly suited to inspect catalytic activities of metal particles deposited at the liquid∣liquid interface towards heterogeneous electron transfer reactions between reactants embedded in immiscible liquids.