Preparation of a silicate membrane at a liquid|liquid interface and its doping with a platinum ion

Silicate films have been reproducibly formed at the interface of two immiscible liquids (water|1,2-dichloroethane) by using a modified sol–gel process in which the template (trimethyloctadecylammonium ion, TODA+), present in the organic phase, is transferred to the interface where it associates with the precursor silicate ions present in the aqueous phase. The process and, consequently, the properties of the film formed are finely controlled by the potential difference across the interface. This potential difference can be varied by applying an external voltage to the interface, or by adding a charged species that is soluble in both the phases. An addition of a further multiply charged anion which can participate in the reaction, i.e., another precursor, to the aqueous phase makes it possible to modify the silicate film formed by various ions, like platinum in the present case. The process mechanism has been experimentally studied in some detail, using surface tension measurement, cyclic voltammetry and ESCA. This approach to preparation of variously modified silicate films, that can also be formed on a solid support and that may exhibit catalytic and chemically selective properties, bears promise for use in catalysis and for application to analytical chemistry, e.g., for pretreatment of the capillary walls in capillary chromatographic and electromigration separations, or for surface modification of chemical sensors.