Multi-layered, vertically-aligned and functionalized mesoporous silica films generated by sequential electrochemically assisted self-assembly

Abstract

Multilayered and vertically-oriented mesoporous silica films are prepared by multiple electrochemically assisted self-assembly (EASA). This is achieved by consecutive potentiostatic EASA steps, implying the application of a negative potential to an electrode immersed in a sol solution containing silica precursors and surfactant molecules, disrupted by open-circuit periods targeted to rinsing of the electrode to avoid the precipitation of silica aggregates. The generated hydroxyl ions in each step catalyze the polycondensation of precursors around the surfactant template and film growth onto the electrode surface. Multilayered films with thicknesses of up to 400nm are obtained, exhibiting a well-ordered hexagonal mesostructured normal to the underlying electrode support. Mass transport through the films and especially between each layer is demonstrated by cyclic voltammetry using a redox probe in solution. In addition, such multilayered films functionalized with ferrocene groups covalently attached to the internal mesopore walls exhibit long-range electron transfer by electron hopping. The charge transfer processes can be modulated by elaborating sandwich silica-ferrocene/silica-alone/silica-ferrocene multilayers in which insulating silica-alone acts as a barrier to electron hopping.