Electro-assisted generation of functionalized silica films on gold

Electrochemical tuning of pH at electrode/solution interfaces is exploited for preparing thiol-functionalized silica films on gold surfaces by the sol–gel process. Film formation is carried out from a sol solution containing various ratios of prehydrolyzed mercaptopropyltrimethoxysilane and tetraethoxysilane precursors. This mixture is allowed to gelify only on the electrode surface by maintaining a negative potential value (to reduce protons and water and to generate hydroxyl species) to increase the local pH, which is known to catalyze polycondensation of the precursors. High mechanical stability of the resulting films is ensured by the strong interactions between thiol functions and the gold surface. Film porosity is very dependent on the amount of mercaptopropyl groups in the composite layer as pointed out by cyclic voltammetry of a redox probe (Fe(CN)₆³⁻). The organic group content is also a key factor influencing the sensitivity of Hg^(II) detection by anodic stripping voltammetry after accumulation at open-circuit. The preparation method can be extended to the deposition of other silica-based films on gold electrodes.