Influence of silanization on voltammetry at electrodes modified with silica films of controlled porosity formed by electrochemically initiated sol-gel processing

Abstract

Silica sol-gel (SG) films with templated pores were deposited on glassy carbon (GC) electrodes by an electrochemically initiated process. Generation-4 poly(amidoamine), PAMAM, dendrimer was included in the tetraethoxysilane precursor to facilitate pore formation. The PAMAM adsorbs to the GC, which blocks SG formation at those sites on the electrode. The pore size was 10 ± 5 nm. After removal of the PAMAM, cyclic voltammetry of Fe(CN)6 3− and Ru(NH3)6 3+ at pH 6.2 showed that the residual negative charge on the silica attenuated the current for the former and increased the current for the latter, presumably by electrostatic repulsion and ion-exchange preconcentration, respectively. This premise was supported by repeating the measurements at the isoelectric point. Methylation of the silanol sites was used to eliminate the charge of the SG. At the end-capped SG, the voltammetry of Fe(CN)6 3− and Ru(NH3)6 3+ yielded currents that were independent of pH over the range 2.1 to 7.2. Circumventing the need for the silanization by using (3-glycidyloxypropyl)trimethoxysilane as the sol-gel precursor failed because the oxygen plasma treatment to remove the PAMAM attacked the organically modified sol-gel backbone. The resulting modified electrode mitigated the influence of proteins on the voltammetry of test species and stabilized functionalize nanoparticle catalysts under hydrodynamic conditions.