Electrochemically Assisted Deposition of Nanoporous Silica Membranes on Gold Electrodes: Effect of 3‐Mercaptopropyl(trimethoxysilane) “Molecular Glue” on Film Formation, Permeability and Metal Underpotential Deposition
Résumé
Gold electrodes have been covered with vertically aligned mesoporous silica thin films by electro-assisted self-assembly. To ensure uniform surface coverage and good adhesion of the membrane to the gold surface, it was necessary to use a (3mercaptopropyl)trimethoxysilane (MPTMS) reagent acting as "molecular glue" thanks to its thiol function able to bind to the gold substrate and to its alkoxysilane moieties enabling condensation with the silica material. The MPTMS layer had however significant effect on film permeability to redox species (Ru(NH3)6 3+ and ferrocenedimethanol (Fc(MeOH)2)). MPTMS adsorption should be long enough to ensure proper adhesion of the film but not too long to avoid surface blocking or film defects; an optimal time window of 60-600 s soaking in 0.1 mM MPTMS in ethanol was evidenced. In addition, Cu underpotential deposition (UPD) experiments revealed that the silica membrane affected significantly the UPD process, suggesting some barrier effect of the porous membrane, but the interface Au/MPTMS/silica is not sharp and allowed metal UPD between the gold substrate and the silica thin film.
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