Immobilization of nanobeads on a surface to control the size, shape, and distribution of pores in electrochemically generated sol–gel films

Abstract

Electrochemically assisted deposition of an ormosil film at a potential where hydrogen ion is generated as the catalyst yields insulating films on electrodes. When the base electrode is modified with 20-nm poly(styrene sulfonate), PSS, beads bound to the surface with 3-aminopropyltriethoxysilane (APTES) and using (CH3)3SiOCH3 as the precursor, the resulting film of organically modified silica (ormosil) has cylindrical channels that reflect both the diameter of the PSS and the distribution of the APTES-PSS on the electrode. At an electrode modified by a 20-min immersion in 0.5 mmol dm-3 APTES followed by a 30-s immersion in PSS, a 20-min electrolysis at 1.5 V in acidified (CH3)3SiOCH3 resulted in an ormosil film with 20-nm pores separated by 100 nm. Cyclic voltammetry of Ru(CN)64- at scan rates above 5 mVs-1 yielded currents controlled primarily by linear diffusion. Below 5 mVs-1, convection rather than the expected factor, radial diffusion, apparently limited the current.

Electroanalysis based on stand-alone matrices and electrode-modifying films with silica sol-gel frameworks: a review

“…These data suggest that the nanopores are perpendicular to the electrode surface. In addition, transmission electron spectroscopy of a cross-section of the ormosil film gave images in agreement with the model [33]. Further evidence of the cylindrical shape was obtained by layer-by-layer assembly of RuOCN and ZrO 2 in 50-nm pores [36] where RuOCN is mixed-valent ruthenium oxide with oxycyano crosslinks that is electrochemically synthesized by cyclic voltammetry of a K 4 Ru(CN) 6 , RuCl 3 mixture [42].…”

“…Cyclic voltammetry of 1.0 mmol dm −3 Ru(CN) 6 4− in 1.0 mol dm −3 KCl showed radial diffusion as the current limiting factor at scan rates below 5 mV s −1 , which was expected for the thickness (pore depth), ca. 200 nm, of the film [33], i.e., the time for diffusion down the pore for a species with a diffusion coefficient of 10 −6 cm 2 s −1 is not a factor in limiting the current in this scan rate range. These and related results suggest potential utility of this method of fabricating a nanopore array.…”

“…Second, the electrode with submonolayer coverage of these islands was immersed in a sol, and electrochemically assisted processing of gelation was performed. As a result, catalysis of sol-gel processing by H + occurred only where these islands were absent [32,33]. Acid catalysis results in linear chains of -Si-O- [12], which in this case grow out from the electrode surface.…”

“…A more direct test of the above hypothesis was by depositing the film on an electrode that was pretreated by binding a sub-monolayer distribution of PSS nanobeads to its surface [32,33,36,37]. Initially, a sub-monolayer of APTES was adsorbed.…”

Electrogeneration of non-electroactive and non-conducting materials: a counterintuitive concept for the functionalization and nanostructuration of electrode surfaces

“…An interesting approach is the controlled growth of sol-gel matrices with different thickness and functional groups as nanoparticle imprinted thin films on electrodes that are likely to recognize and detect selectively gold nanoparticles based on their dimensions [196]. The electrochemical generation of sol-gel films can be also performed in the presence of polymeric nanobeads, leading to their entrapment in the inorganic coatings, and their subsequent dissolution leads to pore formation and enhanced mass transport of the resulting porous films [197]. • Fifthly, adding molecules or biomolecules and even microorganisms in the starting sol enables in principle their entrapment in the film during the formation of the silica framework.…”