Attachment of Pt nanoparticles to a metal oxide surface using a thiol–carboxyl bifunctional molecule

Molecular attachments to platinum have received far less study than binding to gold. Of particular interest is whether the binding of bifunctional molecules, containing both thiol and carboxyl groups, can attach platinum to surfaces such as metal oxides. Attachment of 4-mercaptobenzoic acid (4-MBA) to bulk and nanoparticulate platinum was studied by cyclic voltammetry (CV), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Platinum nanoparticles were attached to TiO2 using 4-MBA and probed for Pt loading and electrocatalytic activity. Currents for reduction and oxidation of a standard redox couple on a Pt wire are sharply decreased when the Pt is previously exposed to 4-MBA, indicating bonding. This effect is not observed for benzoic acid. The absence of the SH stretching vibrational mode in Raman spectra of 4-MBA-modified Pt nanoparticles is consistent with sulfur-bonding of the molecules to the nanoparticle surface. High-resolution XPS studies of S and Pt core electrons show the formation of SPt bonds. Therefore, 4-MBA binds to Pt via the S atom but not via the carboxyl group, enabling Pt attachment to other surfaces such as metal oxides. 4-MBA increased both the amount of Pt bound to a TiO2 surface and the rate of a redox reaction on the surface.