In situ infrared technique for studying adsorption onto particulate silicasurfaces from aqueous solutions

An in situ infrared technique is described which allows the detection of ad sorbed surface species on metal oxide particles in an aqueous environment, The technique involves first formulating a "coating" comprised of high-surf ace-area silica particles and a polymeric binder in a suitable solvent, The resulting coating is applied to the surface of an internal reflection elem ent and mounted in a flow-through attenuated total reflection (ATR) apparat us, The technique is demonstrated with a ZnSe element coated with fumed sil ica particles in a polyethylene (PE) matrix, Access of the silica surface i n the matrix to adsorbates was evaluated by comparing the gas-phase reactio n of silanes on silica/PE-coated CsI windows in transmission with silica/PE -coated ZnSe in an ATR evacuable cell, It is shown that the PE weakly pertu rbs about 25% of the surface hydroxyl groups, and that all surface groups a re available for reaction with silanes, The silica/PE is indefinitely stabl e in an aqueous environment and has advantages of at least 2 orders higher sensitivity and a wider spectral range over studies using oxidized silicon wafers, The usefulness of this technique for studying adsorption on metal o xide surfaces is demonstrated with the reaction of succinic anhydride on an aminosilanized silica surface, This reaction sequence is a common method u sed to prepare glass surfaces in the attachment of probe oligonucliotides f or microarray biochip technology.