Surface Structures of 4-Chlorocatechol Adsorbed on Titanium Dioxide

Abstract

TiO2 has been extensively studied as a photocatalyst for the complete oxidation of a variety of organic pollutants commonly found in groundwater. In this paper, we investigate the surface structures formed between an organic substrate and TiO2 in the context of understanding how these specific surface interactions affect photoreactivity. The surface complexes formed by 4-chlorocatechol (CT) sorbed on TiO2 are investigated as a function of concentration and of pH. Singular-value decomposition of the IR spectra of CT adsorbed on TiO2 indicates that a single bidentate chemisorbed species is present over the pH range of 2−10. The surface-bound species appears to have 40% covalent and 60% ionic bond character. The pH dependence of the adsorption isotherms is modeled using a generalized electric double-layer approach. The data are consistent with the formation of a bidentate binuclear surface group for solution CT concentrations below 50 μM followed by nonspecific multilayer partitioning at concentrations above 100 μM.