Stability of surface complexes formed at the TiO2/water interface

TiO2 surface complexation by bidentate organic ligands is analysed in terms of the ligand Bronstead and Lewis basicities. The complexation and basicity constants comply with linear Gibbs Energy relationships (LGERs). For dicarboxylic acids, the surface chelate bond makes an approximately constant contribution to the stability. The proton transfer to the surface modulates the pH dependence of stability. A correlation exists between the surface complexation constant of the neutral acid H2L and the ligand first acidity constant. On the other hand, the surface complexation constants of dianions L2- of cathecols and aminophenols are positively correlated with the ligand second acidity constant. Apparent stability is determined by the competition of H+ and surface metal ions for the ligand. Stability trends are strongly influenced by the Bronstead acid base reaction between the acid ligands H2L and the surface, whereas the stability of the surface chelate contributes to the overall stability.