Interaction of molecular oxygen with oxygen vacancies on reduced TiO2: Site specific blocking by probe molecules

A heterogeneity of surface sites for superoxide ( O 2 - ) stabilization on thermally reduced TiO2 (P25) have been identified by cw EPR. Two main groups of adsorption sites exist; site I due to O 2 - adsorbed at oxygen vacancies, [ Vac ⋯ O 2 - ] , and sites II–III due to O 2 - adsorbed at five co-ordinate Ti4+ centres. Electron transfer from the precursor Ti3+ centres to O2 (forming O 2 - ) can be prevented at each site through selective site blocking with probe molecules (CO2 and Ar). CO2 preferentially adsorbs at the five co-ordinate Ti non-vacancy 3 + centres, while Ar preferentially adsorbs at the Ti3+ centres associated with the oxygen vacancies ( Ti vacancy 3 + ) .