THE INTERACTION OF H2O WITH A TIO2(110) SURFACE

The interaction of H2O With rutile TiO2(110) surfaces with different defect densities (oxygen vacancies) was studied with TPD, work function measurements and XPS. On the nearly perfect surface, a thermal desorption peak is observed at 250-300 K which is attributed to molecularly adsorbed H2O at Ti4+ sites based on its O(1s) peak position and work function change. The heat of adsorption of water in this state is estimated to be 71-9theta kJ/mol. The coverage of water in this state is estimated from O(1s) signals to be about one per unit cell, or one for every Ti4+ site. A tail of this peak which extends to 375 K is attributed to disproportionation of surface hydroxyl groups present in lower concentrations. Higher coverages of water give rise to a TPD peak at 170 K, which we attribute to water bound to bridging oxygen anion sites. Finally, multilayer water is populated, which desorbs in a peak at 160 K. Surface hydroxyls bound to thermally-induced oxygen vacancies of approximately 1% concentration disproportionate to give a water TPD peak at approximately 500 K.