THE INTERACTION OF H2O WITH A TIO2(110) SURFACE

The interaction of H2O With rutile TiO2(110) surfaces with different d efect densities (oxygen vacancies) was studied with TPD, work function measurements and XPS. On the nearly perfect surface, a thermal desorp tion 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 f unction change. The heat of adsorption of water in this state is estim ated to be 71-9theta kJ/mol. The coverage of water in this state is es timated from O(1s) signals to be about one per unit cell, or one for e very Ti4+ site. A tail of this peak which extends to 375 K is attribut ed to disproportionation of surface hydroxyl groups present in lower c oncentrations. Higher coverages of water give rise to a TPD peak at 17 0 K, which we attribute to water bound to bridging oxygen anion sites. Finally, multilayer water is populated, which desorbs in a peak at 16 0 K. Surface hydroxyls bound to thermally-induced oxygen vacancies of approximately 1% concentration disproportionate to give a water TPD pe ak at approximately 500 K.