Reactivity of Rutile with Oxygen and Hydrogen and Related Charge Transfer

The present work reports the effect of the gas phase including oxygen and an argon-hydrogen mixture on the surface electrical properties of TiO2 (rutile) at 1073 and 298 K. The effect of the gas-phase composition on the electrical properties was monitored using work function measurements. It was found that oxidation of rutile at 1073 and 298 Kin oxygen results in oxygen incorporation and oxygen chemisorption, respectively. In both cases, oxidation leads to a work function increase. On the other hand, exposure of rutile at 298 K to a gas phase involving argon and hydrogen results in the formation of the H4TiO4 surface structure, leading to a work function decrease. The obtained work function data, along with the data on surface photovoltage spectroscopy (reported elsewhere), indicate that the reactivity and photoreactivity of rutile with oxygen are closely related to its defect disorder and the related semiconducting properties.