The electronic properties of titanium dioxide (Ti O2) nanocrystalline films, which were prepared by dip coating from Degussa P25 photocatalyst aqueous suspension, have been investigated by surface photovoltage spectroscopy (SPS). As indicated by the positive contact potential difference (CPD) change in the sub-band-gap region, SPS shows that the molecularly adsorbed H2 O in the freshly prepared P25 film creates an empty electron state, which is distributed within 0.79 eV below the conduction band edge, and acts as an electron trap and carrier recombination center. With film aging or under a drying atmosphere, the H2 O -associated state diminishes, and the occupied electron state due to molecularly adsorbed oxygen, lying within 1.06 eV above the valence band edge, is identified by the reversed polarity of the CPD change in the sub-band-gap region. This information is important in developing a better understanding of real photocatalyst behavior.
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One of the authors (J.Y.) is grateful to all colleagues for their kind help in his research at Otago. The authors acknowledge support from the MacDiarmid Institute for Advanced Materials and Nanotechnology and the University of Otago. The authors are grateful to Professor Y. Shapira and Dr. Y. Zidon for critical reading of the paper.