Photoactivity of nanocrystalline TiO2 films is shown to be strongly affected by the presence in aqueous solution of salicylic acid, known to form Ti(IV)salicylate surface complexes. In particular, the photooxidation of methanol - an effective hole scavenger - at TiO2 appears to be in part, or even completely inhibited by the additions of increasing amounts of salicylic acid. The chemisorption of salicylic and also phthalic acid on TiO2, was followed using quartz crystal microbalance, QCM. The observed resonant frequency changes of the quartz crystal bearing TiO2, films, accompanying increasing additions of the benzoic acids to the contacting solutions, indicate large displacement of water as a consequence of the adsorbent-imparted hydrophobicity of the interface. (C) 2002 Elsevier Science B.V. All rights reserved.