INFLUENCE OF PH AND SURFACE COMPLEXES ON THE RATE OF HYDROGEN EVOLUTION FROM PHOTOCATALYTIC SYSTEMS PT TIO2-ELECTRON DONOR/

The initial rate of hydrogen evolution from aqueous deoxygenated suspe nsions of platinized titanium dioxide in the presence of an electron d onor (ascorbic, benzoic, oxalic acids, triethanolamine) during irradia tion by UV light depends on the pH values of the suspensions for all e lectron donors. The relationships between the rate of hydrogen evoluti on and pH have maxima at pH 1-2 (oxalic acid), pH 3 (benzoic acid), pH 4-5 (ascorbic acid) and pH>7 (triethanolamine). The rate of hydrogen evolution is a function of the surface concentration of the electron d onor on TiO2 for ascorbic and benzoic acids. The effect of pH on the r ate of hydrogen evolution for oxalic acid and triethanolamine is conne cted with the different oxidation rates of various forms of the electr on donor. Photo-induced dissolution of Ti2 is observed in the presence of oxalic acid. Ascorbic acid, the products of the photo-oxidation of benzoic acid, form surface charge transfer complexes with the titaniu m ions on TiO2.