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 suspensions of platinized titanium dioxide in the presence of an electron donor (ascorbic, benzoic, oxalic acids, triethanolamine) during irradiation by UV light depends on the pH values of the suspensions for all electron donors. The relationships between the rate of hydrogen evolution 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 donor on TiO2 for ascorbic and benzoic acids. The effect of pH on the rate of hydrogen evolution for oxalic acid and triethanolamine is connected with the different oxidation rates of various forms of the electron 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 titanium ions on TiO2.