HYDROGEN-PRODUCTION FROM WATER BY VISIBLE-LIGHT USING ZINC PORPHYRIN-SENSITIZED PLATINIZED TITANIUM-DIOXIDE

The rate of H-2 evolution from aqueous suspensions of Pt/TiO2 with dep osited zinc porphyrin in the presence of an electron donor (EDTA, trie thanolamine, ascorbic and oxalic acids) during irradiation by visible light (lambda > 520 nm) was optimized with respect to the concentratio ns of platinum, zinc porphyrin and electron donor. The relationship be tween the rate of hydrogen evolution and pH has a maximum at pH 4-5 fo r EDTA, ascorbic and oxalic acids, as does the adsorption of these don ors on TiO2. In the case of triethanolamine, H-2 production increases sharply in alkaline solutions when the triethanolamine molecules are d eprotonated. The photostability of the photosensitizer increases on th e semiconductor. Turn-over numbers for the zinc porphyrins varied from 50 for water-soluble zinc porphyrin up to 150-185 for water-insoluble sensitizers.