- Email: [email protected]
Photochemical cleavage of H2O by photocatalysis
154 In order to optimize a part of this system, we performed a comparative investigation on the efficiency of some catalysts and we studied the effect of platinum concentration on the rate of hydrogen evolution. Hydrogen evolution was obtained with all the catalysts used, The rate of hydrogen production was found to increase with increasing platinum concentration and to reach a plateau whose value was different for the various catalysts. The results obtained show that the low P)H2values cannot be completely attributed to the low efficiency of the catalysts but are mainly due to the low efficiency of the quenching act leading to free MV+.
Photochemical
cleavage of Hz0 by photocatalysis
E . PELIZZETTI Istituto di Chimica Anaktica, Universitcidi Torino (&a/y) M. VLSCA SIBZT (Montedison), Spinctta Marerrgo (Italy) E. BORGARELLO
and M. GRATZEL
Institut de Chimie Physique, Ecole Pofytechnique Fed&ale de Lausanne, CH-IOIS Luusanne (Switzerland)
Bifunctional redox catalysts composed of platinum and RuOz codeposited onto colloidal semiconductor carriers are highly potent mediators for Hz0 decomposition by visible light. When Ti02 is used as the carrier in a system cuntaining a sensitizer (Ru(bipy)32+) and an electron relay (methyl viologen), the latter is reduced on light excitation and the photoreaction, coupled with catalytic steps, can generate H2 and O2 from HzO. The surprisingly high efficiency of this photoredox system is due to a mechanism involving species adsorbed at the catalyst surface. The use of an amphiphilic surfactant derivative of Ru(bipy)3Z+, which shows an enhanced affinity for adsorption at the particle-water interface, allowed us to observe extremely high activity in promoting the water cleavage process, also in the absence of the electron relay. Adsorption of the sensitizer and electron injection in the conduction band are suggested to explain the observations. In other experiments dispersions of the semiconductor CdS loaded with platinum and RuOz produced H2 and O2 when exposed to visible light. No degradation of the photocatalyst was noted after 60 h of irradiation.
Photochemical
cleavage of Hz0 by photocatalysis
E . PELIZZETTI Istituto di Chimica Anaktica, Universitcidi Torino (&a/y) M. VLSCA SIBZT (Montedison), Spinctta Marerrgo (Italy) E. BORGARELLO
and M. GRATZEL
Institut de Chimie Physique, Ecole Pofytechnique Fed&ale de Lausanne, CH-IOIS Luusanne (Switzerland)
Bifunctional redox catalysts composed of platinum and RuOz codeposited onto colloidal semiconductor carriers are highly potent mediators for Hz0 decomposition by visible light. When Ti02 is used as the carrier in a system cuntaining a sensitizer (Ru(bipy)32+) and an electron relay (methyl viologen), the latter is reduced on light excitation and the photoreaction, coupled with catalytic steps, can generate H2 and O2 from HzO. The surprisingly high efficiency of this photoredox system is due to a mechanism involving species adsorbed at the catalyst surface. The use of an amphiphilic surfactant derivative of Ru(bipy)3Z+, which shows an enhanced affinity for adsorption at the particle-water interface, allowed us to observe extremely high activity in promoting the water cleavage process, also in the absence of the electron relay. Adsorption of the sensitizer and electron injection in the conduction band are suggested to explain the observations. In other experiments dispersions of the semiconductor CdS loaded with platinum and RuOz produced H2 and O2 when exposed to visible light. No degradation of the photocatalyst was noted after 60 h of irradiation.