Immobilized enzymes on semiconducting powder: photogeneration of H2 by TiO2 and CdS bound hydrogenases

Four bacterial hydrogenases were immobilized on TiO 2 and CdS powders. On irradiation of these semiconductor-enzyme particles with a sunlight simulator in the presence of an electron donor and an electron mediator, H 2 was evolved from water at rates comparable to those obtained in platinum-catalyzed photolytic reactions. However, no direct electron transfer from the conduction band of the supporting semiconductor to the active center of the enzyme has been observed. Methylviologen, as well as two of its amphiphilic analogs have been found to mediate this transfer efficiently.