Photobiocatalytic production of hydrogen using sensitized TiO2-MV2+ systemcoupled Rhodopseudomonas capsulata

Intact cells of Rhodopseudomonas capsulata, as photocatalyst for hydrogen p roduction using light of lambda > 400 nm, were added to a slurry of naked o r sensitized TiO2 semiconductor containing MV2+ as electron relay. It is di scussed that the nitrogenase enzyme of the bacterial cells is responsible f or catalyzing hydrogen production. Sensitization of TiO2 was performed in t hree ways: (1) using organic dyes, (2) using Cu(II) ion doping, (3) loading with low-band gap semiconductors (CdS). In the four components, i.e., TiO2 /MV2+/electron donor/bacterial cells, each of the last three components has its own specific function and each facilitates the others' role, thereby e nhancing the yield of hydrogen production. It was found that with sensitize d TiO2 there is a higher amount of hydrogen production than with the naked TiO2. Among the sensitizers used, Rhodamine B and Ru(bpy)(3)(2+) exhibited higher efficiencies compared with other sensitizers, as well as other metho d of sensitization (2 and 3). The effects of electron donors, divalent meta l ions (Mn2+, Mg2+ and Ca2+) to the above system were also studied. Suitabl e mechanisms and schematic models are proposed, in accordance with the obse rvations, for the different kinds of catalytic systems employed in the pres ent study. (C) 2000 Elsevier Science B.V. All rights reserved.