Photobiocatalytic production of hydrogen using sensitized TiO 2–MV 2+ system coupled Rhodopseudomonas capsulata

Abstract

Intact cells of Rhodopseudomonas capsulata, as photocatalyst for hydrogen production using light of λ>400 nm, were added to a slurry of naked or sensitized TiO 2 semiconductor containing MV 2+ as an electron relay. It is discussed that the nitrogenase enzyme of the bacterial cells is responsible for catalyzing hydrogen production. Sensitization of TiO 2 was performed in three 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., TiO 2/MV 2+/electron donor/bacterial cells, each of the last three components has its own specific function and each facilitates the others' role, thereby enhancing the yield of hydrogen production. It was found that with sensitized TiO 2, there is a higher amount of hydrogen production than with the naked TiO 2. Among the sensitizers used, Rhodamine B and Ru(bpy) 3 2+ exhibited higher efficiencies compared with other sensitizers, as well as other method of sensitization (2 and 3). The effects of electron donors, divalent metal ions (Mn 2+, Mg 2+ and Ca 2+) to the above system were also studied. Suitable mechanisms and schematic models are proposed, in accordance with the observations, for the different kinds of catalytic systems employed in the present study.