Photobiocatalysis: hydrogen evolution using a semiconductor coupled with photosynthetic bacteria

Abstract

Photobiocatalytic production of hydrogen in the presence of Bi2O3 semiconductor, methyl viologen (MV2+) as an electron mediator and three different bacteria (Rhodopseudomonas capsulata, Rhodospirillum rubrum and Escherichia coli) as hydrogen evolution enzyme catalysts has been carried out in different environments. Addition of intact bacterial cells is found to increase the hydrogen production efficiency. It has been suggested that the nitrogenase enzymes of the bacterial cells catalyze the hydrogen evolution process rather than the hydrogenase enzymes of the bacteria. The presence of carbohydrates (fructose, dextrose and starch) and organic acids (oxalic acid, EDTA and ascorbic acid) as electron donors with the above system further enhances the hydrogen production efficiency due to the reaction of photogenerated valence band holes of the semiconductor with these substrates, thereby preventing the e−-h+ recombination. The effects of loading the semiconductor with RuO2 and Rh2O3 and addition of divalent metal ions, Ca2+, Mg2+ and Mn2+ to the system towards hydrogen production efficiency were also studied and discussed