Titanium dioxide as photocatalyst in hydrogen production

Photoproduction of hydrogen in aqueous suspensions of titanium dioxide was studied in the presence of organic electron donors. Hydrogen evolved when the following electron donors were used: tris(oxymethyl)aminomethane, triethanolamine, ethanol, glycerol, glucose and EDTA. The quantum yields reached 5 • 10 -3 H 2 molecules per quantum. With cysteine, dithiotreitol, methylamine, and urea no photoproduction of hydrogen was observed, but hydrogen evolved when bacterial hydrogenase was introduced into the system. The efficiency of hydrogen photoproduction was compared to that of the methylviologen photoreduction sensitized by TiO 2 . When electron donors efficient in hydrogen photoproduction were used methylviologen was reduced to the level of the dipyridyl dihydroform, which indicated the generation of a reduction potential up to -0.8 V. If cysteine, dithiothreitol, or methylamine was used as electron donor, methylviologen was reduced only to the level of the blue cation radical (E ’ 0 = - 0.446 V); in this case hydrogenase was required for hydrogen evolution.