Photocatalytic Hydrogen-Generation from Sucrose Using Polyoxotungstate Nano-Clusters

Abstract

The photocatalytic reaction of polyoxotungstate [BW12O40]5-, [SiW12O40]4-, [PW12O40]3- and [AsW9O33]9- led to the generation of hydrogen gas from aqueous sucrose solution under irradiation of UV light. These photoreactions for each polyoxotungstate were investigated for dependence of pH level and it was displayed that hydrogen gas was obtained at low pH (around pH 2-3) without heterogeneous cocatalyst such as platinum or RuO2. The colorless solutions changed to blue-colored solution called heteropoly blue. It indicated that one- or two-electron reduced species were produced with accompanying dehydrogenation of sucrose. Especially, the reaction of [SiW12O40]4- and [BW12O40]5- resulted in the generation of hydrogen gas with a higher yield than others. UV spectra of [SiW12O40]4- and [BW12O40]5-aqueous solution in the presence of sucrose exhibited two absorption peaks around 490 and 730, and 495 and 695 nm, respectively. The intensity increased with elapsing time of UV light irradiation. Moreover, prolonged photolysis of [BW12O40]5- with sucrose gave rise to a decrease of these absorption peaks for the UV spectra of solutions at each pH level, and bluecolored solution changed to brown after irradiation for 10 days. In addition, the photolysis of 1.9 mM solutions of [BW12O40]5- and [SiW12O40]4- were carried out in the presence of sugarcane juice at pH 2 level, and 0.15 ml and 0.51 ml of hydrogen gas were obtained from 60 ml of sugarcane juice, respectively.