Photoreduction of Thiosulfate in Semiconductor Dispersions

Conduction band electrons produced by band gap excitation of TiO₂-particles reduce efficiently thiosulfate to sulfide and sulfite. documentclass{article}pagestyle{empty}begin{document}$ {rm 2e}_{{rm cb}}^ - ({rm TiO}_{rm 2}) + {rm S}_{rm 2} {rm O}_3^{2 - } longrightarrow {rm S}^{2 - } + {rm SO}_3^{2 - } $end{document} This reaction is confirmed by electrochemical investigations with polycrystalline TiO₂-electrodes. The valence band process in alkaline TiO₂-dispersions involves oxidation of S₂O to tetrathionate which quantitatively dismutates into sulfite and thiosulfate, the net reaction being: documentclass{article}pagestyle{empty}begin{document}$ 2{rm h}^{rm + } ({rm TiO}_{rm 2}) + 0.5{rm S}_{rm 2} {rm O}_{rm 3}^{{rm 2} - } + 1.5{rm H}_{rm 2} {rm O} longrightarrow {rm SO}_3^{2 - } + 3{rm H}^{rm + } $end{document} This photodriven disproportionation of thiosulfate into sulfide and sulfite: documentclass{article}pagestyle{empty}begin{document}$ 1.5{rm H}_{rm 2} {rm O } + 1.5{rm S}_{rm 2} {rm O}_{rm 3}^{{rm 2} - } mathop to limits^{hnu} 2{rm SO}_3^{2 - } + {rm S}^{{rm 2} - } + 3{rm H}^{rm + } $end{document} should be of great interest for systems that photochemically split hydrogen sulfide into hydrogen and sulfur.