RuIII-edta (edta4− = ethylenediaminetetraacetate) mediated photocatalytic conversion of bicarbonate to formate over visible light irradiated non-metal doped TiO2 semiconductor photocatalysts

Abstract

Reported in this paper is the first example of a ruthenium(III) complex, [Ru^III(edta)] (edta⁴⁻ = ethylenediaminetetraacetate), that catalyzes the conversion of bicarbonate to formate selectively over a visible light irradiated surface of carbon, nitrogen and sulfur doped TiO₂ (represented as C–TiO₂, N–TiO₂ and S–TiO₂, respectively) semiconductor photocatalyst particles. Formation of formate, the only reduction product, was identified by ¹³C NMR analysis of the reaction mixture. Based on the experimental findings a working mechanism involving activation of bicarbonate (HCO₃⁻) through the formation of a [Ru^III(edta)(HCO₃)]²⁻ intermediate complex followed by the photochemical reduction of the coordinated bicarbonate to produce formate at the surface of non-metal (C, N, S) doped TiO₂ semiconductor particles is proposed. The efficacy of bicarbonate reduction over such photocatalysts decreased in the following order C–TiO₂ > N–TiO₂ > S–TiO₂.