Solid phase photoreduction of methylviologen adsorbed on cellulose

Abstract

There has been a growing interest in photochemical reduction of methylviologen (1,1′-dimethyl-4,4′-dipyridinium dichloride; MV²⁺) as a means of solar energy conversion^1–4, because the cation radical (MV^+˙) can reduce protons to give hydrogen gas⁵. One problem in a photochemical conversion system is the effective separation of the reaction products, because a photochemical reaction in a homogeneous solution usually accompanies a spontaneous backward reaction which consumes the acquired energy. To overcome this problem, macro- or micro-heterogeneous reaction environments such as micelle^6–9 or liposome¹ have been proposed. A solid phase photochemical reaction must also be useful for constructing an effective photoenergy conversion system. We describe here how MV²⁺ adsorbed on solid cellulose could be photoreduced to give MV^+˙, the colour of the cellulose changing from white to deep blue. The reaction could be sensitized by tris(bipyridyl)ruthenium(II) complex (Ru(bpy)₃) and EDTA.