Photochemical reduction of methyl viologen in silicate xerogels obtained by the sol–gel process

Mixture of ruthenium (II) tris-bipyridine complex (Ru(bpy)32+ –– photosensitizer), methyl viologen (MV2+ –– electron acceptor) and EDTA (sacrificial electron donor) has been immobilized in silicate xerogels obtained by the sol–gel technique. Mixtures of Ru(bpy)32+, MV2+ and EDTA are capable of formation of the blue photoreduced MV.+ cation radical in aqueous solutions upon UV (around 280 nm) or visible (around 450 nm) excitations. However, when entrapped in silicate xerogels they do not exhibit blue coloration at all. On the other hand, UV excitation of xerogels doped only with MV2+ results in appearance of blue color indicative of the paraquat photoreduction. It has been shown that in the case of the xerogel-entrapped methyl viologen the source of the reducing photoelectron is ethanol. The alcohol molecules are produced during the tetraethoxysilane (precursor) hydrolysis step of the silicate matrix production occurring via the sol–gel process.