Light induced production of hydrogen from water by catalysis with ruthenium melanoidins

A ruthenium containing melanoidin (a condensation product of amino acids and carbohydrates) was found to photocatalyze hydrogen production from water under light irradiation with λ<320 nm, in the presence of EDTA as an electron donor and methyl viologen as an electron relay. Tracer experiments indicate that the hydrogen evolved originates from water. The bimolecular quenching constant for the quenching of melanoidin fluorescence by methyl viologen is large (kθ∼109) suggesting a diffusion controlled reaction rate. The small Stern–Volmer constant (Ksv∼10) indicates an inefficient electron transfer between the excited melanoidin and the methyl viologen, perhaps due to the difficulties in removing O2 from the polymer. The Ru-melanoidin photocatalyst is stable under prolonged irradiation times and, due to its insolubility in water, is suitable for recycling.