Competitive adsorption of sensitizer and electron transfer agent in an aqueous photolysis system

Tris(2,2'-bipyridine)ruthenium(II) dichloride, ru2+, and methylviologen, mv2+, have been shown to adsorb strongly onto negative surfaces of silica and dhp vesicles. When both ru2+ and mv2+ are present in an aqueous solution mv2+ demonstrates the higher affinity for adsorption. The distribution of ru2+ and mv2+ between the 'adsorbed' and 'bulk solution' states has been found to dramatically affect hydrogen production from a photolysis mixture in which these components function as sensitizer and electron transfer reagent, respectively. In the adsorbed state, charge separation is diminished and reaction of mv+ with platinum catalyst retarded. Enhanced adsorption of mv2+ may render that left in solution more prone to hydrogenation at the metal catalyst surface.