Photo-induced Water Oxidation By Ru Complexes

With the continuous development of society, the consumption of fossil fuel such as coal, oil increased by years. The approaching depletion of traditional fossil fuel and the severity of environmental pollution have made it very apparent that it is time human society find new clean and sustainable energy sources to replace traditional fossil fuel. As is known to all, solar energy and hydrogen energy are wealth and clean sources, so the rational use of solar energy and hydrogen have attracted more and more attentions all over the world.Artificial photosynthesis is considered to be an effective way to solve the energy demand, the ultimate goal is the conversion of solar energy into chemical energy. During the process of water splitting, the half-reaction of water oxidation that describes the conversion of 2H2O into O2 and 4H+, is the vital step to limit the hydrogen production. There are two technical problems in artificial photosynthetic water oxidation reaction. Firstly, designing an efficient, stable and cheap water oxidation catalyst is considered critical. Secondly, to build an efficient system for photo-induced water oxidation is desperately needed.On the basis of 2,2’-alpyridine-6,6’-diphenyl and imidazole, mononuclear Ru catalyst Ru(bpyridylbzim)(pic)2 (C 1) (bpyridylbzim= 2,2’-alpyridine-6,6’ diphenyl and imidazole, pic= 4-methyl pyridine) was designed and synthesized. Chemical catalytic water oxidation measurement was conducted in an acidic solution with [Ce(NH4)2(NO3)6] as a chemical oxidant, the turnover number(TON) of C 1 is obtained to be 65. In addition, photochemical water oxidation measurement was carried out in pH=6.8 phosphate buffer solution containing 10% CH3CN with C 1 as catalyst, [Ru(bpy)2(dcb)]2+(PS 1) (deb=4,4’-two carboxyethyl -2,2’-al pyridine) as photosensitizer, Na2S2O8 as an electron acceptor, the TON based on C 1 is found to be 8. These results display the catalyst C 1 possesses activity on both chemical and photochemical.To construct an efficient system for photo-induced water oxidation, several photochemical systems were built with [Ru(bda)(isoq)2] (C 2) (H2bda= 2,2’-alpyridine-6, 6’-dicarboxylic acid, isoq=isoquinoline) as catalyst, [RuⅡ(bpy)2(tpphz)](PF6)2 (PS 2) (bpy=2, 2’-bipyridine, tpphz=tetrapyrido[3,2-a:2’,3’-c:3",2"-h:2’",3’"-j]phenazine) and PS 1 as photosensitizers, Na2S2O8 as an electron acceptor. Even the oxidation potential of PS 1 is higher than that of PS 2, in pH=6.8 phosphate buffer solution containing 10% CH3CN, the system with PS 2 showed a higher photocatalytic activity than that with PS 1. The possible reason should be that the π-π aromatic supramolecular interactions between PS 2 and C 2 increase the effective electron transfer rate, therefore, the efficiency of photocatalytic water oxidation was improved to some extent.