Synthesis of bio-inspired mononuclear nickel hydrogen production catalysts and photocatalytic efficiency improvement with porphyrin covalently functionalized graphene nanohybrid

Abstract

Eight nickel complexes with chelating N-substituted bis(diphenylphosphanyl)amine and 1,2-benzenedithiolate or 3,4-toluenedithiolate, [RN(PPh2)2]Ni(1,2-SC6H4S) [R=CH(CH3)2, 1; CH2CH(CH3)2, 2; CH2CH2CH2CH3, 3; CH2Ph, 4] and [RN(PPh2)2]Ni[3,4-SC6H3(CH3)S] [R=CH(CH3)2, 5; CH2CH(CH3)2, 6; CH2CH2CH2CH3, 7; CH2Ph, 8], were synthesized and structurally characterized. The measurement of the electrochemical properties revealed that complex 4 can catalyze protons to hydrogen (H2) under weak acidic conditions. Complex 4 can also be used as a molecular catalyst for light-driven H2 evolution with a proton source, a photosensitizer, and an electron donor. Furthermore, by using tetraphenylporphyrin (TPP) amide-covalently functionalized graphene oxide (GO) nanohybrid (TPP-NH-GO) as a photosensitizer, the efficiency of photocatalytic H2 production of complex 4 in aqueous ethanol solution had been astonishingly improved over than for the photocatalytic systems without GO. This result suggests that the excellent properties of GO with respect to electron transfer, surface area, adsorptivity, and hydrophilicity may promote the performance of the photocatalytic H2 production system to a certain extent.