Efficient Visible-Light-Driven Water Oxidation by a Carbon Nitride Modified with Cobalt Polyoxometalate Molecular Catalyst
Yuki Tomita, Natsuki Taira, Ken Sakai, Hironobu Ozawa
Abstract
Solar-driven CO 2 reduction coupled with water oxidation (WO) is regarded as one of the most ideal methodologies to solve global warming and environmental problems. Toward the development of such human technologies, it is crucial to greatly improve the efficiency in the photocatalytic WO, which is considered as a bottleneck reaction. Here we report on the two hybrid photocatalysts for visible-light-driven WO by using graphitic carbon nitride (g-C 3 N 4 ) photocatalysts anchored with a water-insoluble molecular water oxidation catalyst (WOC). The g-C 3 N 4 photocatalysts physisorbed with either the monocobalt polyoxometalate (THA) 3 CoPOM (THA + = tetraheptylammonium, CoPOM 3– = [CoMo 6 O 24 H 6 ] 3– ) or cobalt tetraphenylporphyrin ( CoTPP ) are developed and their photocatalytic WO performances are investigated in the presence of the sacrificial hole donor Ag + . The g-C 3 N 4 /(THA) 3 CoPOM photocatalyst is found to exhibit higher activity by achieving an optimum turnover frequency of 15.8 h –1, which turns out to be the highest among the C 3 N 4 /WOC photocatalysts reported to date. Moreover, due to the photocatalytic performance of this hybrid photocatalyst, the external quantum yield is successfully determined to be ca. 0.01%.