Efficient Visible-Light-Driven Water Oxidation by a Carbon Nitride Modified with Cobalt Polyoxometalate Molecular Catalyst

Solar-driven CO2 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-C3N4) photocatalysts anchored with a water-insoluble molecular water oxidation catalyst (WOC). The g-C3N4 photocatalysts physisorbed with either the monocobalt polyoxometalate (THA)3CoPOM (THA+ = tetraheptylammonium, CoPOM3– = [CoMo6O24H6]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-C3N4/(THA)3CoPOM 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 C3N4/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%.