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A novel C3N4-CDot composite photocatalyst was very recently shown to be highly efficient and very stable in water splitting by solar radiation without using any sacrificial reagent (J. Liu, et al., Science, 2015, 347(6225), 970). This photocatalyst utilizes a two-electron/two-step process in which the production of H2O2 and H2 is photocatalyzed by using C3N4 in the first step and H2O2 is decomposed by using CDots in the second step. The present work is a study on the generality of this approach by application of a C3N4/MnO2 catalyst. This new catalyst indeed splits water by a two step process in a stable way, without any sacrificial agent. It was however found that though the absorbance of the new catalyst in the visible range of 500-600 nm is much larger than that of the C3N4-CDot catalyst, its water splitting efficiency is much lower. These findings add insight into and assist in the further optimization of this new class of photocatalysts to meet the requirements of commercial water splitting systems.

The coordinatively unsaturated metal sites (CUMSs) have attracted widespread attention for enhancing catalytic activity. This study reports a controllable “bibonding” method to construct the coordinatively unsaturated Zni+ (0 < i < 2) active sites by forming N(g‐C3N4)‐Zn—N(imidazole) under mild experimental conditions. The catalysts with Zni+ are used for the photo‐Fenton reaction to degrade methylene blue (MB) without any oxidant. The degradation efficiency is positively correlated with Zni+. The Zni+ improved the Fe2+/Fe3+ conversion efficiency and the H2O2 generation ability of the catalyst. The optimized catalysts with 2.27% of Zni+ present a photo‐Fenton degradation efficiency of MB as 73.45 mg g−1 at pH 7 and 78.54 mg g−1 at pH 4. This strategy can be used to construct CUMSs for a series of narrow bandgap semiconductor materials containing nitrogen atoms.

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