S-Modified Graphitic Carbon Nitride with Double Defect Sites For Efficient Photocatalytic Hydrogen Evolution.

Graphitic carbon nitride (gCN) is an attractive photocatalyst for solar energy conversion due to its unique electronic structure and chemical stability. However, gCN generally suffers from insufficient light absorption and rapid compounding of photogenerated charges. The introduction of defects and atomic doping can optimize the electronic structure of gCN and improve the light absorption and carrier separation efficiency. Herein, the high efficiency of carbon nitride photocatalysis for hydrogen evolution in visible light is achieved by an S-modified double-deficient site strategy. Defect engineering forms abundant unsaturated sites and cyano (─C≡N), which promotes strong interlayer C─N bonding interactions and accelerates charge transport in gCN. S doping tunes the electronic structure of the semiconductors, and the formation of C─S─C bonds optimizes the electron-transfer paths of the C─N bonding, which enhances the absorption of visible light. Meanwhile,C≡N acts as an electron trap to capture photoexcited electrons, providing the active site for the reduction of H to hydrogen. The photocatalytic hydrogen evolution efficiency of SDCN (1613.5 µmol g h) is 31.5 times higher than that of pristine MCN (51.2 µmol g h). The charge separation situation and charge transfer mechanism of the photocatalysts are investigated in detail by a combination of experimental and theoretical calculations.