A novel sulfur-assisted annealing method of g-C3N4 nanosheet compensates for the loss of light absorption with further promoted charge transfer for photocatalytic production of H2 and H2O2

[Display omitted] •A novel co-annealing method was developed for the preparation of sulfur doped g-C3N4.•The prepared SS-CN exhibits enhanced optical absorption, charge separation and surface charge transfer.•DFT calculations revealed the mechanism by which S-doping regulates band structure and charge distribution.•The SS-CN photocatalyst has highly enhanced capacity of H2 evolution and H2O2 production. Exfoliating g-C3N4 into 2D nanosheet to minimize the stacking layer for the improvement of charge transfer and separation is considered to be the effective measure to enhance its photocatalytic performance. However, no matter what method is used, the exfoliated g-C3N4 nanosheet shows decreased optical absorption compared to the pristine bulk-like one. In this work, a simple one-step sulfur doping method is proposed on the basis of exfoliated g-C3N4 nanosheet, which can directly regulate the band structure of g-C3N4 and enhance its optical absorption ability. The proposed sulfur doping method redshift the light absorption edge of g-C3N4 nanosheet to the level of pristine bulk-like g-C3N4, and even induce the generation of a new n→π* absorption band. In addition, the introduced sulfur doping site can form a local electron accumulation point, so that to further improve the charge separation efficiency and surface charge transfer ability of g-C3N4 nanosheets.