Preparation and enhanced photocatalytic performance of sulfur doped terminal-methylated g-C3N4 nanosheets with extended visible-light response

Sulfur atom doping has been utilized to optimize the electronic band structure of g-C3N4; however, most doping can reduce the bandgap by no more than 0.2 eV, corresponding to an improved optical absorption of only about 36 nm. Herein, sulfur doped terminal-methylated g-C3N4 nanosheets (SMCNs) with a tunable bandgap have been prepared for the first time by employing thioacetamide as both the sulfur source and blocking agent. Experimental and DFT studies identify that introducing methyl into the melon framework not only acts as a blocking group during the polymerization reaction to generate the structure edge defects, but also reduces the energy barrier of sulfur atom doping. Specifically, doping sulfur atoms into the methylated melon units can split the valence band near the Fermi level to generate a new empty midgap electronic state, which leads to a significant decrease of the bandgap by about 0.7 eV and extends the light-responsive region up to 700 nm. Moreover, due to the changed local charge distribution and lattice strain, the resulting internal electric field is beneficial for the separation of electron-hole pairs. Thus, the as-synthesized SMCNs exhibit an outstanding photocatalytic performance in the degradation of reactive dyes and photocatalytic H2 generation.