Doping mechanism of S, O co-doped in nitrogen vacancy defect rich g-C3N4 nanosheet photocatalyst

S and O elements doped g-C3N4 nanosheets samples were prepared by calcinating the supramolecular precursor obtained by self-assembly of melamine and cyanuric acid by one-step double crucible method. In the O/S single-element doped sample, doping narrows the layer spacing of g-C3N4. While in the S, O co-doped sample, the phenomenon disappears due to the compensation effect of S and O atoms in adjacent layers. In the g-C3N4 sample doped with O/S single element, the O atom replaces the N atom of sp2 hybrid, and the S atom replaces the C atom of sp2 hybrid. In the S, O co-doped sample, the O atom replaces the N atom of sp2 hybrid, while the S atom replaces the C atom of sp2 hybrid, which greatly increases the electron concentration. The 3 d orbitals of S atoms in the co-doped g-C3N4 sample act as both donor and acceptor levels, contributing to the separation of photo-generated electrons and holes. Therefore, the S, O co-doped g-C3N4 sample shows the best photocatalytic performance.