Nitrogen self-doped g-C3N4 nanosheets with tunable band structures for enhanced photocatalytic tetracycline degradation

Metal-free g-C3N4 is always limited by low surface area, rapid charge recombination and limited visible light absorption. In this study, novel porous nitrogen self-doped g-C3N4 nanosheets were prepared by a combination of N self-doping and thermal exfoliation process. Compared to the bulk g-C3N4, N self-doped g-C3N4 nanosheets possessed a high specific surface area of 74.79 m2 g-1, enhanced visible light absorption, improved photogenerated electron-holes separation, and prolonged lifetime of photogenerated charge carriers. As a consequence, N self-doped g-C3N4 nanosheets exhibited higher photocatalytic activity for tetracycline (TC) degradation than that of bulk g-C3N4, N self-doped g-C3N4 and g-C3N4 nanosheets. It also exhibited remarkable stability and repeatability. The detailed photocatalytic mechanism was proposed. The midgap states created by N doping can significantly enlarge the visible light absorption, reduce the recombination and prolong the lifetime of photogenerated charge carries. The nanosheet construction can provide increased surface area, abundant active sites, short charge diffusion distance, fast separation and promoted redox abilities of photoexcited charge carries.