Green Synthesis Strategy of Template-Free S-Doped g-C3N4 with Cystine for Efficient Photocatalytic Degradation of RhB

Constructing a nanostructure with a high surface area and regulating the band gap by nonmetallic doping are two effective methods for improving the photocatalytic activity of catalysts. A green template-free synthesis strategy of S-doped g-C 3 N 4 nanosheets is proposed via doping cystine as both the structural additive and S source. The features of S-doped samples (GCN- x %) were systematically studied, including morphology and textural and photoelectric properties, which demonstrated that the introduction of cystine and simple manipulation of the preparation process could realize self-exfoliation of g-C 3 N 4 into nanosheets. The GCN-3% sample showed a surface area (131.88 m 2 ·g –1 ) 10.7 times enlarged compared with bulk g-C 3 N 4 (bulk-phase carbon nitride). Obvious redshift on the absorption edge induced by S doping can be observed, revealing a narrowed band gap and enhanced efficiency of photogenerated charge carrier separation. The DFT calculation results also verified that the introduced C–S site could lead to polarization of the local electric field and thus decrease the bandgap of g-C 3 N 4 nanosheets. GCN-3% showed a 99.3% photocatalytic degradation ratio of rhodamine B in 60 min at a rate of 0.17 min –1 . By scavengers experiment revealed that superoxide anion ( · O 2 – ) radicals and holes (h + ) were vital active components during the photocatalytic degradation.