Phosphorus- and Sulfur-Codoped g-C3N4: Facile Preparation, Mechanism Insight, and Application as Efficient Photocatalyst for Tetracycline and Methyl Orange Degradation under Visible Light Irradiation

Phosphorus- and sulfur-codoped graphitic carbon nitride has been successfully synthesized by in situ thermal copolymerization of hexachlorocyclotriphosphazene and thiourea. The phosphorus doping, together with the sulfur doping, would enhance light trapping, surface area, and charge separation, making it serve as a more efficient photocatalyst than its pure g-C3N4 and single-doped g-C3N4 counterpart for the removal of tetracycline (TC) and methyl orange (MO). The optimum photocatalytic activities of a P-, S-codoped g-C3N4 sample for the degradation of TC and MO were about 5.9 times and 7.1 times higher than that of individual g-C3N4, respectively. Furthermore, the optimum TOC removal reached 70.33% and 55.37% for TC and MO within 120 min, respectively. The introduction of a P atom and S atom could significantly change the electronic property of g-C3N4 and suppress the recombination of photogenerated charges. Moreover, the defects in the framework of samples caused by the doping of P and S could serve as centers to trap the photoinduced electrons, thus inhibiting the charge recombination and improving its photocatalytic performance.