Engineering P/g-C3N4-x/bentonite by doping and defect dual strategy to activate peroxymonosulfate for degradation of tetracycline hydrochloride: Critical roles of phosphorus doping and cyano-defects on electrons separation.

Graphitic carbon nitride (g-C3N4) shows promising potential for activating peroxymonosulfate (PMS), however, its practical application is hindered by poor light absorption and inefficient electron-hole pairs (e-/h+) separation. Additionally, there are limited reports on preparing the g-C3N4 with a dual modification of doping and defect through the simple and low-toxic strategy to simultaneously enhance the catalytic capacity of material and the generation of non-radicals. In this work, the phosphorus doping(P doping)and cyano-defects co-modified g-C3N4 (P/g-C3N4-x) via thermal co-polymerization of precursors followed by treatment of molten salt (NaCl/KCl) was obtained. Subsequently, the P/g-C3N4-x/bentonite (P/g-C3N4-x/Bt) composite was constructed by the impregnation-calcination method. The P/g-C3N4-x/Bt promoted PMS activation, thereby improving the degradation efficiency of tetracycline hydrochloride (HTC). Experiments and DFT calculations disclosed that the co-modification of P doping and cyano-defects modulated the electronic structure and narrowed the band gap, improving the light absorption and enhancing the separation of e-/h+. Moreover, the formation of enhanced positive and negative electrostatic regions on catalyst promoted the generation of singlet oxygen (1O2). The detection experiments of reactive species revealed that both radicals and non-radicals contributed to HTC degradation, with 1O2 playing a decisive role. Besides, the incorporation of bentonite (Bt) enhanced the adsorption of pollutants due to the increased specific surface area. Furthermore, LC-MS analysis and toxicity assessment indicated that HTC decomposed into low-toxic small molecules. This work offers new ideas for developing efficient and eco-friendly photocatalysts to simultaneously enhance the photocatalytic activity and the generation of 1O2.