Enhancing the photocatalytic efficiency of sulfamethoxazole by regulating the band gap structure of g-C3N4 through phosphorus element doping

Holes and O2− have been proved the primary species for sulfamethoxazole (SMX) degradation in g-C3N4 photocatalytic system. On the basis, P doped g-C3N4 (PCN) photocatalyst with midgap states was prepared by the polymerization of urea and etidronic acid, in order to enhance the role of main species in SMX removal via tailoring band gap structure. Compared with g-C3N4, the energy gap, CB position and VB position of PCN change little, however, PCN shows lower recombination efficiency of photogenerated carriers, strong adsorption and harvest of more visible light due to the midgap states induced by P doping, which is favorable to improve the photocatalytic activity. When the additive amount of etidronic acid is 0.03 g for 10 g urea, the obtained PCN-0.03 exhibits excellent visible-driven photocatalytic ability on SMX degradation. The kinetic constant is 2.1 times than that of pure g-C3N4. Electron spin resonance tests and trapping experiments imply that OH, holes and O2− are produced and enhanced by PCN-0.03 under visible light in comparison with g-C3N4. Holes and O2− take the primary role in SMX photodegradation. The detailed and systematical work may provide an effective strategy for water purification, especially containing SMX.