Fabrication of visible-light-driven tubular F, P-codoped graphitic carbon nitride for enhanced photocatalytic degradation of tetracycline

The fluorine and phosphorus co-doped tubular g-C3N4 (CNPF) photocatalyst has been successfully synthesized through hydrothermally supramolecular self-assembly at 180 ºC for 10 h followed by the crystallization at 500 ºC for 4 h in N2. The as-prepared CNPF was then used for the photocatalytic degradation of tetracycline (TC) under visible-light irradiation at 460 nm. Tubular CNPF structures can shorten the diffusion length thereby increasing the electric conductivity and electron transfer rate. The P element can replace C atoms in g-C3N4 to delocalize the π-conjugated triazine structure. Moreover, addition of F atoms significantly reduces the bandgap and recombination rate of holes and electrons, leading to the enhanced photocatalytic degradation of TC under different environmental conditions. The as-prepared CNPF exhibits TC photodegradation rate 4.2–11.7 times higher than that of pristine g-C3N4 under different environmental conditions. CNPF also shows significant stability and reusability with 98% of mineralization efficiency in 5 cycles. Results of radical trapping experiments clearly indicate that hole and superoxide radical are the dominant reactive species enhancing TC photodegradation. Moreover, the possible reaction mechanism for TC photodegradation over CNPF are proposed.