Degradation mechanism and pathway of tetracycline in milk by heterojunction N-TiO2-Bi2WO6 film under visible light.

N-doped TiO2-Bi2WO6 (NTB) three-component photocatalyst was prepared using a glycol solvothermal method. The photocatalysts and films were characterized, and applied to the degradation of tetracycline (TC) in milk and its effect on the quality of milk. The results show that the NTB photocatalyst exhibits good photocatalytic activity under visible light, and its TC degradation rate is increased by 1.76, 1.49, 1.42, 1.16, and 1.13 times higher than that of TiO2, Bi2WO6, N-TiO2, N-Bi2WO6 and TiO2-Bi2WO6, respectively. Due to the N doping, the photogenerated electron-hole pair recombination rate of photocatalyst is greatly reduced, which improving its photocatalytic performance. Additionally, the absorption wavelength threshold is enlarged by 459 nm, the gap width is reduced to 2.69 eV, and the degradation rate of TC is still 83.24 % after 5 repetitions. HPLC-MS revealed the active species, intermediates and photodegradation pathways in the photocatalytic process.