The transition of tetragonal to monoclinic phase in BiVO4 coupled with peroxymonosulfate for photocatalytic degradation of tetracycline hydrochloride

At present, the mechanism difference between tetragonal BiVO4 (t-BiVO4) and monoclinic BiVO4 (m-BiVO4) coupled peroxymonosulfate (PMS) to realize photocatalysis is still unclear. In this study, m-BiVO4 and t-BiVO4 were obtained by adjusting the bismuth-vanadium ratio in the precursor solution (Bi:V = 3:1; 1:1; 1:2 and 1:3). The results of photocatalytic experiments showed that both t-BiVO4 and m-BiVO4 had certain activation effects on PMS, and the prepared monoclinic B1V2 has the strongest photocatalytic performance. Using 20 mg B1V2 to activate 4 mmol L-1 PMS in 30 min, the degradation rate of tetracycline hydrochloride (TCH) reached 92.8%. The free radical quenching experiment and EPR test showed that when m-BiVO4 coupled PMS degraded TCH, the contribution of active species was SO4 center dot->center dot OH>center dot O-2(-) > h(+). Compared with m-BiVO4, the wide band gap of t-BiVO4 makes the photogenerated carrier recombination. When t-BiVO4 coupling PMS, the contribution of active species is center dot O-2(-) > SO4 center dot->center dot OH>h(+). In addition, the intermediate products of TCH degradation were analyzed by LC-MS, and three possible degradation paths of TCH were proposed.