BiVO4 prepared by the sol–gel doped on graphite felt cathode for ciprofloxacin degradation and mechanism in solar-photo-electro-Fenton

In this research, bismuth vanadate-doped graphite felt (GF-BiVO4) was successfully prepared by sol–gel method, in which BiVO4 owned superior electro-Fenton (EF) and solar-photo-electro-Fenton (SPEF) performance. Combined with the analysis by X-ray diffractometer (XRD), field emission transmission electron microscopy (FE-TEM), nitrogen adsorption–desorption isotherms and cyclic voltammetry (CV), the changes of electrodes were reflected in structure and physicochemical properties. The doping of monoclinic BiVO4 endued GF with a higher surface area and more electro-active sites and better electrode activity in comparison to Raw-GF. Then, the GFs were used as cathodes to detect •OH concentration with coumarin (COU) as probe molecule and to evaluate photoelectric performance with ciprofloxacin (CIP) in photocatalysis, EF and SPEF processes. The results demonstrated that the concentration of •OH followed an order of SPEF> EF> photocatalysis, which was consistent with the removal rate of CIP (99.8%, 99.4% and 21.2%, respectively) on GF-BiVO4 at 5 min. Further, five degradation pathways of CIP in SPEF system were proposed including the attack on piperazine ring, oxidation on cyclopropyl group, decarboxylation and hydroxyl radical addition, oxidation on benzene group and defluorination. The study provides insights into the enhancement of EF and SPEF performance and the degradation pathway of CIP in SPEF.