Synthesis of Bi₂WO₆/ZnFe₂O₄ magnetic composite photocatalyst and degradation of tetracycline hydrochloride under visible light

Enhanced visible light photocatalytic activity of Bi₂WO₆/ZnFe₂O₄ magnetic composite photocatalyst was synthesized by a two step facile solvothermal process. The as-prepared photocatalysts were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectra and electrochemical impedance spectroscopy. The TCH visible-light photocatalytic degradation and magnetic performance of Bi₂WO₆-based magnetic composite catalysts were also measured. Results showed that an appropriate combining of ZnFe₂O₄ improved the adsorption performance and photocatalytic activity of Bi₂WO₆ catalysts, and enhanced the magnetism, recovery rate and practical values of catalysts. Among them, BZn3 (combined with 0.15 wt% ZnFe₂O₄) exhibited the best photocatalytic activity for degradation ratio of TCH reaching 96.85% in 90 min. The TCH degradation over each composite catalyst within the first 0–60 min obeyed a first-order kinetic equation, the maximum of kinetic constant reached 0.03659 min⁻¹ (BZn3). In comparison, after combining with ZnFe₂O₄, the specific surface area of BZn3 was slightly increased (66.53 m²/g) and the adsorption performance was changed. BZn3 had smaller impedance arc radii under both dark-state and visible-slight state, suggested that the photo-generated electron-cavity in BZn3 was efficiently separated and the transfer of photo-generated electrons at the interface of composite electrode/electrolyte was accelerated upon the visible-light excitation. Moreover, these composite catalysts were also highly stable and underlie the further application of Bi₂WO₆-based magnetic composite catalysts.