Degradation of tetracycline by activating persulfate with ZnFe₂O₄-Bi₂MoO₆ catalyst under visible light

The ZnFe₂O₄-Bi₂MoO₆ composite photocatalyst was applied to construct a persulfate activation system combined with photocatalysis. The composite material was synthesized by a simple hydrothermal method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectroscopy (UV-Vis DRS) to study the phase formation, morphology, valence state of elements and light absorption property, respectively. The experimental results showed that the degradation efficiency of tetracycline can reach 84 % in 40 min under visible light, with K₂S₂O₈ as the co-catalyst. The principal advantage of this system is that it can be applied to a wide pH range (3−11) with negligible influence. This system is also less affected by anions (HCO₃^2-, NO₃^-, Cl^-,) and humic acid (HA). The excellent catalytic performance may be due to the retention of electron hole pairs with high redox ability after the construction of heterojunction and the formation of active radicals, O₂^•-, SO₄^•- and •OH. In addition, the ZnFe₂O₄/Bi₂MoO₆ composite catalyst showed good stability and recyclability.