Tetracycline degradation by persulfate activated with magnetic Cu/CuFe2O4 composite: Efficiency, stability, mechanism and degradation pathway

Magnetically separable Cu/CuFe2O4 composite obtained by a solvothermal method was used to active persulfate (PS) for the removal of tetracycline (TC). Under different pH conditions, Cu/CuFe2O4 catalyst exhibited a higher catalytic activity for PS activation to degrade TC than that of CuFe2O4. The effects of some key parameters including initial pH value, PS concentration, catalyst dosage, reaction temperature and coexisting ions on TC degradation were investigated in Cu/CuFe2O4/PS system. The reuse of Cu/CuFe2O4 catalyst at pH 3.50, 7.00 and 11.00 indicated that the catalyst showed a low stability due to the corrosion of metallic copper (Cu°), but bicarbonate ions could enhance the stability and recyclability of this catalyst through the suppression of copper leaching. Both sulfate and hydroxyl radicals were the main reactive species in Cu/CuFe2O4/PS system. Cu° can not only work as electron donor to active PS to produce the reactive radicals but also act as an electron bridge to facilitate the fast electron transfer between PS and catalyst. The structural cuprous and ferrous ions on the surface of CuFe2O4 participated in the PS activation process through the redox reactions, as confirmed by XPS analysis. The possible degradation pathways of TC were proposed based on the identified intermediates.