Tetracycline removal by a magnetic heterojunction Cu2O/CoFe2O4 activating peroxymonosulfate

The electron transfer mechanism in the process of peroxymonosulfate (PMS) activation using heterojunction catalyst was controversial. In this work, magnetic heterojunction Cu2O/CoFe2O4 (CC) was first synthesized to activate PMS. An innovative reaction mechanism based on built-in electric field-driven electron migration from Cu2O to CoFe2O4 and effective magnetic moment of CC for enhancing PMS activation was proposed. Meanwhile, the CC/PMS system was used for efficient removal of antibiotic tetracycline (TC). Under optimal conditions, 98.0% TC could be removed using CC/PMS catalytic system after only 30 min. The catalytic activity was higher than that of Cu2O/PMS and CoFe2O4/PMS. Meanwhile, the impact of solution pH on TC removal was insignificant, suggesting the pH-insensitive PMS activation ability of CC. Besides, the coexisting inorganic ions in the environment, such as HCO3-, H2PO4-, NO3-, Cl- and humic acid (HA) as representative of natural organic matter, did not inhibit TC removal in CC/PMS system. Furthermore, CC/PMS system exhibited excellent reusability with more than 94.0% TC removal after the 5th reuse. Electron paramagnetic resonance (EPR) tests and quenching experiments showed that O-2 center dot(-) and O-1(2) played vital roles in TC removal. The intermediate products and corresponding toxicity assessment revealed that this catalytic system could reduce TC toxicity. This work provided new insights into the PMS activation mechanism using heterogeneous magnetic catalysts, including transition metal oxide.