Efficient activation of peroxymonosulfate by Co/Cu co-substituted-ferrite and carbon composite for rapid degradation of tetracycline in aqueous phase: Performance evaluation and mechanisms

Abstract

In this study, a novel Co/Cu co-substituted ferrite-carbon composite CoxCu1-xFe2O4@C (x = 0.1, 0.3, 0.5, 0.7, and 0.9) was prepared by gel-thermolysis to activate peroxymonosulfate (PMS) for tetracycline (TC) removal. The materials were comprehensively characterized using different instruments. Batch experiments were conducted to investigate the effects of different operating parameters on TC removal. Our findings indicated that appropriate amount of Co and Cu substitution was very important. Co0.5Cu0.5Fe2O4@C (CoCF-0.5@C) exhibited the best activity. Using 0.1 g/LCoCF-0.5@C and 0.15 g/LPMS achieved 90.06 % TC removal (0.4091 min−1) in 6 min. Humic acid significantly inhibited TC removal, whereas the impact of coexisting anions varied. Thereinto, CO32− displayed moderate inhibitory effect, Ca2+ and NH4+ showed weak inhibitory effect, and SO42− exhibited insignificant effect. CoCF-0.5@C demonstrated not only excellent activity but also remarkable stability and anti-interference ability, achieving over 60 % TC removal under diverse conditions, such as a wide pH range (pH 3–11), different coexisting ions, and various matrices. Even after 5 cycles, CoCF-0.5@C could maintain 78.4 % TC removal. Compared to other catalysts in previous studies, CoCF-0.5@C combines the dual advantages of high activity and reproducibility. The results of quenching experiments, EPR/ESR and electrochemical tests showed that TC removal mechanism were dominated by non-radical 1O2 and direct electron transfer. The cycling of Cu2+/Cu+, Fe3+/Fe2+, and Co3+/Co2+ in CoCF-0.5@C played a pivotal role in PMS activation, accelerating electron transfer and reactive oxygen species (ROS) generation. The carbon helped to disperse ferrite and avoid its agglomeration, which significantly enhanced electron transfer. Based on the degradation products of TC, two possible pathways for TC degradation were proposed. This study provides a new approach for development of efficient PMS activators to promote TC degradation.