Synergistic degradation of oxytetracycline and rhodamine B in Cu(II)/peroxymonosulfate process: Two distinct oxidation mechanisms

Although Cu(II)/peroxymonosulfate (PMS) process has been successfully applied to degrade varied organic contaminants in water, the slow transformation of Cu(II) to Cu(I) that works only in alkaline conditions retards the treatment efficiency of this process. In this study, a new finding was observed, that is, oxytetraczdycline (OTC) could effectively enhance the degradation of organic pollutants in Cu(II)/PMS process where it was also removed in acidic conditions. With the addition of OTC in Cu(II)/PMS system, 85.5% of rhodamine B (RhB) was degraded in 90 min at pH 4.0, which was far more than that without OTC (36.1%), and simultaneously 98.1% of OTC was eliminated. The added OTC could form OTC-Cu(II) complexes which might powerfully improve the reduction of Cu(II) to Cu(I), exerting a positive effect on the PMS activation and subsequent degradation of RhB. Electron paramagnetic resonance (EPR) experiments assisted with radical scavenging experiments and Raman spectrum detection results suggested that Cu(III) and hydroxyl radical (HO • ) were the predominant reactive species for RhB degradation, while OTC removal in this system was mainly ascribed to direct PMS oxidation. The Cu(II)/PMS process also showed a promising success on the synergistic degradation of OTC with the other four refractory organic pollutants , indicating the potential application of PMS oxidation in water treatment .