Efficient degradation of organic pollutants by low-level Co2+ catalyzed homogeneous activation of peroxymonosulfate

Dissolved cobalt ions (Co2+) are an excellent catalyst for activating peroxymonosulfate (PMS) to generate SO4− for the degradation of organic pollutants, but fairly high level of Co2+ is generally required, which may cause secondary pollution due to its toxicity. Herein, we demonstrate a novel strategy for this catalytic oxidation treatment in which the required Co2+ addition is very small, being much less than the emission limit of 17 μmol L−1. This new strategy is based on the much enhanced catalytic effect by the addition of small organic acids (SOAs). In a typical case, all the added diclofenac (30 μmol L−1) was degraded in 20 min by using 2 μmol L−1 Co2+, 0.15 mmol L−1 PMS and 0.5 mmol L−1 acetate with a degradation rate constant of 0.482 min−1, which was about 10 times higher than that (0.048 min−1) of equivalent Co2+-PMS system without acetate. The formation of SO4− was greatly enhanced by introducing acetate, and this novel system is universal for enhanced degradation of various organic pollutants. Similarly, formate, propionate, and butyrate also exhibited enhancing effects on the catalytic ability of Co2+. The enhancement mechanism of SOAs on catalytic activation of PMS by low-level Co2+ was also proposed.