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

Highlights: • Efficient catalyzed activation of peroxymonosulfate with low-level Co²⁺ was realized. • Acetate enhanced the catalytic activity of Co²⁺ and increased the formation of SO₄⁻. • The enhancement was attributed to the coordinating and electron donating abilities. -- Abstract: 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.