The effects of nonredox metal ions on the activation of peroxymonosulfate for organic pollutants degradation in aqueous solution with cobalt based catalysts: A new mechanism investigation

Herein, a new peroxymonosulfate (PMS) activation system was proposed employing nonredox metal ions as Lewis acids (LA), which have been widely recognized to play important roles in many biological and chemical oxidations. With Co2+ ions as model catalysts, it was found that oxidizing power of PMS was enhanced after binding weak LA such as Ca2+ ions, leading to its easier reduction to active radicals and substantial enhancement of dye degradation. The promoting effect of Ca2+ was also observed with other cobalt catalysts including CoFe2O4 and Co3O4. The rate of PMS decomposition in Co2++LA/PMS system was correlated with Lewis acidity; while in the presence of strong LA including La3+ and Y3+, the dye degradation rate declined. The interactions of LA with PMS were characterized and the detailed mechanism was proposed. The present study provides the first example of the promoting effect of weak LA on PMS activation with cobalt based catalysts.