New insights into the CuFe2O4/PMS process: The roles of surface Cu(III) species and free radicals

Transition metal oxides have been recognized as promising catalysts for the activation of peroxymonosulfate (PMS), while the underlying mechanism involved in the relevant processes remains obscure. Here, we identify the reactive species generated in the CuFe2O4/PMS process and illustrate their roles in the degradation of aromatic compounds with different substituent groups (i.e., phenol and benzoic acid). Experimental results showed that free radicals (i.e., sulfate radicals (SO4•−) and hydroxyl radicals (HO•), surface Cu(III) species, and singlet oxygen (1O2) coexist in the CuFe2O4/PMS process. The free radicals are mainly responsible for the oxidation of aromatic compounds with electron-withdrawing group (i.e., benzoic acid), while the surface Cu(III) is the major reactive species for the removal of aromatic compounds with electron-donating group (i.e., phenol). In addition, 1O2 plays a negligible role in the oxidation of both benzoic acid and phenol. This study enhances the fundamental understanding of the underlying mechanism involved in the transition metal oxides-catalyzed PMS activation process.