Integration of adsorption and simultaneous heterogeneous catalytic oxidation by defective CoFe2O4 activated peroxymonosulfate for efficient As(III) removal: Performance and new insight into the mechanism

The iron-rich Co0.5Fe2.5O4 and stoichiometric CoFe2O4 magnetic nanoparticles with oxygen vacancies were applied to activate peroxymonosulfate (PMS) for adsorption and simultaneous oxidation of As(III) to As(V) in this work. The Co0.5Fe2.5O4/PMS system was effective in As(III) removal with 100 % total arsenic removal efficiency within 15 min. Additionally, the Co0.5Fe2.5O4 exhibited high stability and excellent recyclability in 3 repeated cycles, and the Co0.5Fe2.5O4/PMS system effectively removed total arsenic from arsenic-containing underground water and mineral processing wastewater with residual arsenic below 10 µg/L, meeting the World Health Organization (WHO) guideline. The Fourier transform infrared (FT-IR) and density functional theory (DFT) calculations indicated that surface hydroxyl groups on catalyst were active centers for the As(III) adsorption to form bidentate biconuclear complex. The nonradical active species (1O2 and Fe(IV)) were responsible for As(III) oxidation to As(V). This work proposes the mechanism of CoFe2O4/PMS for As(III) oxidation based on 1O2 and Fe(IV) for the first time, and provides a reliable treatment system for As removal from actual wastewater.