Activated peracetic acid by Mn3O4 for sulfamethoxazole degradation: A novel heterogeneous advanced oxidation process

In this study, a novel peracetic acid (PAA)-based advanced oxidation process using Mn3O4 as a catalyst was proposed. A thorough sulfamethoxazole (SMX) removal could be achieved within 12 min in Mn3O4/PAA system at neutral pH. The characterization results of fresh and used Mn3O4 suggested that ≡Mn(II), ≡Mn(III) and ≡Mn(IV) on Mn3O4 were the Mn species for PAA activation, constituting the redox cycles of ≡Mn(II)/≡Mn(III) and ≡Mn(III)/≡Mn(IV) simultaneously. Organic radicals (i.e., CH3C(O)O• and CH3C(O)OO•) were verified to be the dominant reactive species responsible for SMX degradation in Mn3O4/PAA system by radical scavenging experiments. The neutral condition was the most favorable pH for SMX removal in Mn3O4/PAA system and the increase of PAA or Mn3O4 dosage could enhance SMX degradation. Presence of HCO3- and natural organic matter (NOM) could inhibit SMX degradation, while Cl-, NO3- and SO42- had a negligible effect on SMX removal. The thorough SMX removal in successive experiments and characterization results of used Mn3O4 suggested the good reusability and stability of Mn3O4 for PAA activation. Based on six detected transformation products of SMX, hydroxylation, nitration, bond cleavage and coupling reaction were proposed to be its degradation pathways in Mn3O4/PAA system.