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 SO₄^2- 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.