Mn(II) enhanced permanganate oxidation of trace organic pollutants in water: Critical role of in situ formation of colloidal MnO2

Studies widely acknowledge the enhancement of permanganate (Mn(VII)) oxidation of organic contaminants by coexisting matrices in water. This study investigated the positive influence of Mn(II), a common soluble metal ion, on the removal of trace organic pollutants by Mn(VII). Results showed that introducing 20 μmol/L Mn(II) at pH 5.0 accelerated trace organic pollutant removal by promoting colloidal MnO2 formation. UV−visible spectrum, quenching, and probe experiments confirmed role of MnO2 in sulfamethoxazole (SMX) oxidation, with Mn(III) playing a predominant role. Meanwhile, in situ-generated MnO2 facilitated Mn(VII)* formation, enhancing oxidation performance, as indicated by Raman spectroscopy and electrochemical analysis. Eleven transformation products (TPs) of SMX in the Mn(VII)/Mn(II) process were detected by UPLC-QTOF-MS/MS. Subsequently, the reaction pathways of SMX were elucidated through Fukui index analysis and the identification of TPs. Additionally, toxicity simulations with Toxicity Estimation Software Tool (T.E.S.T.) software revealed significantly lower cytotoxicity of TPs of SMX compared to the parent compound. This study unveils an effective strategy to enhance Mn(VII)-mediated degradation of organic pollutants in water, elucidating Mn(II)-induced Mn(VII) activation mechanisms. [Display omitted] The transformation of sulfamethoxazole by permanganate was greatly enhanced in the presence of Mn(II) where in situ formed manganese dioxide played oxidative and catalytic role.