Sulfamethoxazole degradation by alpha-MnO2/periodate oxidative system: Role of MnO2 crystalline and reactive oxygen species.

Abstract

Pollutant degradation via periodate ([Formula: see text]) and transitional metal oxides provides an economical, energy-efficient way for chemical oxidation process in environmental remediation. However, catalytic activation of periodate by manganese dioxide and the associated mechanism were barely investigated. In this study, four MnO2 polymorphs (α-, β-, γ- and δ-MnO2) were synthesized and tested to activate [Formula: see text] for the degradation of sulfamethoxazole (SMX). The reactivity of different MnO2 structures followed the order of α-MnO2 > β-MnO2 > γ-MnO2 > δ-MnO2, suggesting that the particular crystalline structure in α-MnO2 would exhibit higher activities via [Formula: see text] activation. Herein, in α-MnO2/[Formula: see text] system, 91.1% of SMX was eliminated within 30min with degradation rate constant of 0.0649min-1, and the neutral pH exhibited higher efficiency in SMX degradation compared with acidic and alkaline conditions. Singlet oxygen (1O2) was unveiled to be the dominant ROS according to the results of electron paramagnetic resonance, chemical probes and radical quenching experiments, whereas [Formula: see text] and •OH were mainly acted as a free-radical precursor. Six oxidation products were identified by LC-MS, and the elimination of sulfonamide bond, hydroxylation and direct oxidation were found to be the important oxidation pathways. The study dedicates to the mechanistic study into periodate activation over alpha-MnO2 and provides a novel catalytic activation for selective removal in aqueous contaminants.