Sulfamethoxazole degradation by alpha-MnO 2 /periodate oxidative system: Role of MnO 2 crystalline and reactive oxygen species.

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 MnO 2 polymorphs (α-, β-, γ- and δ-MnO 2 ) were synthesized and tested to activate [Formula: see text] for the degradation of sulfamethoxazole (SMX). The reactivity of different MnO 2 structures followed the order of α-MnO 2  > β-MnO 2  > γ-MnO 2  > δ-MnO 2 , suggesting that the particular crystalline structure in α-MnO 2 would exhibit higher activities via [Formula: see text] activation. Herein, in α-MnO 2 /[Formula: see text] system, 91.1% of SMX was eliminated within 30 min with degradation rate constant of 0.0649 min -1 , and the neutral pH exhibited higher efficiency in SMX degradation compared with acidic and alkaline conditions. Singlet oxygen ( 1 O 2 ) 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-MnO 2 and provides a novel catalytic activation for selective removal in aqueous contaminants.