Adsorbed hydroxyl radicals dominated peroxymonosulfate activation in acetaminophen degradation using modified electrolytic manganese anode slime: Catalyst evaluation and free radical identification

Abstract

A new type of catalyst based on electrolytic manganese anode slime (EMAS) for heterogeneous peroxymonosulfate (PMS) activation in acetaminophen (APAP) degradation was prepared. The EMAS was modified by washing, pickling, and calcination to produce the DEMAS200 catalyst, and multi-types of refractory organic matter could be degraded by the DEMAS200/PMS system, of which 20 mg/L APAP can be removed within 4 min. A radical activation mechanism based on PMS was proposed through a series of APAP degradation experiments and material characterization. By quenching, probing, PMSO experiments, and electron paramagnetic resonance (EPR), the major contribution of various reactive oxygen species (ROS) (such as ·OHfree, SO4·−, high-valent Mn species, 1O2 and O2·−) was excluded, and ·OHads was verified as the major ROS. Nuclear magnetic resonance (NMR) was applied to identify active hydrogen using the D2O exchange method to qualitatively identify the presence of ·OHads, which was determined by comparing the appearance and disappearance of chemical shifts at 1.90 ppm (active hydrogen) and 7.96 ppm (hydrogen at the benzene ring on TPA). In this study, the modified EMAS was innovatively introduced for PMS activation in the degradation of APAP, and NMR technology successfully identified the presence of different hydroxyls.