Insights into the mechanism of nonradical reactions of persulfate activated by carbon nanotubes: Activation performance and structure-function relationship

This study aimed to elucidate the intrinsic mechanisms of PS activation by carbon nanotubes (CNTs). Singlet oxygen generation (O-1(2)) and direct CNTs-mediated electron transfer were hypothesized to be two major pathways of the oxidation of 2,4-dichlorophenol (2,4-DCP) by PS in the presence of both unmodified and modified CNTs. For the first time, roles of CNT active sites responsible for PS activation were determined using CNT derivatization and structural characterization. By selectively deactivating the carbonyl, hydroxyl or carboxylic groups on CNTs surface and linear sweep voltammetry (LSV) analysis, -C=0 groups were determined to be the main active sites contributing to the direct electron transfer oxidation, while singlet oxygen was generated at CNTs defects. Subsequent UV irradiation was shown to cause the recovery of surface defects with I-D/I-G of CNTs increasing by 21%. This resulted in the regeneration of the performance for the coupled system and allowed for multi-cycle activation of PS by CNTs. These results suggest that CNTs/PS system combined with regeneration based on UV irradiation can be used as an effective alternative process for continuous degradation of recalcitrant aqueous contaminants through the non-radical mechanism. (C) 2019 Elsevier Ltd. All rights reserved.