Surface defect and carbonyl engineering of CNTs via oxygen-plasma etching: Oriented production of singlet oxygen from peroxymonosulfate activation

A facile oxygen-plasma strategy was used to engineer carbon nanotubes (CNTs) surface with defects and carbonyl groups for organic water decontamination. The plasma-treated CNTs (E-CNTs) displayed a remarkable efficacy to catalyze peroxymonosulfate (PMS) activation for degrading electron-rich pollutants across a broad range of pH levels and under natural water conditions. Moreover, the kinetic constant for E-CNTs was found to be 4.1 times that of raw CNTs, attaining 97 % 2,4-DCP degradation in 20 min. The in situ capturing by electron paramagnetic resonance, chemical probing, and selectively scavenging tests collectively reveal that singlet oxygen (1O2) was the dominant reactive species with 54.9 % contribution to 2,4-DCP removal. The structure-activity relationship analysis and density functional theory (DFT) revealed that defects and carbonyl groups were the intrinsic catalytic sites for PMS activation. A comprehensive degradation pathway was proposed based on the properties of pollutant and degradation products from HPLC-MS and DFT calculations. Based on the ECOSAR analyses, the toxicity of the treated water (degradation intermediates) dramatically declined except for a polymerized bipolymer TP6 (m/z = 266.9). This article provides a novel method to create PMS-oriented active sites on carbon materials for selective singlet oxygen production and water purification.