Metal-free carbon nanotube boosted periodate oxidation towards organic pollutants: Identification of active sites and activation mechanism

Abstract

Recent studies have indicated that metal-free carbon material-enhanced periodate (PI) oxidation is a promising strategy for mitigating organic pollution in water. However, the complicated physicochemical properties of carbon materials make it challenging to determine the activation mechanism and roles of the active sites. In this study, various metal-free carbon materials (GO, GP, ND, CNF, and MCNT) were used as catalysts for activating PI in the degradation of organic pollutants, with a focus on elucidating the underlying reaction mechanisms. All of these materials were found to be highly effective in PI activation, and MCNT showed the best catalytic performance. Quenching experiments and EPR results show that the MCNT/PI system primarily oxidizes organic contaminants via two non-radical oxidation routes as electron donors and electron mediators, respectively. Specifically, the oxygen-containing groups of MCNT (particularly carbonyl groups) play a crucial role in electron donation to enhance PI oxidation. Moreover, the structural defects of MCNT significantly accelerate electron transfer from the SIZ (target contaminant) to PI. These insights contribute to unveiling the activation of PI using metal-free carbon materials and hold substantial promise for advancing carbon-based catalysts in environmental cleanup efforts.