A comparison of SMX degradation by persulfate activated with different nanocarbons: Kinetics, transformation pathways, and toxicity

Nanocarbon-based advanced oxidation processes (AOPs) are widely used in wastewater purification. However, the properties of different carbon catalysts lead to differences in the organic degradation mechanism and toxicity of wastewater treatment. Herein, this study provides insight into the differences between the oxidation of sulfamethoxazole (SMX) by carbon nanotube (CNT)/peroxymonosulfate (PMS), nanodiamond (ND)/PMS and PMS-alone systems. The pseudo-first-order reaction constant of the reaction of the SO4•--dominated CNT/PMS system with SMX is 19-fold and 30-fold higher than those of the 1O2-dominated ND/PMS system and PMS direct oxidation system at pH= 7, respectively. In addition, density functional theory (DFT) calculations and product analysis show that SO4•- mainly attacks the aniline and sulfonyl groups, while oxidation of the aniline group is the dominant mode of PMS direct oxidation and 1O2 reactivity. The formation of nitro and nitroso byproducts after SMX degradation determines the toxicity difference, and the CNT/PMS system is even more advantageous.