Mechanistic study of electrooxidation of coexisting chloramphenicol and natural organic matter: Performance, DFT calculation and removal route

Abstract

The electrooxidation performance of coexisting chloramphenicol (CAP) and natural organic matter (NOM) by Ti4O7 anode was systematically investigated in this study. Intrinsic reaction kinetics showed that the removal of CAP followed pseudo-first-order kinetics, 72.42 ± 0.20 % removal with 40.79 ± 0.41 % mineralization rate of CAP was achieved in 60 min using 5 mA cm−2. The oxidation mechanisms of CAP were elucidated by density functional theory (DFT) simulations and experiments involving hydroxyl free radical (•OH) scavenger, which indicated that the efficient degradation of CAP was attributed to the combined action of •OH attack and direct electron transfer (DET) reaction. The degradation pathway of CAP was proposed based on frontier electron densities (FEDs) calculation and intermediate products identification, and less ecological risks of CAP degradation solution were also proved by acute toxicity test. Humic acid (HA), selected as the typical NOM, could inhibit the degradation of CAP to a certain extent by competitive action for electrooxidation with effective removal and mineralization of HA, which was further confirmed based on real wastewater treatment experiments. Specifically, the degree of humification and aromaticity of HA was weakened, and some complex small molecular organic matters such as aromatic proteins were generated. These findings proved the feasibility of Ti4O7 anode electrooxidation to remove CAP antibiotics and organic matter from water, in consideration of the potential negative role of CAP and organic matter for ecological environment and human health.