Insight into homogeneous activation of sodium hypochlorite by dithionite coupled with dissolved oxygen (DO@NaClO/DTN) for carbamazepine degradation

Abstract

Emerging contaminants (ECs) including carbamazepine (CBZ) in aquatic systems pose non-target risks to wildlife. We introduce an innovative advanced oxidation process (AOP) utilizing sodium hypochlorite (NaClO), which achieved 45.3 % degradation and mineralization of CBZ within 60 mins. Natural saturated state dissolved oxygen (DO, ∼7.5 mg·L^-1) played a crucial role in synergistically activating NaClO with dithionite (DTN) without extra energy consumption. In DO@NaClO/DTN system, scavenging tests and electron spin resonance (ESR) analysis confirmed that ·OH and Cl· were dominant for CBZ degradation. The critical DO was responsible for the direct simultaneous production of ·OH and Cl·, confirmed by the greater thermodynamic data ΔG from density functional theory (DFT) calculation. These reactive species participate in subsequent transformations of SO₄^·-, O₂^·-, and ¹O₂. Preferential hydroxylation of CBZ first occurred due to the attacking at the reactive sites of C(21) and C(22) atoms. LC-MS/MS detection and DFT theoretical calculations also verified the sequent mechanisms of Meinwald rearrangement, deamidation and hydroxylation, cyclized hydroxylated and dehydrated with the decreasing ΔG. Ubiquitous Cl^- accelerated CBZ degradation remarkably, regardless of its concentration. The significant enhancement of Cl^- for CBZ degradation in DO@NaClO/DTN system suggest its promising application for ECs degradation in high-chloride seawater including offshore wastewater and tailwater in mariculture.