Significant enhancement on diclofenac removal in the Cu(II)/peroxymonosulfate process with neocuproine under neutral pH conditions: Performances, mechanism and anti-interference capability

The application of the Cu-catalyzed peroxymonosulfate (PMS) in pratical is seriously restricted due to its weak anti-interference capability against the natural water matrix and the slow conversion of Cu(II) by PMS under conditions of neutral pH. In this study, neocuproine (NCP) was found to greatly improve the performance of diclofenac elimination in the Cu(II)-catalyzed PMS process across a broad pH range of 7.0–10.0. The pseudo-first-order rate constant of diclofenac abatement in the NCP/Cu(II)/PMS process was 56.0 times greater compared to that in the Cu(II)-catalyzed PMS process at pH 8.0, and superior to the previously-reported hydroxylamine and gallic acid-enhanced Cu(II)-catalyzed PMS processes. Cu(III)-(NCP)₂, as opposed to radicals, served as the major reactive species accountable for diclofenac abatement. Cu(II)-(NCP)₂ having higher oxidation–reduction potential was firstly produced by the complexation of Cu(II) with NCP, Cu(I)-(NCP)₂ was then produced via the interaction of Cu(II)-(NCP)₂ with the deprotonated form of PMS (i.e., SO₅²⁻), Cu(III)-(NCP)₂ was finally produced by the reaction between Cu(I)-(NCP)₂ and PMS. Three potential degradation pathways of diclofenac were inferred from the determined nine degradation intermediates. Significant reduction in the toxicity of reaction solutions was discovered following diclofenac removal. Furthermore, the NCP/Cu(II)/PMS process demonstrated high anti-interference performance to inorganic anions (NO₃⁻, SO₄²⁻, HCO₃⁻ and Cl⁻), humic acid and actual water. Overall, this research provided an efficient approach to enhance the abatement of contaminants in the Cu(II)-catalyzed PMS process under neutral pH environments and to boost its anti-interference capability, which was favorable for its potential utilization in water treatment.