Hydroxylamine enhanced the degradation of diclofenac in Cu(II)/peracetic acid system: Formation and contributions of CHC(O)O, CHC(O)OO, Cu(III) and OH.

The slow reduction of Cu(II) into Cu(I) through peracetic acid (PAA) heavily limited the widespread application of Cu(II)/PAA system. Herein, hydroxylamine (HA) was proposed to boost the oxidative capacity of Cu(II)/PAA system by facilitating the redox cycle of Cu(I)/Cu(II). HA/Cu(II)/PAA system was quite rapid in the removal of diclofenac within a broad pH range of 4.5-9.5, with a 10-fold increase in the removal rate of diclofenac compared with the Cu(II)/PAA system at an optimal initial pH of 8.5. Results of UV-Vis spectra, electron paramagnetic resonance, and alcohol quenching experiments demonstrated that CHC(O)O, CHC(O)OO, Cu(III), and OH were involved in HA/Cu(II)/PAA system, while CHC(O)OO was verified as the predominant reactive species of diclofenac elimination. Different from previously reported Cu-catalyzed PAA processes, CHC(O)OO mainly generated from the reaction of PAA with Cu(III) rather than CHC(O)O and OH. Four possible elimination pathways for diclofenac were proposed, and the acute toxicity of treated diclofenac solution with HA/Cu(II)/PAA system significantly decreased. Moreover, HA/Cu(II)/PAA system possessed a strong anti-interference ability towards the commonly existent water matrix. This research proposed an effective strategy to boost the oxidative capacity of Cu(II)/PAA system and might promote its potential application, especially in copper-contained wastewater.