Hydroxylamine enhanced Cu(II)/peroxydisulfate system for diclofenac degradation: Efficiency, influence factors and mechanism

Abstract

In this work, diclofenac (DCF), a nonsteroidal anti-inflammatory drug, was effectively removed in Cu(Ⅱ)/hydroxylamine (HAm)/peroxydisulfate (PDS) system in neutral condition. It was proved that the introduction of HAm significantly enhanced DCF degradation in Cu(Ⅱ)/PDS system by accelerating Cu(Ι)/Cu(Ⅱ) cycle. According to the results of electron paramagnetic resonance (EPR) and scavenging experiments, the contribution of SO4•- and •OH to DCF degradation in Cu(Ⅱ)/HAm/PDS system was comparable at pH 7. The effects of operational parameters including initial pH, Cu(Ⅱ) dose, HAm concentration, PDS concentration and initial DCF concentration on the removal of DCF were systematically investigated, and the influence of water matrix components (i.e., SO42-, NO3-, Cl-, HCO3- and natural organic matter) on DCF degradation were also studied. Five degradation products were detected using UPLC-Q-TOF-MS, and four degradation pathways were thereby proposed including hydroxylation, dehydrogenation, dehydration and decarboxylation. The mineralization of DCF in Cu(Ⅱ)/HAm/PDS system was limited according to the result of total organic carbon (TOC) test. Various emerging contaminants were also effectively degraded in Cu(Ⅱ)/HAm/PDS system, suggesting the applicability of this system in degradation of other refractory organic contaminants. This study provides a method to enhance the treatment efficiency of Cu(Ⅱ)/PDS system and an effective way to degrade emerging contaminants at mild condition.