Removal of diclofenac with zinc in the presence of Cu(II) and Co(II): Influence factors, products and mechanism

Abstract

Diclofenac (DCF) is one kind of pharmaceuticals and personal care products (PPCPs), and it is imperative to develop a green and efficient method to remove it. The removal of DCF with zinc (Zn) in the presence of Cu(II) and Co(II) were investigated on the influence factors, products, and mechanism. The results showed that with the increasing of Cu(II) and Co(II) concentrations, the reactions were accelerated. The removal rate was higher with lower pH value. In all the systems, the DCF removal rate hardly changed when the dissolved oxygen (DO) concentration was 0–8 mg·L−1 and increased at 20 mg·L−1. Products analysis showed that the products were hydroxylated DCF (DCF0) and an unknown product (DCFu) in Zn system, monochlorinated DCF (DCF1) in Zn/Cu(II) system, DCF1 and dechlorinated DCF (DCF2) in Zn/Co(II) system. The order of toxicity from highest to lowest was DCF, DCF0, DCF1, DCF2. The corrosion degree of zinc powder surface increased in the presence of Cu(II) and Co(II). After 48 h, ZnO formed in Zn system. In Zn/Cu(II) system, CuO and Cu2O formed in addition to ZnO. In the Zn/Co(II) system, Co3O4, ZnO and Zn(OH)2 formed. After adding Cu(II) and Co(II), the corrosion currents increased. In Zn/Cu(II) system, DCF was dechlorinated to DCF1 by catalytic hydrogenation. In Zn/Co(II) system, DCF was mainly dechlorinated to DCF1 and DCF2 by catalytic hydrogenation. This technique provides an alternative method for DCF removal and expands the application field of Zn reduction technology.