Catalytic Oxidation of Imidacloprid Insecticide by Cu(II)/Peroxymonosulfate System

Abstract

Water contamination by synthetic organic compounds is one of the major environmental issues facing the world today. Among the available methods to treat them, catalytic advanced oxidation processes using Cu(II) ions to activate peroxymonosulfate is a potential candidate at slightly alkaline conditions (pH 8). In this work, we investigated the influence of PMS concentration (0–1000 μmol L^–1), solution pH (7–10), and the effect of water matrix (ultrapure, tap, and simulated municipal wastewater—SMWW) on imidacloprid (IMD) insecticide oxidation. After optimization of the investigated variables (500 μmol L^–1 PMS and pH 8), almost complete IMD oxidation was achieved in 6 h using ultrapure and tap water. The main detected byproducts resulting from IMD oxidation in ultrapure water are due to hydroxylation reactions and rupture of the imidazolidine ring. When SMWW was used, IMD oxidation was only 10% in 6 h, probably due to the scavenging effect of inorganic and organic compounds. The main produced working oxidants were radical (mainly HO^● and SO₄^●–) and non-radical (¹O₂, Cu(I), and Cu(III)) species, based on scavenging experiments and mass spectrometry detection of produced DMPO byproducts. Among these, HO^● species seems to promptly oxidize IMD.