Mineralization of Ionic Liquids by Catalytic Ozonation over ZnO/Ca2Fe2O5

Abstract

Imidazolyl-based ionic liquids (ILs) have been widely used in many fields, leading to potential environmental problems due to the toxicity of ILs. In this work, ZnO/Ca₂Fe₂O₅ was prepared and used as an efficient catalyst to mineralize 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) ILs using the catalytic ozonation process. [BMIM]Cl was mineralized to CO₂, H₂O, NH₄⁺, and Cl^– in a short time. The mineralization efficiency of [BMIM]Cl can reach up to >92% in 120 min with a catalyst dosage of 3.3 g/L, an ozone flow rate of 72 mg/min, an initial pH of 10.5, and an initial [BMIM]Cl concentration of 175 mg/L. Meanwhile, the degradation pathway of [BMIM]Cl was also proposed. The physical and chemical properties of the catalysts were characterized by XRD, FTIR, N₂ physical adsorption–desorption profiles, TEM, and XPS. The results showed that the ZnO/Ca₂Fe₂O₅ catalyst had good stability, and the presence of Zn²⁺ promoted the decomposition of ozone and the production of ^•OH, which increased the degradation efficiency of [BMIM]Cl. The catalytic mechanism was also discussed. This research showed a promising way to prepare efficient catalysts for the treatment of [BMIM]Cl using the catalytic ozonation process.