Catalytic ozonation of an imidazole ionic liquid via Fe3O4/ZnO nanocomposites: Performance, products and reaction mechanism

This study aimed to investigate the catalytic performance of Fe 3 O 4 /ZnO in the ozonation of 1-hexyl-3-methyl imidazolium bromide ([HMIM]Br). The Fe 3 O 4 /ZnO composite was prepared by a quick and convenient two-step coprecipitation method, and the optimum mass ratio of Fe 3 O 4 :ZnO was determined as 1:8. The structure, surface morphology, and chemical composition of the Fe 3 O 4 /ZnO composites were studied by characterization methods. The degradation efficiency of [HMIM]Br reached 96% in 5 min in catalytic ozonation with the Fe 3 O 4 /ZnO composite, an increase of 20% compared with ozonation alone. Moreover, the pseudo-first-order rate constant was 1.5 times higher than ozonation alone. With the increase in the catalyst dosage, the degradation efficiency of [HMIM]Br first improved and then decreased, and the optimum dosage was 0.25 g/L. The increase in pH value and the introduction of Cu 2+ effectively promoted the catalytic ozonation of [HMIM]Br with Fe 3 O 4 /ZnO, while the reducing inorganic ions inhibited the ozonation reaction. Different water matrices had little influence on the catalytic performance of Fe 3 O 4 /ZnO. Radical scavenging and EPR experiments showed that hydroxyl radicals (•OH), superoxide radicals (O 2 •- ) and singlet oxygen ( 1 O 2 ) were the main active species in this system. Meanwhile, product identification showed that the degradation of [HMIM]Br mainly included hydroxylation, imidazole ring cleavage and bond cleavage. Toxicity prediction illustrated that the catalytic ozonation of [HMIM]Br could effectively reduce its toxicity. The efficiency, toxicity, reusability, and stability experiments suggested that the developed catalyst, Fe 3 O 4 /ZnO composite, had promising prospects in catalytic ozonation. • Fe 3 O 4 /ZnO with effective catalytic performance for the ozonation of [HMIM]Br was prepared by a two-step coprecipitation method. • OH, O 2 •- , and 1 O 2 were the main reactive oxygen species in catalytic ozonation. • Fe 3 O 4 /ZnO had good application potential and stability in ozone catalysis. • Hydroxylation, imidazole ring cleavage, bond cleavage and bromate formation were the main degradation pathways. • Catalytic ozonation could effectively reduce toxicity of [HMIM]Br.