Fe3O4 catalytic ozonation of iohexol degradation in the presence of 1-hydroxybenzotriazole: Performance, transformation mechanism, and pathways

Abstract

This study explored the degradation of an iodine X-ray contrast media, iohexol, under heterogeneous ozone-catalyzed oxidation by adding Fe3O4 and 1-hydroxybenzotriazole (HBT). Results show that increasing the dosages of Fe3O4 catalyst and ozone as well as solution pH were beneficial to the degradation of iohexol. The presence of low background humic acid (HA) concentration (≤10 mg/L) promoted iohexol degradation, but high HA concentration (≥20 mg/L) inhibited it. Adding HBT exhibited a similar effect on iohexol degradation as HA. The degradation rate constant of iohexol was calculated as 0.07108 min−1 in the Fe3O4/O3/HBT process ([HBT] = 5 μM) at pH 7.0, which was approximately 1.5 times higher than that in the Fe3O4/O3 process (0.04533 min−1), and 4 times higher than that in the O3 process (0.01742 min−1). Fe3O4/O3/HBT process was pH-dependent with high degradation efficiency of iohexol at pH 5 or 7. Singlet oxygen (1O2), hydroxyl radical (OH∙), and superoxide radical (O2-∙) have been identified in the Fe3O4/O3/HBT process, and the conversion of Fe2+ to Fe3+ was more obvious on the surface of Fe3O4 compared to that in the Fe3O4/O3 process. Transformation intermediates were identified, and the degradation pathways of iohexol were proposed. Overall, Fe3O4/O3 could enhance iohexol degradation compared with ozone-only system, and adding trace HBT in Fe3O4/O3 system can further enhance heterogeneous ozone-catalyzed process for rapid organic matter degradation.