Enhanced catalytic ozonation by highly dispersed CeO2 on carbon nanotubes for mineralization of organic pollutants

Heterogeneous catalytic ozonation, in which ozone is activated by various catalysts to produce reactive oxygen species (ROS), is an effective approach to degrade persistent organic pollutants in water. However, catalyst with high activity and good stability for catalytic ozonation still remains rare. In this work, a highly dispersed cerium oxide on oxidized carbon nanotubes (CeO2-OCNT) were prepared and characterized by X-ray diffractometer (XFtD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction using hydrogen (TPR-H-2) experiments. The as-synthesized CeO2-OCNT showed significantly enhanced catalytic performance for degrading organic pollutants during catalytic ozonation. The removal efficiency of optimized CeO2-OCNT for phenol mineralization was 2-3 times of pure CeO2 and OCNT, and was also better than that of a composite with the same composition, which demonstrated a synergic effect between OCNT and CeO2 on CeO2-OCNT for catalytic ozonation. The TOC removal efficiency exhibited no obvious reduction after five cycling experiments, indicating the synthesized CeO2-OCNT possessed good reusability. Moreover, electron paramagnetic resonance (EPR) and radicals quenching experiments revealed that hydroxyl radicals ((OH)-O-center dot) were the dominant ROS for organic pollutants degradation. The superior activity of CeO2-OCNT for catalytic ozonation could be attributed to the well-dispersed CeO2, the improved mass transfer, and the facilitated redox Ce3+/Ce4+ cycling.