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 (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction using hydrogen (TPR-H₂) 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) 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.