Oxygen Functionalization\nof Carbon Nanotubes Shifted\nthe Formation Pathway of Hydroxyl Radicals in Catalytic Ozonation:\nThe Overlooked Role of Hydrogen Peroxide

The oxygen functionalization of multiwalled carbon nanotubes\n(CNTs)\ncould enhance their reactivity in catalytic ozonation for hydroxyl\nradical (<sup>•</sup>OH) formation. However, the detailed pathway\nfor the transformation of ozone to <sup>•</sup>OH and the mechanism\nfor the decreased treatment performance at acidic pH values remain\nunclear. In this study, surface oxygen-functionalized CNTs (O-CNTs)\nwere prepared and used in catalytic ozonation to reveal the pathway\nfor <sup>•</sup>OH formation. The efficiencies of ozone utilization\nand its conversion to <sup>•</sup>OH were increased by 2.7\nand 554.8 times, respectively, under the catalysis of the O-CNTs.\nThe great reactivity of the O-CNTs was related to their high surface\noxygen contents and increased dispersion. Hydrogen peroxide was generated\nas a significant intermediate during the catalytic ozonation of the\nO-CNTs. The exposure of this substance linearly correlated with <sup>•</sup>OH exposure and pollutant degradation constants, with\ncorrelation coefficients of 0.991 and 0.911, respectively. The formation\nof hydrogen peroxide was relatively slower at acidic pH values, which\nexplains the low performance of catalytic ozonation. A mechanism was\nproposed that involved the generation of hydrogen peroxide to trigger\nthe peroxone process for free <sup>•</sup>OH formation. These\nfindings deepen our understanding of oxygen functionalization and\noffer insights into the catalytic ozonation of surface oxygen-rich\ncarbonaceous materials.