Unravelling the facets-dependent behavior among H2O2, O3 and oxygen vacancies on CeOx and the promotion of peroxone reaction at under acidic conditions

In this study, CeOx with different exposed facets was prepared to investigate their potential effect on activating the peroxone reaction (H2O2/O-3) and breaking through the restriction of solution pH on peroxone. By controlling the concentration of hydroxide, cube CeOx with a (100) facet, rod CeOx with a (110) facet and octahedron CeOx with a (111) facet were prepared by the hydrothermal precipitation method, and they all promoted heterogeneous peroxone for oxalic acid (OA) under acidic conditions. The catalytic activity of CeOx was highly related to their surface oxygen vacancies (OVs) and the interfacial electron transfer process. Both experiments and theoretical calculations showed that CeOx with different exposed facets activated peroxone in different ways and (111) CeOx possessed better activity than (100) or (110) CeOx. The low efficiencies of (100) and (110) CeOx were due to their inefficient use of H2O2 to reduce surface Ce4+ and their large energy gap to generate surface peroxide (OVs-OOH). (111) CeOx was stable with surface-adsorbed H2O2, and the rich electrons at OVs could be donated to H2O2 and generate OVs-OOH, which then triggered O-3 decomposition into hydroxyl radical (OH) and superoxide radical (O-2(-)). These electron migration processes depended on the electron-donating ability of the OVs rather than solution pH, therefore, still greater amounts of reactive species were generated under acidic conditions. The flexibility of the (111) CeOx/H2O2/O-3 process was further investigated for removing 20 kinds of pharmaceuticals. The synergy effect of (111) CeOx/O-3 and H2O2 varied with the structure of the pharmaceuticals.