Efficiency and mechanism of pollutant degradation and bromate inhibition by faceted CeO2 catalyzed ozonation: Experimental and theoretical study

Reduction of potential carcinogenic bromate formation is a big challenge for the application of ozone in the treatment of Br − -containing wastewater. Three CeO 2 nanocrystals individually with exposed (1 0 0), (1 1 0), and (1 1 1) facets were prepared and adopted as catalysts for the ozonation of Br − containing wastewater. It is found that faceted CeO 2 greatly inhibited the bromate formation and simultaneously enhanced the pollutant removal. The catalytic activity follows the order of (1 0 0) > (1 1 0) > (1 1 1). In the presence of CeO 2 (1 0 0), there is 71.4 ± 2.9% of sulfamethoxazole (SMZ) degradation (only 24.9 ± 1.8% in ozone alone). Moreover, the generation of bromate was reduced by 29.6%, 38.8%, 52.4%, 66.4%, respectively, when the initial Br − concentration is 1.0, 2.0, 34.0, 65.0 mg L −1 . Meanwhile, the antibacterial-active groups in most of the identified intermediates were destroyed and much lower biotoxicity of the treated wastewater is observed. The good reducibility and Lewis acidity of CeO 2 (1 0 0) favors the activation of ozone and the redox cycle of ceria. DFT calculations show that ozone facilely dissociates into surface O and O 2 through interaction with the (1 0 0) facet. It is demonstrated that O 2 − , its derivatives (i.e. OH and 1 O 2 ) and surface O are generated and get involved in SMZ degradation. It is noted that O 2 − also functions as a key reductant to convert Ce 4+ to Ce 3+ which reduce HBrO/BrO − and BrO 3 − to Br − and therefore inhibit the formation of bromate. These results indicate that CeO 2 (1 0 0) catalyzed ozonation is a promising advanced oxidation process for the treatment of Br-containing wastewater, and crystal facet engineering is an efficient strategy to enhance the catalytic performance.