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

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Reduction of potential carcinogenic bromate formation is a big challenge for the application of ozone in the treatment of Br−-containing wastewater. Three CeO2 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 CeO2 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 CeO2(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 CeO2(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 O2 through interaction with the (1 0 0) facet. It is demonstrated that O2−, its derivatives (i.e. OH and 1O2) and surface O are generated and get involved in SMZ degradation. It is noted that O2− also functions as a key reductant to convert Ce4+ to Ce3+ which reduce HBrO/BrO− and BrO3− to Br− and therefore inhibit the formation of bromate. These results indicate that CeO2(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.