Catalytic performance and an insight into the mechanism of CeO2 nanocrystals with different exposed facets in catalytic ozonation of p-nitrophenol

Ceria based catalysts have been widely applied in ozonation of organic pollutants in wastewater treatment. Ceria with different exposed facets have not been used in catalytic ozonation. In this study, ceria nanorods (R-CeO2), nanocubes (C-CeO2) and nanooctahedra (O-CeO2) with different exposed facets (110) + (100), (100) and (111)) respectively were used in catalytic ozonation of p-nitrophenol. Two calcination temperatures 300 and 500 degrees C were selected for comparative catalytic activity. Ceria nanoparticles (NP-CeO2) were also prepared for comparative catalytic activity. Approximately 86%, 71%, 68%, 64%, 60% and 40% TOC was removed by ozonation catalyzed by R300-CeO2, C300-CeO2, CeO2-NP, O300-CeO2, R500-CeO2 and ozonation alone respectively. Nanorod calcined at 500 degrees C (R500-CeO2) showed lower catalytic activity as compared to R300-CeO2. O-3 was also rapidly decomposed by R300-CeO2 as compared to other catalysts and single ozonation. Inorganic hydroxyl radical scavengers and several characterization techniques were applied for investigating the underlying mechanism of catalytic ozonation. Hydroxyl radicals, surface peroxide and surface atomic oxygen as reactive oxygen species were generated for enhancing the catalytic activity. Furthermore, irrespective of surface area, the difference in catalytic activity of ceria nanoshapes were assigned to the differences in the abundance of surface basic sites, defects densities/oxygen vacancies (OVs) and coordination number of surface atoms. This study provides an insight to use other metals with variety of exposed facets for catalytic ozonation.