Catalytic ozonation for water and wastewater treatment: Recent advances and perspective.

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 °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 °C (R500-CeO2) showed lower catalytic activity as compared to R300-CeO2. O3 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.

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

Catalytic ozonation is believed to belong to advanced oxidation processes (AOPs). Over the past decades, heterogeneous catalytic ozonation has received remarkable attention as an effective process for the degradation of refractory organics in wastewater, which can overcome some disadvantages of ozonation alone. Metal oxides, metals, and metal oxides supported on oxides, minerals modified with metals, and carbon materials are widely used as catalysts in heterogeneous catalytic ozonation processes due to their excellent catalytic ability. An understanding of the application can provide theoretical support for selecting suitable catalysts aimed at different kinds of wastewater to obtain higher pollutant removal efficiency. Therefore, the main objective of this review article is to provide a summary of the accomplishments concerning catalytic ozonation to point to the major directions for choosing the catalysts in catalytic ozonation in the future.

Tingting Zhou

Papers

Efficiencies and mechanisms of ZSM5 zeolites loaded with cerium, iron, or manganese oxides for catalytic ozonation of nitrobenzene in water.