Kaolinite based catalysts for efficient ozonation of recalcitrant organic chemicals in water

Abstract

Kaolinite has been widely utilized as a raw material in industrial and agricultural fields. Kaolinite derived materials can be used as catalysts in a catalytic ozonation process (COP) of recalcitrant organic chemicals in wastewater with decreased costs and improved profitability. The silicon (Si), aluminum (Al) and oxygen (O) in layered silicate of kaolinite and amorphous aluminum silicate of metakaolinite contribute to the formation of catalytic active sites. Kaolinite contains surface OH groups, SiO and AlO structures that promote oxidation through the formation of hydroxyl radicals (OHs) mineralizing the pollutant p-nitrophenol. Different metakaolinite has surface SiO and AlO structures that enhance mineralization through surface reaction. Catalytic ozonation of p-nitrophenol using kaolinite and metakaolinite increased the total organic carbon removal (46% and 41%, respectively) relative to single ozonation (32%). Introduction of Mn into kaolinite and metakaolinite further accelerate OH generation, improving the catalytic activity. Among the catalysts, the highest activity was observed using Mn loaded kaolinite (TOC removal 66%). Its enhanced activity may be mainly attributed to cooperative interactions from the distributed Mn oxides (Mn2+, Mn3+, and Mn4+) and surface OH groups. This study introduces the potential application of kaolinite and metakaolinite for the treatment of recalcitrant chemical wastewaters in catalytic ozonation processes.