Catalytic ozonation of aqueous 4-methylquinoline by fluorinated ceramic honeycomb

Metal-free catalysts for catalytic ozonation have attracted more and more attentions to eliminate the risk of secondary pollution of heavy metals in water or wastewater treatment. Herein we prepared fluorinated ceramic honeycomb (FCH) with the dip-calcination method using NH₄F as the modifier over ceramic honeycomb (CH) to catalyze the ozonation of 4-methylquinoline (4-Meq), a typical harmful quinoline derivate discharged from coal or petroleum industries. The ozonation degraded 54.9% of 4-Meq and removed 14.4% of chemical oxygen demand (COD) in 30 min, while the FCH catalytic ozonation degraded 77.8% of 4-Meq and removed 29.2% of COD. In addition, FCH has a stable catalytic performance and can effectively remove 4-Meq as well as COD in real coal gasification wastewater. The fluorination endows the surface of the FCH with abundant Si-F groups as active acid sites and aluminum-attached hydroxyl groups, and then enhance the ozone decomposition to generate free reactive oxygen species (ROS). Those ROS includes free hydroxyl radicals, free superoxide radicals as well as singlet oxygen, and the free hydroxyl radical plays a major role in the degradation and COD removal of 4-Meq. The degradation of 4-Meq follows two pathways of the demethylation, benzene ring opening and the pyridine ring-opening. This work demonstrates an efficient catalyst for ozonation to root out the risk of the heavy metals pollution from catalysts, and provides an insightful understanding of the FCH catalytic ozonation.