A dual approach for 4-fluorophenol degradation: Catalytic hydrodefluorination and ozonation

The issue of freshwater scarcity is a pressing global concern that poses significant challenges to human societies and ecosystems, and contaminants of emerging concern impose even more limits since they compromise the quality of water. One such fluorinated organic carbon molecule that should be degraded because of its toxic characteristics is 4-fluorophenol (4-FP), which may be found in drinking water. Some methodologies have emerged to remove and degrade this type of organic pollutants. However, due to the strong C-F bond, the degradation becomes very challenging. Catalytic hydrodehalogenation and ozonation (simple and catalytic) were employed in this study to degrade this contaminant. In catalytic hydrodehalogenation, four catalysts were synthesized, two of which became promising catalysts, namely 5 % Pd/CNT and 5 % Pd/TiO 2 . Nevertheless, no complete degradation was observed in the reaction time (5 h). Similar reaction pathways were observed, since similar selectivities were registered. However, 5 % Pd/CNT provided a higher conversion rate, and the H-F formation effect was evaluated in a solution of 2 mM NaOH, and also its stability through reutilization tests was evaluated. The addition of a base favoured the degradation of 4-FP due to the neutralization of HF formed during the reaction. The reutilization tests showed a decrease in catalytic activity even in this more alkaline environment. Ozonation proves to be a more promising technique, leading to the complete degradation of 4-fluorophenol in the absence and presence of catalysts (CNT and TiO 2 ), since a complete degradation was achieved in 1 h and also a higher degree of mineralization in 180 min. Sequential treatment, catalytic hydrogenation followed by ozonation, was also performed, revealing great results for achieving an even higher mineralization. • The removal of 4-fluorophenol (4-FP) was compared using two catalytic approaches. • 5 % Pd/CNT was the best hydrogenation catalyst in aqueous media. • Hydrogenation at higher pH promotes a greater 4-FP removal over 5 % Pd/CNT. • Ozonation lead to the complete removal of 4-FP and also when CNT and TiO2 were used. • Sequential catalytic hydrogenation and ozonation promoted a higher TOC removal.