Photocatalytic mechanisms and photocatalyst deactivation during the degradation of 5-fluorouracil in water

Photocatalytic oxidation and micropollutants have both attracted extensive attention in the field of wastewater treatment. However, invalidation mechanism of photocatalytic system and target transformation are still a challenge. Here, we used TiO2 supported on nickel foam (TiO2/NF) and 5-fluorouracil (5-FU) as model photo -catalyst and pharmaceutical micropollutant to investigate photocatalytic transformation pathways of 5-FU and inhibition mechanisms of its degradation efficiency reduction. Incredibly, removal efficiency of 5-FU dramati-cally decreased from 80% to 20% after 120 h continuous operation, owning to the competition for hydroxyl radical (center dot OH) between trans-intermediates and 5-FU, accumulated in the solution. Using HR-MS, the produced intermediates during photocatalytic degradation of 5-FU were revealed to be that mono/polyhydroxylated compounds, short-chain oxides and carboxylation ones were main trans-intermediates. Combining ATR-FTIR, SEM-EDS and validation experiments for factors, it was found that the inhibition of 5-FU degradation should be contributed to the competition for center dot OH in the bulk or preferential consumption of center dot OH in TiO2 diffusion layer, by the aforementioned intermediates. The present study provides insights into photocatalytic oxidation of 5-FU and basic information about mechanisms of inhibition on target contaminant removal.

Automated summary

This study investigated the photocatalytic transformation pathways of 5-fluorouracil (5-FU) and the inhibition mechanisms of its degradation efficiency reduction using TiO2 supported on nickel foam (TiO2/NF) as the photo-catalyst and pharmaceutical micropollutant. The produced intermediates during the photocatalytic degradation of 5-FU were identified as mono/polyhydroxylated compounds, short-chain oxides, and carboxylation ones. The inhibition of 5-FU degradation was found to be attributed to the competition for hydroxyl radical (center dot OH) and the preferential consumption of center dot OH in the TiO2 diffusion layer by the intermediates.