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

Abstract

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 photocatalyst 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 dramatically decreased from 80% to 20% after 120 h continuous operation, owning to the competition for hydroxyl radical (•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 •OH in the bulk or preferential consumption of •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.