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 TiO 2 supported on nickel foam (TiO 2 /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 TiO 2 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.