Photocatalytic degradation of flumequine with B/N codoped TiO2 catalyst: Kinetics, main active species, intermediates and pathways

Abstract

N doped and B/N codoped TiO2 photocatalysts were synthesized by liquid phase precipitation combined with solid phase thermal decomposition method. For comparison, the same method was also used to prepare undoped TiO2 samples. The prepared catalysts were characterized using various techniques including XRD, BET, FT-IR, UV–vis DRS, XPS, SEM and Raman spectroscopy. BET results showed that 300B-N/TiO2 sample has higher BET surface area than undoped TiO2 and N-TiO2 samples. XPS analysis indicated that the B atoms mainly occupy the interstitial position of the TiO2. The photocatalytic performance of prepared undoped and doped TiO2 catalysts was evaluated under simulated sunlight irradiation by employing flumequine (FLU) as a target compound. The photocatalytic performance of TiO2 catalyst can be obviously enhanced by B/N codoping. In addition, B/N codoped TiO2 catalysts exhibit excellent cycling stability. The photocatalytic activity remained 90.1% for 300B-N/TiO2 after four repeated runs. The scavenger study shows that the main reactive species in the photocatalytic degradation process of FLU were superoxide radical (O2−) and photogenerated electrons (e−). Based on detected degradation intermediates of FLU, three possible degradation pathways for FLU were proposed. The degradation of FLU occurs mainly by means of hydroxyl addition and subsequent demethylation and decarboxylation reactions, substitution of fluorine atom by hydroxyl and ring opening of quinolone ring. This work offers a simple method for fabrication of B/N codoped TiO2 photocatalysts, which will be effective in the removal of fluoroquinolones (FQs) in real wastewater.