Selective oxidation of aniline contaminants via a hydrogen-abstraction pathway by BiWO under visible light and alkaline conditions.

Conversion of aniline wastes to value-added products is always a promising method to treat aniline wastewater. In this study, a selective oxidation of aniline contaminants by BiWO was carried out under visible light and alkaline conditions. Kinetic results show that the oxidation rates of aniline increase with increasing pH values under visible light. UV-vis absorption spectra and GC-MS analysis confirm that azobenzene is the primary oxidation product with aminophenol and N,N'-diphenylhydrazine as the secondary products. The analyses from Mott-Schottky, electrochemical impedance spectroscopy (EIS), transient photocurrent and photoluminescence (PL) further indicate that OH promotes the separation and transfer of photogenerated electron-hole pairs on the surface of BiWO, thus facilitating oxidation of aniline. Quenching experiments and electron spin resonance (ESR) analysis confirm that h is the predominant specie in the BiWO system and aniline radical cation (PhNH) is an important intermediate. The Hammett and ΔBDE plots further reveal that e abstraction from aniline with the formation of PhNH, followed by H abstraction from PhNH with the formation of anilino radicals (PhNH), is the prerequisite for the formation of N,N'-diphenylhydrazine, which is then oxidized to azobenzene via the hydrogen-abstraction pathway. This work provides a cost-effective method to selectively oxidize aniline to azobenzene.