Chemical and photocatalytic oxidative degradation of carbamazepine by using metastable Bi3+ self-doped NaBiO3 nanosheets as a bifunctional material

Abstract

Metastable Bi3+ self-doped NaBiO3 (NBO) nanosheets were prepared by using acidic hydrolysis of NaBiO3·2H2O in HNO3 solutions. It was found that the as-prepared NBO nanosheets showed both chemical oxidation ability and photocatalytic oxidation activity for the degradation of carbamazepine under visible light irradiation. The pseudo-zero order reaction kinetic constant for the photodegradation of carbamazepine (20mmolL−1) over the metastable NBO nanosheets was 0.087min−1, being 10.4 and 5.0 times that of the photocatalytic oxidation over the stable NBO nanosheets and the chemical oxidation over the metastable NBO nanosheets in dark, respectively. The enhanced photodegradation of carbamazepine over the metastable NBO nanosheets was mainly attributed to a reaction process of photocorrosion of the NBO nanosheets, which increased generation of singlet oxygen from the lattice oxygen of NBO and promoted a synergistic effect between the chemical oxidation and the photocatalytic oxidation. Singlet oxygen and photo-generated holes were identified as the major reactive species for photodegradation of carbamazepine. By a rough estimation, the (dark) chemical oxidation, photocorrosion process and photocatalysis contributed 19.4%, 60% and 20.6% of the total degradation of carbamazepine, respectively. Based on the identification of intermediates by GC– and LC–MS, two degradation pathways of carbamazepine in both chemical oxidation system and photocatalytic system were proposed. The developed dual-reactive-species-based photocatalysis may be a useful technology for the purification of water containing carbamazepine.