Photocatalytic oxidation of trace carbamazepine in aqueous solution by visible-light-driven Znln2S4: Performance and mechanism

In this work, visible-light-driven Znln2S4 photocatalyst (band gap 1.98 eV, absorption wavelength 300–600 nm) was synthesized by a facile hydrothermal method for photocatalytic degradation of trace pharmaceutical carbamazepine (CBZ) in aqueous solution, and characterized by UV–Vis diffusive reflectance spectroscopy, BET, SEM and XRD, respectively. It demonstrated that a complete degradation of CBZ was achieved with an optimal Znln2S4 dosage of 30 mg/L under a 100 W iodine-gallium lamp irradiation of 20 min, which afforded the reaction rate constant and half-life being respectively 10.44 times higher and 1/8 less than that obtained by a direct photolysis without Znln2S4 photocatalyst. A negligible influence of initial solution pH on photocatalytic degradation of CBZ was confirmed under the given pH range of 5.0–9.0. The degradation efficiency of CBZ was slightly decreased from 91% to 84% after five consecutive cycles. Hydroxy radical (·OH) plays an important role in CBZ degradation accompanying a synergistic effect of photogenerated hole (h+) and O2− active species during reaction. Further, 44 intermediates were detected by LCMS-IT-TOF technique and tentative degrading pathways were proposed on the basis of the experimental results.