Microwave-assisted synthesis of triple 2D g-C₃N₄/Bi₂WO₆/rGO composites for ibuprofen photodegradation: Kinetics, mechanism and toxicity evaluation of degradation products

In this study, the visible-light-driven Z-scheme g-C₃N₄/Bi₂WO₆/rGO heterojunctions with 2D/2D/2D configurations are prepared via a facile, rapid and low temperature microwave-assisted method. The physicochemical properties and morphologies of these heterostructured photocatalysts are characterized by various spectroscopies such as XRD, XPS, TEM/SEM, PL, FT-IR, UV–Visible spectroscopy and nitrogen adsorption measurements. The prepared g-C₃N₄/Bi₂WO₆/3 wt% rGO photocatalysts (incorporated with optimal 3 wt% of rGO) possess ca. 86 and 98% of ibuprofen (IBF) photodegradation under the visible light (λ > 420 nm) and solar light irradiation, respectively. The formation of well crystallized structure, morphology (nanoplates structure of Bi₂WO₆), higher visible light absorption and specific surface area (25.4 m² g⁻¹) are responsible for the superior performance of g-C₃N₄/Bi₂WO₆/3 wt% rGO. Moreover, the larger interfacial contact (identified by HRTEM) between triple 2D g-C₃N₄/Bi₂WO₆/rGO heterostructures can lead to surpassing interfacial charge carrier dynamics and reduce the combination of electron-hole pairs. IBF photodegradation intermediates and the corresponding reaction mechanisms are further investigated by using LC-MS/MS, indicating the superoxide radical ([rad]O₂⁻) and hydroxyl radicals ([rad]OH) are involved in the photodegradation of IBF and accordingly five intermediates are produced via three possible reaction pathways. The anti-hormonal effects of IBF and the photodegraded intermediate products are also evaluated by yeast-based bioassays. The results show that the intermediate products of photodegraded IBF have lower antagonistic effect on human hormone receptors than the pristine IBF.