Fabrication of g-C₃N₄ nanosheet/Bi₅O₇Br/NH₂-MIL-88B (Fe) nanocomposites: Double S-scheme photocatalysts with impressive performance for the removal of antibiotics under visible light

Novel graphitic carbon nitride (g-C₃N₄) nanosheet/Bi₅O₇Br/NH₂-MIL-88B (Fe) photocatalysts (denoted as GCN-NSh/Bi₅O₇Br/Fe-MOF, in which MOF is metal–organic framework) with double S-scheme heterojunctions were synthesized by a facile solvothermal route. The resultant materials were examined by X-ray photoelectron spectrometer (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence spectroscopy (PL), Fourier transform infrared spectroscopy (FT-IR), UV-Vis diffuse reflection spectroscopy (UV-vis DRS), photocurrent density, electrochemical impedance spectroscopy (EIS), and Brunauer–Emmett–Teller (BET) analyses. After the integration of Fe-MOF with GCN-NSh/Bi₅O₇Br, the removal constant of tetracycline over the optimal GCN-NSh/Bi₅O₇Br/Fe-MOF (15wt%) nanocomposite was promoted 33 times compared with that of the pristine GCN. The GCN-NSh/Bi₅O₇Br/Fe-MOF (15wt%) nanocomposite showed superior photoactivity to azithromycin, metronidazole, and cephalexin removal that was 36.4, 20.2, and 14.6 times higher than that of pure GCN, respectively. Radical quenching tests showed that ^•O_2^- and h⁺ mainly contributed to the elimination reaction. In addition, the nanocomposite maintained excellent activity after 4 successive cycles. Based on the developed n–n heterojunctions among n-GCN-NSh, n-Bi₅O₇Br, and n-Fe-MOF semiconductors, the double S-scheme charge transfer mechanism was proposed for the destruction of the selected antibiotics.