Bi₂O₃ particles decorated on porous g-C₃N₄ sheets: Enhanced photocatalytic activity through a direct Z-scheme mechanism for degradation of Reactive Black 5 under UV–vis light

Synthesis of a composite photocatalyst is a good approach to utilize higher portion of solar spectrum and improves separation of electron-hole pairs. Herein, a novel Bi₂O₃/porous g-C₃N₄ synthesized using impregnation method showed dramatic photo-activity improvement under irradiation of UV–vis light. Further characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively-coupled plasma atomic emission spectroscopy (ICP-AES), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) proved the existence of both g-C₃N₄ and Bi₂O₃ in which Bi₂O₃ particles are decorated on porous g-C₃N₄ sheets. Photocatalytic activity test of Bi₂O₃/porous g-C₃N₄ composites shows that 9 wt% Bi₂O₃/porous g-C₃N₄ is the best photocatalyst with 84 % of Reactive Black 5 (RB 5) degradation under 120 min of UV–vis light. It was confirmed that the photocatalytic activity improvement are due to the reduction of electron-hole recombination and wider absorption of light which were proven using photoluminescence (PL) and UV–vis diffuse reflectance spectroscopy (DRS), while surface area plays an insignificant role in the photocatalytic performance. In addition, process parameters studies concluded that 9 wt% Bi₂O₃/porous g-C₃N₄ worked best in RB 5 with concentration of 10 ppm, pH 5.7 and by using 1 g/L photocatalyst loading. From radicals quenching test, superoxide radical (O₂•⁻) was found to be the most active radical which mineralizes RB 5 by following the mechanism of direct Z-scheme pathway. Lastly, 9 wt% Bi₂O₃/porous g-C₃N₄ is stable and preserved its photocatalytic activity up to three times for degradation of RB 5.