Highly improved photocatalytic degradation of rhodamine B over Bi2Ga4−xFexO9 solid solutions under visible light irradiation

Abstract

In this work, Bi₂Ga_4−xFe_xO₉ (0 ≤ x ≤ 1.2) solid solutions were prepared via the traditional high-temperature solid-state reaction. The Le Bail fitting on the powder X-ray diffraction patterns shows that these solid solutions were successfully synthesized. Scanning electron microscopy showed that the Bi₂Ga_3.2Fe_0.8O₉ sample was composed of sub-micron particle crystallites. Energy dispersive spectroscopy analysis and X-ray photoelectron spectroscopy were used to identify that the Fe element is trivalent when doping into the crystal structure. Ultraviolet-visible diffused reflectance spectra suggested that the bandgap of Bi₂Ga_3.2Fe_0.8O₉ is narrower than that of the undoped Bi₂Ga₄O₉ sample. Three strategies, including Fe³⁺ doping, addition of H₂O₂, and loading of the cocatalyst, were utilized to improve the photocatalytic degradation activity. The optimum photocatalytic performance was obtained over 2.5 wt% Cu/Bi₂Ga_3.2Fe_0.8O₉ sample in 20 ppm RhB aqueous solution (containing 1.5 mL H₂O₂) under visible light irradiation. Its photodegradation rate is 8.0 times that of Bi₂Ga₄O₉ containing 0.5 mL H₂O₂. The 2.5 wt% Cu/Bi₂Ga_3.2Fe_0.8O₉ photocatalyst remained stable and active even after four cycles. Also, its photocatalytic conversion efficiency for RhB was nearly 100%, which was achieved in 3 hours. The photocatalytic mechanism indicated that ·OH and h⁺ played an important role in the photocatalytic degradation reaction.