Synthesis of doped and undoped Bi_1-xM_xFeO₃ porous networks (M = La, Gd, Nd; x = 0, 0.03, 0.05, 0.10) with enhanced visible-light photocatalytic activity

Doped and undoped Bi_1-xM_xFeO₃ porous networks (M = La, Gd, Nd; x = 0, 0.03, 0.05, 0.10) were synthesized by a facile glycine-nitrate combustion technique. The samples were analyzed by X-ray powder diffraction, scanning electron microscopy and UV–vis diffuse reflectance spectroscopy. For the first time, these Bi_1-xM_xFeO₃ porous networks were applied in photocatalytic degradation reactions in aqueous solution under visible light irradiation using the dye Rhodamine B as a model. Our studies reveal that the type of rare-earth dopant as well as its concentration has no impact on phase purity and particle morphology and that the dopant significantly affects the optical absorption properties: the micrometer sized porous networks exhibited band gap values and optical absorption properties similar to those reported for nanometer sized samples. Furthermore, all samples showed enhanced photocatalytic activities. Based on its highest overall photocatalytic activity, Bi_0.95Gd_0.05FeO₃ was chosen for stability, optimization and mechanistic experiments. Notably, the Bi_0.95Gd_0.05FeO₃ photocatalyst not only demonstrated very high efficiencies but also a remarkable stability under visible light irradiation, much superior than those of doped Bi_1-xM_xFeO₃ nanoparticles reported previously. This constitutes an important step towards industrial wastewater treatment applications. Under optimal reaction conditions, complete degradation of Rhodamine B was achieved in 1 h. The possible mechanism in the photodegradation process has been discussed in detail on the basis of radical trapping experiments.