A facile approach to pure-phase Bi₂Fe₄O₉ nanoparticles sensitive to visible light

Graphical abstract: - Highlights: • Pure-phase Bi₂Fe₄O₉ nanoparticles were prepared by a facile and environmentally benign sol–gel method. • The multiband characteristic of the nanoparticles greatly expands the visible light absorption. • The visible-light-driven photocatalytic activity of the obtained nanoparticles was improved by 30-fold as compared to the bulk. - Abstract: Pure-phase Bi₂Fe₄O₉ nanoparticles with mullite-type structure were successfully fabricated through a facile and environmentally benign sol–gel process. According to the UV–Vis diffuse reflection spectrum, the multiband structure and the band edge position of the nanoparticles were confirmed, indicating the prominent absorption in the expanded visible-light region. As compared to the bulk, the visible-light-driven photocatalytic activity of the obtained nanoparticles was improved by 30-fold. The much improved photocatalytic efficiency of the sample mainly owed to the small crystal size and the multiband characteristic as well as the adding of H₂O₂ as electron scavenger and a source of hydroxide free radicals instead of Fenton-like reaction, leading to a low recombination of the photogenerated e⁻/h⁺ pairs