Single-crystalline Bi2Fe4O9 synthesized by low-temperature co-precipitation: performance as photo- and Fenton catalysts

Abstract

Multi-functional, self-assembled mullite bismuth ferrites (Bi₂Fe₄O₉) have been synthesized by a facile co-precipitation method at a low temperature of 95 °C. The Bi/Fe precursor molar ratio and the reaction time were investigated for their influences on the resulting Bi₂Fe₄O₉ nanopads. The Bi₂Fe₄O₉ nanopads were formed via self-assembled crystal growth along the (001) plane, with an average thickness of 170 nm. The most well crystalline nanopads were produced at a reaction time of 36 h, beyond which the nanopads started to dissolve. The produced pure Bi₂Fe₄O₉ nanopads exhibit a high degree of elemental stoichiometry with uniform elemental distribution. The Bi₂Fe₄O₉ exhibits double bandgaps of 1.9 and 2.3 eV, and shows surface area of 5.8 m² g⁻¹. It can be photoexcited by visible light of up to 656 nm. The Bi₂Fe₄O₉ can be used as a photocatalyst and Fenton catalyst. Its catalytic activities were evaluated using bisphenol A (BPA) as the model pollutant. Under visible-light irradiation from a solar simulator, 34% of BPA could be removed (compared to only ∼3% with Evonik P25) via visible-light photocatalysis. With addition of H₂O₂ (16 mM), 54% and 73% of BPA could be removed within 1 h via dark Fenton-like and visible-light photo-Fenton reactions, respectively. The Bi₂Fe₄O₉ also exhibits a weak magnetism of 0.99 emu g⁻¹. The multi-functional Bi₂Fe₄O₉ nanopad has the potential to be used for continuous solar catalytic treatment of wastewater over an alternating day/night cycle and is recoverable via magnetically-enhanced gravity separation.