EDTA-Assisted Sonochemical Synthesis of Polymorphic Bismuth Ferrites: Structural and Photocatalytic Characterization

This study investigated the sonochemical synthesis of bismuth ferrite (BFO) systems, focusing on how varying EDTA concentrations influence crystalline phases and photocatalytic performance. X-ray diffraction (XRD) analysis showed that 33EDTA uniquely formed single-phase BiFeO₃, while other EDTA concentrations resulted in secondary phases like Bi₂₅FeO₄₀ and Bi₂Fe₄O₉. EDTA concentration was crucial for phase control, with higher concentrations favoring the Bi₂Fe₄O₉ phase (67.8% phase for 100EDTA sample). All samples exhibited consistent band gap energies (2.25-2.28 eV), indicating visible light absorption. X-ray photoelectron spectroscopy (XPS) revealed increased oxygen vacancy concentrations in multiphase samples due to secondary phases and heterojunctions. Magnetic characterization showed an almost magnetic behavior in 33EDTA and 100EDTA (<i>M</i> _s of 0.0002 and 0.001 emu/g), with higher Bi₂Fe₄O₉ content contributing to increased magnetism in 100EDTA. Photoluminescence (PL) measurements indicated higher electron-hole recombination in single-phase 33EDTA compared to multiphase samples with heterojunctions. Photocatalytic tests with methylene blue (MB) showed that at neutral pH, multiphase samples generally had higher, though still low, efficiency due to heterojunctions, degrading approximately 46% for the 100EDTA sample. Despite poor performance at neutral pH (32%), single-phase 33EDTA exhibited significantly improved photocatalytic activity at pH 3, achieving complete MB degradation after 120 min. This was attributed to the positive surface charge at lower pH, minimizing adsorptive effects. Mechanistic studies confirmed both electrons and holes are active in pure BiFeO₃ photocatalysis, while heterojunctions primarily limited the mechanism to superoxide formation in multiphase samples.