Plant extract mediated synthesis of BiFeO₃ nanoparticles for photocatalytic degradation of methylene blue dye

The present study aimed at investigating the photocatalytic activity of biosynthesized bismuth ferrite (BiFeO₃) nanoparticles as catalysts for the degradation of toxic methylene blue (MB) dye. The BiFeO₃ nanoparticles were synthesized using a simple and low-cost method, mediated by leaf extract of Strychnos nux-vomica plant. Several characterization techniques, including XRD, FTIR, Raman spectroscopy, DLS, Zeta potential, FESEM with EDX, HRTEM, SQUID and UV–vis spectroscopy were employed to investigate the properties of these nanoparticles. The XRD analysis coupled with Rietveld refinement, indicated the purity of the material, showing a rhombohedral phase, which was further validated by Raman analysis. FTIR analysis revealed the presence of various phytochemicals, which perhaps have played a great role in synthesis process of nanoparticles. The estimated optical band gap was nearly 1.98 eV, smaller than the previously reported data. The SQUID measurements indicated weak ferromagnetic nature of these nanoparticles, possibly due to the formation of canted Fe sublattice, influenced by Dzyaloshinskii–Moriya interactions. The FESEM and HRTEM images revealed the irregular shape of nanoparticles with an average size of around 37 nm. The prepared nanoparticles were used as photocatalyst for photodegradation of MB dye under sunlight irradiation. The synthesized nanoparticles demonstrated effective photocatalytic activity, achieving complete degradation of MB dye under sunlight exposure with optimal conditions: pH 2, catalyst dose of 50 mg, and irradiation time of 80 min. The scavenger test indicated the important role of superoxide radicals and hydroxyl radicals in the photodegradation mechanism. Furthermore, the reusability test demonstrated stability even after three cycles without significant loss in its activity. Therefore, these results demonstrate that these biosynthesized BiFeO₃ nanoparticles are promising for the efficient removal of organic pollutants from wastewater.