Green route synthesis and characterization of β-Bi₂O₃/SiO₂ and β-Bi₂O₃/Bi₂O_2.75/SiO₂ using Juglans regia L. shell aqueous extract and photocatalytic properties for the degradation of RB-5

Background: Photocatalyst oxides added with silicon improve their photocatalytic properties. In this research, nanostructured β-Bi₂O₃/SiO₂ and β-Bi₂O₃/Bi₂O_2.75/SiO₂ were obtained by means of a green method mediated by the using the aqueous extract of J. regia shell as the source of reducing biomolecules and as a natural source of plant silicon. Method: The β-Bi₂O₃/SiO₂ and β-Bi₂O₃/Bi₂O_2.75/SiO₂ nanostructures were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy (HR-TEM), field emission scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), and photoluminescence spectroscopy. The photocatalytic activity was measured by the degradation of Reactive Black 5 dye (RB-5). Results: FT-IR and XPS demonstrated the presence of plant silicon in the bismuth oxide photocatalysts. HR-TEM showed that the crystal size of the as-synthesized materials is ~ 25 nm and revealed that the β-Bi₂O₃ synthesized with ground shell extract and heat-treated at 300 °C contains the Bi₂O_2.75 phase. Good photocatalytic activity was found in all the studied materials; particularly, the heat-treated nanostructures showed excellent properties resulting in 92% degradation of RB-5 under UV–Vis light after 15 min of exposure, and 98% after 180 min. Conclusions: The findings of this research suggest that the metabolites coating the Bi₂O₃, which generate a large amount of hydroxyl radicals, the plant silicon content, and the crystalline defects conferred by the synthesis medium, all contribute to the improved degradation of the azo dye, providing the nanostructures with better photocatalytic activity.