Biochar-capped iron oxide nanocomposites prepared by ultrasonic method as nanophotocatalysts for the degradation of organic dyes using response surface methodology

Abstract

Iron oxide nanocomposites (Fe₃O₄@BC–1, Fe₃O₄@BC–2, and Fe₃O₄@BC–3) were synthesized via an ultrasound-assisted method at 5, 10, and 15 min to investigate their morphological, optical, and photocatalytic properties. Powder X-ray diffraction (P-XRD) analysis confirmed the formation of Fe₃O₄ with a cubic spinel structure. TEM analysis revealed that Fe₃O₄@BC–1 exhibited irregular rod- and plate-like structures with a particle size of 6.4 nm, Fe₃O₄@BC–2 displayed square-shaped particles with a mean size of 8.3 nm, and Fe₃O₄@BC–3 consisted of agglomerated particles with a size of 9.8 nm. Optical analysis showed a redshift in absorption peaks from 400 nm (2.36 eV) for Fe₃O₄@BC–1 to 417 nm (2.28 eV) for Fe₃O₄@BC–2, and 418 nm (2.32 eV) for Fe₃O₄@BC–3. The nanocomposites were evaluated as photocatalysts against Congo red (CR) and crystal violet (CV) using response surface methodology. Fe₃O₄@BC–3 exhibited the highest photocatalytic degradation efficiency of 99.86% of CR under optimal conditions (120 min, 3 mg, 15 ppm, pH 3) and Fe₃O₄@BC–2 achieved 99.28% degradation of CV under 90 min, 8 mg, and pH 8 for 5 ppm CV. Reactive species analysis confirmed hydroxyl (˙OH) and superoxide radicals (˙O₂⁻) as the dominant contributors to the dye's degradation.