Photocatalytic degradation of single and binary mixture of malachite green and rhodamine B dyes by biochar-capped iron oxide nanocomposites

Synthetic dyes widely used in textile are continuously being discharged into water sources and constitute significant hazard to the environment and human health. This study reports the synthesis, characterization, and photocatalytic performance of iron oxide nanocomposites using biochar carbonized at different temperatures for efficient degradation of malachite green (MG) and rhodamine B (RhB) dyes. Portulacaria afra leaves were carbonized at 200℃ to prepare Fe₃O₄@BC-1, at 400℃ to prepare Fe₃O₄@BC-2, and at 600℃ to prepare Fe₃O₄@BC-3 iron oxide nanocomposites. Powder X-ray diffraction analysis revealed a cubic Fe₃O₄ crystalline phase of iron oxide regardless of the carbonization temperature of the biochar. HRTEM images showed different morphologies with average particle sizes of 11.2-13.3 nm. Energy band gaps of 1.85 eV (Fe₃O₄@BC-1), 1.79 eV (Fe₃O₄@BC-2), and 1.97 eV (Fe₃O₄@BC-3) were obtained from the Tauc plot. The as-prepared iron oxide nanocomposites were used as photocatalysts for the degradation of malachite green (MG), rhodamine B (RhB), and their binary mixture under visible light irradiation. Fe₃O₄@BC-2 exhibited the highest photocatalytic degradation efficiencies of 99.74% for MG and 98.89% for RhB in the binary dye mixture. Optimal degradation of malachite green and rhodamine B was achieved at pH 10 and the iron oxide nanocomposites exhibited good photostability and reusability over five consecutive cycles.