Photocatalytic degradation of Rhodamine B using a reusable and magnetically separable Fe3O4/rGO/ZnO nanocomposite synthesized through green approach utilizing plant leaf extracts

Abstract

We propose the magnetically separable, green synthesis of Fe₃O₄/rGO/ZnO using a higher mass ratio of Fe₃O₄/rGO and varying ZnO concentration to degrade an aqueous solution of Rhodamin B under Fenton reaction and UV light irradiation. Fe₃O₄ had been synthesized under the coprecipitation method utilizing Moringa oleifera leaf, while rGO had been fabricated by sonicating GO utilizing Amaranthus viridis leaf. Afterward, Fe₃O₄/rGO was composited under a facile method with a mass ratio of 5:5. And the last, Fe₃O₄/rGO/ZnO was green-synthesized through precipitation method using Amaranthus viridis leaf with various molarity ratio of Fe₃O₄/rGO: ZnO equal to 1:1, 1:2, 1:3, 1:4, and 1:5. X-ray diffraction revealed the presence of Fe₃O₄ and ZnO phases, while Raman spectroscopy confirmed the successful reduction of GO to rGO. The morphological analysis demonstrated that the particles were nearly spherical, nonuniform, and slightly dispersed, with some agglomeration observed on the rGO sheets. Fourier-transform infrared spectroscopy identified metallic functional groups, including Fe–O and Zn–O, at 524–570 cm⁻¹ and 447–462 cm⁻¹, respectively. However, redshift absorption and band gap narrowing were observed as the ZnO concentration increased. Photoluminescence analysis revealed that increased ZnO concentration reduces recombination and improves charge separation efficiency. The vibrating sample magnetometer exhibited soft magnetic properties. The magnetization of Fe₃O₄/rGO saturated at 21.7 emu/g and diminished as incorporated ZnO. The photodegradation increased with the increase of ZnO concentration, reaching its optimum at 1:5, about 89.9%. Fe₃O₄/rGO/ZnO demonstrates a possible ecologically friendly photocatalyst for wastewater remediation. The photocatalyst can be reused for up to three cycles with no significant change in its performance. Scavenger evaluation indicates that electrons and holes are the predominant reactive species in the photocatalytic reaction involving Fe₃O₄/rGO/ZnO.