The efficient adsorption removal of Cr(vi) by using Fe3O4 nanoparticles hybridized with carbonaceous materials

Abstract

Fe₃O₄ nanoparticles hybridized with carbonaceous materials, such as pinecone and graphene, were successfully synthesized by a facile hydrothermal method, which could be applied for Cr(VI) removal in aqueous solution. The nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N₂ adsorption–desorption isotherms. Due to the combination of pinecone and graphene, both the surface properties and morphologies of Fe₃O₄ were modified. Fe₃O₄ spherical particles were distributed and firmly anchored on the loose surface of pinecone or wrinkled graphene layers. The specific surface area increased from 23.85 to 27.86 and 121.17 m² g⁻¹ for Fe₃O₄/P and Fe₃O₄/G, respectively. It enhanced the adsorption capacity for Cr(VI) of Fe₃O₄/P (62.5 mg g⁻¹) and Fe₃O₄/G (78.5 mg g⁻¹). Study of the kinetics and isotherms showed that the pseudo-second-order kinetic and Langmuir isotherm models fitted the adsorption data well. There were three steps in the adsorption process, namely an instantaneous adsorption step, intraparticle diffusion and a final equilibrium stage. The reaction rate decreased along with temperature increasing, which indicated that Cr(VI) adsorption was an exothermic process. The E_a values were 34.39, 25.77 and 34.92 kJ mol⁻¹ for Fe₃O₄, Fe₃O₄/P and Fe₃O₄/G, respectively, which illustrated that the adsorption of Cr(VI) onto the surface of the nanocomposites was a physical process. In no more than 5 h, about 92.6% and 94% Cr(VI) were desorbed from the surface of Fe₃O₄/P and Fe₃O₄/G, respectively, which indicated that the adsorption–desorption process for Cr(VI) was reversible. The results demonstrated that Fe₃O₄/P and Fe₃O₄/G exhibited excellent adsorption performance in the removal of Cr(VI). It was proved that carbonaceous materials, such as pinecone or graphene, could enhance the adsorption performance of Fe₃O₄, and could be used as adsorbents to remove heavy metals in industrial effluents.