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

Abstract

Fe 3 O 4 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 N 2 adsorption-desorption isotherms. Due to the combination of pinecone and graphene, both the surface properties and morphologies of Fe 3 O 4 were modified. Fe 3 O 4 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 m 2 g À1 for Fe 3 O 4 /P and Fe 3 O 4 / G, respectively. It enhanced the adsorption capacity for Cr(VI) of Fe 3 O 4 /P (62.5 mg g À1 ) and Fe 3 O 4 /G (78.5 mg g À1 ). 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 À1 for Fe 3 O 4 , Fe 3 O 4 /P and Fe 3 O 4 /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 Fe 3 O 4 /P and Fe 3 O 4 /G, respectively, which indicated that the adsorptiondesorption process for Cr(VI) was reversible. The results demonstrated that Fe 3 O 4 /P and Fe 3 O 4 /G

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