Preparation, decoration and characterization of graphene sheets for methyl green adsorption

Graphene sheets were produced from natural graphite using a two-step process. First, graphite oxide (GO) was obtained from graphite powder using Hummer's method. Second, graphene sheets were produced by the reduction of exfoliated graphite oxide using hydrazine hydrate in a microwave. The produced sheets were decorated with CoFe2O4 nanoparticles using hydrothermal precipitation method. The prepared samples were characterized by SEM, TEM and XRD. BET surface area was measured for graphene sheets and was found to be 40.6 m(2)/g. This study examined the feasibility of removing methyl green dye from aqueous solutions using graphene sheets and graphene sheets decorated with CoFe2O4 nanoparticles. Pseudo first-order, Pseudo second-order and intraparticle diffusion models were adopted to evaluate experimental data and thereby elucidate the kinetic adsorption process. Additionally, this study used the Langmuir and Freundlich isotherms to describe equilibrium adsorption. The pseudo second-order model is the best represented adsorption kinetics. Based on the regressions of intraparticle diffusion, experimental data showed that the adsorption of methyl green onto graphene sheets involved intraparticle diffusion, which was not the only rate-controlling step. The equilibrium adsorption of methyl green is best fitted in the Langmuir isotherm. Enthalpy (Delta H-0) and entropy (Delta S-0) were 36.38 kJ/mol and 87.54 J/mol K, respectively. The values of Delta H-0, Delta G(0) and E-a all indicated that the adsorption of methyl green onto graphene sheets was a physisorption process. (C) 2012 Elsevier B.V. All rights reserved.