Modified nano-graphite/Fe3O4 composite as efficient adsorbent for the removal of methyl violet from aqueous solution

Nano-graphite/Fe3O4 composite (NG/FC) synthesized through deposition-precipitation method, was developed for the removal of methyl violet (MV) from aqueous solution. The parameters including pH, temperature and shaking time on MV removal efficiency were extensively investigated. The adsorption of MV increased smoothly in the pH range of 2.0-4.0, then remained at a higher level for the pH range of 4.0-10.0, but increased sharply at pH > 10.0, which demonstrated that the adsorption was affected strongly by pH. On the other hand, the adsorption capacity was increased sharply with the temperature rising. The adsorption equilibrium time could be reached in 10 min. The adsorption thermodynamics and kinetics were also investigated. The equilibrium data could fit the Langmuir isothermal model very well, and the thermodynamic analysis suggested that the adsorption of MV on the nano-graphite/Fe3O4 composites is a spontaneous, physical and endothermic process. To gain deep insight into the adsorption kinetics, both the pseudo-kinetic and particle diffusion models were examined. The results indicated the pseudo-second-order kinetic model fitted the experimental data better and the particle diffusion was proved to be the rate-determining step in the adsorption process of MV on NG/FC. The adsorbent exhibits excellent stability and remarkable regeneration ability as well. (C) 2014 The Authors. Published by Elsevier B.V.