Few-layered graphene oxides as superior adsorbents for the removal of Pb(II) ions from aqueous solutions

Few-layered graphene oxides (GOs) were successfully synthesized from graphite using Hummers' method. The synthesized GOs were characterized in detail by SEM, AFM, XRD, and FTIR spectroscopy. The prepared GOs were used as adsorbents to preconcentrate Pb(II) ions from large volumes of aqueous solutions. The effects of pH, ionic strength and temperature on the removal of Pb(II) ions from solution to GOs were investigated. The sorption of Pb(II) on GOs was dependent on pH values and independent of ionic strength, which suggested that Pb(II) sorption on GOs was mainly dominated by strong inner-sphere surface complexation. The maximum adsorption capacities (C_smax) of Pb(II) on GOs were calculated to be 344 mg/g at 293 K, 487 mg/g at 308 K, and 758mg/g at 333 K, respectively. The C_smax values are the highest sorption capacities of today's materials for the sorption of Pb(II) ions from aqueous solutions. The thermodynamic parameters were calculated from the temperature-dependent sorption isotherms, and the results indicated that Pb(II) sorption on GOs was spontaneous and endothermic. The results suggested that the GOs were promising materials for the preconcentration of Pb(II) and other kinds of heavy metal ions from aqueous solutions in environmental pollution cleanup in real work