The aim of this work is to investigate the ability of a new functionalized graphene oxide 3-amino-5-phenylpyrazole (F-GO) in the adsorption and removal of Hg2+ from aqueous solution. Both untreated graphene oxide (GO) and F-GO were characterized using FT-IR, EDX, FE-SEM, XRD and TGA analysis. The effects of three operational variables (pH, adsorbent dose and initial metal ion concentrations) on Hg2+ adsorption capacity of F-GO were investigated by central composite design. This technique aims to find a simple way to optimize the adsorption process and to analyze the interaction between the significant parameters. A quadratic model suggested for the analysis of variance found that the adsorption of metal ions heavily depend upon pH of the solution. The adsorption mechanism has been determined by pseudo-first-order kinetic models and the adsorption behavior was modeled by Freundlich isotherm. Results demonstrated that the adsorption capacities of F-GO for removal of Hg2+ were generally higher than those of GO, which is attributed to a decrease in the agglomeration of graphene layers due to the presence of amino-functional moieties with their bulky phenyl groups. Thermodynamic data indicated that the functionalization significantly affects the thermostability of the GO precursor materials. The desorption study demonstrated favorable regenerability of the F-GO adsorbent, even after three adsorption–desorption cycles.

    Abstract
    1 Introduction
    2 Experimental section
        2.1 Materials and characterization
        2.2 Preparation of functional F-GO and metal stock solution
        2.3 Adsorption procedure
        2.4 Experimental design by CCD of RSM
        2.5 Desorption studies
    3 Results and discussion
        3.1 Characterization of F-GO
        3.2 Adsorption process modeling by CCD
        3.3 Response surface plotting
        3.4 Adsorption equilibrium study
        3.5 Kinetic study
        3.6 Thermodynamic parameters
        3.7 The effect of interfering ions
        3.8 Desorption and regeneration study
        3.9 Comparison with other adsorbents
        3.10 Practical application
    4 Conclusions
    References

• Mobina Alimohammady(Department of Chemical Engineering, Golestan University)
• Mehdi Ghaemi(Department of Chemistry, Faculty of Science, Golestan University)