Highly efficient adsorption behavior of benzoylthiourea functionalized graphene oxide with respect to the removal of Hg(II) from aqueous solutions: isothermal, kinetic and thermodynamic studies

Graphene oxide (GO) was successfully functionalized with benzoylthiourea groups through a silanization reaction between hydroxyl groups on the surface of GO and N-((3-(triethoxysilyl)propyl)carbamothioyl)benzamide (CTBz). The synthesis and immobilization processes were characterized by FT-IR, XRD, CHN, TGA, SEM, TEM and BET. The CTBz-GO was rendered to sequestrate Hg(II) from aqueous solution and exhibited a higher adsorption capacity compared to many other previous reports based on the ion exchange, electrostatic attractions, and specifically, metal-complexing capability of the CTBz moieties on the surface of GO. The effects of pH, contact time, temperature and initial concentration of specious metal were investigated to optimize the adsorption conditions. The adsorption kinetic data was described well using the pseudo-second-order model, and the equilibrium data fitted well to a Langmuir isotherm and followed the chemisorption mechanism. Furthermore, CTBz-GO exhibited much better selectivity towards Hg(II) over the other metal ions, and the maximum saturated adsorption capacity estimated from the Langmuir model was 950 mg/g at pH = 6.0, and T = 25 degrees C. The calculated thermodynamic parameters suggested that the adsorption process was endothermic and spontaneous. Moreover, the regeneration study using 2 mol/L nitric acid as a regeneration agent indicated high reusability, up to five cycles of activity.