Comparative studies on the adsorption of metal ions from aqueous solutions using various functionalized graphene oxide sheets as supported adsorbents.

Graphene oxide (GO) was chemically modified by bis(2-pyridylmethyl)amino groups (BPED) through a multistep procedure. For comparison, and to justify the grafting of BPED groups onto the GO sheets, the GO-based material obtained after each step was used as a solid phase adsorbent for removing Cu(II), Ni(II) and Co(II) metal ions from aqueous solutions. The influence of metal ion concentrations, pH, contact time and temperature on their adsorption onto the GO-based adsorbents was investigated and the GO-EDA-CAC-BPED adsorbent showed the highest ability to adsorb Cu(II), Ni(II) and Co(II) with a concentration of 250 mg.L-1 at pH = 7. Additionally, it was demonstrated that the equilibrium adsorption capacities of these metal ions followed the order of Cu(II)>Ni(II)>Co(II) whatever the GO-based adsorbent. Moreover, to examine the underlying mechanism of the adsorption process, pseudo-first order, pseudo-second order, Elovich or Roginsky-Zeldovich and intraparticle diffusion models were fitted to experimental kinetic data. It was shown that the pseudo-second-order model was the most appropriate one to describe the adsorption of heavy metal ions by the GO-based materials. Finally, it was demonstrated that their desorption/regeneration capacities were higher than 10 cycles, opening the path to the removal of metal ions from wastewater solutions.