Ionic liquid functionalized graphene oxide for the adsorption of Ca2+ and Mg2+ ions from saline aqueous feed

Abstract

The development of an efficient adsorbent for removal of Ca2+ and Mg2+ ions using ionic liquid (IL) (1-Ethyl-3-methylimidazolium amino acetate) functionalized graphene oxide (GO) (IL-GO) is reported. The formation of IL-GO adsorbent was confirmed by FTIR, Raman, TGA, TEM and SEM-EDX analysis. The loading of IL within the IL-GO adsorbent was found to be 39 wt%. A minimum amount of IL (∼2%) leached from IL-GO after continuous stirring in DI water for 24 h. The IL-GO adsorbent exhibited high adsorption capacity towards Ca2+ and Mg2+ ions and stable recovery without cross-contamination of the feed water. The structural integrity of IL-GO was preserved after functionalization and adsorption of Ca2+ and Mg2+ from aqueous solution. Adsorption kinetics results show that the adsorption rates of Ca2+ and Mg2+ follow a pseudo second-order kinetic model. Moreover, the adsorption data of both Ca2+ and Mg2+ on IL-GO is well fitted using the Langmuir isotherm, implying that active sites for adsorption are homogeneously distributed on the IL-GO surface. IL-GO adsorbent shows promise in the removal of Ca2+ and Mg2+ ions from saline water, as part of a pretreatment process in reverse osmosis (RO) desalination plants, to control the inorganic fouling of RO membranes. Finally, since the adsorption capacity of IL-GO for Ca2+ and Mg2+ has been found to be much greater than that for Na+, the developed adsorbent could be a very good candidate for the separation of monovalent and divalent cations from an aqueous feed.

Keywords: Graphene Oxide, Ionic Liquid, Adsorption, Ca2+ and Mg2+, Membrane Fouling, Desalination