Ionic liquid-modified graphene oxide sponge for hexavalent chromium removal from water

Abstract

Chromium pollution in groundwater is a major cause of concern due to significant health risks of hexavalent chromium (Cr(VI)) ions. Graphene oxide (GO) covalently modified with 1-aminopropyl-3-methylimidazolium bromide (mimNH2) and freeze-dried to give 1-aminopropyl-3-methylimidazolium bromide functionalized graphene oxide sponge (mimGO sponge). mimGO sponge effectively adsorbed hexavalent chromium (Cr(VI), toxic) by electrostatic interactions and reduced Cr(VI) to trivalent chromium (Cr(III), less toxic) by an indirect mechanism with the contribution of delocalized π-electrons on the six-membered aromatic ring of mimGO sponge. The change in contact time, adsorbent loading, initial Cr(VI) solution concentration, and different types of adsorbents were investigated. The experimental data were fitted to the pseudo-second order kinetic model, which showed hydro-chromate adsorption on mimGO sponge was surface adsorption with chemical interaction. The adsorption process was well-defined by the Langmuir isotherm model, and equilibrium adsorption capacity was 208.3 mg/g at 23 ℃ in an acidic environment. The electrostatic interaction between the chromate ions and mimGO sponge also caused a reduction of Cr(VI) to less benign Cr(III) on the adsorbent surface. Thus, mimGO sponge has a green adsorbent that showed the potential for Cr(VI) removal from water.