Abstract
New functional ionic liquid (IL) capped graphene quantum dot (GQD) was synthesized as an adsorbent for the removal of toxic heavy metal chromium(VI) ion (Cr6+). The physicochemical properties of the adsorbent (IL-GQD) were investigated by Fourier transform infrared, Xray diffraction, atomic force microscopy, Raman, scanning electron microscopy, energy dispersive X-rays, and transmission electron microscopy analyses. The adsorption parameters, namely equilibrium time, solution pH, competing co-ions, dosage, and initial chromium concentration, were optimized for maximum Cr6+ adsorption. The maximum adsorption capacity reached 934.62 mg/g at 40 min in neutral pH; this is much better than most of the other adsorbents reported earlier. In addition, the effect of pH in solution was investigated in the range of 3.0-12.0. The result showed that the lower pH value was found to favor the adsorption. The adsorption kinetics and isotherms fitted well with Langmuir isotherm model and pseudo-second-order kinetic model. The thermodynamic studies indicated that the chromium adsorption process followed a spontaneous and endothermic model. This new functionalization of ionic liquid moieties into graphene quantum dot provides excellent results for the removal of toxic Cr6+. This can be utilized for field applications to reduce the chromium concentration to below the tolerance limit (>0.05 mg L-1).