Facile and green synthesis of reduced graphene oxide for remediation of Hg(II)-contaminated water

Abstract

Mercury contamination of freshwater supplies poses a significant challenge to fresh water supplies, particularly in regions with historical or current gold mining. Nanomaterials are increasingly explored for the remediation of mercury-contaminated water due to their unique properties. Here, we report on the application of reduced graphene oxide (rGO) obtained via a facile, one-pot, green synthetic approach for treatment of Hg(II) contaminated water. In this approach, graphene oxide (GO) nanosheets prepared by a modified Hummer’s method were reacted with L-cysteine under mild conditions, resulting in nanosheets that were both reduced, and thiol functionalized. After characterization, the rGO nanosheets were used in batch studies to test the effect of time, solution pH, adsorbate and adsorbent concentrations on Hg removal. The reduction and functionalization of GO to rGO was confirmed by FTIR, XRD and elemental analysis. TEM images revealed a tendency for nanosheets stacking, particularly after functionalization. The adsorption of Hg(II) from solution was found to be optimal at pH 4 and reduction and functionalisation by cysteine increased Hg(II) removal by >15%. These data show that (i) L-cysteine affords an efficient, green, and relatively cheap means to produce rGO that can be applied for the treatment of Hg-contaminated water, (ii) Treatment with rGO yields a high efficiency for removal of Hg(II) ions by exploiting the affinity of Hg(II) ions for thiol groups contained in cysteine.