Cr(VI) removal from aqueous solution using chemically reduced and functionalized graphene oxide

Chemically reduced and functionalized graphene oxide (GO) was prepared by refluxing of GO with ethylenediamine (ED) using dimethyl formamide (DMF) as solvent. It was confirmed that both ED and DMF contributed to the reduction and functionalization of GO. The resulting adsorbent (ED–DMF–RGO) with amine groups was highly efficient in removing Cr(VI) from its aqueous solution and could be easily separated by filtration. The optimum pH for total Cr removal was observed at pH 2.0 and the Cr(VI) removal capacity of ED–DMF–RGO at this pH was 92.15 mg g−1, which was about 27 times higher than that of activated carbon, even nearly 4–8 times higher than that of various modified activated carbons. The presence of other ions such as Na+, K+, Ca2+, Cl−, and Br− had little effect on the removal of Cr(VI). Interestingly, Cr(VI) was reduced to low-toxic Cr(III) during the adsorption process, which followed an indirect reduction mechanism. Both the Cr(VI) adsorption and subsequent reduction of adsorbed Cr(VI) to Cr(III) contributed to the Cr(VI) removal. The obtained ED–DMF–RGO may be applicable in Cr(VI) removal if they are produced on a large scale and at low price in near future.