Thiosemicarbazide-grafted graphene oxide as superior adsorbent for highly efficient and selective removal of mercury ions from water

Abstract

In this work, the superior nanoadsorbent (GO-TSC) for highly effective adsorption of mercury ions from water solutions was developed, by grafting the thiosemicarbazide molecules (TSC) to the graphene oxide (GO) nanosheets. GO-TSC combines the extraordinary properties of GO, such as high specific surface area and an excellent dispersibility in aqueous solutions with strong affinity of TSC molecules to Hg(II) ions. The experiments show that the adsorption of Hg(II) on the GO-TSC is significant in a broad pH range, and reaches maximum value (close to 100%) at pH 3–4, with the maximum adsorption capacity of 231 mg g−1 at pH 3.5. Due to the excellent dispersibility of GO-TSC nanosheets, an extremely small GO-TSC dosage of 5 mg L-1 is required to remove Hg(II) ions from aqueous solution in a short contact time (from 10 to 30 min for adsorption of 90–95% Hg(II)). X-ray photoelectron spectroscopy indicate that the adsorption of Hg(II) is based on the chemisorption, and Hg(II) ions can be complexed by a single TSC molecule as bidentate chelating agent (S–Hg–N), or two neighboring TSC molecules (S–Hg–S). Due to the formation of strong S–Hg–N and S–Hg–S interactions, the selectivity of the GO-TSC toward Hg(II) is impressive. Hg(II) ions can be removed from aqueous solutions with very high ionic strength and high concentration of potentially coexisting ions.