Superior Heavy Metal Ion Adsorption Capacity in Aqueous Solution by High-Density Thiol-Functionalized Reduced Graphene Oxides.

The preparation of mercapto-reduced graphene oxides ( m -RGOs ) via a solvothermal reaction using P 4 S 10 as a thionating agent has demonstrated their potential as an absorbent for scavenging heavy metal ions, particularly Pb 2+ , from aqueous solutions due to the presence of thiol (-SH) functional groups on their surface. The structural and elemental analysis of m -RGOs was conducted using a range of techniques, including X-ray diffraction (XRD), Raman spectroscopy, optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy equipped with energy-dispersive spectroscopy (STEM-EDS), and X-ray photoelectron spectroscopy (XPS). At pH 7 and 25 °C, the maximum adsorption capacity of Pb 2+ ions on the surface of m -RGOs was determined to be approximately 858 mg/g. The heavy metal-S binding energies were used to determine the percent removal of the tested heavy metal ions, with Pb 2+ exhibiting the highest percentage removal, followed by Hg 2+ and Cd 2+ ions having the lowest percent removal, and the binding energies observed were Pb-S at 346 kJ/mol, Hg-S at 217 kJ/mol, and Cd-S at 208 kJ/mol. The time-dependent removal study of Pb 2+ ions also yielded promising results, with almost 98% of Pb 2+ ions being removed within 30 min at pH 7 and 25 °C using a 1 ppm Pb 2+ solution as the test solution. The findings of this study clearly demonstrate the potential and efficiency of thiol-functionalized carbonaceous material for the removal of environmentally harmful Pb 2+ from groundwater.