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.