| Summary: | The preparation of mercapto-reduced graphene oxides (<b><i>m</i>-RGOs</b>) via a solvothermal reaction using P<sub>4</sub>S<sub>10</sub> as a thionating agent has demonstrated their potential as an absorbent for scavenging heavy metal ions, particularly Pb<sup>2+</sup>, from aqueous solutions due to the presence of thiol (–SH) functional groups on their surface. The structural and elemental analysis of <b><i>m</i>-RGOs</b> 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<sup>2+</sup> ions on the surface of <b><i>m</i>-RGOs</b> 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<sup>2+</sup> exhibiting the highest percentage removal, followed by Hg<sup>2+</sup> and Cd<sup>2+</sup> 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<sup>2+</sup> ions also yielded promising results, with almost 98% of Pb<sup>2+</sup> ions being removed within 30 min at pH 7 and 25 °C using a 1 ppm Pb<sup>2+</sup> 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<sup>2+</sup> from groundwater.
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