Abstract
<title>Abstract</title> <p>This work presents thermodynamic studies of the adsorptive separation mechanism and the properties of S-modified graphene nanosheets (S-GNS) using density functional theory (DFT). The B97-3c composite method and the COSMO solvent model (normal hexane) are used to determine adsorption geometry, binding energies, and thermodynamic parameters. The molecules interact with S-GNS active sites through π–π stacking and donor–acceptor interactions involving S–S and S–H bonds. Neither π–π stacking nor donor–acceptor interactions alone provide substantial binding to S compounds. However, their combined effect retains diphenyl sulfide, diphenyl disulfide, and thiophenol. Experimental characterization of S-GNS using SEM, XRD, and FTIR confirms successful incorporation of S into the graphene structure, transforming it from an inert carbon surface into a chemically active adsorbent. The proposed adsorbent shows high selectivity for aromatic sulfides, disulfides, and thiophenols, along with excellent reusability. The adsorption equilibrium constant for diphenyl sulfide is 833.423 in the liquid phase (normal hexane) and 1.22 × 10⁻² in the gaseous phase at 298 K. For diphenyl disulfide, these values are 458.705 and 6.44 × 10⁻³, respectively, and for thiophenol, they are 3.646 and 8.58 × 10⁻³. In the gas phase, all equilibrium constants are less than 0.01, indicating easy regeneration. Thus, S-GNS shows potential for the adsorptive removal of S compounds and remains suitable for the desulfurization of petroleum.</p>