Understanding the interactions of (dimethyl)dibenzothiophene sulfones on functionalized graphene surfaces and carbons based on theoretical and experimental studies

In this work adsorption of dibenzothiophene (DBT) from a few non-polar hydrocarbon solvents, as well as from acetonitrile (ACN) on the selected commercial and oxidized carbonaceous materials was studied. In addition, adsorption of dibenzothiophene sulfone (DBTO₂) from the ACN solvent was compared to that of DBT. DBT shows gradually decreasing trend for adsorption on all adsorbents along with the increase of the length of the hydrocarbon chain. Adsorption of DBT from ACN is shown to be preferred on surfaces sparing with functional groups. DBTO₂ adsorption from ACN leads to significantly lower efficiencies as compared to DBT. Calculations reveal that retention of the sulfone molecules is to a great extent of dispersion type between the polarizable π systems of both the DBTO₂ molecule and the graphene surface (π-π stacking) which is magnified either by hydrogen bond formation between O=S=O moiety and OH or NH surface moieties, or by dipole-quadrupole interactions (depending on surface). Similar calculations performed for DMDBT sulfone (DMDBTO₂) reveal similar trends, but interaction energies with surfaces are, on average, higher. Experimental tests were in line with theoretical calculations of DBTO₂ interaction energies with the functionalized graphene surfaces. Sulfones were found to exhibit stronger affinity toward the adsorbent surface as compared to non-oxidized compounds. This provides the grounds for the oxidation step in the combined oxidative-adsorptive desulfurization process. However, the presence of ACN solvent, which exhibits quite significant affinity to DBTO₂ as well as to polar surface groups may hinder accessibility of the graphene active sites for sulfone molecules.