First principles analysis of graphene and its ability to maintain long-ranged interaction with H₂S

We determine the chemical activity of (a) carbon site of pristine graphene, (b) Stone-Wales (SW) defect site, and (c) BN-sites of BN-doped graphene towards adsorption of a toxic gas H₂S, through comparative analysis based on first-principles density functional theoretical calculations incorporating van der Waals (vdW) interactions. While the adsorption of H₂S is weak at both C and BN sites with a binding energy of 15 k J/mol, it is significantly stronger at the Stone-Wales defect site with a much higher binding energy of 26 k J/mol. This is clearly reflected in the contrasting orientation of H ₂S molecule in the relaxed geometries: the sulfur atom of H ₂S is closer to graphene (at a distance 3.14 Å) during physisorption at C and BN sites, while the molecule's H atoms come closer to graphene (at a distance 2.84 Å) during physisorption at the Stone-Wales defect site. The origin of the stronger binding interaction between H ₂S and a SW defect site is attributed to two possible reasons: (i) an increase in the vdW interaction; and (ii) the lowering of both energy of the HOMO level and the total energy of the H₂S molecule in attaining a stable configuration. Our findings are compared to the available theoretical results and their technological relevance is further discussed.