Density Functional Investigation of Thioepoxidated and Thiolated Graphene

Abstract

Employing first-principle calculations, we have investigated the interaction between graphene and the thioepoxide and thiol groups. The SH radical cannot be chemisorbed on perfect graphene, although it is physisorbed. The chemisorption energy can be increased to 0.4 eV if multiple SH groups are bonded to the sheet or if they are attached to Stones-Wales defects. However, when free-energy corrections are considered, the addition of SH groups to perfect graphene is not spontaneous. In the case of the SW defects, the addition is favorable if two SH groups are attached to the shortest CC bond and in opposite sites of the sheet. The single vacancy defect site has the highest affinity for the SH radical, which is dissociatively attached. Finally, employing nanoribbons, we have simulated the reactivity of bare and hydrogen-terminated edges of graphene. The SH group is dissociatively bonded to bare edges. However, hydrogen-terminated zigzag edges prefer to bind the SH group. Considering the different reactivities observed, the defect sites and edges of graphene can be labeled by employing SH radicals. The sites containing sulfur can be used to attach gold nanoparticles or create vertical arrays of graphene sheets on Au surfaces. Finally, for thioepoxidated graphene, we have determined that the binding energy per S atom is 0.49 eV, larger than that determined for the thiol group but very small to be achieved experimentally because the free-energy change is expected to be close to 0 for this process. These results confirm the experimental evidence, which indicated that the sulfur-containing groups present in sulfur-graphite nanocomposites are attached to the edges of graphite, although vacancy defect sites must be considered. The electronic properties of the functionalized and defective graphene sheets are discussed. As a byproduct, we have found that the free-energy term may turn the attachment of a single HO group to graphene to be not spontaneous. Thus, the OH groups observed in graphene oxide are present at defect sites or agglomerated, to have their binding energy increased due to cooperative effects, confirming earlier experimental results.

Nature of Graphene Edges: A Review

“…For instance, Denis et al showed with first principles calculations that hydrogen-terminated zigzag edges prefer to bind to thiol (-SH) groups while bare edges are not reactive with thiol groups. 105) Using first-principles calculations, interactions among the SW defects present near GNR edges are also found to cause compressive or tensile stress. 106) In principle, compressive stress is known to be responsible for depression, local warping or wrinkles of GNRs, which results in delocalization of electrons in the defect states although the structure remains planar otherwise.…”

Microporous sulfur-doped carbon from thienyl-based polymer network precursors

“…in sulfur-doped graphene. 29,30 These sulfur-doped graphenes can be synthesised by adsorption of thiol groups at defect sites, 29,31 and they are discussed as potential sensors for polluting gases, such as NO x . 32 Furthermore, S-doped carbon nanotubes with altered electronic properties, 33 or even S-doped graphitic carbon nitride materials for photocatalysis 34 are discussed.…”

On the Addition of Aryl Radicals to Graphene: The Importance of Nonbonded Interactions

“…It is similar to the one used in our previous works about the reactivity of graphene. [20][21][22][23][24][25] The 6-31G* and 6-311G* basis sets [51] were selected and the ultrafine grid was utilized for the M06-2X and M06-L calculations. Free energy changes were estimated at 298 K and 1 atm.…”

“…The procedure to compute such values was the same as the one we used to study different covalently modified graphenes. [20][21][22][23][24][25] The approach relies on the fact that the quantity DG8 298 ÀDE eq is similar for different carbon structures used. In effect, for the addition of a thiyl radical, it is similar for ethane, pyrene, or the C 48 H 18 graphene flake.…”

“…In effect, for the addition of a thiyl radical, it is similar for ethane, pyrene, or the C 48 H 18 graphene flake. [21] Most of the periodic calculations performed with Gaussian 09 involved a 5 5 graphene unit cell, even though some comparisons were made with the 6 6 unit cell. In all cases, the structures were optimized with 50 k-points and electronic properties were obtained with a higher density, namely 500 k-points.…”