Meta-Hybrid Density Functional Theory Study of Adsorption of Imidazolium- and Ammonium-Based Ionic Liquids on Graphene Sheet

Abstract

In this study, two types of ionic liquids (ILs) based on 1-butyl-3-methylimidazolium [Bmim] + and butyltrimethylammonium [Btma] + cations, paired to tetrafluoroborate [BF 4 ] − , hexafluorophosphate [PF 6 ] − , dicyanamide [DCA] − , and bis(trifluoromethylsilfonyl)imide [Tf 2 N] − anions, were chosen as adsorbates to investigate the influence of cation and anion type on the adsorption of ILs on the graphene surface. The adsorption process on the graphene surface (circumcoronene) was studied using M06-2X/cc-pVDZ level of theory. Empirical dispersion correction (D3) was also added to the M06-2X functional to investigate the effects of dispersion on the binding energy values. The graphene•••IL configurations, binding energies, and thermochemistry of IL adsorption on the graphene surface were investigated. Orbital energies, charge transfer behavior, the influence of adsorption on the hydrogen bond strength between cation and anion of ILs, and the significance of noncovalent interactions on the adsorption of ILs on the graphene surface were also considered. ChelpG analysis indicated that upon adsorption of ILs on the graphene surface the overall charge on the cation, anion, and graphene surface changes, enabled by the charge transfer that occurs between ILs and graphene surface. Orbital energy and density of states calculations also show that the HOMO−LUMO energy gap of ILs decreases upon adsorption on the graphene surface. Quantum theory of atoms in molecules analysis indicates that the hydrogen-bond strength between cation and anion in ILs decreases upon adsorption on the graphene surface. Plotting the noncovalent interactions between ILs and graphene surface shows the role and significance of cooperative π•••π, C−H•••π, and X•••π (X = N, O, F atoms from anions) interactions in the adsorption of ILs on the graphene surface. The thermochemical analysis also indicates that the free energy of adsorption (ΔG ads ) of ILs on the graphene surface is negative, and thus the adsorption occurs spontaneously.

Surface Charge‐Transfer Doping of Graphene Nanoflakes Containing Double‐Vacancy (5‐8‐5) and Stone–Wales (55‐77) Defects through Molecular Adsorption

“…To understand graphene behavior by quantum mechanical calculations, a one‐layer plate of six‐membered aromatic rings is often regarded as an appropriate graphene model. Hydrogen termination is usually used to saturate the boundaries of graphene and defective graphene models . Thus, in this work, the model structure of isolated nanoflakes was taken from the literature, and we were aware of the fact that, due to the presence of finite size and edges, the properties might vary from the real system to some extent.…”

“…To build the DV (5‐8‐5) and SW (55‐77) defects, first, we built up a perfect GNF model with 54 carbon atoms and 18 hydrogen atoms (C 54 H 18 ; circumcoronene). This model has been widely used as a suitable model for graphene and defective graphene surfaces in the literature . Second, a C−C bond in the GNF model was rotated by 90° to give an ideal SW defect in the GNF model.…”

“…Calculated vibrational frequencies without imaginary frequencies ensured stable structures for the complexes investigated. The M06-2X computational method has already been reported in the literature for investigations into the interactions of ionic liquids with graphene and hexagonal boron-nitride sheets, [43,44] nucleo- bases and amino acids with graphene, graphene oxide, defective graphene sheets, [36,45] and electron D/A organic molecules with graphene sheets. [46,47] Empirical dispersion-correction (D3) developed by Grimme et al [48] was also added to the M06-2X functional to investigate the effects of dispersion on the binding energy values.…”

“…Hydrogen termination is usually used to saturate the boundarieso fg raphene and defective graphene models. [43][44][45][59][60][61][62][63] Thus, in this work, the models tructure of isolated nanoflakes was taken from the literature,a nd we were aware of the factt hat, due to the presence of finite size and edges, the properties might vary from the real system to some extent. Therefore, we considered the effect of size on their properties.…”

Structural and electronic properties of alumaphosphinine complexes with metal ions: A theoretical study

“…The sign of H(r) determines whether the accumulation of charge at a given point (r) is stabilizing (H(r) < 0) or destabilizing (H(r) > 0). The energies for interaction of phosphorous atom and metal cation (E P M ) are calculated by the following equation [26][27][28][29]:…”