Unraveling the effect of nitrogen doping on graphene nanoflakes and the adsorption properties of ionic liquids: A DFT study

Geminal Dicationic Ionic Liquids (GDILs) and Their Adsorption on Graphene Nanoflakes

In this work, the configuration and stability of 15 geminal dicationic ionic liquids (GDILs) and their adsorption mechanism on the graphene nanoflake (GNF) are investigated using the density functional theory (DFT) method. We find that the interactions of dications ([DAm]+, [DIm]+, [DImDm]+, [DPy]+, and [DPyrr]+)) are stabilized near the anions ([BF4]-, [PF6]-, and [Tf2N]-) in the most stable configurations of GDILs through electrostatic interactions, van der Waals (vdW) interactions, and hydrogen bonding (H-bonding). Our calculations show that the adsorption of the GDILs on the GNF is consistent with the charge transfer and occurs via X···π (X = N, O, F), C-H···π, and π···π noncovalent interactions, leading to a decrease in the strength of the intermolecular interactions between the dications and anions in the GDILs. The thermochemistry calculations reveal that the formation of GDIL@GNF complexes is an exothermic and favorable reaction. The adsorption energy (Eads) calculations show that the highest Eads values for the interaction of GDILs containing [BF4]-, [PF6]-, and [Tf2N]- anions with the GNF are observed for the [DPy][BF4]@GNF (-23.56 kcal/mol), [DPy][PF6]@GNF (-29.29 kcal/mol), and [DPyrr][Tf2N]@GNF (-24.74 kcal/mol) complexes, respectively. Our results show that the adsorption of the GDILs on the GNF leads to the decrease of the chemical potential (μ), chemical hardness (η), and HOMO-LUMO energy gap (Eg) values and an increase in the electrophilicity index (ω) value of the GNF. In addition, the effect of GDIL adsorption on the UV-vis absorption spectrum was studied at the TD-M06-2X/cc-pVDZ level of theory. We find that the adsorption of GDILs results in minimal change in the shape of the main absorption peak (at λ = 363 nm) in the GNF spectrum and only shifts it to higher wavelengths. On the other hand, a new peak appears in the GNF spectrum upon adsorption of [DPy][Y] (Y = [BF4]-, [PF6]-, and [Tf2N]-) due to the relatively strong π···π interactions between the [DPy]+ dication and GNF. Finally, the transition density matrix (TDM) heat maps show that electron transfers related to the excitation states in the GDIL@GNF complexes occur mainly through π(C=C) → π*(C=C) transitions in the GNF and the transitions from [DPy]+ dication to the GNF.

Adsorption of Choline Phenylalanilate on Polyaromatic Hydrocarbon-Shaped Graphene and Reaction Mechanism with CO2: A Computational Study

The interaction of ionic liquids (ILs) with carbon materials is of fundamental importance in several areas of materials science, physics, and chemistry. Their adsorption on pristine and N-doped graphene surfaces is discussed here on the basis of results of density functional theory calculations. The nature of adsorption was investigated for an amino acid (AA)-based IL consisting of the choline cation [Ch] and the l-phenylalanilate anion [Phe] that interacts with a sheet of N-doped graphene. The interaction mechanism, binding energy, electron density, and non-covalent interaction analysis were evaluated by considering the cation, anion, and ion pair adsorbed on graphene separately. The distribution of cations and anions in the liquid bulk and on the graphene surface was then analyzed by molecular dynamics simulations. Since AA-based ILs are efficient absorbents for capture of CO2 due to the pronounced affinity of carbon dioxide to react with amino groups, we investigated the capacity of [Ch][Phe] to react with CO2 under various conditions. We considered the multistep mechanism of the reaction of [Phe] with CO2 first for the anion in the liquid bulk and then for the [Phe] anion adsorbed on the graphene surface. The initial step, the formation of the zwitterionic addition product, is followed by its structural rearrangement through intramolecular proton transfer and conformational isomerization processes to form carboxylic acid derivatives. The entire mechanism was evaluated for the [Phe] anion before and after adsorption on graphene to investigate how interactions with surfaces of carbon materials can affect the CO2 capture capacity of an AA-based IL such as [Ch][Phe].

The Influence of Ionic Liquids Adsorption on the Electronic and Optical Properties of Phosphorene and Arsenene with Different Phases: A Computational Study

Density functional theory (DFT) calculations have been performed to investigate the interfacial interactions of ionic liquids (ILs) on the α- and β-phases of phosphorene (P) and arsenene (As). Nine representative ILs based on the combinations of 1-ethyl-3-methylimidazolium ([EMIM]⁺), N-methylpyridinium ([MPI]⁺), and trimethylamine ([TMA]⁺) cations paired to tetrafluoroborate ([BF₄]⁻), trifluoromethanesulfonate ([TFO]⁻), and chloridion (Cl⁻) anions were used as adsorbates on the 2D P and As nanosheets with different phases to explore the effect of IL adsorption on the electronic and optical properties of 2D materials. The calculated structure, adsorption energy, and charge transfer suggest that the interaction between ILs and P and As nanosheets is dominated by noncovalent forces, and the most stable adsorption structures are characterized by the simultaneous interaction of the cation and anion with the surface, irrespective of the types of ILs and surfaces. Furthermore, the IL adsorption leads to the larger change in the electronic properties of β-phase P and As than those of their α-phase counterparts, which demonstrates that the adsorption properties are not only related to the chemical elements, but also closely related to the phase structures. The present results provide insight into the further applications of ILs and phosphorene (arsenene) hybrid materials.

DFT study of interaction of Palladium Pdn (n = 1-6) nanoparticles with deep eutectic solvents

In this study, we use density functional theory (DFT) calculations to investigate the stability, reactivity and interactions of Palladium Pd_n (n = 1-6) nanoparticles with ChCl:U and ChCl:EG based deep eutectic solvents (DESs). We find that the DES … Pd_n complexes are stabilized by two types of binding; Pd_n-X anchoring bonds (X = N atom of -NH₂ group in urea and [Cl]^- anion) and Pd_n…H-X (X = C, N and O) unconventional H-bonds. Analyses based on AIM, NBO, NCI, and EDA suggest that the anchoring bonds, which are electrostatic in nature are stronger than the unconventional H-bonds, which are van der Waals in nature. The Energy Decomposition Analysis reveals that the charge transfer plays an important role in the stability of DES…Pd_n complexes. Thermochemical calculations, including enthalpy (ΔH) and free energy (ΔG), indicate that the formation of the DES…Pd_n complexes is exothermic and occurs spontaneously. The binding energy (ΔE_b) calculations show that the ChCl:U DES has a stronger interaction with the Pd_n nanoparticles than their ChCl:EG DES counterparts. On the other hand, a similar trend for the ΔE_b, ΔH and ΔG values of the complexes is observed with increasing nanoparticle size of Pd_n (DES…Pd₅> DES…Pd₆> DES…Pd₄> DES…Pd₃> DES…Pd₂> DES…Pd₁). Our results show that the magnitude of charge transfer (ΔQ) value in the complexes follow the order observed for the ΔE_b values. It is also observed that increasing the energy gap E_g values of the complexes decreases the ΔE_b and ΔQ values of the complexes. The reactivity parameter calculations of the complexes show that the E_g and chemical hardness (η) values of ChCl:U…Pd_n and ChCl:EG…Pd_n complexes decrease with an increase in the nanoparticle size. Additionally, the global electrophilicity index (ω) values of the DES…Pd_n complexes increase with an increase in the Pd_n nanoparticle size, while no clear trend is seen for the chemical potential (μ) values of the complexes. The urea-based DES shows better suitability towards Pd_n nanoparticles than the ethylene glycol-based DES. Overall, such DESs are potentially promising green solvents for nanoparticle synthesis and activity.

Interaction of Cun, Agn and Aun (n = 1-4) nanoparticles with ChCl:Urea deep eutectic solvent

In this study, the interaction of noble metal nanoparticles (M_n, M = Cu, Ag, and Au; n = 1-4) with ChCl:Urea deep eutectic solvent was investigated using density functional theory (DFT) method. We find that ChCl:Urea mostly interact with the M_n nanoparticles through [Cl]^- anion ([Cl]^-…M_n) and nonconventional H-bonds of C-H⋯M_n and N-H⋯M_n. NBO, QTAIM, NCI and EDA analyses show that [Cl]^-…M_n interactions are stronger than the nonconventional H-bonds interactions. Our results indicate that the nature of [Cl]^-…M_n interactions is electrostatic, while the nonconventional H-bonds of C-H⋯M_n and N-H⋯M_n are van der Waals in nature. The negative values of enthalpy (ΔH) and free energy (ΔG) for the ChCl:Urea…M_n complexes reveal that the formation of ChCl:Urea…M_n complexes is exothermic and proceeds spontaneously. The calculation of binding energy (ΔE_b) of M_n nanoparticles with ChCl:Urea shows that the strength of interaction of Au_n nanoparticles with ChCl:Urea is more favorable than Cu_n and Ag_n, following the order ChCl:Urea…Au_n > ChCl:Urea…Cu_n > ChCl:Urea…Ag_n. Furthermore, the ΔE_b, ΔH and ΔG values enhance with increasing nanoparticle size from n = 1 to n = 4, ChCl:Urea…M₄> ChCl:Urea…M₃> ChCl:Urea…M₂> ChCl:Urea…M₁ (M = Cu, Ag, and Au).