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This work employs a combination of density functional theory-infrared (IR), conductor-like screening model for real solvents (COSMO-RS), and molecular dynamic (MD) methods to investigate the impact of hydroxyl functional groups on CO2 capture within dicationic ionic liquids (DILs). The COSMO-RS reveals that hydroxyl groups in DILs reduce the macroscopic solubility of CO2 but improve the selectivity of CO2 over CO, H2, and CH4 gases. Quantum methods in the gas phase and MD simulations in the liquid phase were conducted to delve deeper into the underlying mechanisms. The IR spectrum analysis confirms red shifts in CO2's asymmetric stretching mode and blue shifts in the CR–HR bond of the dication, indicating CO2–DIL interactions and the weakening of the anion–cation interactions caused by the presence of CO2. The results show that the positioning of anions around hydroxyl groups and HR atoms in rings inhibits the proximity of CO2 molecules, causing the hydrogen atoms within methylene groups to accumulate CO2. van der Waals forces were found to dominate the interaction between ions and CO2. The addition of hydroxyl groups strengthens the electrostatic interactions and hydrogen bonds between dications and anions. The stronger interaction energy between ions in [C5(mim)2-(C2)2(OH)2][NTf2]2 limits the displacement of CO2 molecules within this DIL compared to [C5(mim)2-(C4)2][NTf2]2. Compared to [C5(mim)2-(C4)2][NTf2]2, [C5(mim)2-(C2)2(OH)2][NTf2]2 exhibits stronger ion–ion interactions, higher density, and reduced free volume, resulting in a reduction in CO2 capture. These results provide significant insights into the intermolecular interactions and vibrational properties of CO2 in DIL complexes, emphasizing their significance in developing efficient and sustainable strategies for CO2 capture. [ABSTRACT FROM AUTHOR]

Dicationic ionic liquids (DILs) have been shown to be useful as an effective solvent for the absorption of CO2. However, compared to monocationic ionic liquids (MILs), they have been less investigated for this application. Previous studies on MIL–CO2 systems have shown that anions play the main role in tuning CO2 capture, but the partial negative charge on the oxygens of CO2 may interact with cation centers and, especially, for DILs with two charge centers, the role of cations can be significant. Therefore, the current work focuses on how cation symmetry and the length of side chains affect interactions and also the dynamical and structural properties of DIL–CO2 systems using molecular dynamics simulation. In addition, the effect of CO2 on the infrared vibrational spectra of isolated ions and ion triplet (DIL molecules) was studied using density functional theory calculations and the observed red and blue shifts have been interpreted. The results indicated that symmetric cation with longer side chains tend to interact more strongly with CO2 molecules. It seems that increasing the length of the side chains causes more bending of the middle chain, and in addition to increasing the free fraction volume, it weakens the interaction between cations and anions, and as a result more interaction between gas and cation. The results of this work may contribute to the rational molecular design of DILs for CO2 capture, DIL-based gas sensors, etc. [ABSTRACT FROM AUTHOR]

The nanoscopic structure of biodegradable choline-based naphthenic acid ionic liquids near the hexagonal boron-nitride (h-BN) surface was analyzed using quantum mechanics calculations and molecular dynamics simulations. The effects of the type of the ring (aliphatic or aromatic) and the size of the ring in the anion counterpart of the aliphatic ionic liquids (ILs) on the configurations, binding energies, orbital energies, density of states, charge transfer, and thermochemistry of adsorption of ILs on the h-BN surface were investigated. Also the significance of non-covalent interactions on the adsorption of ILs was disclosed from the quantum theory of atoms in molecule. The results of radial distribution functions, number density, and also charge density profiles showed the existence of a solid-like bottom layer in the vicinity of the surface. Angular distribution functions revealed that while the most probable orientation in aromatic anions is parallel to the h-BN sheet, the most probable orientation in aliphatic rings apparently is perpendicular to the surface. The mobility of cations and anions in the studied ILs with respect to the h-BN sheet was analyzed using their mean square displacements. For all ions near the surface, dynamics in the parallel direction were faster than those in the z-direction due to the structuring of the solid-like layer of ILs near the h-BN surface. Altogether, this study provides new insights into the physisorption of this new class of biodegradable ILs on h-BN nanosheets at the molecular level. [ABSTRACT FROM AUTHOR]

Highlights: [•] α-Amylase enzyme was covalently immobilized on the surface of silica-coated modified magnetite nanoparticles. [•] Magnetite (Fe3O4) nanoparticles have been considered suitable for immobilization of enzymes. [•] The EDX spectrum showed that magnetite nanoparticles were successfully coated with silica. [•] The TEM images showed that the diameter of silica-coated magnetite NPs was about 20nm. [ABSTRACT FROM AUTHOR]

A few studies on CO 2 capture using dicationic ionic liquids (DILs) show that they are more promising absorbents for CO 2 capture than monocationic ILs (MILs). Ion-ion, ion-CO 2 and DIL molecule-CO 2 interactions are important for understanding the performance-structure-property relationships for the rational design of DILs for CO 2 capture applications. However, the role of these interactions in determining CO 2 solubility in DILs is unclear. In this study, we used DFT methods to understand these interactions in three selected DILs)considering the effects of alkyl side chain length and symmetry in cations (by exploring different aspects, such as the electronic and geometrical structures, topological properties and the strength and nature of interactions, charge transfer, etc. The results showed that the most suitable solvent for CO 2 is the symmetric DIL with a longer side chain length, i.e. [Bis(mim)C 5 -(C 4 ) 2 ][NTf 2 ] 2 . In addition, we used the COSMO-RS calculations to obtain the macroscopic solubility of CO 2 in the studied DILs, which was in good agreement with the DFT results. Gas selectivity results calculated using COSMO-RS theory indicated that the selectivity of CO 2 from H 2 , CO and CH 4 gases decreases slightly with increasing the length of side alkyl chains., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (This journal is © The Royal Society of Chemistry.)