(29c) Electrostatic Potential of Ionic Liquids As an Effective Screening Approach for CO2 Capture

In response to the need to improve energy efficiency in separations processes such as CO₂capture from combustion point sources, natural gas sweetening, syngas processing and air separation, several polymers, inorganic and hybrid materials have been developed in recent years as advanced membranes. In the past several years, ionic liquids (ILs) have emerged as potential candidates for CO₂capture and separation due to their tunability,^1-2but there is now more interest in designing composite materials that can circumvent some of the common drawbacks of ILs. Accordingly, a better understanding of structure-property relationship of ionic liquids for CO₂capture is essential for designing new task-specific ILs for future use in composite membrane materials.³

Our work aims to provide rational design guidance and structure-property relationships for screening industrial solvents and polymeric membranes based on IL functionalities. It is well-known that quantum mechanical calculation can be used to theoretically study the structure, properties and reaction mechanisms of ionic liquids, but length and time scales are very limited. For decades, it has been recognized that electrostatic potential calculations can provide a great deal of insight for understanding and predicting molecular properties, and this information can be extrapolated from relatively small systems to bulk phase properties. The structural properties (density, molar volume, surface area) and electrostatic potential (ESP) of cations, anions, and combined ion pairs can be generated from first-principles density functional theory (DFT) calculations, as implemented in Gaussian 09,⁴ followed by further analysis by the Multiwfn⁵ program. Using small DFT-based models, CO₂ molecular probes can be used to sample interactions with IL ion pairs. This provides rapid information about the interaction of CO₂ with ILs that can be used to predict the Gibbs solvation energy and selective adsorption of CO₂ in different IL solvents and IL-based membrane materials. Thus, the structure-property-performance relationships of IL materials for CO₂ capture can be simulated directly from DFT calculations, and the detailed site-site interactions can also be predicted.

Reference:

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