Local environment structure and dynamics of CO2 in the 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and related ionic liquids

Understanding the interactions between the bis(trifluoromethylsulfonyl)imide anion and absorbed CO2 using X-ray diffraction analysis of a soft crystal surrogate

The selective carbon dioxide (CO₂) absorption properties of ionic liquids (ILs) are highly pertinent to the development of methods to capture CO₂. Although it has been reported that fluorinated components give ILs enhanced CO₂ solubilities, it has been challenging to gain a deep understanding of the interactions occurring between ILs and CO₂. In this investigation, we have utilized the soft crystalline material [Cu(NTf₂)₂(bpp)₂] (NTf₂^‒ = bis(trifluoromethylsulfonyl)imide, bpp = 1,3-bis-(4-pyridyl)propane) as a surrogate for single-crystal X-ray diffraction analysis to visualize interactions occurring between CO₂ and NTf₂^‒, the fluorinated IL component that is responsible for high CO₂ solubility. Analysis of the structure of a CO₂-loaded crystal reveals that CO₂ interacts with both fluorine and oxygen atoms of NTf₂^‒ anions in a trans rather than cis conformation about the S-N bond. Theoretical analysis of the structure of the CO₂-loaded crystal indicates that dispersion and electrostatic interactions exist between CO₂ and the framework. The overall results provide important insight into understanding and improving the CO₂ absorption properties of ILs.

Electrochemically mediated gating membrane with dynamically controllable gas transport

The regulation of mass transfer across membranes is central to a wide spectrum of applications. Despite numerous examples of stimuli-responsive membranes for liquid-phase species, this goal remains elusive for gaseous molecules. We describe a previously unexplored gas gating mechanism driven by reversible electrochemical metal deposition/dissolution on a conductive membrane, which can continuously modulate the interfacial gas permeability over two orders of magnitude with high efficiency and short response time. The gating mechanism involves neither moving parts nor dead volume and can therefore enable various engineering processes. An electrochemically mediated carbon dioxide concentrator demonstrates proof of concept by integrating the gating membranes with redox-active sorbents, where gating effectively prevented the cross-talk between feed and product gas streams for high-efficiency, directional carbon dioxide pumping. We anticipate our concept of dynamically regulating transport at gas-liquid interfaces to broadly inspire systems in fields of gas separation, miniaturized devices, multiphase reactors, and beyond.

Anion Effect on Gas Absorption in Imidazolium-Based Ionic Liquids

We performed classical Molecular Dynamics computer simulations to analyze solutions of the gases CO₂, N₂, and CH₄ in four 1-n-butyl-3-methylimidazolium-based ionic liquids (1-n-butyl-3-methylimidazolium acetate, 1-n-butyl-3-methylimidazolium prolinate, 1-n-butyl-3-methylimidazolium bromide, and 1-n-butyl-3-methylimidazolium tetrafluoroborate). Typical experimental conditions (10 bar gas pressure and room temperature) have been chosen to study mixtures of the ionic liquids with the gases at a single gas molar fraction of 0.25. Structural aspects are discussed to judge the absorption capacities of the ionic liquids. We observed that CO₂ coordinates preferentially within the polar domain of the ionic liquids with the bromide and tetrafluoroborate anions presenting the best performances. The other gases, N₂ and CH₄, remain in the less polar domains of the ionic liquids. Cluster size analysis indicates phase separation for these two gases. Considering both, the absorption tendency and gas separation capacity of the ionic liquids, the anion is desired to be small and possessing multiple coordination sites. In this aspect, the tetrafluoroborate anion accomplished the best results.