Relationship between Diffusion and Chemical Exchange in Mixtures of Carbon Dioxide and an Amine-Functionalized Ionic Liquid by High Field NMR and Kinetic Monte Carlo Simulations

Abstract

NMR exchange spectroscopy (EXSY) and NMR diffusion spectroscopy (PFG NMR) were applied in combination with kinetic Monte Carlo (MC) simulations to investigate self-diffusion in a mixture of carbon dioxide and an amine-functionalized ionic liquid under conditions of an exchange of carbon dioxide molecules between the reacted and unreacted states in the mixture. EXSY studies enabled residence times of carbon dioxide molecules to be obtained in the two states, whereas PFG NMR revealed time-dependent effective diffusivities for diffusion times comparable with and larger than the residence times. Analytical treatment of the PFG NMR attenuation curves as well as fitting of the PFG NMR effective diffusivities by KMC simulations enabled determination of diffusivities of carbon dioxide in the reacted and unreacted states. In contrast to carbon dioxide, the ion diffusivities were found to be diffusion time independent.

Role of a Multivalent Ion–Solvent Interaction on Restricted Mg2+ Diffusion in Dimethoxyethane Electrolytes

“…In order to obtain the actual self-diffusivities D 0 (free DME) and D 0 (bound DME) before the exchange happens (at “diffusion time 0”), the 1 H attenuation curves are fit into the analytical formulas of the two-site exchange diffusion model in the slow-exchange limit (eqs S4 and S5) − using the exchange rates obtained from 2D-EXSY and peak width analyses. Since the exchange experiments and DOSY measurements were performed on different instruments at different times, we do not use the exact exchange rates obtained from 2D-EXSY but set a range of ±20% during fitting to accommodate for experimental error.…”

Modern Room Temperature Ionic Liquids, a Simple Guide to Understanding Their Structure and How It May Relate to Dynamics

“…The past 10 years have witnessed tremendous expansion in the design and synthesis of modern room-temperature ionic liquids (ILs). We now have task specific ionic liquids, − ionic liquid drugs, − ionic liquids for energy applications such as batteries and supercapacitors, − those that capture carbon dioxide, ,− and those that dissolve cellulose − and proteins. − In terms of their structure, interesting work has surfaced on protic ionic liquids, − ILs that are highly fluorinated, − ILs with polar tails, − ILs with paramagnetic ions, , those containing silicon, − and some that are triphillic ,− just to mention a few examples. Not all ionic liquids but a vast number of them can be categorized as having both charged components and also apolar components .…”

Pulsed Field Gradient Nuclear Magnetic Resonance and Diffusion Analysis in Battery Research

“…The signal intensities during diffusion measurements under the conditions of slow exchange between the two sites (A and B) can be written as a function of diffusion area ( q 2 = γ 2 g 2 δ 2 ), diffusion time (Δ), exchange rates ( k A and k B ), diffusion coefficients of A and B before the exchange occurs ( D A and D B ), and magnetizations of A and B at equilibrium ( M A 0 and M B 0 ): ,, Here, bound DME coordinates to Mg 2+ before the exchange occurs, and it is reasonable to assume that D Mg ≈ D bound,DME (0); then, we can estimate D Mg in an electrolyte, indirectly from D bound,DME (0), which is the apparent diffusion coefficient of DME molecules binding to Mg 2+ ions at diffusion time Δ = 0 (see Figure a).…”

“…It is clear that the fitting to the Stejskal−Tanner equation does not work well when M Z /M 0 < 0.1 due to the exchange. In this case, an analytical formula for diffusion under slow exchange 56 is necessary to obtain the correct diffusion coefficients of free DME and bound DME at Δ ∼ 0.…”

“…The signal intensities during diffusion measurements under the conditions of slow exchange between the two sites (A and B) can be written as a function of diffusion area (q 2 = γ 2 g 2 δ 2 ), diffusion time (Δ), exchange rates (k A and k B ), diffusion coefficients of A and B before the exchange occurs (D A and D B ), and magnetizations of A and B at equilibrium (M A 0 and M B 0 ): 54,56,57…”