Potentials and challenges of high-field PFG NMR diffusion studies with sorbates in nanoporous media
- PDF / 4,287,986 Bytes
- 17 Pages / 595.276 x 790.866 pts Page_size
- 85 Downloads / 210 Views
Potentials and challenges of high‑field PFG NMR diffusion studies with sorbates in nanoporous media Amineh Baniani1 · Samuel J. Berens1 · Matthew P. Rivera2 · Ryan P. Lively2 · Sergey Vasenkov1 Received: 1 June 2020 / Revised: 30 July 2020 / Accepted: 12 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract High magnetic fields (up to 17.6 T) in combination with large magnetic field gradients (up to 25 T/m) were successfully utilized in pulsed field gradient (PFG) NMR studies of gas and liquid diffusion in nanoporous materials. In this mini-review, we present selected examples of such studies demonstrating the ability of high field PFG NMR to gain unique insights and differentiate between various types of diffusion. These examples include identifying and explaining an anomalous relationship between molecular size and self-diffusivity of gases in a zeolitic imidazolate framework (ZIF), as well as revealing and explaining an influence of mixing different linkers in a ZIF on gas self-diffusion. Different types of normal and restricted selfdiffusion were quantified in hybrid membranes formed by dispersing ZIF crystals in polymers. High field PFG NMR studies of such membranes allowed observing and explaining an influence of the ZIF crystal confinement in a polymer on intra-ZIF self-diffusion of gases. This technique also allowed measuring and understanding anomalous single-file diffusion (SFD) of mixed sorbates. Furthermore, the presented examples demonstrate a high potential of combining high field PFG NMR with single-crystal infrared microscopy (IRM) for obtaining greater physical insights into the studied diffusion processes. Keywords PFG NMR · High field NMR · Normal diffusion · Anomalous diffusion · ZIFs · MMMs Notations ⟨r2 ⟩ Mean square displacement ⟨z2 ⟩ Z-Direction mean square displacement c Mass concentration D Self-diffusion coefficient D0 Corrected diffusion coefficient DT Transport diffusion coefficient Deff Effective diffusion coefficient D∗0 Pre-exponential factor in the Arrhenius equation for self-diffusion coefficient deff Diameter of spherical pores—see also Eq. 4 Ea Activation energy of diffusion F Single-file mobility factor g Amplitude of the magnetic field gradient l Channel length p Pressure
* Sergey Vasenkov [email protected] 1
Department of Chemical Engineering, University of Florida, Gainesville, FL 32611, USA
School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
2
pi PFG NMR signal fraction of component “i”—see Eq. 3 q Constant defined as 𝛾g𝛿 R Gas constant S PFG NMR signal intensity t Diffusion time T Temperature T1 Longitudinal NMR relaxation time T2 Transverse NMR relaxation time γ Gyromagnetic ratio Γ Thermodynamic factor equal to dln(p)/dln(c) δ Effective gradient pulse duration corresponding to the width of the gradient pulses with a rectangular shape θ Fractional loading in the channels λ Particle elementary displacement Ψ Attenuation of PFG NMR signal
1 I
Data Loading...
