Observing solvent dynamics in porous carbons by nuclear magnetic resonance: Elucidating molecular-level dynamics of in-pore and ex-pore species

Cervini, L. and Barrow, N. and Griffin, J. (2020) Observing solvent dynamics in porous carbons by nuclear magnetic resonance: Elucidating molecular-level dynamics of in-pore and ex-pore species. Johnson Matthey Technology Review, 64 (2). pp. 152-164.

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Abstract

The adsorption and diffusion of species in activated carbons is fundamental to many processes in catalysis and energy storage. Nuclear magnetic resonance (NMR) gives an insight into the molecular-level mechanisms of these phenomena thanks to the unique magnetic shielding properties of the porous carbon structure, which allows adsorbed (in-pore) species to be distinguished from those in the bulk (ex-pore). In this work we investigate exchange dynamics between expore and in-pore solvent species in microporous carbons using a combination of one-dimensional (1D) and two-dimensional (2D) NMR experiments. We systematically compare the effects of four variables: particle size, porosity, solvent polarity and solvent viscosity to build up a picture of how these factors influence the exchange kinetics. We show that exchange rates are greater in smaller and more highly activated carbon particles, which is expected due to the shorter in-pore-ex-pore path length and faster diffusion in large pores. Our results also show that in-pore-ex-pore exchange of apolar solvents is slower than water, suggesting that the hydrophobic chemistry of the carbon surface plays a role in the diffusion kinetics, and that increased viscosity also reduces the exchange kinetics. Our results also suggest the importance of other parameters, such as molecular diameter and solvent packing in micropores.

Item Type:
Journal Article
Journal or Publication Title:
Johnson Matthey Technology Review
Uncontrolled Keywords:
/dk/atira/pure/subjectarea/asjc/2500/2506
Subjects:
ID Code:
147857
Deposited By:
Deposited On:
01 Oct 2020 10:05
Refereed?:
Yes
Published?:
Published
Last Modified:
27 Oct 2020 10:26