Final published version
Licence: CC BY-NC-ND: Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License
Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
}
TY - JOUR
T1 - Observing solvent dynamics in porous carbons by nuclear magnetic resonance: Elucidating molecular-level dynamics of in-pore and ex-pore species
AU - Cervini, L.
AU - Barrow, N.
AU - Griffin, J.
PY - 2020/4/1
Y1 - 2020/4/1
N2 - 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.
AB - 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.
KW - Diffusion
KW - Energy storage
KW - Kinetics
KW - Magnetic shielding
KW - Magnetism
KW - Microporosity
KW - Nuclear magnetic resonance spectroscopy
KW - Particle size
KW - Porous materials
KW - Solvents
KW - Viscosity
KW - Activated carbon particles
KW - Diffusion kinetics
KW - Micro-porous carbons
KW - Molecular diameter
KW - Molecular level mechanisms
KW - Nuclear magnetic resonance(NMR)
KW - Shielding properties
KW - Two Dimensional (2 D)
KW - Nuclear magnetic resonance
U2 - 10.1595/205651320X15747624015789
DO - 10.1595/205651320X15747624015789
M3 - Journal article
VL - 64
SP - 152
EP - 164
JO - Johnson Matthey Technology Review
JF - Johnson Matthey Technology Review
IS - 2
ER -