KES7-1302
129Xe-NMR Spectroscopy: A New Pore Structure Analysis Method for Nanoporous Materials
Topic
S7. Innovations in Polymeric Composites: From Design and Processing to Industrial Applications
When and Where
Sep 29, 2026
11:40 - 12:05
Room 107
Session Chairs
Kyung Jin LEE
Presenter(s)
Jin Miyawaki (Kyushu University)
Co-Author(s)
Abstract
Nanoporous materials and their composites are widely used in various application fields of separation, catalysis, and energy storage due to their high specific surface area, adjustable pore size, and unique pore network structure. As the performances of porous materials are highly dependent on the pore structure, an evaluation of the pore structure of nanoporous materials is indispensable for maximizing their performance in practical applications. However, to calculate the pore size and the distribution from data measured by traditional gas adsorption methods requires an assumption of pore shape, whilst limited methods are available for pore shape evaluation.
In this talk, we’d like to introduce that xenon isotope nuclear magnetic resonance (129Xe−NMR) spectroscopy can estimate the pore size of porous materials without the pore shape assumption [1]. Furthermore, we also report our recent finding that adsorption-controlled 129Xe-NMR spectroscopy serves not only as a practical method for pore size analysis but also as a versatile technique for analyzing pore shapes and connectivity across a variety of nanoporous materials [2].
129Xe−NMR spectroscopy has been widely applied to evaluate the pore size of various nanoporous materials such as zeolites, silica-based materials, clathrates, and polymers. However, few studies have explored the validity of 129Xe−NMR spectroscopy for nanoporous carbons. Therefore, we first verified the applicability of the 129Xe−NMR spectroscopy for pore size determination in nanoporous carbon materials by using microporous activated carbons (ACs) with relatively uniform pore size distribution.
The results revealed that the 129Xe-NMR chemical shift, δ(Xe), of adsorbed Xe molecules depends on the amount of adsorbed Xe (AXe) and the adsorbent itself, but is independent of the Xe adsorption temperature (TXe) and pressure (PXe). Furthermore, at least within the TXe and PXe ranges measured in this study, it was confirmed that the adsorption of Xe molecules on ACs occurs through surface covering rather than pore filling. Additionally, a plot of the surface density of adsorbed Xe molecules (ρXe) versus δ(Xe) revealed a linear correlation between the two, except in the low- and high-ρXe regions: Downward deviations from this linear relationship were attributed to the influence of paramagnetism in ACs and a change in the adsorption form in the low- and high-ρXe regions, respectively. Meanwhile, the intercepts of straight lines extrapolated in the middle-ρXe region of the ρXe−δ(Xe) plots were linearly correlated with the isosteric heat of adsorption of Xe (Qst), indicating that these extrapolated values genuinely reflected the interaction between AC pore surfaces and adsorbed Xe molecules (δS). Moreover, the δS values showed a single correlation curve with an average pore size factor−the ratio of the total pore volume and internal specific surface area (V/SSA)– for ACs, regardless of the number of oxygen-containing surface functional groups. Note that both V and SSA were estimated from nitrogen adsorption isotherms at 77 K without assuming any specific pore shape. From the correlation curve for δS versus V/SSA, an approximation formula was obtained: The universality of the proposed empirical equation was confirmed by the results for commercial ACs prepared from different raw materials. These findings confirm that the adsorption-controlled 129Xe-NMR method is suitable for estimating the interaction between ACs and adsorbed Xe molecules, and that 129Xe-NMR is a useful technique tool for estimating AC pore sizes without assuming the pore shape [1].
Based on this verification, we next investigated the potential of this 129Xe−NMR technique for analyzing pore shape in nanoporous materials using various carbon- and silica-based nanoporous materials with pores of different shapes ranging in size from micropores to mesopores.
The results revealed that by using the inverse pore size factor (SSA/V), nanoporous materials with cylindrical pores exhibit δS−SSA/V plots clearly distinct from those of materials with slit-type pores, regardless of the elemental composition. At the same pore size, δS values were higher for cylindrical pores than for slit-shaped pores, consistent with the stronger solid−fluid interaction for the former estimated by integrated Lennard−Jones calculations. Moreover, in δS−V/SSA plots, four distinct correlations were obtained, presumably depending on the pore connectivity. These results demonstrate the potential of adsorption-controlled 129Xe−NMR for analyzing the pore shape and connectivity as well as the pore size in various nanoporous materials [2].
In summary, these studies verified that the adsorption-controlled 129Xe-NMR spectroscopy is a useful method for analyzing the pore structure of nanoporous materials.
References
[1] M. Li, et al., “Reevaluation of the suitability of 129Xe nuclear magnetic resonance spectroscopy for pore size determination in porous carbon materials,” J. Am. Chem. Soc., 146(50), 34401−34412 (2024).
[2] M. Li, et al., “A new pore shape analysis method based on the adsorption-controlled 129Xe−NMR technique,” J. Am. Chem. Soc., 148(4), 3933−3937 (2026).
In this talk, we’d like to introduce that xenon isotope nuclear magnetic resonance (129Xe−NMR) spectroscopy can estimate the pore size of porous materials without the pore shape assumption [1]. Furthermore, we also report our recent finding that adsorption-controlled 129Xe-NMR spectroscopy serves not only as a practical method for pore size analysis but also as a versatile technique for analyzing pore shapes and connectivity across a variety of nanoporous materials [2].
129Xe−NMR spectroscopy has been widely applied to evaluate the pore size of various nanoporous materials such as zeolites, silica-based materials, clathrates, and polymers. However, few studies have explored the validity of 129Xe−NMR spectroscopy for nanoporous carbons. Therefore, we first verified the applicability of the 129Xe−NMR spectroscopy for pore size determination in nanoporous carbon materials by using microporous activated carbons (ACs) with relatively uniform pore size distribution.
The results revealed that the 129Xe-NMR chemical shift, δ(Xe), of adsorbed Xe molecules depends on the amount of adsorbed Xe (AXe) and the adsorbent itself, but is independent of the Xe adsorption temperature (TXe) and pressure (PXe). Furthermore, at least within the TXe and PXe ranges measured in this study, it was confirmed that the adsorption of Xe molecules on ACs occurs through surface covering rather than pore filling. Additionally, a plot of the surface density of adsorbed Xe molecules (ρXe) versus δ(Xe) revealed a linear correlation between the two, except in the low- and high-ρXe regions: Downward deviations from this linear relationship were attributed to the influence of paramagnetism in ACs and a change in the adsorption form in the low- and high-ρXe regions, respectively. Meanwhile, the intercepts of straight lines extrapolated in the middle-ρXe region of the ρXe−δ(Xe) plots were linearly correlated with the isosteric heat of adsorption of Xe (Qst), indicating that these extrapolated values genuinely reflected the interaction between AC pore surfaces and adsorbed Xe molecules (δS). Moreover, the δS values showed a single correlation curve with an average pore size factor−the ratio of the total pore volume and internal specific surface area (V/SSA)– for ACs, regardless of the number of oxygen-containing surface functional groups. Note that both V and SSA were estimated from nitrogen adsorption isotherms at 77 K without assuming any specific pore shape. From the correlation curve for δS versus V/SSA, an approximation formula was obtained: The universality of the proposed empirical equation was confirmed by the results for commercial ACs prepared from different raw materials. These findings confirm that the adsorption-controlled 129Xe-NMR method is suitable for estimating the interaction between ACs and adsorbed Xe molecules, and that 129Xe-NMR is a useful technique tool for estimating AC pore sizes without assuming the pore shape [1].
Based on this verification, we next investigated the potential of this 129Xe−NMR technique for analyzing pore shape in nanoporous materials using various carbon- and silica-based nanoporous materials with pores of different shapes ranging in size from micropores to mesopores.
The results revealed that by using the inverse pore size factor (SSA/V), nanoporous materials with cylindrical pores exhibit δS−SSA/V plots clearly distinct from those of materials with slit-type pores, regardless of the elemental composition. At the same pore size, δS values were higher for cylindrical pores than for slit-shaped pores, consistent with the stronger solid−fluid interaction for the former estimated by integrated Lennard−Jones calculations. Moreover, in δS−V/SSA plots, four distinct correlations were obtained, presumably depending on the pore connectivity. These results demonstrate the potential of adsorption-controlled 129Xe−NMR for analyzing the pore shape and connectivity as well as the pore size in various nanoporous materials [2].
In summary, these studies verified that the adsorption-controlled 129Xe-NMR spectroscopy is a useful method for analyzing the pore structure of nanoporous materials.
References
[1] M. Li, et al., “Reevaluation of the suitability of 129Xe nuclear magnetic resonance spectroscopy for pore size determination in porous carbon materials,” J. Am. Chem. Soc., 146(50), 34401−34412 (2024).
[2] M. Li, et al., “A new pore shape analysis method based on the adsorption-controlled 129Xe−NMR technique,” J. Am. Chem. Soc., 148(4), 3933−3937 (2026).
