The Experts below are selected from a list of 735 Experts worldwide ranked by ideXlab platform
John A. Ripmeester - One of the best experts on this subject based on the ideXlab platform.
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A New Approach to Characterizing Sorption in Materials with Flexible Micropores
Chemistry of Materials, 2008Co-Authors: Roberto Anedda, Igor L. Moudrakovski, Dmitriy V. Soldatov, Mariano Casu, John A. RipmeesterAbstract:Microporous dipeptides, also known as organic zeolites or biozeolites, as examples of small-pore peptide nanotubes provide a convenient set of materials for developing a systematic approach based on 129Xe NMR Spectroscopy for the derivation of thermodynamic and molecular scale information on temperature dependent pore filling. The sorption of xenon in the isolated 1D chiral nanochannels of eight microporous dipeptides Ala-Val (AV), Val-Ala (VA), Leu-Ser (LS), Ala-Ile (AI), Val-Val (VV), Ile-Ala (IA), Ile-Val (IV), Val-Ile (VI) (all LL isomers) was monitored in situ with continuous-flow 129Xe NMR Spectroscopy over a temperature range of 173−343 K. The materials all showed strongly anisotropic signals, with isotropic chemical shift changing from 95 to 281 ppm depending on the dipeptide used and/or temperature. The isosteric heats of sorption (qst) and entropy factors were determined from two independent models. The sorption process was complicated by reversible phase transformations of some dipeptides and i...
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Distribution of Gallium Nanocrystals in Ga/MCM-41 Mesocomposites by Continuous-Flow Hyperpolarized 129Xe NMR Spectroscopy
Analytical chemistry, 2005Co-Authors: Weiping Zhang, Christopher I. Ratcliffe, Igor L. Moudrakovski, Chung-yuan Mou, John A. RipmeesterAbstract:The distribution of gallium nanocrystals in mesoporous MCM-41 host were analyzed by continuous-flow hyperpolarized 129Xe NMR Spectroscopy. In contrast to unclear TEM images for the high metal contents, laser-polarized 129Xe probe can detect the whole distribution of gallium in the MCM-41 host. It is found that gallium nanocrystals are included in the mesochannels of MCM-41; a part of them also remains in the interparticle voids. The distribution of gallium metal in MCM-41 is heterogeneous. Not all the mesochannels host metallic gallium even at a high gallium loading of 65.1 wt %. Variable temperature measurements can provide information on the xenon adsorption parameters. This approach opens a sensitive way to probe the distribution of high content species in porous host materials.
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Probing the Alkyl Ligands on Silylated Mesoporous MCM-41 Using Hyperpolarized 129Xe NMR Spectroscopy
The journal of physical chemistry. B, 2005Co-Authors: Shing-jong Huang, John A. Ripmeester, Chin-hui Huang, Wen-hua Chen, Xianping Sun, Xizhi Zeng, Huang-kuei Lee, Chuan-yuan Mou, Shang-bin LiuAbstract:Variable-temperature hyperpolarized (HP) Xe-129 NMR Spectroscopy has been employed to characterize surface properties of mesoporous MCM-41 modified by silylation treatment. The characteristic chemical shifts responsible for Xe-surface interactions exhibit strong correlations with both the surface coverage and chain length of the grafted alkylsilanes. Consequently, the deshielding medium contribution due to individual alkyl ligand can be deduced based on the group contribution analysis revealing the potential use of HP Xe-129 NMR for probing the surface properties of organic-functionalized porous materials.
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Distribution and modification of sorption sites in amphiphilic calixarene-based solid lipid nanoparticles from hyperpolarized 129Xe NMR Spectroscopy.
Journal of the American Chemical Society, 2004Co-Authors: A. Dubes, Christopher I. Ratcliffe, Igor L. Moudrakovski, P. Shahgaldian, Anthony W. Coleman, John A. RipmeesterAbstract:The site distribution and accessibility in amphiphilic calixarenes-based solid lipid nanoparticles were determined as a function of lipid chain length using in situ 129Xe NMR Spectroscopy with flowing hyperpolarized Xe gas. The study illustrates that host cavities in as-prepared materials are increasingly occluded by the lipid chain for compounds with chain lengths from C6 to C12 and are almost completely occluded for C14 and C16 chain lengths. Host cavities present at the surface of the particles are still accessible to small atoms (xenon) and organic molecules (methylene chloride, etc). The Xe spectra show that the accessible void space can be increased remarkably by exposure of the particle surface to suitably sized guest molecules that appear to displace the occluding hydrocarbon chains from the host cavities by competitive adsorption. This postsynthesis treatment thus modifies the state of self-assembly and improves sorption capability. The HP Xe NMR approach presented is suitable for small samples (...
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Probing the geometry and interconnectivity of pores in organic aerogels using hyperpolarized 129Xe NMR Spectroscopy.
Journal of the American Chemical Society, 2004Co-Authors: Igor L. Moudrakovski, Christopher I. Ratcliffe, Li Q. Wang, Theodore F. Baumann, Joe H. Satcher, Gregory J. Exarhos, John A. RipmeesterAbstract:Aerogels represent a class of novel open-pore materials with high surface area and nanometer pore sizes. They exhibit extremely low mass densities, low thermal conductivity, good acoustic insulation, and low dielectric constants. These materials have potential applications in catalysis, advanced separation techniques, energy storage, environmental remediation, and as insulating materials. Organic aerogels are stiffer and stronger than silica aerogels and are better insulators with higher thermal resistance. Resorcinol-Formaldehyde (RF) aerogels are typically prepared through the base-catalyzed sol-gel polymerization of resorcinol with formaldehyde in aqueous solution to produce gels, which are then dried in supercritical CO2.1,2 The [resorcinol]/ [catalyst] (R/C) ratio of the starting sol-gel solution has been determined to be the dominant factor that affects the properties of RF aerogels. Since the unique microstructures of aerogels are responsible for their unusual properties, characterizing the detailed porous structures and correlating them with the processing parameters are vital to establish rational design principles for novel organic aerogels with tailored properties. In this communication we report the first use of hyperpolarized (HP) 129Xe NMR to probe the geometry and interconnectivity of pores in RF aerogels and to correlate these with synthetic conditions. Our work demonstrates that HP 129Xe NMR is so far themore » only method for accurately measuring the free volume-to-surface-area (Vg/S) ratios for soft mesoporous materials without using any geometric models.« less
Stefan Kaskel - One of the best experts on this subject based on the ideXlab platform.
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The impact of defects and crystal size on negative gas adsorption in DUT-49 analyzed by in situ 129Xe NMR Spectroscopy.
2020Co-Authors: Simon Krause, Irena Senkovska, Stefan Kaskel, Volodymyr Bon, Florian Reuter, Sebastian Ehrling, Eike BrunnerAbstract:The origin of crystal size-dependent adsorption behavior of flexible metal-organic frameworks is increasingly studied. In this contribution, we probe the solid-fluid interactions of DUT-49 crystals of different size by in situ 129Xe NMR Spectroscopy at 200 K. With decreasing size of the crystals, the average solid-fluid interactions are found to decrease reflected by a decrease in chemical shift of adsorbed xenon from 230 to 200 ppm explaining the lack of adsorption-induced transitions for smaller crystals. However, recent studies propose that these results can also originate from the presence of lattice defects. To investigate the influence of defects on the adsorption behavior of DUT-49 we synthesized a series of samples with tailored defect concentrations and characterized them by in situ 129Xe NMR. In comparison to the results obtained for crystals with different size we find pronounced changes of the adsorption behavior and influence of the chemical shift only for very high concentrations of defects, which further emphasizes the important role of particle size phenomena.
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In Situ Monitoring of Unique Switching Transitions in the Pressure-Amplifying Flexible Framework Material DUT-49 by High-Pressure 129Xe NMR Spectroscopy
The Journal of Physical Chemistry C, 2017Co-Authors: Jana Schaber, Irena Senkovska, Stefan Kaskel, Silvia Paasch, Simon Krause, Volodymyr Bon, Daniel M. Többens, Dirk Wallacher, Eike BrunnerAbstract:The pronounced flexibility of special metal–organic frameworks (MOFs), so-called soft porous crystals, is attracting increasing research interest. Studies of host–guest interactions in such materials are especially powerful if the measurements are performed in situ. 129Xe NMR Spectroscopy is favorable because it provides characteristic, structure-sensitive parameters such as chemical shifts. The combination of high-pressure xenon adsorption with 129Xe NMR Spectroscopy was used to elucidate the adsorption-induced phase transitions in the recently discovered pressure-amplifying framework material DUT-49, showing a unique negative gas adsorption (NGA) transition. In the open-pore state, DUT-49op exhibits a hierarchical pore system involving both micro- and mesopores. After reaching a critical relative pressure of ca. 0.15, adsorbed xenon induces mesopore contraction, resulting in a purely microporous contracted-pore phase. This contraction is accompanied by release of xenon from the mesopores. Further increa...
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In Situ Monitoring of Unique Switching Transitions in the Pressure-Amplifying Flexible Framework Material DUT-49 by High-Pressure 129Xe NMR Spectroscopy
2017Co-Authors: Jana Schaber, Irena Senkovska, Stefan Kaskel, Silvia Paasch, Simon Krause, Volodymyr Bon, Dirk Wallacher, Daniel M. Többens, Eike BrunnerAbstract:The pronounced flexibility of special metal–organic frameworks (MOFs), so-called soft porous crystals, is attracting increasing research interest. Studies of host–guest interactions in such materials are especially powerful if the measurements are performed in situ. 129Xe NMR Spectroscopy is favorable because it provides characteristic, structure-sensitive parameters such as chemical shifts. The combination of high-pressure xenon adsorption with 129Xe NMR Spectroscopy was used to elucidate the adsorption-induced phase transitions in the recently discovered pressure-amplifying framework material DUT-49, showing a unique negative gas adsorption (NGA) transition. In the open-pore state, DUT-49op exhibits a hierarchical pore system involving both micro- and mesopores. After reaching a critical relative pressure of ca. 0.15, adsorbed xenon induces mesopore contraction, resulting in a purely microporous contracted-pore phase. This contraction is accompanied by release of xenon from the mesopores. Further increase of the pressure initiates the recovery of the mesopores without any indication of a structural intermediate in the NMR spectra. According to the NMR data, the structural transition induced by xenon is a collective, stepwise phenomenon rather than a continuous process. This is the first time that NGA has been studied by directly monitoring the guest and its interaction with the host framework
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Structural Characterization of Micro- and Mesoporous Carbon Materials Using In Situ High Pressure 129Xe NMR Spectroscopy
Chemistry of Materials, 2014Co-Authors: Martin Oschatz, Herbert C. Hoffmann, Julia Pallmann, Jana Schaber, Lars Borchardt, Winfried Nickel, Irena Senkovska, Soledad Rico-francés, Joaquín Silvestre-albero, Stefan KaskelAbstract:In situ high pressure 129Xe NMR Spectroscopy in combination with volumetric adsorption measurements were used for the textural characterization of different carbon materials with well-defined porosity including microporous carbide-derived carbons, ordered mesoporous carbide-derived carbon, and ordered mesoporous CMK-3. Adsorption/desorption isotherms were measured also by NMR up to relative pressures close to p/p0 = 1 at 237 K. The 129Xe NMR chemical shift of xenon adsorbed in porous carbons is found to be correlated with the pore size in analogy to other materials such as zeolites. In addition, these measurements were performed loading the samples with n-nonane. Nonane molecules preferentially block the micropores. However, 129Xe NMR Spectroscopy proves that the nonane also influences the mesopores, thus providing information about the pore system in hierarchically structured materials.
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Structural Characterization of Micro- and Mesoporous Carbon Materials Using In Situ High Pressure 129Xe NMR Spectroscopy
2014Co-Authors: Martin Oschatz, Herbert C. Hoffmann, Julia Pallmann, Jana Schaber, Lars Borchardt, Winfried Nickel, Irena Senkovska, Joaquín Silvestre-albero, Soledad Rico-francés, Stefan KaskelAbstract:In situ high pressure 129Xe NMR Spectroscopy in combination with volumetric adsorption measurements were used for the textural characterization of different carbon materials with well-defined porosity including microporous carbide-derived carbons, ordered mesoporous carbide-derived carbon, and ordered mesoporous CMK-3. Adsorption/desorption isotherms were measured also by NMR up to relative pressures close to p/p0 = 1 at 237 K. The 129Xe NMR chemical shift of xenon adsorbed in porous carbons is found to be correlated with the pore size in analogy to other materials such as zeolites. In addition, these measurements were performed loading the samples with n-nonane. Nonane molecules preferentially block the micropores. However, 129Xe NMR Spectroscopy proves that the nonane also influences the mesopores, thus providing information about the pore system in hierarchically structured materials
Victor Lara - One of the best experts on this subject based on the ideXlab platform.
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Complementary Physicochemical Characterization by SAXS and 129Xe NMR Spectroscopy of Fe-ZSM-5: Influence of Morphology in the Selective Catalytic Reduction of NO
Industrial & Engineering Chemistry Research, 2006Co-Authors: Ariel Guzmán-vargas, Enrique Lima, Gérard Delahay, Bernard Coq, Victor LaraAbstract:Fe-ZSM-5 catalysts were prepared by FeCl3 sublimation (CVD method) and impregnation in aqueous media. To describe the morphology of the iron species, the materials were characterized by XRD, SAXS, and 27Al and 129Xe NMR Spectroscopy. In the catalysts prepared by impregnation, XRD detected large hematite particles at the external surface of the zeolite. In contrast, the Fe2O3 phase was not detectable by XRD in the materials prepared by CVD, indicating much smaller species. The 129Xe NMR results show that, in the CVD-prepared materials, the amount of free space inside the zeolite cavities was decreased appreciably by the presence of the Fe oxo species. Furthermore, 129Xe NMR Spectroscopy reveals a sharp peak for the CVD-prepared material with Fe (3.8 wt %), indicating that this catalyst exhibits strong adsorption sites that are not detectable in the sample of similar Fe content that was prepared by impregnation. Morphology appears to be strongly affected by the method of preparation of the catalyst. The fra...
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Complementary Physicochemical Characterization by SAXS and 129Xe NMR Spectroscopy of Fe-ZSM-5: Influence of Morphology in the Selective Catalytic Reduction of NO
Industrial and engineering chemistry research, 2006Co-Authors: Ariel Guzmán-vargas, Enrique Lima, Gérard Delahay, Bernard Coq, Victor LaraAbstract:Fe-ZSM-5 catalysts were prepared by FeCl3 sublimation (CVD method) and impregnation in aqueous media. To describe the morphology of the iron species, the materials were characterized by XRD, SAXS, and 27Al and 129Xe NMR Spectroscopy. In the catalysts prepared by impregnation, XRD detected large hematite particles at the external surface of the zeolite. In contrast, the Fe2O3 phase was not detectable by XRD in the materials prepared by CVD, indicating much smaller species. The 129Xe NMR results show that, in the CVD-prepared materials, the amount of free space inside the zeolite cavities was decreased appreciably by the presence of the Fe oxo species. Furthermore, 129Xe NMR Spectroscopy reveals a sharp peak for the CVD-prepared material with Fe (3.8 wt %), indicating that this catalyst exhibits strong adsorption sites that are not detectable in the sample of similar Fe content that was prepared by impregnation. Morphology appears to be strongly affected by the method of preparation of the catalyst. The fractal dimension of the metal phase was associated with the catalytic activity in the selective catalytic reduction (SCR) of NO using ammonia and n-decane as reducing agents.
Christopher I. Ratcliffe - One of the best experts on this subject based on the ideXlab platform.
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Distribution of Gallium Nanocrystals in Ga/MCM-41 Mesocomposites by Continuous-Flow Hyperpolarized 129Xe NMR Spectroscopy
Analytical chemistry, 2005Co-Authors: Weiping Zhang, Christopher I. Ratcliffe, Igor L. Moudrakovski, Chung-yuan Mou, John A. RipmeesterAbstract:The distribution of gallium nanocrystals in mesoporous MCM-41 host were analyzed by continuous-flow hyperpolarized 129Xe NMR Spectroscopy. In contrast to unclear TEM images for the high metal contents, laser-polarized 129Xe probe can detect the whole distribution of gallium in the MCM-41 host. It is found that gallium nanocrystals are included in the mesochannels of MCM-41; a part of them also remains in the interparticle voids. The distribution of gallium metal in MCM-41 is heterogeneous. Not all the mesochannels host metallic gallium even at a high gallium loading of 65.1 wt %. Variable temperature measurements can provide information on the xenon adsorption parameters. This approach opens a sensitive way to probe the distribution of high content species in porous host materials.
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Distribution and modification of sorption sites in amphiphilic calixarene-based solid lipid nanoparticles from hyperpolarized 129Xe NMR Spectroscopy.
Journal of the American Chemical Society, 2004Co-Authors: A. Dubes, Christopher I. Ratcliffe, Igor L. Moudrakovski, P. Shahgaldian, Anthony W. Coleman, John A. RipmeesterAbstract:The site distribution and accessibility in amphiphilic calixarenes-based solid lipid nanoparticles were determined as a function of lipid chain length using in situ 129Xe NMR Spectroscopy with flowing hyperpolarized Xe gas. The study illustrates that host cavities in as-prepared materials are increasingly occluded by the lipid chain for compounds with chain lengths from C6 to C12 and are almost completely occluded for C14 and C16 chain lengths. Host cavities present at the surface of the particles are still accessible to small atoms (xenon) and organic molecules (methylene chloride, etc). The Xe spectra show that the accessible void space can be increased remarkably by exposure of the particle surface to suitably sized guest molecules that appear to displace the occluding hydrocarbon chains from the host cavities by competitive adsorption. This postsynthesis treatment thus modifies the state of self-assembly and improves sorption capability. The HP Xe NMR approach presented is suitable for small samples (...
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Probing the geometry and interconnectivity of pores in organic aerogels using hyperpolarized 129Xe NMR Spectroscopy.
Journal of the American Chemical Society, 2004Co-Authors: Igor L. Moudrakovski, Christopher I. Ratcliffe, Li Q. Wang, Theodore F. Baumann, Joe H. Satcher, Gregory J. Exarhos, John A. RipmeesterAbstract:Aerogels represent a class of novel open-pore materials with high surface area and nanometer pore sizes. They exhibit extremely low mass densities, low thermal conductivity, good acoustic insulation, and low dielectric constants. These materials have potential applications in catalysis, advanced separation techniques, energy storage, environmental remediation, and as insulating materials. Organic aerogels are stiffer and stronger than silica aerogels and are better insulators with higher thermal resistance. Resorcinol-Formaldehyde (RF) aerogels are typically prepared through the base-catalyzed sol-gel polymerization of resorcinol with formaldehyde in aqueous solution to produce gels, which are then dried in supercritical CO2.1,2 The [resorcinol]/ [catalyst] (R/C) ratio of the starting sol-gel solution has been determined to be the dominant factor that affects the properties of RF aerogels. Since the unique microstructures of aerogels are responsible for their unusual properties, characterizing the detailed porous structures and correlating them with the processing parameters are vital to establish rational design principles for novel organic aerogels with tailored properties. In this communication we report the first use of hyperpolarized (HP) 129Xe NMR to probe the geometry and interconnectivity of pores in RF aerogels and to correlate these with synthetic conditions. Our work demonstrates that HP 129Xe NMR is so far themore » only method for accurately measuring the free volume-to-surface-area (Vg/S) ratios for soft mesoporous materials without using any geometric models.« less
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Applications of Hyperpolarized 129Xe NMR Spectroscopy to the Study of Materials
Magnetic Resonance in Colloid and Interface Science, 2002Co-Authors: Igor L. Moudrakovski, Andrei Nossov, Christopher I. Ratcliffe, Victor V. Terskikh, Stephen Lang, Eric B. Brouwer, Dmitriy V. Soldatov, John A. RipmeesterAbstract:The use of 129Xe NMR Spectroscopy in the study of porous materials is by now a well- established method that has been reviewed many times [1–3]. The main idea is that the chemical shift tensor of Xe nuclides is extremely sensitive to local surroundings, primarily because of the large number of polarizable electrons [4, 5]. For small pore systems this is best summarized by stating that the isotropic shift is dependent on the size of the void space available to a xenon atom, whereas the anisotropic shift is sensitive to shape [4, 5]. These simple ideas are often modified by the need to take into account dynamics as well as Xe-Xe interactions (especially in large-pore materials), and it must be considered that if an isotropic line is observed in non-cubic solids, this can only be ascribed to the presence of fast dynamic processes [6–8]. As such, one must take into account the pore volume sampled by a xenon atom on the appropriate time scale in order to understand chemical shifts and relaxation parameters [6–8]. Dynamic processes also lend themselves to study, but only as equilibrium processes, eg by 2D EXSY or polarization transfer experiments [9]. As in the case of many NMR applications, the utility of the technique is limited by the need to acquire sufficient signal in a time that is short compared to the time scale of the process itself. The enhancement of the 129Xe NMR signal by the optical pumping of Rb, followed by spin exchange with Xe, has allowed an entire new approach to the study of materials [10–14]. Some of the main advantages include the rapid acquisition of spectra, which allows the study of non- equilibrium processes, and the acquisition of spectra at very low concentrations of Xe, which allow the efficient acquisition of “zero-loading” spectra and the use of Xe as a tracer to follow adsorption-desorption processes, phase transitions, etc.
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Continuous flow NMR with hyperpolarized xenon for the characterization of materials and processes
Chemistry of Materials, 2000Co-Authors: Igor L. Moudrakovski, Christopher I. Ratcliffe, Stephen Lang, Andrej Nossov, Steven R. Breeze, Benoit Simard, And Giles Santyr, John A. RipmeesterAbstract:129Xe NMR Spectroscopy with a continuous flow of dilute hyperpolarized xenon directed into the sample region of an NMR probe (either static or spinning) allows the rapid recording of spectra that are characteristic of the void space in micro- and mesoporous solids. The high sensitivity of the method allows the time-resolved, in-situ monitoring of processes involving sorbents such as activation, adsorption, and desorption.
Irena Senkovska - One of the best experts on this subject based on the ideXlab platform.
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The impact of defects and crystal size on negative gas adsorption in DUT-49 analyzed by in situ 129Xe NMR Spectroscopy.
2020Co-Authors: Simon Krause, Irena Senkovska, Stefan Kaskel, Volodymyr Bon, Florian Reuter, Sebastian Ehrling, Eike BrunnerAbstract:The origin of crystal size-dependent adsorption behavior of flexible metal-organic frameworks is increasingly studied. In this contribution, we probe the solid-fluid interactions of DUT-49 crystals of different size by in situ 129Xe NMR Spectroscopy at 200 K. With decreasing size of the crystals, the average solid-fluid interactions are found to decrease reflected by a decrease in chemical shift of adsorbed xenon from 230 to 200 ppm explaining the lack of adsorption-induced transitions for smaller crystals. However, recent studies propose that these results can also originate from the presence of lattice defects. To investigate the influence of defects on the adsorption behavior of DUT-49 we synthesized a series of samples with tailored defect concentrations and characterized them by in situ 129Xe NMR. In comparison to the results obtained for crystals with different size we find pronounced changes of the adsorption behavior and influence of the chemical shift only for very high concentrations of defects, which further emphasizes the important role of particle size phenomena.
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In Situ Monitoring of Unique Switching Transitions in the Pressure-Amplifying Flexible Framework Material DUT-49 by High-Pressure 129Xe NMR Spectroscopy
The Journal of Physical Chemistry C, 2017Co-Authors: Jana Schaber, Irena Senkovska, Stefan Kaskel, Silvia Paasch, Simon Krause, Volodymyr Bon, Daniel M. Többens, Dirk Wallacher, Eike BrunnerAbstract:The pronounced flexibility of special metal–organic frameworks (MOFs), so-called soft porous crystals, is attracting increasing research interest. Studies of host–guest interactions in such materials are especially powerful if the measurements are performed in situ. 129Xe NMR Spectroscopy is favorable because it provides characteristic, structure-sensitive parameters such as chemical shifts. The combination of high-pressure xenon adsorption with 129Xe NMR Spectroscopy was used to elucidate the adsorption-induced phase transitions in the recently discovered pressure-amplifying framework material DUT-49, showing a unique negative gas adsorption (NGA) transition. In the open-pore state, DUT-49op exhibits a hierarchical pore system involving both micro- and mesopores. After reaching a critical relative pressure of ca. 0.15, adsorbed xenon induces mesopore contraction, resulting in a purely microporous contracted-pore phase. This contraction is accompanied by release of xenon from the mesopores. Further increa...
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In Situ Monitoring of Unique Switching Transitions in the Pressure-Amplifying Flexible Framework Material DUT-49 by High-Pressure 129Xe NMR Spectroscopy
2017Co-Authors: Jana Schaber, Irena Senkovska, Stefan Kaskel, Silvia Paasch, Simon Krause, Volodymyr Bon, Dirk Wallacher, Daniel M. Többens, Eike BrunnerAbstract:The pronounced flexibility of special metal–organic frameworks (MOFs), so-called soft porous crystals, is attracting increasing research interest. Studies of host–guest interactions in such materials are especially powerful if the measurements are performed in situ. 129Xe NMR Spectroscopy is favorable because it provides characteristic, structure-sensitive parameters such as chemical shifts. The combination of high-pressure xenon adsorption with 129Xe NMR Spectroscopy was used to elucidate the adsorption-induced phase transitions in the recently discovered pressure-amplifying framework material DUT-49, showing a unique negative gas adsorption (NGA) transition. In the open-pore state, DUT-49op exhibits a hierarchical pore system involving both micro- and mesopores. After reaching a critical relative pressure of ca. 0.15, adsorbed xenon induces mesopore contraction, resulting in a purely microporous contracted-pore phase. This contraction is accompanied by release of xenon from the mesopores. Further increase of the pressure initiates the recovery of the mesopores without any indication of a structural intermediate in the NMR spectra. According to the NMR data, the structural transition induced by xenon is a collective, stepwise phenomenon rather than a continuous process. This is the first time that NGA has been studied by directly monitoring the guest and its interaction with the host framework
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Structural Characterization of Micro- and Mesoporous Carbon Materials Using In Situ High Pressure 129Xe NMR Spectroscopy
Chemistry of Materials, 2014Co-Authors: Martin Oschatz, Herbert C. Hoffmann, Julia Pallmann, Jana Schaber, Lars Borchardt, Winfried Nickel, Irena Senkovska, Soledad Rico-francés, Joaquín Silvestre-albero, Stefan KaskelAbstract:In situ high pressure 129Xe NMR Spectroscopy in combination with volumetric adsorption measurements were used for the textural characterization of different carbon materials with well-defined porosity including microporous carbide-derived carbons, ordered mesoporous carbide-derived carbon, and ordered mesoporous CMK-3. Adsorption/desorption isotherms were measured also by NMR up to relative pressures close to p/p0 = 1 at 237 K. The 129Xe NMR chemical shift of xenon adsorbed in porous carbons is found to be correlated with the pore size in analogy to other materials such as zeolites. In addition, these measurements were performed loading the samples with n-nonane. Nonane molecules preferentially block the micropores. However, 129Xe NMR Spectroscopy proves that the nonane also influences the mesopores, thus providing information about the pore system in hierarchically structured materials.
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Structural Characterization of Micro- and Mesoporous Carbon Materials Using In Situ High Pressure 129Xe NMR Spectroscopy
2014Co-Authors: Martin Oschatz, Herbert C. Hoffmann, Julia Pallmann, Jana Schaber, Lars Borchardt, Winfried Nickel, Irena Senkovska, Joaquín Silvestre-albero, Soledad Rico-francés, Stefan KaskelAbstract:In situ high pressure 129Xe NMR Spectroscopy in combination with volumetric adsorption measurements were used for the textural characterization of different carbon materials with well-defined porosity including microporous carbide-derived carbons, ordered mesoporous carbide-derived carbon, and ordered mesoporous CMK-3. Adsorption/desorption isotherms were measured also by NMR up to relative pressures close to p/p0 = 1 at 237 K. The 129Xe NMR chemical shift of xenon adsorbed in porous carbons is found to be correlated with the pore size in analogy to other materials such as zeolites. In addition, these measurements were performed loading the samples with n-nonane. Nonane molecules preferentially block the micropores. However, 129Xe NMR Spectroscopy proves that the nonane also influences the mesopores, thus providing information about the pore system in hierarchically structured materials
