Water-filled MCM-41 characterized by double-quantum-filtered2H NMR spectral analysis

Yu, Tsyr‐Yan; Cheng, Chi‐Yuan; Hwang, Don-Ha; Huang, Hsuan‐Ming; Hwang, Lian‐Pin

doi:10.1007/bf03162157

Cited by 6 publications

(5 citation statements)

References 24 publications

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“…Therefore, water molecules at site b represent the surface water in the pores. The surface water in this model generally stands for the water strong bound to the surface, and it may be inside or outside the pore. − This observation is consistent with the result that adsorbed water molecules mainly interact with bridging SiOHAl groups, as reported previously. − A comparison of panels a and c in Figure shows that the motional correlation time of water molecules at site c is not significantly influenced by the water content. Since water is first adsorbed in the smaller pores, water in site c is the free water inside the small pores in H-ZSM-5.…”

Section: Resultssupporting

confidence: 89%

Dynamics of Water in Hierarchical Mesoporous H-ZSM-5 by Fast Field-Cycling NMR Relaxometry

et al. 2014

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The dynamics of water molecules adsorbed in hierarchical mesoporous H-ZSM-5 was investigated by fast field-cycling NMR relaxometry. Three distinct sites in H-ZSM-5 that can host water molecules, designated a, b, and c, have been identified; no significant exchange of water molecules among these sites was observed. Investigations into the relative populations of molecules confined at sites c (P c ) and b (P b ) revealed that the population ratio (P c /P b ) does not change significantly over the temperature and water-content ranges investigated. Furthermore, the motion of water at site b is very slow and shows almost no dependence on temperature. While H-ZSM-5 has pores of two different sizes (mesopores and micropores), the low population and observed slow motion of water at site b indicates a strong interaction between water molecules and the zeolite materials, which is possible only when water is adsorbed on the surface. The temperature of the phase transition of water provides insight into the properties of water adsorption. The transition temperature of water confined at site a varies with water content in the sample, indicating that it is located in a larger space; thus, site a represents mesopores. The transition temperature of water and the population of water molecules at site c are independent of water content, indicating that this site has been saturated; therefore, site c is the micropore, which is saturated because of capillary condensation.

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Section: Resultssupporting

confidence: 89%

Dynamics of Water in Hierarchical Mesoporous H-ZSM-5 by Fast Field-Cycling NMR Relaxometry

et al. 2014

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Section: Resultsmentioning

confidence: 50%

“…The order of magnitude of the effective correlation times (τ c ≈ 10 -10 s) in our MCM-41 sample is lower than of bulk water, with a typical correlation time of the order of ∼10 -12 s. Evidence for a lowering of mobility of water in MCM-41 has already been provided by other spectroscopic methods, like neutron scattering 36 and NMR using both pulse field gradient 37 and Carr-Purcell-Meiboom-Gill 35 techniques and 2 H NMR. 38,39 Before studying the mobility of the surface hydroxyl groups we should have a look at the actual values of the water chemical shifts as a function of temperature in order to further characterize the nature of the volume and surface water. To do so we measured the chemical shift values of the sample loaded with 39.6% removable water in the temperature range 235-295 K. Upon cooling, the volume water chemical shift increases by about 0.5 ppm with respect to the value at room temperature, while the chemical shift of the surface water decreases insignificantly (∼0.1 ppm).…”

Section: Mobility Of the Water In Mcm-41mentioning

confidence: 99%

NMR Study of the Adsorption−Desorption Kinetics of Dissolved Tetraalanine in MCM-41 Mesoporous Material

et al. 2005

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In this study we show how deuterium magic-angle spinning NMR spectroscopy can be used to investigate the adsorption-desorption kinetics of molecules in solution at surface-liquid interfaces. An aqueous solution of deuterium-labeled tetraalanine is inserted in the pores of MCM-41 mesoporous material, and its 2H MAS NMR spectrum is measured as a function of temperature and fraction of filling of the pores. Prior to this study, the different types of water in MCM-41 are characterized as a function of water loading of the pores. Analysis of 2H MAS sideband line shapes enabled the determination of the adsorption and desorption rates and the activation energies of desorption.

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“…Recent advances in theory and experimental techniques have substantially increased the information obtainable by NMR characterization of porous materials. − The use of double quantum filtered (DQF) NMR spectroscopy as a diagnostic tool for the detection of anisotropy in porous systems has recently been demonstrated, for example, as a sensitive method for the determination of the residual quadrupolar interaction in adsorbed layers. For a spin-1 system, the double quantum coherence vanishes in an isotropic medium.…”

Section: Introductionmentioning

confidence: 99%

Water Dynamics on the Surface of MCM-41 via ²H Double Quantum Filtered NMR and Relaxation Measurements

et al. 2001

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Dynamics of water adsorbed on MCM-41 has been investigated by line shape analyses of 2 H double quantum filtered (DQF) NMR and T 1 measurements. From temperature-dependent studies with various water loadings on MCM-41, it is found that there are three sites for water adsorption on MCM-41, namely, a "slow site", a "fast site I", and a "fast site II". The signal of water molecules in the slow site dominates in the observed DQF NMR. Fast site I is adjacent to the slow site, and the water molecules are exchangeable in these two sites. The fast site II is next to the fast site I, and water in the fast site II is only exchangeable with that in the fast site I. The influence of silanol groups on the MCM-41 surface strongly affects the motion of water molecules in the slow site, resulting in a residual quadrupolar interaction. As the signal of water in the fast site I dominates that observed in single quantum spectra, it also appears in DQF spectra through an exchange process. We found that when the fast site I is saturated, it has no influence on the internal rotation, but the wobbling motion of adsorbed D 2 O in the slow site becomes faster, i.e., the translational diffusion of D 2 O in the fast site I may increase the wobbling motion of adsorbed D 2 O through collision.

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Water-filled MCM-41 characterized by double-quantum-filtered2H NMR spectral analysis

Cited by 6 publications

References 24 publications

Dynamics of Water in Hierarchical Mesoporous H-ZSM-5 by Fast Field-Cycling NMR Relaxometry

Dynamics of Water in Hierarchical Mesoporous H-ZSM-5 by Fast Field-Cycling NMR Relaxometry

NMR Study of the Adsorption−Desorption Kinetics of Dissolved Tetraalanine in MCM-41 Mesoporous Material

Water Dynamics on the Surface of MCM-41 via ²H Double Quantum Filtered NMR and Relaxation Measurements

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Water-filled MCM-41 characterized by double-quantum-filtered2H NMR spectral analysis

Cited by 6 publications

References 24 publications

Dynamics of Water in Hierarchical Mesoporous H-ZSM-5 by Fast Field-Cycling NMR Relaxometry

Dynamics of Water in Hierarchical Mesoporous H-ZSM-5 by Fast Field-Cycling NMR Relaxometry

NMR Study of the Adsorption−Desorption Kinetics of Dissolved Tetraalanine in MCM-41 Mesoporous Material

Water Dynamics on the Surface of MCM-41 via 2H Double Quantum Filtered NMR and Relaxation Measurements

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Water Dynamics on the Surface of MCM-41 via ²H Double Quantum Filtered NMR and Relaxation Measurements