Effect of Adsorbed Water Molecules on the Surface Acidity of Niobium and Tantalum Oxides Studied by MAS NMR

2021 ◽  
Author(s):  
Xin Chen ◽  
Daofeng Huang ◽  
Lulu He ◽  
Li Zhang ◽  
Yuanhang Ren ◽  
...  
Keyword(s):  
Surface Acidity ◽  
Adsorbed Water ◽  
Mas Nmr ◽  
Water Molecules

Restricted Rotational Motion of InterlayerWaterMolecules in Vanadium Pentoxide Hydrate, V2O5·n D2O, as Studied by Deuterium NMR

2002 ◽  
Vol 57 (6-7) ◽  
pp. 419-424 ◽  
Author(s):  
Sadamu Takeda ◽  
Yuko Gotoh ◽  
Goro Maruta ◽  
Shuichi Takahara ◽  
Shigeharu Kittaka
Keyword(s):  
Double Layer ◽  
Vanadium Pentoxide ◽  
Rotational Motion ◽  
Interlayer Space ◽  
Layer Structure ◽  
Bond Distance ◽  
Adsorbed Water ◽  
Deuterium Nmr ◽  
Water Molecules ◽  
Layer Structures

The rotational behavior of the interlayer water molecules of deuterated vanadium pentoxide hydrate, V2O5.nD2O, was studied by solid-state deuterium NMR for the mono- and double-layer structures of the adsorbed water molecules. The rotational motion was anisotropic even at 355 K for both the mono- and double-layer structures. The 180° flipping motion about the C2-symmetry axis of the water molecule and the rotation around the figure axis, which makes an angle Ɵ with the C2-axis, occurred with the activation energy of (34±4) and (49±6) kJmol-1, respectively. The activation energies were almost independent of the mono- and double-layer structures of the water molecules, but the angle Ɵ made by the two axes varied from 33° for the monolayer to 25° for the double-layer at 230 K. The angle started to decrease above 250 K (e. g. the angle was 17 at 355 K for the double-layer structure). The results indicate that the average orientation of the water molecules in the two dimensional interlayer space depends on the layer structure and on the temperature. From the deuterium NMR spectrum at 130 K, the quadrupole coupling constant e2Qq/h = 240 kHz and the asymmetry parameter η= 0.12 were deduced. These values indicate the average hydrogen bond distance R(O H) = 2.0 Å for the D2O molecules in the 2D-interlayer space

scholarly journals Water in cellulose: evidence and identification of immobile and mobile adsorbed phases by 2H MAS NMR

2017 ◽  
Vol 19 (6) ◽  
pp. 4360-4369 ◽  
Author(s):  
E. L. Lindh ◽  
C. Terenzi ◽  
L. Salmén ◽  
I. Furó
Keyword(s):  
Physical Chemistry ◽  
Mas Nmr ◽  
Water Molecules ◽  
Natural Polymers

The organization of water molecules adsorbed onto cellulose and the supramolecular hydrated structure of microfibril aggregates represents, still today, one of the open and complex questions in the physical chemistry of natural polymers.

Relaxation dynamics of surface-adsorbed water molecules in nanoporous silica probed by terahertz spectroscopy

2015 ◽  
Vol 107 (8) ◽  
pp. 081607 ◽  
Author(s):  
Yu-Ru Huang ◽  
Kao-Hsiang Liu ◽  
Chung-Yuan Mou ◽  
Chi-Kuang Sun
Keyword(s):  
Terahertz Spectroscopy ◽  
Adsorbed Water ◽  
Nanoporous Silica ◽  
Water Molecules ◽  
Relaxation Dynamics

scholarly journals Calorimetric and Spectroscopic Studies of Water Adsorption onto Alkaline Earth Fluorides

2005 ◽  
Vol 23 (6) ◽  
pp. 425-436
Author(s):  
Toshinori Mori ◽  
Yasushige Kuroda ◽  
Ryotaro Kumashiro ◽  
Koji Hirata ◽  
Hidehiro Toyota ◽  
...  
Keyword(s):  
Alkaline Earth ◽  
Water Adsorption ◽  
Adsorbed Water ◽  
Spectroscopic Studies ◽  
Water Molecules ◽  
Earth Fluoride ◽  
Alkaline Earth Fluoride ◽  
Pretreatment Temperature ◽  
Argon Adsorption ◽  
Ir Bands

Interactions between the surfaces of alkaline earth fluorides (CaF2, SrF2 and BaF2) and water molecules were investigated by calorimetric and spectroscopic methods. The exposed surfaces of the alkaline earth fluoride samples, with which the (100) crystalline plane is mainly associated, were found to be fully covered with strongly adsorbed water molecules, resulting in characteristic IR bands at 3684, 2561, 1947 and 1000 cm−1, respectively. This surface was homogeneous towards further water adsorption. The strongly adsorbed water molecules were almost completely desorbed from the surface on evacuating the sample up to 473 K. The heat of immersion in water also increased with increasing pretreatment temperature; this may be attributed to surface rehydration of the alkaline earth fluorides. The state of the surface changed drastically as the pretreatment temperature was increased and stabilized towards incoming water molecules. Thus, the surface formed after evacuation at temperatures greater than 473 K was resistant to hydration even after immersion in water at room temperature. This surface was relatively heterogeneous towards water adsorption, although it behaved homogeneously towards argon adsorption. These facts indicate that strongly adsorbed water molecules appear to be somewhat specific towards the adsorption of further incoming water molecules. The adsorption properties of the (100) plane of alkaline earth fluorides towards water and argon molecules depend strongly on both the electrostatic field strength and the extent of rehydration of the alkaline earth fluoride surface.

scholarly journals First-Principles Study of AlPO4-H3, a Hydrated Aluminophosphate Zeotype Containing Two Different Types of Adsorbed Water Molecules

Molecules ◽  
2019 ◽  
Vol 24 (5) ◽  
pp. 922 ◽  
Author(s):  
Michael Fischer
Keyword(s):  
Density Functional ◽  
Computational Study ◽  
Pore Space ◽  
Experimental Studies ◽  
Adsorbed Water ◽  
Working Fluid ◽  
Water Molecules ◽  
Small Pore ◽  
Experimental Crystal ◽  
Heat Transformation

Porous aluminophosphate zeotypes (AlPOs) are promising materials for heat transformation applications using water as a working fluid. Two “types” of adsorbed water molecules can be distinguished in hydrated AlPOs: Water molecules adsorbed in the direct proximity of framework aluminium atoms form bonds to these Al atoms, with the coordination number of Al increasing from four to five or six. The remaining water molecules that are adsorbed in other parts of the accessible pore space are not strongly bonded to any framework atom, they interact with their environment exclusively through hydrogen bonds. The APC-type small-pore aluminophosphate AlPO4-H3 contains both types of H2O molecules. In the present work, this prototypical hydrated AlPO is studied using dispersion-corrected density functional theory (DFT) calculations. After validating the computations against experimental crystal structure and Raman spectroscopy data, three interrelated aspects are addressed: First, calculations for various partially hydrated models are used to establish that such partially hydrated phases are not thermodynamically stable, as the interaction with the adsorbed water molecules is distinctly weaker than in fully hydrated AlPO4-H3. Second, IR and Raman spectra are computed and compared to those of the dehydrated analogue AlPO4-C, leading to the identification of a few “fingerprint” modes that could be used as indicators for the presence of Al-coordinated water molecules. Finally, DFT-based molecular dynamics calculations are employed to study the dynamics of the adsorbed water molecules. All in all, this in-depth computational study of AlPO4-H3 contributes to the fundamental understanding of hydrated AlPOs, and should therefore provide valuable information for future computational and experimental studies of these systems.

Sign in / Sign up

Export Citation Format

Share Document