Search results for "Sorption"
showing 10 items of 4623 documents
Reflection anisotropy spectroscopy of decanethiol adsorbed at Au(110)/liquid interfaces
2008
Reflection Anisotropy Spectroscopy (RAS) has been used to monitor the adsorption of decanethiol as a function of coverage on the Au(110)/ethanol interface. The coverage saturates after 60 minutes for a solution of 0.5 µM. It is found that the RAS observed after 30 minutes can be represented as a linear sum of the RAS observed after 15 minutes and after saturation coverage. This implies that the molecule does not change its orientation as function of coverage. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
High-resolution physisorption techniques for the characterization of adsorbents and catalysts
1991
Abstract High-resolution physisorption techniques performed in the continuous volumetric mode have been developed to investigate the surface and pore structure properties of porous solids. Physisorption data on well-defined microporous solids (zeolites and aluminophosphates) provide novel information on the mechanism of micropore filling, the behavior of the adsorbed phase and the pore structure of the adsorbent. The combination of physisorption with high-resolution analytical techniques such as calorimetry and neutron diffraction further expands our knowledge and understanding of physisorption processes. The results are not only important for fundamental research but can be applied in the …
The Use of 15N NMR for the Understanding of Nitrogen Physisorption.
1994
Abstract Nitrogen adsorption at liquid nitrogen temperature, 77K, is universally employed to determine pore dimensions. The nature of nitrogen physisorbed within the micropores of ZSM-5 zeolite was studied by in situ15N NMR as it depends on the partial pressure of the nitrogen and the temperature above and below 77K. An increase in the volume of adsorption of nitrogen at 77K occurs at a relative pressure of ~0.18 for this zeolite. The nature of the nitrogen was studied below and above this increase in nitrogen adsorption. We find that two states (phases) of nitrogen are evident. We conclude that two phases can be present but that a solid phase of nitrogen is not evident even as the temperat…
Microscopic Insights into the Fluorite/Water Interfaces from Vibrational Sum Frequency Generation Spectroscopy
2016
Water/mineral interfaces are central to a wide range of environmental and technological processes. In this report we provide a quantitative, molecular-level understanding of the CaF2/water interface using Density Functional Theory-based molecular dynamics simulations. In particular through the comparison of calculated Vibrational Sum Frequency Generation spectra to the experimental ones, we give a structural characterisation of the interface at different pH. At low pH, the surface is positively charged, causing a substantial degree of water ordering. Our results suggest that the surface charge originates from the dissolution of fluoride ions of the topmost layer, rather than from proton ads…
Study of Selective Adsorption of Gases by Calorimetry
2013
This chapter is devoted to the study of coadsorption of gases in nanoporous solids by using the differential calorimetry. In the first part, the thermodynamic principles of adsorption of gases are recalled. Some of them have already presented in chapter one. However a special attention has been paid here to the determination of the adsorption enthalpies and entropies and we focused on the selective adsorption of binary mixtures. Then the specific experimental technique based on the combination of differential calorimetry with manometry and gas phase chromatography or mass spectrometry is shown in details. In the last part, the thermodynamic concepts on coadsorption are illustrated with expe…
Some intriguing items in the history of adsorption
1994
Abstract Clay was already used in antiquity as a drying and bleaching agent, a carrier for paints, and for various medical purposes. Sand was applied for water desalination. Charcoal was recommended as an antidote Based on Lowitz' discovery of the decolorizing effect in 1785, charcoal was used for the purification first of sugar. The patents of Ostrejko in 1900 opened the way for its industrial application. Already in the Bible we find the description of an adsorption experiment. The systematic research began 1773 when Scheele observed the adsorption of air by charcoal using a volumetric apparatus. The first adsorption measuring instruments were hygrometers as described by Nicholas of Cues …
Sorption Kinetics of Xenon on MFI-Type Zeolite Molecular Sieves
1990
Kinetic uptake data for xenon adsorbed onto large and uniform silicalite-I crystals are presented over a temperature range of 121 K to 296 K. — Adsorption isotherms and corrected diffusion coefficients derived from the uptake curves are given. The heat of adsorption and activation energy of diffusion were estimated from the plots of reciprocal temperature against the logarithm of equilibrium pressure and corrected diffusion coefficients, respectively. — While the corrected diffusion coefficient is independent of coverage for the higher temperatures, it decreases significantly at the lower temperatures investigated (<170 K) when the limiting adsorption capacity has been reached. — Comparing …
Study of the Pore Network of Dealuminated Faujasites by Water Vapor Adsorption
1991
Summary The adsorption and desorption isotherms of water vapor are drawn at 25°C for dealuminated HY zeolites upon framework Si/Al ratio. The isotherms are compared to that of the parent NaY zeolite. The isotherm changes in shape from the type I to the type IV with an hysteresis loop changing from the type H 4 to the type H 2 , as increases the Si/Al ratio. The POLANYI-DUBININ theory is used to determine the micropore volume accessible to water. It decreases with increasing Si/Al ratios, down to zero at a Si/Al ratio of 35. Such a result is accounted by the adsorption on the hydrophilic centers which are the cations (H + ) associated with the structural aluminium ions, each cation being coo…
25-hydroxy vitamin D levels in healthy premenopausal women: Association with bone turnover markers and bone mineral density
2008
Abstract Background Vitamin D deficiency is very common in elderly people while there are very few reports on its incidence, determinants and metabolic consequences in young subjects. Results In 608 young healthy premenopausal women participating in the BONTURNO study, levels of 25-hydroxyvitamin D [25(OH)D] below 20 ng/ml were found in almost a third of the women. Its levels were inversely ( P 2 ) and directly with sunlight exposure during the summer time, and latitude: i.e. the higher the latitude over Italy, the higher the 25(OH)D level. In women on contraceptive pill the mean 25(OH)D level was significantly increased even when the data were adjusted for age, BMI and sun exposure. 25(OH)…
Is bone loss the reversal of bone accrual? Evidence from a cross-sectional study in daughter-mother-grandmother trios.
2011
Bone adapts to mechanical loads applied on it. During aging, loads decrease to a greater extent at those skeletal sites where loads increase most in earlier life. Thus, the loss of bone may occur preferentially at sites where most bone has been deposited previously; ie, bone loss could be the directional reversal of accrual. To test this hypothesis, we compared the bone mass distribution at weight-bearing (tibia) and non-weight-bearing (radius) bones among 18-year-old girls, their premenopausal mothers, and their postmenopausal maternal grandmothers. Bone and muscle properties were measured by pQCT, and polar distribution of bone mass was obtained in 55 girl-mother–maternal grandmother trio…