Water Adsorption Properties Research Articles

Thermal behavior and water adsorption of natural and modified sepiolite having dolomite from Turkey

The water adsorption properties of sepiolite having dolomite supplied from Eskisehir region and their exchanged forms (K+, Na+, Mg2+ and Ca2+) were investigated. The sepiolite samples were characterized using XRD, TG-DTA, DSC and nitrogen adsorption methods. The temperature ranges were determined for the dehydrations of hydroscopic and zeolitic water as 30–200°C, for the dehydration of the bound water as 250–750°C and for the dehydroxylation of hydroxyls as 810–850°C in the sample. It was observed that the value of percent mass loss for natural and modified samples varied in the range from 36.70 to 39.05%. Two mass loss steps for all samples were observed using a differential scanning calorimetry (DSC) in the range of 30–550°C. Adsorption isotherms for water on natural and modified forms were obtained at pressures up to 2.39 kPa. Uptake of water increased as K-SEP.<Na-SEP.<Mg-SEP.<Ca-SEP. for sepiolite samples at 293 K.

Surface composition and contact angle relationships for differently prepared solid dispersions

Solid dispersions are promising drug delivery forms which offer the possibility to disperse a hydrophobic drug in a hydrophilic matrix and thereby improve the dissolution behavior and the bioavailability of the drug. One important aspect and a prerequisite in understanding the drug dissolution mechanism from solid dispersions is a better analytical monitoring of the solid dispersion surface properties, such as powder surface composition and water adsorption properties. In this paper, we have considered chemical and structural surface analysis data for solid dispersions processed by spray drying or roto-evaporation and compared these data with information obtained by contact angle measurements. Firstly, we establish the usefulness and suitability of X-ray photoelectron spectroscopy (XPS) for determination of surface chemical composition and scanning electron microscopy (SEM) for determining the structure of solid dispersions composed of different types of carriers, drugs and drug concentrations. Secondly, we measure contact angles of solid dispersions to describe wettability, to finally establish a link between the surface chemical composition, the powder structure and the wetting behavior. These experimental methods offer a rapid screening tool for the selection of carrier, drug concentration and/or process in early development. In addition, they provide a useful tool for investigating structural aspects of solid dispersions which have intrinsic relevance for drug dissolution and stability.

A Comparative Study of Structural, Acidic and Hydrophilic Properties of Sn−BEA with Ti−BEA Using Periodic Density Functional Theory

Periodic density functional theory has been employed to characterize the differences in the structural, Lewis acidic and hydrophilic properties of Sn-BEA and Ti-BEA. We show that the incorporation of Sn increases the Lewis acidity of BEA compared to the incorporation of Ti. Hence, the present work gives insight into the role of Sn in increasing the efficiency of the oxidation reactions. The results also justify that the percentage of Sn substituted in BEA is less than Ti. The structural analysis shows that the first coordination shell of Sn is larger than that of Ti. However, the second coordination of both sites remains the same. The water adsorption properties of these substituted zeolites are quantified. Moreover, we explain the higher Lewis acidity of Sn than the Ti site on the basis of the Fukui functions and charge population analysis.

Synthesis and characteristic properties of Rb-mordenite

Rb-mordenite, namely RMA-1, with a Si/Al ratio of 5.3–8.3 in a pure phase was hydrothermally synthesized for the first time from Rb-aluminosilicate gel without using any organic structure-directing agent under stirring condition. The crystal structure was analyzed by the Rietveld refinement of the XRD data, and the sites of extra framework Rb ions and water molecules were determined. The adsorption properties of water and benzene on the mordenites with different Si/Al ratios were evaluated. The adsorption capacities of water and benzene on Rb-mordenites were lower than those of Na-mordenites because of larger ionic diameter of Rb.

Dynamic wetting of plasma-treated polypropylene nonwovens

Various techniques have been employed to improve the wettability of polypropylene materials for a wide range of applications. In this study, polypropylene nonwovens were treated in oxygen plasma for improving water adsorption properties. The effects of plasma treatment on wetting and water adsorption behavior were characterized using dynamic contact angle measurements and dynamic sorption measurements. The introduction of hydrophilic groups was detected by attenuated total reflection–Fourier transform infrared spectroscopy. The plasma treatment roughened the fiber surface revealed by atomic force microscopy. The roughened and hydrophilic surface resulted in the change in advancing and receding contact angles. The dynamic sorption measurements also examined the water adsorption behavior of the materials. The investigation revealed that plasma treatment could significantly improve the water adsorption properties of polypropylene nonwovens. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2157–2160, 2007

Effect of protein concentration on the surface composition, water sorption and glass transition temperature of spray-dried skim milk powders

The effects of dilution of protein content in skim milk (34–8.5% protein content), by lactose addition, on the surface composition, water sorption property and glass transition temperatures of spray-dried powders were investigated. The X-ray photoelectron spectroscopy (XPS) study of spray-dried powders showed preferential migration of proteins toward the surface of the milk particles whereas the lactose remained in the bulk. Sorption studies showed that the lower protein concentration in milk powders is linked to an increased water adsorption property and lowering of water activity ( a w) for lactose crystallization. Analysis of glass transition temperature ( T g) of the powders sorbed at different humidities showed no distinct change in T g values, indicating the dominant effect of lactose on the glass transition temperature of all the powders.

A novel hydrogel crosslinked hyaluronan with glycol chitosan

A novel hydrogel was prepared by crosslinking hyaluronan with glycol chitosan in aqueous solution using water soluble carbodiimide at nearly neutral pH and room temperature. The products can be easily formulated into injectable gels, various films, membranes and sponges for soft tissue augmentation, viscosupplementation, drug delivery, preventing adhesion of post operation, wound dressing and tissue engineering scaffolds. The said hydrogel has high water adsorption property and biostability. Rheololgical results of the gel showed a soft and viscoelastic structure. FTIR further confirmed the formation of amide bonds between carboxyl groups of hyaluronan and amine groups of glycol chitosan and no N-acylurea and other derivatives were identified.

Water adsorption and desorption on ultra-low friction sulfur-doped hydrogenated carbonfilms

Water adsorption on hydrogenated carbon film surfaces can drastically affect frictionbehaviour. In this work, we investigate water adsorption and desorption properties ofsulfur-doped hydrogenated films, which we have observed to retain ultra-low frictionproperties of hydrogenated carbon films in humid air. Water adsorption studies using aquartz crystal microbalance show that there is an almost threefold reduction inequilibrium water coverage at room temperature on hydrogenated carbon filmsdoped with 5 at.% sulfur. Thermal desorption studies indicate that sulfur dopingweakens the binding of water molecules on hydrogenated carbon film surfaces.

Dynamic water adsorption behaviour of plasma-treated polypropylene nonwovens

Plasma surface treatment has been extensively applied in the textile industry for the modification of polymer materials. In this study, polypropylene (PP) nonwovens were treated with cold oxygen gas plasma for improving the water adsorption properties of the materials. The effects of plasma treatment on wetting and water adsorption behaviour of the materials were examined using environmental scanning electron microscopy (ESEM) and dynamic adsorption measurements (DAM). ESEM observations revealed the behaviour of water droplets formed on the fibre surfaces. DAM also showed the effect of plasma treatment on the dynamic water adsorption behaviour of the materials. The investigation revealed that plasma treatment could significantly improve the dynamic water adsorption properties of PP nonwovens. It was also found that the fibre fineness influenced the water adsorption behaviour of the plasma-treated materials.

Effect of tin on Nb 2O 5/ α-Al 2O 3 catalyst for ethylene oxide hydration

The effect of tin on the structure, acidity, and water adsorption property of Nb 2O 5/ α-Al 2O 3 catalyst and on this catalyst's performance for ethylene oxide (EO) hydration were studied by XRD, Raman spectroscopy, NH 3-TPD, IR of pyridine and of H 2O adsorption, and catalytic tests. Characterization results revealed that the density of acidic sites decreased with the addition of tin and with increasing Sn/Nb ratio in the cases studied, whereas the acidity exhibited minimum strength at Sn / Nb = 0.08 . The IR of water adsorption indicated that addition of tin significantly enhanced the water adsorption property of the catalyst. The catalytic tests revealed that monoethylene glycol (MEG) selectivity increased from 89.8% of the Nb 2O 5/ α-Al 2O 3 catalyst to 94.0% of the tin-promoted catalyst maintaining the EO conversion at 99.7%, and the catalyst exhibited excellent stability. The enhanced water adsorption property of the tin-promoted catalyst is proposed to be responsible for the significant improvement in MEG selectivity.

Spectroscopic measurement and analysis of water and oil in transformer insulating paper

A portable fiber-optic spectroscopic system (TRANSPEC) has been developed for nondestructive measurement of aged transformer insulating paper. Following successful measurement of degree of polymerization (DP) of a range of transformer-aged paper samples, the system has now been shown to separate the oil and paper information for measurement of DP in oil-wetted paper samples. In addition, the system has been shown to be capable of the prediction of both oil and water content of paper to a high accuracy, and is also capable of identifying and quantifying different water species. Spectroscopic measurements have been used together with gravimetric water adsorption measurements to investigate the kinetics of uptake of water vapour into paper from air in the case of nominally dry and oil-impregnated samples. Relationships between water adsorption parameters and properties of the paper insulation have also been investigated using measurements under controlled conditions.

Adsorption Properties of Water and Oxygen Molecules on the Surfaces of Photo-Catalysts: First Principles Theoretical Investigations on InVO4

not Available.

Development of porphyrin dispersed sol–gel films as HCl sensitive optochemical gas sensor

The porphyrin dispersed sol–gel composite films were prepared from the different molar ratios of methyltriethoxysilane (MTEOS) to tetraethoxysilane (TEOS), M/T (=4, 8, 16 and 32), and optochemical detection of hydrogen chloride (HCl) gas (0.5–5.0 ppm) was examined by using the photo-reflection spectral technique. The optical spectra of the films showed an intense Soret-band at λ max of 419.3 nm for M/T = 4–16 and 418.3 nm for M/T = 32. The sensitivity of the sensors measured at the Soret-band strongly depended on the M/T ratio of the sol–gel films and to 0.5 ppm it resulted in the order of M/T = 8 > 4 ≈ 16 > 32. From the thermogravimetric (TG) analysis, it was found that M/T = 4 contained a predominantly large amount of water adsorption. It is predicted that M/T = 8 has the highest adsorption capacity of HCl to exhibit the highest sensitivity. However, at high concentration of HCl (≥2.8 ppm) M/T = 4 exhibited a comparable sensitivity to M/T = 8 probably due to the large amount of water adsorption property of M/T = 4. In spite of the high sensitivity to HCl gas, the M/T = 8 sensor was almost silent to the 0.5 ppm SO 2 exposure.

Investigation of the water sorption properties of Mars-relevant micro- and mesoporous minerals

Encouraged by recent results of the Mars Odyssey spacecraft mission and the OMEGA team (Mars Express) concerning water in equatorial latitudes between ±45° on Mars and the possible existence of hydrated minerals, we have investigated the water sorption properties of natural zeolites and clay minerals close to martian atmospheric surface conditions as well as the properties of Mg-sulfates and gypsum. To quantify the stability of hydrous minerals on the martian surface and their interaction with the martian atmosphere, the water adsorption and desorption properties of nontronite, montmorillonite, chabazite and clinoptilolite have been investigated using adsorption isotherms at low equilibrium water vapor pressures and temperatures, modeling of the adsorption equilibrium data, thermogravimetry (TG), differential scanning calorimetry (DSC), and proton magic angle spinning nuclear magnetic resonance measurements ( 1H MAS NMR). Mg-sulfate hydrates were also analyzed using TG/DSC methods to compare with clay mineral and zeolites. Our data show that these microporous minerals can remain hydrated under present martian atmospheric conditions and hold up to 2.5–25 wt% of water in their void volumes at a partial water vapor pressure of 0.001 mbar in a temperature range of 333–193 K. Results of the 1H MAS NMR measurements suggest that parts of the adsorbed water are liquid-like water and that the mobility of the adsorbed water might be of importance for adsorption-water-triggered chemistry and hypothetical exobiological activity on Mars.

Determination of physical behaviour of feed pellets in Mediterranean water

Settled uneaten feed causes the most intense impact under sea cages, and settling velocity of the feed pellets represents a key parameter for waste dispersion models. Even if some data about physical properties of feed pellets have been published in the framework of salmonid rearing, there is a complete lack of information related to the Mediterranean Sea, as regards typical values of temperature, salinity and feed composition for Gilthead Sea Bream (Sparus aurata L.) and Sea Bass (Dicentrarchus labrax L.). In this study we try to fill this lack, determining dimensions, water adsorption properties, floating times and settling velocities of a typical growing sequence of pellets for the species mentioned above, under defined laboratory conditions reproducing Mediterranean Sea water. The settling velocity increases with pellet size from 0.087, for the smallest pellet (3 mm), to 0.144 m s−1, for the 5 mm pellet. The biggest extruded pellet (6 mm) falls slower (0.088 m s−1). The floating time before pellet's fall is found to be a critical parameter in determining settling velocity. The latter depends on pellet's size, water temperature and salinity. The examined pellets reach a 42% of weight increase after 10 min of immersion, while no appreciable dimension change is observed. Our results are in part different from previous ones and could play a role in evaluating and modelling Mediterranean aquaculture environmental impact.

Effects of Subsurface Boron and Phosphorus on Surface Reactivity of Si(001): Water and Ammonia Adsorption

Using density functional slab calculations with planewave basis set and pseudopotentials, we have examined the effect of subsurface boron and phosphorus on the surface chemical properties of Si(001). We compare the adsorption behaviors of water and ammonia between B- or P-modified and clean Si(001) surfaces. On the B-modified surface, the charge polarization of two B-connected dimers is altered significantly. Our calculation shows that approximately one electron is transferred from the local surface to the subsurface boron, thereby leading both buckled-up and -down atoms of B-connected dimers to be electron-poor (electrophilic). On the other hand, subsurface P brings about no significant change in surface electronic structure. Only about one-tenth of an electron is transferred from the subsurface P to the local surface. As a result, relative to the clean surface, the adsorption properties of water and ammonia change noticeably on the B-modified surface while varying insignificantly on the P-modified surface.

Surface area, porosity and water adsorption properties of fine volcanic ash particles

Our understanding on how ash particles in volcanic plumes react with coexisting gases and aerosols is still rudimentary, despite the importance of these reactions in influencing the chemistry and dynamics of a plume. In this study, six samples of fine ash ( 500 A. All the specimens had similar pore size distributions, with a small peak centered around 50 A. These findings suggest that fine ash particles have relatively undifferentiated surface textures, irrespective of the chemical composition and eruption type. Adsorption isotherms for water vapour revealed that the capacity of the ash samples for water adsorption is systematically larger than predicted from the nitrogen adsorption a s values. Enhanced reactivity of the ash surface towards water may result from (i) hydration of bulk ash constituents; (ii) hydration of surface compounds; and/or (iii) hydroxylation of the surface of the ash. The later mechanism may lead to irreversible retention of water. Based on these experiments, we predict that volcanic ash is covered by a complete monolayer of water under ambient atmospheric conditions. In addition, capillary condensation within ash pores should allow for deposition of condensed water on to ash particles before water reaches saturation in the plume. The total mass of water vapour retained by 1 g of fine ash at 0.95 relative water vapour pressure is calculated to be ~10−2 g. Some volcanic implications of this study are discussed.

A comparison of water adsorption on ordered and disordered silica substrates

The adsorption properties of water adsorbed on various silica substrates are investigated by way of Grand Canonical Monte Carlo simulations (GCMC). The SPC and PN-TrAZ potential are used to describe water–water and water–silica interactions. The numerical sample of mesoporous silica glass (pore size: 3.6 nm) was obtained by off-lattice reconstruction, known to reproduce in a realistic way the geometrical complexity of high specific surface Vycor. The chemistry of the surface is made realistic by hydroxylation. The simulated adsorption isotherm and isosteric differential enthalpy of adsorption compare well to experimental data for Vycor, showing the ability of the PN-TrAZ potential to describe the hydrophilic properties of silica surfaces. This study was extended to several crystallographic faces of cristobalite. Their adsorption properties differ widely from each other. It is shown that the hydrophilic properties are not simply related to surface hydroxyl density but are also related to the local structure of the silica surface. In spite of these large variations, it is possible to reproduce the adsorption isotherm of the mesoporous disordered sample by applying a natural averaging procedure over the different crystallographic faces of cristobalite.

Water adsorption and energetic properties of spark discharge soot: Specific features of hydrophilicity

Water adsorption was studied for spark discharge soot which is often used as a surrogate for atmospheric soot. Analysis by adsorption gravimetry and calorimetry showed that spark discharge soot exhibits specific features of hydrophilicity. Analysis of the isotherms and heats of water adsorption revealed the peculiarities of the mechanism of surface wetting related to significant changes in the soot microstructure. The first water adsorption/desorption cycle led to irreversible water adsorption and a decrease of the surface area available for water adsorption. Repeated water adsorption/desorption cycles demonstrated swelling phenomena related to the increase of the nitrogen surface area due to interparticle microporosity. The maximum effect of the transformation was observed under exposure to saturated water vapor following the microstructure stabilization. With decreasing temperature the amount of adsorbed water also decreased. Once emitted into the atmosphere the spark discharge soot particles will exhibit irreversible changes in surface area, porosity and hygroscopicity as a result of numerous humidity fluctuations until approaching a stable state of their microstructure due to long exposure to saturated water vapor.

Water adsorption on hydrophilic mesoporous and plane silica substrates: A grand canonical Monte Carlo simulation study

The adsorption properties of water on silica surfaces at 300 K are evaluated by way of grand canonical Monte Carlo simulations, a well suited technique to investigate thermodynamical properties of interfacial fluids. The PN–TrAZ potential is used to describe atomic interactions between water and substrate, and the SPC model for water–water interactions. To measure confinement effects, we compare adsorption on different plane surfaces to a realistic disordered mesoporous material previously obtained by off lattice reconstructions known to reproduce in a realistic way the geometrical complexity of real Vycor of high specific surface, in terms of surface area, chord distribution, and correlation peak in small angle neutron scattering spectra. The adsorption isotherm, and isosteric heat of adsorption are calculated and compared to experimental data found in the literature for Vycor. They show good agreement, the PN–TrAZ potential for the adsorbate–surface interaction being able to give a satisfactory description of hydrophilic properties of plane and curved silica surfaces. For pressure less than 0.65 times the vapor pressure of SPC water at 300 K, the model shows identical adsorption properties for plane and mesoporous surfaces, validating the t-plot concept for such materials, i.e., the fact that the amount of fluid adsorbed is proportional to the surface area of the substrate irrespective of the pore size, as long as the surface chemistry (the OH density in this case) is kept constant. However, for very low relative pressure (10−3) an analysis of the isosteric heat of adsorption shows the presence of highly energetic sites on the mesoporous Vycor sample probably related to curvature, defects or roughness absent from perfectly plane surfaces. For relative pressure higher than 0.65 a sudden rise in Vycor adsorption is the signature of capillary condensation in the mesoporosity of the material, in agreement with experimental measurements in Vycor. Such a rise is absent on plane surfaces as expected for this confinement-induced capillary condensation.