Water Adsorption Isotherms Research Articles

Water adsorption fingerprinting of structural defects/capping functions in Zr-fumarate MOFs: a hybrid computational-experimental approach.

Engineering structural defects in MOFs has been intensively applied to modulate their adsorption-related properties. Zr-fumarate MOF (also known as MOF-801) is a prototypical defective MOF with proven versatile adsorption/separation performances depending on the synthetic conditions, however the relationship between the nature/concentration of both structure defects/capping functions and its adsorption features is still far from being fully understood. In this work, we first present a systematic theoretical exploration of the individual contributions of linker and cluster defects as well as of the capping functions to the overall water adsorption profile of the MOF-801 framework. This computational effort based on the construction of defective structure models and the use of Grand Canonical Monte Carlo simulations further enabled the identification of the overarching defective structure for two MOF-801 samples based on their experimental adsorption isotherms reported previously. An experimental effort was then deployed to synthesize two Zr-fumarate MOF samples with controlled nature and concentration of structural defects as well as capping functions. This computational-experimental hybrid strategy revealed the water adsorption isotherm as a fingerprint of the nature and concentration of structural defect/capping groups exhibited by the MOF adsorbent. We expect this study to deliver meaningful insights to further design MOFs with target adsorption features through a rational engineering of structural defects.

Screening adsorbent–water adsorption heat pumps based on an experimental water adsorption isotherm database

Computational screening of adsorbent-water working pairs for adsorption heat pumps is carried out based on the experimental water adsorption isotherm database containing 231 adsorbents, from which the coefficient of performance can be evaluated.

Modified Silicone-SAPO34 Composite Materials for Adsorption Thermal Energy Storage Systems

In this work, novel silicone-SAPO34 composite materials are proposed for application in adsorption thermal energy storage systems. The innovative composite materials were obtained through a mold foaming process activated by a dehydrogenative coupling reaction between properly selected siloxane compounds. Morphology analysis by optical microscopy and measurement of the mechanical properties of the foamed materials at varying zeolite content demonstrated a quite homogeneous open-cell structure and good structural stability of the foam. Water adsorption isotherms of the adsorbent foams expanded in free space and inside paperboard were measured by a gravimetric adsorption apparatus, demonstrating that the presence of the polymeric fraction does not affect the adsorption capacity of the SAPO34 fraction added in the composite foam. Finally, main adsorption and thermodynamic properties of the proposed foam have been compared with those of other adsorbent materials, confirming the possible use of these new composite foams as adsorbent materials for adsorption thermal energy storage systems.

Water sorption properties of papaya seeds (Carica papaya L.) formosa variety: An assessment under storage and drying conditions

In this research, sorption isotherms and thermodynamic properties of papaya seeds were evaluated by simulating storage and drying temperatures. Papaya seeds and its oil were evaluated for their proximate composition and physicochemical parameters, respectively. Water adsorption isotherms of papaya seeds were determined at seven temperatures (20–80 °C) by the gravimetric-static method. The net isosteric heat of sorption was determined by using Clausius-Clapeyron Equation. The differential enthalpy and entropy and the free Gibbs energy were calculated using the sorption data. The adsorption surface area was determined using the monolayer moisture content obtained from GAB model fitting. Peleg model was selected to describe the sorption isotherms of papaya seeds because it presented great precision (RAdj2> 0.993 and χ2 ≤0.00031). The equilibrium moisture content of the papaya seeds decreased with increasing temperature. At all temperatures, sorption isotherms exhibited type II sigmoid shape. The net isosteric heat of sorption (0.56–8.71 kJ/mol), differential enthalpy (−8.71 to −0.56 kJ/mol), and entropy (0.08–20.13 J/molK) decreased with the increasing of equilibrium moisture content. The enthalpy-entropy compensation theory was validated. The increase in temperature decreased the value of the surface area of sorption. The process was enthalpy-driven and nonspontaneous (+ΔGB).

Sorption and thermal characteristics of ancient grain pasta of various compositions

The effect of ancient grain pasta composition on its sorption properties and phase transitions was evaluated. Three pasta samples were prepared from ancient grain flours: spelt wheat, einkorn wheat, emmer wheat and quinoa, and for comparison purposes one pasta sample from durum wheat flour. Water adsorption and desorption isotherms of pasta were determined and they were fitted by the Guggenheim–Anderson–de Boer equation. The state diagrams of pasta samples were developed by measuring their freezing points, glass transition temperatures, and the maximum-freeze-concentration conditions by Differential Scanning Calorimetry. All the pasta samples exhibited sorption hysteresis with higher equilibrium water content determined for desorption. Substitution of spelt wheat flour with other ancient grain flours in pasta samples resulted in decreased glass transition temperature, freezing temperature and the end point of freezing. The amount of un-freezable water in ancient wheat flour-based pasta was significantly higher than in durum wheat pasta. The results showed that the modification of chemical composition of pasta as a result of replacing semolina with flours from ancient grains is accompanied by a change in their sorption and thermal properties.

Do Internal and External Surfaces of Metal-Organic Frameworks Have the Same Hydrophobicity? Insights from Molecular Simulations.

Reliable information on the hydrophobicity of porous materials is important in the design of many catalytic and separation processes. In general, hydrophobicity is assessed by measuring the contact angle of water (external surface) or the adsorption isotherm of water (internal surface). However, it is not clear how these different assessments are related. In this paper, molecular dynamics simulations of microscopic water droplets on the external surfaces of metal-organic frameworks are used to investigate the influence of the surface nature and hydrophobicity on the contact angle. The metal-organic frameworks MOF-5 and CAU-10 were modeled with external surfaces of different hydrophobicities, while the internal surface was maintained. It was observed that microscopic droplets orientate their spreading to the nature of the external surfaces. Comparing the simulated contact angles and adsorption isotherms confirms the necessity to distinguish between internal and external hydrophobicity.

Characterization of the physicochemical, structural and thermodynamic properties of encapsulated garlic extract in multilayer wall materials

Garlic extract (GE) was encapsulated into the matrices of two types of multilayer walls composed of whey protein isolate (WPI)/chitosan (CH)/polydextrose (POL) and gum Arabic (GA)/CH/POL. Fourier transform infrared spectroscopy (FTIR) indicated that the compounds of GE were encapsulated within the matrices of the wall materials by physical interactions. The water adsorption isotherms of the powders were determined at 30, 40 and 50 °C. The GAB model was the most suitable to fit the adsorption data. The adsorption sorption of the powders was enthalpy-controlled and the thermodynamic functions demonstrated that the WPI/CH/POL powders had hydrophilic surface with higher number of polar sites available to binding with water molecules than GA/CH/POL powders. The experimental data of water and nitrogen adsorption isotherms were used to determine the surface areas and pore sizes of the powders. All the results can be used to improve the processing, handling, and storage conditions of the powders.

The effect of heat treatment on the moisture absorption characteristics of Cu-impregnated Masson’s pine wood

The accumulation of water inside wood creates a favorable environment not only for molds, but also for wood-decaying fungi and insects. Therefore, the ability to limit water adsorption and retention is key to the longevity and performance of wood. In this study, the effect of heat-treatment and Cu nanoparticle (CuNP) impregnation on surface contact angle, specific surface area, and hygroscopicity of Masson’s pine wood was examined. Heat-treatment caused thermal degradation of hydroxyl-rich biopolymers, leading to an increase in hydrophobicity; while the resulting breakdown and blockage of the interior cell cavity network caused a decrease in effective surface area. In turn, the hygroscopicity of the heat-treated wood was considerably lower than the untreated wood. Analysis of water adsorption isotherms enabled the differentiation between bound water and free water, where the latter was a prerequisite for mold growth. The research showed that the amount of free water was reduced by both impregnation with CuNP and heat-treatment, but the previously observed antimicrobial activity was shown to rely on the presence of CuNPs as opposed to the reduced free water content. This study presented a detailed methodology for the preparation and analysis of heat-treated, CuNP-impregnated wood, and provided further insight into the mechanism of antimicrobial action of treated woods.

Quantification and prediction of water uptake by soot deposited on ventilation filters during fire events

Soot samples from different fuels were produced in small and pilot combustion test benches at various O2 concentrations, and were then characterized in terms of primary particle diameter, specific surface area and oxygen content/speciation. Water sorption measurements were then carried out for soot compacted into pellet form and in powder form, using both a gravimetric microbalance and a manometric analyser. Water adsorption isotherms are all found to be Type V, and reveal the central role of the specific surface area and the oxygen content of soot. A single parametrization of the second Dubinin-Serpinsky model gives a proper fit for all isotherms. To the best of our knowledge, this is the first study to provide physico-chemical parameters and water sorption results for fire soot. This enables a better description of the soot cake formed on filters during a fire, in particular in industrial confined facilities as simulated in this study. Humidity can be then explicitly considered in the same way as other parameters influencing the aeraulic resistance of soot cakes. These results can be used to improve predictions of the consequences of fires on the containment of toxic materials within industrial facilities.

Sorption properties, glass transition and state diagrams for pumpkin powders containing maltodextrins

The state diagrams of freeze-dried pumpkin powders with different maltodextrin additions were developed using glass transition line, freezing curve and maximal-freeze-concentrations conditions. The freezing curve was plotted employing Clausius – Clapeyron equation and glass transition lines were developed using Gordon – Taylor model. The ultimate maximum-freeze-concentration conditions of the powders were observed in range from 0.685 to 0.745 g solids/g sample. Characteristic glass transition temperature of maximum-freeze-concentration (Tg’) of the pumpkin was equal to - 83.7 °C and was increase with increasing maltodextrin addition. Adsorption isotherms of pumpkin – maltodextrin powders were determined at 25 °C by static - gravimetric method and the experimental data was modelled with BET and GAB equations. Monolayer moisture content of the pumpkin powder decreased with increasing maltodextrin additions. The state diagram and water adsorption isotherms of the pumpkin – maltodextrin powders are useful for predicting suitable storage and processing conditions.

Structure and water uptake in BaLnCo2O6−δ (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy)

The structure of BaLnCo2O6-δ (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy) was studied by the means of synchrotron radiation powder X-ray diffraction, neutron powder diffraction and Transmission Electron Microscopy (TEM), while water uptake properties were analysed with the use of thermogravimetry (TG) and water adsorption isotherms. The structure refinement revealed that the dominant phase in all compositions was orthorhombic with an ordering of the A-site cations along the c-axis and ordering of oxygen vacancies along the b-axis, which was also directly evidenced by TEM. It was shown that both unit cell volume and average Co-oxidation state at room temperature decrease linearly with decreasing Ln radius. TG water uptake experiments in humidified N2–O2 gas mixture at 300 °C revealed that among all compositions, only BaLaCo2O6-δ and BaGdCo2O6-δ exhibit significant water uptake. Surface water adsorption studies showed that the α, a normalised parameter reflecting the surface hydrophilicity, mostly independently of Ln radius was close to 0.5, which means that the surface is neither hydrophobic nor hydrophilic. The results indicated that water uptake observed at 300 °C is a bulk process, which cannot be described by standard hydration/hydrogenation reaction and it is related to the layered structure of the perovskite lattice and characteristic to La or Gd being present in the lattice.

Adsorption Isotherm Modelling of Water on Nano-Tailored Mesoporous Silica Based on Distribution Function

A new model of adsorption isotherms Type IV and V is proposed as a basis for theoretical calculations and modelling of adsorption systems such as adsorption heat storage and heat pumps. As the current models have decent yet limited applicability, in this work, we present a new combined model with universal use for micro-mesoporous silica/water adsorption systems. Experimental measurement of adsorption isotherm of water onto seven different samples of micro and mesoporous silica and aluminium-silica were used to fit new adsorption models based on a combination of classical theories and a distribution function related to the pore-size distribution of the selected materials. The fitting was conducted through a repeated non-linear regression using Trust Region Reflective algorithm with weighting factors to compensate for the scalability of the adsorption amount at low relative pressure with optimization of the absolute average deviation fitting parameter. The results display a significant improvement for most of the samples and fitting indicators compared to more common models from the literature with average absolute deviation as low as AAD = 0.0025 g g−1 for material with maximum uptake of q = 0.38 g g−1. The newly suggested model, which is based on a combination of BET theory and adjusted normal distribution function, proved to bring a higher degree of precision and universality for mesoporous silica materials with different levels of hydrophilicity.

Experimental investigation on water adsorption and desorption isotherms of the Longmaxi shale in the Sichuan Basin, China

The understanding of water adsorption and desorption behavior in the shale rocks is of great significance in the reserve estimation, wellbore stability and hydrocarbon extraction in the shale gas reservoirs. However, the water sorption behavior in the shales remains unclear. In this study, water vapor adsorption/desorption isotherms of the Longmaxi shale in the Sichuan Basin, China were conducted at various temperatures (30 °C, 60 °C) and a relative pressure up to 0.97 to understand the water sorption behavior. Then the effects of temperature and shale properties were analyzed, and the water adsorption, hysteresis, saturation and capillary pressure were discussed. The results indicate that water adsorption isotherms of the Longmaxi shale exhibit the type II characteristics. The water molecules initially adsorb on the shale particle/pore surfaces at low relative pressure while the capillary condensation dominates at high relative pressure. Temperature favors the water sorption in the shales at high relative pressure, and the GAB isotherm model is found to be suitable for describe the water adsorption/desorption behavior. The high organic carbon and full bedding are beneficial to water adsorption in the shales while the calcite inhibits the behavior. There exists the hysteresis between water adsorption and desorption at the whole relative pressure, which suggests that the depletion of condensed water from smaller capillary pores is more difficult than that from larger pores, and the chemical interaction contributes to the hysteresis loop for water sorption. The capillary pressure in the shales can be up to the order of several hundreds of MPa, and thus the desorption of water from the shales may not be as easy as the water adsorption due to the high capillary pressure, which results in water retention behavior in the shale gas reservoirs. These results can provide insights into a better understanding of water sorption behavior in the shale so as to optimize extraction conditions and predict gas productivity in the shale gas reservoirs.

Influence of water activity on the heat resistance of Salmonella enterica in selected low-moisture foods

Low-moisture foods (LMF with water activity, aw < 0.85) including pet foods and black pepper powder have consistently been associated with foodborne disease caused by Salmonella enterica. Increased heat resistance and prolonged survival at low-moisture conditions, however, remain major challenges to achieve effective inactivation of Salmonella in low-moisture foods. At low water activity (aw) conditions, heat resistance of Salmonella is greatly enhanced when compared to high aw conditions. This study aimed to quantify the effect of aw on the heat resistance of Salmonella enterica in pet food pellets and black pepper powder. Pet food pellets were inoculated with two strains of heat resistant S. enterica and black pepper powder was inoculated with a 5-strain cocktail of Salmonella. Both inoculated food samples were equilibrated at 0.33, 0.54, and 0.75 aw in controlled humidity chambers. Inoculated pet food pellets and black pepper powder in closed aluminum cells were heat treated at specific temperatures for selected times. The results showed that the Weibull model fitted well the inactivation data. At a specific temperature, the rate of inactivation increased with the increase in the aw from 0.33 to 0.75, and the 3-log reduction times decreased for Salmonella in both food samples with the increase in aw. Water adsorption isotherms of pet food pellets and black pepper powder at initial and treatment temperatures were developed to understand the change in aw during heat treatments. The change in aw during heat treatment was dependent on the type of food matrix, which possibly influenced the thermal inactivation of Salmonella in pet food pellets and black pepper powder. The quantitative analysis of heat reduction of Salmonella with respect to aw aids in selection of the appropriate initial aw to develop effective heat treatment protocols for adequate reduction of Salmonella in pet foods and black pepper powder.

Hygroscopicity of Castor Bean Seeds (Ricinus communis L.)

The hygroscopic balance of castor bean seeds (Ricinus communis L.) assists the proper handling of the product to preserve its water content at the levels recommended for safe storage. The objective of this work was to determine the water adsorption isotherms of castor bean seeds (EVF103 and EVF106) to obtain information on the amount of water that this product adsorb at temperatures of 10, 20, 30, 40oC and water activities between 0.20 and 0.89, as well as adjusting different mathematical models to the experimental data. To obtain the hygroscopic equilibrium, the indirect static method was used, using Hygropalm Model Aw 1 equipment, analyzing castor bean seeds of the genotypes EVF103 and EVF106. The Copace model (for the EVF103) and Modified Oswin model (for the EVF106), according to the statistical parameters and Akaike’s information criterion (AIC) and Schwarz’s bayesian information criterion (BIC) information criteria, represent the hygroscopicity of castor bean seeds in the temperature range of 10 to 40oC. In a same water activity, the water content of the castor bean seeds of the genotypes EVF103 and EVF106 reduces with increasing temperature.

Arbuscular Mycorrhizal Fungi in Tropical Ecosystems: Towards its Management?

The hygroscopic balance of castor bean seeds (Ricinus communis L.) assists the proper handling of the product to preserve its water content at the levels recommended for safe storage. The objective of this work was to determine the water adsorption isotherms of castor bean seeds (EVF103 and EVF106) to obtain information on the amount of water that this product adsorb at temperatures of 10, 20, 30, 40oC and water activities between 0.20 and 0.89, as well as adjusting different mathematical models to the experimental data. To obtain the hygroscopic equilibrium, the indirect static method was used, using Hygropalm Model Aw 1 equipment, analyzing castor bean seeds of the genotypes EVF103 and EVF106. The Copace model (for the EVF103) and Modified Oswin model (for the EVF106), according to the statistical parameters and Akaike’s information criterion (AIC) and Schwarz’s bayesian information criterion (BIC) information criteria, represent the hygroscopicity of castor bean seeds in the temperature range of 10 to 40oC. In a same water activity, the water content of the castor bean seeds of the genotypes EVF103 and EVF106 reduces with increasing temperature.

Zr(OH)4/GO Nanocomposite for the Degradation of Nerve Agent Soman (GD) in High-Humidity Environments.

Zirconium hydroxide, Zr(OH)4 is known to be highly effective for the degradation of chemical nerve agents. Due to the strong interaction force between Zr(OH)4 and the adsorbed water, however, Zr(OH)4 rapidly loses its activity for nerve agents under high-humidity environments, limiting real-world applications. Here, we report a nanocomposite material of Zr(OH)4 and graphene oxide (GO) which showed enhanced stability in humid environments. Zr(OH)4/GO nanocomposite was prepared via a dropwise method, resulting in a well-dispersed and embedded GO in Zr(OH)4 nanocomposite. The nitrogen (N2) isotherm analysis showed that the pore structure of Zr(OH)4/GO nanocomposite is heterogeneous, and its meso-porosity increased from 0.050 to 0.251 cm3/g, compared with pristine Zr(OH)4 prepared. Notably, the composite material showed a better performance for nerve agent soman (GD) degradation hydrolysis under high-humidity air conditions (80% relative humidity) and even in aqueous solution. The soman (GD) degradation by the nanocomposite follows the catalytic reaction with a first-order half-life of 60 min. Water adsorption isotherm analysis and diffuse reflectance infrared Fourier transform (DRIFT) spectra provide direct evidence that the interaction between Zr(OH)4 and the adsorbed water is reduced in Zr(OH)4/GO nanocomposite, indicating that the active sites of Zr(OH)4 for the soman (GD) degradation, such as surface hydroxyl groups are almost available even in high-humidity environments.

Molecular dynamics simulation of bis(2-chloroethyl) sulfide gas separation by metal-organic and porous aromatic frameworks

Abstract Separation of chemical warfare agents, specially sulfur mustard, is one of the most critical issues in environmental and military objects. Investigating the ability of some porous materials to separate mustard gas is the main aim of this work, and for this purpose, molecular simulation was selected. Dreiding model has been utilized for intra-molecule and van der Waals potentials of mustard gas and ab-initio calculations have been carried out to estimate partial charge of the atoms. The model was validated by comparison between liquid density and heat of vaporization obtained from molecular simulation and experimental values. Zn4O(3,5-dimethyl-4-carboxypyrazolato)3 and Cu(1,3,5-benzenetricarboxylate) are chosen in this work due to high active metal sites and previous studies which have reported high adsorption for mustard and similar molecules (i.e. diethyl sulfide). Moreover, two porous aromatic frameworks (PAFs), with and without NO2 functional group, which have different pore sizes have been studied to intensify the performance of mustard separation. The adsorption isotherm of water on PAFs has been also calculated by grand canonical Monte Carlo simulation to inspect the influence of humid condition on the separation process.

Ionosilica-based anion exchangers for low-temperature thermochemical storage of energy under mild conditions of adsorbent regeneration and saturation

Three ionosilica materials have been tested for low-temperature thermochemical storage of energy under mild conditions of adsorbent regeneration and saturation. The previous synthesis procedures were adapted to prepare materials possessing an organosilica framework with silylated cationic blocs and Cl-, HSO4-, SO42- anions in various proportions as extra-framework compensating counter-ions. Transmission and Scanning Electron Microscopy, Wavelength Dispersive X-Ray Fluorescence, Energy Dispersive X-ray Spectroscopy, Thermogravimetric analysis, adsorption of gaseous nitrogen at 77 K, 29Si Solid-State Nuclear Magnetic Resonance spectroscopy were employed to establish the key characteristics of the three ionosilica samples in terms of elemental composition, particle morphology and textural properties, thermal stability and regenerability, or variability of surface activity during repeated hydration-dehydration cycles. Their capacity to adsorb water vapor at cool and moderate ambient temperatures after incomplete surface drying was demonstrated by means of the scanning microscopy operating in low-vacuum mode at 275 K, or more precisely by measuring the water adsorption isotherms at 313 K and the related differential heats under static conditions. Finally, flow calorimetry operating in the moist-gas flow mode was used to measure the integral heat accompanying the adsorption of water vapor at its partial pressure of 2.8 kPa and 296 K as well as the kinetics of heat release in three drying-saturation cycles. After a drying procedure carried out under helium flow at 353 K, the thermal performance of two ionosilica samples containing both HSO4- and SO42- counter-ions was sufficient enough to consider them as potential adsorbents for auxiliary space heating in homes, small businesses, or public buildings.

Moisture adsorption in water caltrop (Trapa bispinosaRoxb.) pericarps: Thermodynamic properties and glass transition

AbstractMoisture sorption isotherms of water caltrop pericarp (WCP) powders were determined at 20, 30, and 40°C over water activity (Aw) range of 0.11 and 0.97. The adsorption isotherms decreased with the increase of temperature and exhibited Type II BET adsorption characteristics. The monolayer moisture content values calculated by the Guggenheim–Anderson–de Bor equation were found to be 0.0561, 0.0509, and 0.0409 g/g solids at 20, 30, and 40°C, respectively. The values of net isosteric heat of adsorption and differential entropy decreased from 26.094 to 0.250 kJ/mol, 76.665 to 0.358 J mol−1 K−1 with water content varying from 0.30 to 0.07 g/g solids, respectively. The isokinetic theory showed that the water adsorption process of WCP powders was governed by enthalpy. The values of specific surface area available for adsorption at 20, 30, and 40°C were 198.95, 180.40, and 145.11 m2/g, respectively. The spreading pressure increased with the increase of Aw values at a fixed temperature and decreased when temperature rising at a given Aw level. The effective pore size for WCP powders increased with the increment of water content and temperature, ranging from 1.648 to 21.761 nm. The glass transition temperature (T g) of WCP powders was examined by differential scanning calorimetry and its values decreased from 72.34 to 2.42°C as water content ranged from 0.0499 to 0.352 g/g solids. The result showed that WCP powders remained stable at 30°C when the moisture content was lower than 0.149 g/g solids.Practical applicationsWater caltrop (Trapa bispinosa Roxb) has been widely cultivated in China and other Southeast Asia because of its medical functions and delicious taste. The micronized water caltrop pericarp (WCP) is an excellent source of dietary fiber and phenolics and has been applied in various food and nonfood sectors. The objectives of this work were to evaluate the thermodynamic properties of water adsorption isotherms of WCP powders. In addition, a state diagram was established based on the water activity concept and glass transition theory. The results documented in this study will help design the energy process for producing WCP powders and predicting storage stability.