Water Adsorption Isotherms Research Articles

An optimized purple corn cob extract as an ingredient for the development of maize-based extrudates with novel characteristics

Purple corn cobs (PCC) are normally discarded although containing valuable components of potential application in the development of foods and ingredients. Optimum extraction conditions for PCC bioactive compounds were defined considering maximum antioxidant activity (AA), anthocyanins concentration (TAC), and total phenolic content (TPC). The optimized PCC extract (Opt-PCC) was added to a maize-based extruded formulation, and the obtained products were compared with a control sample without extract regarding their color, TPC, AA, physical properties, water adsorption isotherms, thermal transitions, and microstructure. Besides significantly modifying the color of extrudates, the addition of Opt-PCC increased their physical stability since higher glass transition temperatures were obtained when compared to the control at similar water contents. Differences in water sorption behavior could be attributed to the hygroscopicity of the compounds present in the extract. The incorporation of Opt-PCC increased TPC and AA of the extrudates by 14 and 4 times, respectively. The results confirmed a significant increase in the functional properties and physical stability of the extrudates with the addition of Opt-PCC, encouraging its use as a natural ingredient in the development of novel foods with improved characteristics.

Model-based investigation of water adsorption in Achira (Canna edulis K.) biscuits

The water adsorption properties of Achira biscuits were investigated using a mathematical model-based strategy to understand the relationship between water activity and moisture content due to the fact that it is highly relevant for its storage. For this purpose, the water adsorption isotherms of commercial Achira biscuits were firstly experimentally determined by the dynamic dew point (DDI) method at 25, 35, and 45 °C and ATR–FTIR spectroscopy was used to detect the functional groups. Secondly, the Guggenheim-Anderson-de Boer (GAB) equation, 4 empirical models (Smith, Oswin, Peleg and DLP), and 5 machine-learning techniques (Regression trees, Random Forest, k-Nearest Neighbors, Artificial Neural Networks and Support Vector Machine) were used to model the isotherms. The fundamentals of water adsorption were analyzed via GAB model parameters, adsorption surface area, spreading pressure, effective pore size, and thermodynamic properties, such as enthalpy-entropy and Gibbs free energy. The experimental results reflected a type III water isotherm and a moderate temperature effect. The GAB model quantified the effect of temperature on the adsorption properties, which reflected a lower degree of hygroscopicity at high temperatures. The Support Vector Machine Learning model provided the best mathematical description of the water adsorption isotherms considering the temperature effect (MRE<3% and R2adj>99%).

Anthocyanin-based indicators design by polyelectrolyte complexation: A study on structural and thermodynamic properties, and application for milk freshness assessment

Non-pomace residue of grape juice powder (NPG) was used in the development of indicator films for food freshness assessment by polyelectrolyte complexation of alginate and gelatin, and alginate and chitosan. The surface topography of the films was evaluated qualitatively by the 3D plot of scanning electron microscopy images and quantitatively by mechanical profilometry, which demonstrated the formation of a heterogeneous surface. Higher NPG contents increased the average and the root mean square roughness of the films, with values of 0.450 and 0.634, respectively, for the alginate and chitosan complex with 1.0 g NPG 100 g complex−1. The diffractograms of the samples, as well as the FTIR spectra, demonstrated that NPG interacted differently with the two complexes. This behavior was evidenced in the evaluation of wettability, which was increased by the addition of NPG, as well as in the evaluation of thermodynamic properties. The water adsorption isotherms of the films were determined at 20, 30, and 40 °C. The GAB model presented the best fit for the adsorption data, which was an enthalpy-controlled process. The films demonstrated to be efficient in evaluating the freshness of whole milk samples acidified with lactic acid through the quantification of red chromatic shift as a function of pH, which proved to be a promising way to interpret the visual result of color change by digital image analysis.

The Competitive Adsorption of Water and Methanol on a Hybrid Silica Stationary Phase in Supercritical Fluid Chromatography

This study investigates the adsorption of methanol, water, and their mixture in a hybrid silica stationary phase with supercritical carbon dioxide as a mobile phase in supercritical fluid chromatography (SFC). The adsorption isotherms of methanol and water were determined by two dynamic methods: the elution by characteristic point (ECP) method and the inverse method (IM). Both the single-component and competitive bi-Langmuir models were pre-selected for the inverse method. The initial parameters of the single-component isotherm for both methanol and water were estimated with the ECP method by fitting the experimental data to the bi-Langmuir isotherm model. Then, using the inverse method, we refined the single-component isotherm parameter values, which were then further used for determining the competitive isotherm of the methanol–water mixture. The elution profile of the (methanol–water) mixture sample was calculated by the equilibrium-dispersive (ED) model. The results indicated that there is a good agreement between the experimental band profile and the calculated band profile, which was obtained from the parameters of the competitive bi-Langmuir isotherm model, revealing a competition between methanol and water to reach the adsorption sites. Furthermore, the saturation capacity of the adsorption sites in the stationary phase decreased in the case of the mixture sample compared to those for the single-component sample.

Water adsorption isotherms and phase transitions of spray-dried chickpea beverage

Chickpea hydrolysate powders were obtained by spray-drying (70 and 60 °C as outlet and 180 °C inlet air temperatures), using inulin and maltodextrin as adjuvants (12 or 25 g/100 g solids). No effects of the variables studied were observed on solubility (88–93 g/100 g solids) and final moisture (3.50–6.15 g/100 g db). Yields were 49.44–61.24 and 44.53–51.55% at 70° and 60 °C respectively. Moisture adsorption isotherms (25°, 35° and 45 °C) were obtained by dynamic dew point method and modeled with GAB and BET equations. BET monolayer moisture values (5.53–9.66 g/100 g db), were slightly different and higher than those obtained for the GAB model. Critical values of water activity (awc) and critical moisture (Mc), related with phase transitions, were determined using the second derived from moisture change with respect to water activity (Sovitsky-Golay 2nd derivate). At 25 °C the highest awc and Mc values, 0.515 and 0.535, and 8.5 and 9.35 g/100 g db occur for products dried at 60 °C and with the lowest level of both adjuvants, while the product without adjuvant has an awc and Mc f 0.466 and 7.46 g/100 g db. The increase in awc and Mc, due to the presence of the inulin and maltodextrin reflects their protective effect. According to these results spray-drying (Tout = 60 °C) could be used to generate a stable dehydrated hydrolysate chickpea beverage basis using 12.5 g/100 g db of the adjuvants evaluated.

Synthesis of Aluminum-Based Metal-Organic Framework (MOF)-Derived Carbon Nanomaterials and Their Water Adsorption Isotherm.

The characteristics of water vapor adsorption depend on the structure, porosity, and functional groups of the material. Metal-organic framework (MOF)-derived carbon (MDC) is a novel material that exhibits a high specific area and tunable pore sizes by exploiting the stable structure and porosity of pure MOF materials. Herein, two types of aluminum-based MOFs were used as precursors to synthesize hydrophobic microporous C-MDC and micro-mesoporous A-MDC via carbonization and activation depending on the type of ligands in the precursors. C-MDC and A-MDC have different pore characteristics and exhibit distinct water adsorption properties. C-MDC with hydrophobic properties and micropores exhibited negligible water adsorption (108.54 mgg-1) at relatively low pressures (P/P0~0.3) but showed a rapid increase in water adsorption ability (475.7 mgg-1) at relative pressures of about 0.6. A comparison with the isotherm model indicated that the results were consistent with the theories, which include site filling at low relative pressure and pore filling at high relative pressure. In particular, the Do-Do model specialized for type 5 showed excellent agreement.

Surfactant-Assisted Synthesis of Mesoporous Metal Phosphonates to Control Surface Properties Including an Opportunity to Organize a Bulky Biphenyl Linker.

A wide variety of properties by the presence of functional organic groups have so far been investigated by using periodic mesoporous organosilica (PMO)-type materials but not yet discussed with surface properties that are controlled through the success in synthesizing analogous non-silica-based hybrid mesoporous materials and subsequent evaluation and/or comparison of their properties. Here, we demonstrated the advance in synthesizing biphenyl group (-Ph-Ph-, also expressed as -2Ph)-containing mesoporous metal phosphonates with a rational understanding of surface properties. Ordered mesoporous films of aluminum and titanium ones (AOP-2Ph and TiOP-2Ph) were fabricated by spin-coating and their powders were recovered by spray-drying with the confined assembly of spherical mesopores. As in the case of PMO-type materials, the possibility to organize a -Ph-Ph- linker at the molecular scale was found in the powder samples of AOP-2Ph and TiOP-2Ph because thick frameworks would give an opportunity to organize the bulky -Ph-Ph- linker as the small-sized domains even around spherical mesopores. Surface properties of AOP-2Ph and TiOP-2Ph were evaluated by using the data of water (H2O) adsorption isotherms and compared with those containing different organic groups. The unique hydrophilicity starting from the hydration of AlO4 units was drastically reduced by the presence of -Ph-Ph- groups with a disappearance of the capillary condensation by the presence of mesopores. In addition, a partial replacement of TiO6 units with AlO4 and/or its hydrated AlO6 species was proposed for decreasing the strong hydrophobicity of TiOP-2Ph. The contact angle over the spin-coated films was also measured by using a droplet of H2O, indicating that the surface of the films, especially TiOP-2Ph, was extremely hydrophilic. Although surface properties at the molecular scale can be evaluated by using molecular H2O vapor during the measurement of H2O adsorption isotherms, the interaction of the H2O cluster (droplet) with the bulk surface seems to be predominated by inorganic moieties.

Impacts of kerogen type and thermal maturity on methane and water adsorption isotherms: A molecular simulation approach

The molecular structure of kerogen is known to control the type, amount of petroleum generated as well as its interaction with reservoir fluids. The adsorption behavior of kerogen with respect to reservoir fluids can enhance our understanding of kerogen wetting properties. Therefore, quantifying the governing factors controlling the adsorption of water and methane in organic pores is critical in understanding fluid flow and adsorption phenomena in organic-rich mudrocks. In this paper, we perform molecular simulations (MS) and quantify water and methane adsorption isotherms on kerogen pore surfaces for the purpose of investigating the impact of kerogen molecular structure on kerogen-fluid interfacial interaction. To realistically represent kerogen structures, we use different kerogen molecular models to emulate kerogen of different types and thermal maturity. The kerogen molecules are condensed to form a porous kerogen structure. The Grand Canonical Monte Carlo simulation (GCMC) method is applied to calculate adsorption isotherms of methane and water molecules in kerogen nanopores. We compute the adsorption behavior of water and methane molecules on type I, II and III kerogen samples. The molecular simulations of increasing thermal maturity from IIA to IID at low pressures (less than 10 MPa) and temperature of 300 K in type II kerogen resulted in increasing methane adsorption capacity. At 5 MPa, the methane adsorption relatively increased 81% from IIA to IID. The adsorption capacity of methane is also shown to increase from type IA to IIA to IIIA. Similarly to methane, water adsorption capacity is found to increase from type IA to IIA to IIIA. However, water adsorption capacity on kerogen of different thermal maturity increases from IIB to IIA. Kerogen structures of types IID and IIC show very similar adsorption capacity nearly overlapping at four different pressures. However, water adsorption on IID and IIC kerogen is still found to be smaller compared to IIA and IIB. The outcomes of this work contribute to improving the understanding of the impact of kerogen molecular structure on adsorption of fluids on kerogen surfaces. Moreover, it can provide insights into fluid mobility assessments in organic-rich mudrocks by providing information about the adsorbed gas content on kerogen surfaces.

Water Harvesting at the Single-Crystal Level.

Metal-organic frameworks (MOFs) have emerged as a class of porous materials with facile uptake and release of water, turning them into excellent substrates for real-world atmospheric water harvesting applications. The performance of different MOF systems was experimentally characterized at the bulk level by assessing the total amount of water taken up and the release kinetics, leaving the question behind of what the upper limit of the pristine materials actually is. Moreover, recent devices rely on fluidized bed reactors that exploit the harvesting capacities of MOFs at the single-crystal (SC) level. In this publication, we present a novel methodology based on Raman spectroscopy, for acquiring water adsorption isotherms and kinetic curves with a sub-micrometer resolution that provides valuable insights into the material behavior probing the pristine MOF at the SC level. We investigated isolated MOF-801 particles in situ and could dissect contributions of intra- and inter-particle effects on the water harvesting performance of MOF-801 via adsorption-desorption isotherms and kinetic curves. Using spontaneous Raman spectroscopy, we found an almost 20-fold faster uptake for the undisturbed crystalline material. Correlative imaging based on four-wave mixing and coherent anti-Stokes Raman scattering further localized the uptaken water inside MOF-801 and identified inter-particle condensation as the main source for the discrepancies between the performance at the bulk and SC level. Our studies determined an upper limit of around 91.9 L/kgMOF/day for MOF-801.

Simulating water adsorption in metal–organic frameworks with open metal sites using the 12-6-4 Lennard–Jones potential

ABSTRACT Metal–organic frameworks (MOFs) with coordinatively unsaturated open metal sites (OMSs) are promising sorbent materials in atmospheric water harvesting (AWH) systems at low relative humidity (RH) due to their strong interactions with water molecules. However, accurate computational modelling of water adsorption in those materials are challenging, as standard force fields (FFs) based on the 12-6 Lennard–Jones (L–J) potential cannot properly describe the water–OMS interactions. In biomolecular simulations, the 12-6-4 L–J potential has been successfully used to model metal ion–water interactions in which the extra 1/r 4-term is for charge-induced dipole electrostatics. In this work, we adopted this strategy and used the 12-6-4 L–J potential to model water–OMS interactions in MOFs for low RH AWH applications. Without any modifications, the parameters used for aqueous metal ions were able to greatly improve the accuracy in predicting water adsorption isotherms in MOF-74, which highlights the simplicity and transferability of this method.

Comparative analysis of four metal-organic frameworks for adsorption desalination

The adsorption desalination cycle is a promising technique to address water scarcity. However, its production rate is low due to the low capacity of adsorbent materials. In this study, four metal organic frameworks namely aluminum fumarate, MOF–801, MIL–100(Fe), and CAU–10 H are synthesized and characterized and are tested for an application in adsorption desalination. After synthesizing the adsorbents, powder x-ray diffraction patterns for the samples are obtained to ensure a successful synthesis. The samples then undergo thermogravimetric water adsorption measurements at three different temperatures of 30 °C, 50 °C, and 70 °C at varying evaporator pressures. The water adsorption isotherms are also correlated with the Sun-Chakraborty adsorption isotherm model. It is found that the maximum water uptakes of aluminum fumarate, MOF–801, MIL–100(Fe), and CAU–10 H are 0.47, 0.35, 0.72, and 0.31 kg of water/kg of adsorbent, respectively. The highest water uptake of MIL–100(Fe) is due to its largest BET surface area and pore volume of 1634 m2/g and 0.47 m3/g, respectively. Consequently, MIL–100(Fe) provides the highest specific daily water production for adsorption desalination. Adsorption desalination cycles using MIL–100(Fe) could produce 2.2 and 2.3 times the freshwater obtained employing silica gel and CAU–10 H, respectively, with a heat recovery loop between the evaporator and condenser sections.

MODELING OF THE WATER ADSORPTION ISOTHERM OF MANGO SLICES (MANGIFERA INDICA L.) DRIED UNDER HOT AIR

The general objective of this work is to contribute to the reduction of post-harvest losses of mangoes by the transformation into stable dried products.This research aims to determine the best storage conditions for dried mangoes.Thus, the water adsorption isotherms of mango slices dried under hot air were experimentally determined by the static thermogravimetric method at 25°C.Eight mathematical models from the literature were used (GAB, BET, Hasley, Henderson, Harking and Dura, Oswin, Chung and Pfost, Smith) to describe the hygroscopic behavior of dried mango slices.Regression analysis was performed using MatLab R2016a software to determine the coefficients, model parameters and statistical parameters of the smoothing.The results revealed that the equilibrium is obtained from 35 days for the two samples and the adsorption isotherms determined are of type II characterized by a sigmoidal shape.In addition, the three-parameter (GAB) model showed good agreement with the experimental data (r= 0.999 and 0.997 respectively for slices with thicknesses of 1cm and 1.5cm) at 25°C.The water content of the mono-molecular layer is 2.295% at 25°C for the 1cm slices and 2.289% at 25°C for the 1.5cm slices.The net isosteric heat of adsorption tends towards zero for high water contents (0.052KJ/mol at 44.472% water).The linearity between enthalpy (net isosteric heat) and differential entropy of adsorption shows their compensation.

Metal–Organic Frameworks for Water Harvesting: Machine Learning-Based Prediction and Rapid Screening

Atmospheric water harvesting based on metal–organic frameworks (MOFs) is an emerging technology to potentially mitigate water scarcity. Because of the tremendously large number of existing MOFs, it is challenging to find suitable candidates. In this context, a data-driven approach to identify top-performing MOFs represents an important direction. Herein, we develop a machine learning (ML) method to predict water adsorption in MOFs and screen out top-performing MOFs for water harvesting. First, experimental water adsorption isotherms in MOFs are collected and water adsorption properties are extracted. Quantitative structure–property relationships are analyzed in terms of pore structure and framework chemistry, providing task-specific design principles. Then, ML models are trained and interpreted to predict water adsorption properties by using structural and chemical features, as well as operating conditions as descriptors. The transferability of the ML models is validated by out-of-sample predictions in seven newly reported MOFs. Finally, the ML models are applied to screen ∼8000 “Computation-Ready, Experimental” (CoRE) MOFs. Top-performing candidates are identified including 149 MOFs with the maximum adsorption capacity ≥35 mmol/g, 39 MOFs with working capacity ≥10 mmol/g in a relative pressure window 0.1–0.3, and 139 MOFs with working capacity ≥8.7 mmol/g in a relative pressure window 0.6–0.9. The developed ML-based method would advance task-oriented design and rapid discovery of reticular materials for energy and environmental applications.

Confined Water Cluster Formation in Water Harvesting by Metal-Organic Frameworks: CAU-10-H versus CAU-10-CH3.

Several metal-organic frameworks (MOFs) excel in harvesting water from the air or as heat pumps as they show a steep increase in water uptake at 10-30 % relative humidity (RH%). A precise understanding of which structural characteristics govern such behavior is lacking. Herein, CAU-10-H and CAU-10-CH3 are studied with H, CH3 corresponding to the functions grafted to the organic linker. CAU-10-H shows a steep water uptake ≈18 RH% of interest for water harvesting, yet the subtle replacement of H by CH3 in the organic linker drastically changes the water adsorption behavior to less steep water uptake at much higher humidity values. The materials' structural deformation and water ordering during adsorption with in situ sum-frequency generation, in situ X-ray diffraction, and molecular simulations are unraveled. In CAU-10-H, an energetically favorable water cluster is formed in the hydrophobic pore, tethered via H-bonds to the framework μOH groups, while for CAU-10-CH3, such a favorable cluster cannot form. By relating the findings to the features of water adsorption isotherms of a series of MOFs,it is concluded that favorable water adsorption occurs when sites of intermediate hydrophilicity are present in a hydrophobic structure, and the formation of energetically favorable water clusters is possible.

Hydration Mechanisms of Tungsten Trioxide Revealed by Water Adsorption Isotherms and First-Principles Molecular Dynamics Simulations

WO3 is one of the most interesting materials for photocatalysis due to its optical absorption in UV–vis, good charge carrier transport, and stability against photocorrosion. A detailed knowledge of the hydration state of WO3 is indispensable to gain more precise mechanistic insights into its photocatalytic activity. To the best of our knowledge, the hydration process of WO3 has been scarcely studied so far and only from a theoretical point of view, mostly by means of static density functional theory calculations. Here, we use manometric gas sorption experiments combined with extensive ab initio molecular dynamics simulations to investigate the hydration mechanisms of WO3 at room temperature. We demonstrate that water adsorbs molecularly in a two-step mechanism: the first water sublayer interacts with the under-coordinated surface tungsten atoms through electrostatic interactions, and, in a second step, a full layer is formed through hydrogen bonds established with the pre-adsorbed water molecules and with the under-coordinated surface oxygen atoms. The computed value of −90 kJ·mol–1 for the isosteric enthalpy of adsorption of the first water molecules is in excellent agreement with the experimental value estimated using the Clausius–Clapeyron approach from the experimental adsorption isotherms. The isosteric enthalpy of adsorption steadily decreases in absolute value when the surface coverage is increased to tend toward the enthalpy of condensation of water after three adsorption layers.

Mesoporous poly(ionic liquid) solid acid for sequential dehydration of sorbitol to isosorbide

The catalytic conversion of the biomass platform compound sorbitol to isosorbide is an important reaction for the production of relevant renewable chemicals. The development of highly efficient heterogeneous catalyst materials offers promising perspectives for the sorbitol dehydration reaction. The complex competitive reactions, such as degradation and polymerization, are still a major challenge to obtain isosorbide in high yield. In this work, a series of ionic liquid functionalized polymer catalysts, P-[C3/4R]-SF, were successfully prepared by hydrothermal synthesis, which has a high surface area and strong acidity. And the catalysts were fully characterized by the N2 sorption–desorption isotherms, elemental analysis, water adsorption isotherms, FT-IR, TGA and 31P NMR, etc. As a result, the as-prepared P-[C3/4R]-SF catalysts exhibited excellent catalytic activity and stability under mild reaction condition (140 °C, 6 h). The yield of isosorbide is up to 75 %, and it still has good catalytic activity after five cycles. This work provides a synthesis method of ionic liquid functionalized polymer catalyst and its application in sorbitol dehydration reaction.

Water sorption properties of brewer's spent grain: A study aimed at its stabilization for further conversion into value-added products

Due to its high moisture content and perishability, the water adsorption isotherms, and thermodynamic properties of brewer's spent grain obtained from barley malt (BSGL) and wheat malt based (BSGW) were evaluated under storage and drying conditions. Chemically characterized BSGs were subjected to the static gravimetric method to experimentally obtain the water adsorption isotherms at ten temperatures (5–90 °C). As the best-fitted model (R2adj > 0.9928 e χ2 ≤ 0.0001), the GAB parameters were used to determine the adsorption surface area, spreading pressure, and thermodynamic properties. At temperatures from 5 to 50 °C, the adsorption isotherms of BSGL and BSGW showed convex curves, typical of type III isotherms. However, at temperatures above 60 °C, the curves started to present typical type II isotherms with sigmoid-shaped sorption behavior. The equilibrium moisture content of BSGs increased with increasing relative humidity and/or decreasing temperature. The spreading pressure increased as the water activity and temperature increased, contrary to that observed for the adsorption surface area. Thermodynamic analysis showed that the net isosteric heat of adsorption, enthalpy, and differential entropy decreased as the equilibrium moisture increased. The compensation theory was confirmed, and its results indicated that the adsorption processes were enthalpy-driven. The positive values for Gibbs free energy indicated that the adsorption processes were not spontaneous, which may be related to the composition of BSGs in terms of lipids and proteins. From an energy and stability point of view, a water activity of 0.4 is the ideal condition for the storage of BSGs.

Experimental investigation of porous carbon for cooling and desalination applications

Adsorption cooling and desalination (ACD) system presents a solution for water, energy, and environmental dilemma. This study expresses an enhancement of adsorption system performance in terms of cooling and desalination effects by improving an activated carbon Maxsorb III (Max) as an adsorbent. Max has been initially treated with HCl. Then, it has been activated by impregnating it in salt hydrates ((NH4)2CO3). Characterization methods, including XRD, N2 and water adsorption isotherm, and water adsorption kinetics have been conducted for raw Max, treated Max, and activated Max with (NH4)2CO3. The experimental values have been fitted with the Dubinin & Astakhov equilibrium model for isotherm and the model of linear driving force for kinetics. These fitted parameters have been utilized in a previously validated model to estimate adsorption cooling-desalination system performance with and without heat recovery. Max/(NH4)2CO3 achieves a water uptake of 0.53 kgH2O.kg-1. Max/(NH4)2CO3 produces 13.2 m3.ton-1 of freshwater per day with a specific cooling power of 373 W.kg-1 and 0.63 COP. Also, the freshwater reaches 22.5 m3.ton-1 of Max/(NH4)2CO3 per day with condenser-evaporator heat recovery. These results indicate the potential of utilizing the Max material in dual cooling and desalination applications to achieve double what silica gel can offer.

Effects of crystal chemistry on adsorption, occurrence, and mobility of water in palygorskite tunnels

Abstract Palygorskite is a fibrous magnesium-rich clay mineral with a typical tunnel structure, and its adsorption properties make it an ideal adsorbent for broad applications. Thus, revealing the confinement effects on tunnel species can help in understanding its adsorption properties. Grand canonical Monte Carlo and molecular dynamics simulations were performed to analyze the effects of the crystal chemistry of palygorskite on the adsorption, occurrence, and mobility of tunnel water. Water adsorption isotherm, distribution models, and mobility were achieved from these simulations. Zeolitic water emerges into the tunnels even at a low relative humidity (RH) (such as 5%) and completely fills the tunnels as the RH increases to 10%. In neutral palygorskite, the influence of the octahedral type on water adsorption is not obvious, but the influence of tunnel cations is obvious. The occupation of Na+ ions in tunnels can reduce the maximum water amount and affect the spatial distribution of zeolitic water. The water distribution in tunnels can be described by a two-zeolitic water-site model for neutral palygorskite and a one-zeolitic water-site model for the charged one. The zeolitic water confined in the tunnel presents very low mobility, and the appearance of Na+ ions in the charged palygorskite further reduces the mobility of zeolitic water. Compared with other clay minerals, the much lower water mobility of palygorskite implies that it may have a more efficient fixation on foreign molecules or ions in environmental applications.

Machine learning-assisted prediction of water adsorption isotherms and cooling performance

Efficient machine learning models were demonstrated to predict water adsorption isotherms of various adsorbents based on uptake pressures and structure properties, as well as predict adsorption cooling performance based on isotherm features.