Water Desorption Kinetics Research Articles

An Atmospheric Water-Harvester with Ultrahigh Uptake-Release Efficiency at Low Humidity.

Atmospheric water harvesting is a practical strategy that is achieved by removing materials from air moisture to relieve global water scarcity. Here we design a water-harvester (i.e., MOF-303/thiolated polymer composite (MTC)) by using a metal-organic framework (MOF-303) and thiolated chitosan (TC) skeleton. Intermolecular hydrogen bonding between TC and MOF-303 facilitates porous structures with enlarged air-polymer interfaces for long cycling life and high capacity at low relative humidity. Benefiting from synergetic effects on porosity and anchorage for accelerating the uptake-release of moisture, MTC exhibits a rapid water uptake capacity of 0.135 g/g in 60 min under 12.5 RH% and ultrafast water desorption kinetics of 0.003 g/g/min at 8.5 RH%, which is superior to the as-reported MOF-303 based adsorbents. At low heat (∼40 °C), the water desorption and collection rate, respectively, are 0.0195 and 0.0168 g/g/min within 210 min, showing ultrahigh harvesting efficiency. These results highlight the enormous potential as promising materials for solving the world's water scarcity crisis. This study offers an insight into the design of AWH materials, which can be extended into applications in some realms, e.g., freshwater development for industry in arid areas, water engineering-related devices and systems, etc.

Effect of Reinforcement Ratio and Particle Size on the Physical and Mechanical Performance of Epoxy Matrix Panels and Waste Wood from Iroko Chlorophora excelsa from Cameroon

The use of local materials developed from natural reinforcements remains a major challenge for many researchers in the development of the industry and the fight against pollution. The wood industry generates large quantities of environmental waste, including Iroko wood. To give Iroko a second life, this study uses Iroko sawdust waste to make an epoxy matrix composite material. The composite was produced using a cold pressing technique based on moving the top and bottom plates to a thickness of 10 mm. On this basis, three particle sizes [t < 0.35[, [0.35–0.63[, and [0.63–1[ were used, as well as three reinforcement (R)/matrix (M) percentages of 50R/50M, 60R/40M, and 70R/30M, where R is the reinforcement percentage and M is the matrix percentage. The physical tests, apparent and real density, porosity, moisture content, water absorption rate, absorption and desorption kinetics, diffusion theory, and activation energy were determined by the gravimetric method. A three-point bending test was carried out in accordance with the ASTM D790 for mechanical tests. The results show that the addition of Iroko particles lightens the material by reducing its density. The hydrophilic nature of Iroko particles increases the absorption rate and porosity, with good diffusion capacity as the particle size and percentage increase. The material produced can be light and porous, with possible applications in thermal insulation. In terms of kinetics, Verma et al.’s model best correlates the experimental desorption points for the 3 isotherms, while Page’s model best correlates the water absorption points. The mechanical results show that Young’s modulus and stress at break decrease with an increase in the reinforcement percentage and particle size. The mechanical results can be used to define the material’s applications in construction and furniture. In accordance with the EN312 standard, the composites produced can be classified as type 2 lightweight materials, suitable for use in dry and damp areas.

Coverage-dependent desorption kinetics of water on a well-ordered alumina thin film surface.

We have developed an experimental and analytical setup for thermal desorption spectroscopy of solid water films on surfaces. We obtain the coverage-dependent desorption kinetics of water molecules from a well-defined ultra-thin alumina/NiAl(110) surface in the coverage range of 0-2 monolayers. We use a novel deconvolution technique to eliminate the pumping delay of water vapor in the vacuum system, which has previously hindered the accurate estimation of desorption kinetic parameters, such as activation energy and pre-exponential factor. The coverage-dependent Arrhenius analysis reveals that the desorption activation energy decreases with increasing coverage in the sub-monolayer range, indicating that the water-water interaction is not attractive. We also find that the pre-exponential factor for the second layer is higher than that for the sub-monolayer. We explain this difference in terms of transition state theory and propose that entropic effects play a significant role in water desorption kinetics.

Polymer gel amended sandy soil with enhanced water storage and extended release capabilities for sustainable desert agriculture

Herein, we report a facile preparation of super-hydrophilic sand by coating the sand particles with cross-linked polyacrylamide (PAM) hydrogels for enhanced water absorption and controlled water release aimed at desert agriculture. To prepare the sample, 4 wt% of aqueous PAM solution is mixed with organic cross-linkers of hydroquinone (HQ) and hexamethylenetetramine (HMT) in a 1:1 weight ratio and aqueous potassium chloride (KCl) solution. A specific amount of the above solution is added to the sand, well mixed, and subsequently cured at 150 °C for 8 h. The prepared super-hydrophilic sands were characterized by Fourier-transform infrared spectroscopy (FT-IR) for chemical composition and X-ray diffraction (XRD) for successful polymer coating onto the sand. The water storage for the samples was studied by absorption kinetics at various temperature conditions, and extended water release was studied by water desorption kinetics. The water swelling ratio for the super-hydrophilic sand has reached a maximum of 900% (9 times its weight) at 80 °C within 1 h. The desorption kinetics of the samples showed that the water can be stored for up to a maximum of 3 days. Therefore, super-hydrophilic sand particles were successfully prepared by coating them with PAM hydrogels, which have great potential to be used in sustainable desert agriculture.

Kinetics of the Water Release of Hygroscopic Acrylamide Gel Embedded in Calcium Chloride by Thermogravimetric Analysis

Poly (acrylamide) gel was synthesized by radical polymerization of acrylamide and N, N'-methylene-bisacrylamide in the presence of benzoyl peroxide and carbon nanotubes. The dry product was saturated with calcium chloride and prepared for water absorption and desorption. The kinetics of water desorption of poly (acrylamide) gel embedded with hygroscopic calcium chloride (DHG), was studied from thermograms data of thermogravimetric analysis (TGA). DHG captures vapor from the environment and releases it as fresh water; it can be used as the condenser to build atmospheric water generators (AWGs) to alleviate the freshwater stress rusting from innovative activities such as industrial, agricultural, rural, and defense endeavors. The kinetics parameters of the synthesized DHG showed that it absorbed environmental vapor at room temperature and released water below its boiling point (40 to 90 °C), temperatures achievable under sunlight via the photothermal effect.

Hygroscopic-Microgels-Enabled Rapid Water Extraction from Arid Air.

Sorbent-based atmospheric water harvesting (AWH) has emerged as a promising decentralized water-production technology to mitigate the freshwater crisis in arid areas. Hydrogels have been regarded as attractive sorbents due to their high water retention and tailorable polymer-water interactions. Yet, the kinetics of water sorption and desorption at low relative humidity (RH) shall be improved for their practical implementation. Here, hygroscopic microgels (HMGs) composed of hydroxypropyl cellulose (HPC) and hygroscopic salt are reported, which achieve a water uptake of ca. 0.5-0.8g g-1 at 15-30% RH. HMGs enable rapid sorption-desorption kinetics owing to the short-distance diffusion in the microgels and hydrophilicity-hydrophobicity switching of the thermoresponsive HPC. To validate the feasibility of HMGs for moisture extraction, a potential daily water collection of up to equivalent 7.9-19.1 L kg-1 at low RH is demonstrated, enabled by 24-36 operation cycles per day based on the material-level experiments. With renewable raw materials and superior performance, HMGs provide a sustainable approach for rapid moisture extraction in arid climates.

Alginate- and sulfonate-based superabsorbent polymers for application in cementitious materials: Effects of kinetics on internal curing and other properties

Superabsorbent polymers have been widely investigated for internal curing in cementitious materials. In most cases, commercial SAPs are used and not enough information is available regarding their chemical composition. Efficient and optimal application of SAPs in cementitious materials depends on chemical composition and its effects on the properties of the material. Being able to relate and predict the behavior of SAPs and fine tune properties for specific applications are of utmost importance. In this paper, eight different innovative and “in-house” produced polymers (based on alginates and sulfonates) are studied as internal curing agents in cement pastes and compared to commercially available SAPs. The different kinetics of water sorption and desorption and its effects on mitigation of autogenous shrinkage and other properties are thoroughly discussed and linked to chemical composition of SAPs, providing recommendations on the selection of the appropriate SAPs for different application in cementitious materials.

In situ investigation of water on MXene interfaces

A continuum of water populations can exist in nanoscale layered materials, which impacts transport phenomena relevant for separation, adsorption, and charge storage processes. Quantification and direct interrogation of water structure and organization are important in order to design materials with molecular-level control for emerging energy and water applications. Through combining molecular simulations with ambient-pressure X-ray photoelectron spectroscopy, X-ray diffraction, and diffuse reflectance infrared Fourier transform spectroscopy, we directly probe hydration mechanisms at confined and nonconfined regions in nanolayered transition-metal carbide materials. Hydrophobic (K+) cations decrease water mobility within the confined interlayer and accelerate water removal at nonconfined surfaces. Hydrophilic cations (Li+) increase water mobility within the confined interlayer and decrease water-removal rates at nonconfined surfaces. Solutes, rather than the surface terminating groups, are shown to be more impactful on the kinetics of water adsorption and desorption. Calculations from grand canonical molecular dynamics demonstrate that hydrophilic cations (Li+) actively aid in water adsorption at MXene interfaces. In contrast, hydrophobic cations (K+) weakly interact with water, leading to higher degrees of water ordering (orientation) and faster removal at elevated temperatures.

A systematic experimental and modeling study of water adsorption/desorption behavior in organic-rich shale with different particle sizes

Understanding the behavior of water-shale adsorption/desorption is of fundamental importance in evaluating in situ shale oil/gas reserves, improving shale oil/gas production and reducing the environmental impact of fracturing fluids. The isotherms and kinetics of water adsorption and desorption in organic-rich shale with three particle sizes (20–40 mesh, 40–60 mesh and 60–80 mesh) were measured at temperatures of 293 K, 303 K and 313 K, and the unclosed hysteresis behavior in water-shale adsorption/desorption isotherms was studied. Then, six thermodynamic models (including the DS1, DS2, DW, BET, GAB and Dent models) and four kinetic models (including the PFO, PSO, DE and Unipore models) were used to interpret the isotherms and kinetics, respectively. Furthermore, thermodynamic parameters, including ΔH, ΔS and ΔG, and kinetic parameters, including the rate constants and activation energy, were extracted. Finally, these results are discussed in relation to the pore structure, surface functional groups, temperature, relative pressure and particle size. This work provides a systematic understanding of the isotherms, hysteresis, thermodynamics and kinetics of water adsorption/desorption in organic-rich shale.

The Effect of Straining in Liquid Nitrogen Medium on the Kinetics of Water Desorption from Copper and Iron during Heating

The Effect of Straining in Liquid Nitrogen Medium on the Kinetics of Water Desorption from Copper and Iron during Heating

Kinetics of Water Desorption in Select Marine Ferromanganese Crust materials by Stepped Isothermal Evolved Gas Analysis

Kinetics of Water Desorption in Select Marine Ferromanganese Crust materials by Stepped Isothermal Evolved Gas Analysis

Quasi-equilibrium predictions of water desorption kinetics from rapidly-heated metal oxide surfaces

Controlling sub-microsecond desorption of water and other impurities from electrode surfaces at high heating rates is crucial for pulsed power applications. Despite the short time scales involved, quasi-equilibrium ideas based on transition state theory (TST) and Arrhenius temperature dependence have been widely applied to fit desorption activation free energies. In this work, we apply molecular dynamics (MD) simulations in conjunction with equilibrium potential-of-mean-force (PMF) techniques to directly compute the activation free energies (ΔG*) associated with desorption of intact water molecules from Fe2O3 and Cr2O3 (0001) surfaces. The desorption free energy profiles are diffuse, without maxima, and have substantial dependences on temperature and surface water coverage. Incorporating the predicted ΔG* into an analytical form gives rate equations that are in reasonable agreement with non-equilibrium molecular dynamics desorption simulations. We also show that different ΔG* analytical functional forms which give similar predictions at a particular heating rate can yield desorption times that differ by up to a factor of four or more when the ramp rate is extrapolated by 8 orders of magnitude. This highlights the importance of constructing a physically-motivated ΔG* functional form to predict fast desorption kinetics.

Study of the Kinetics of Adsorption and Desorption of Water Vapor on Low-Silica Zeolites

Granular LTA and SOD zeolites have been synthesized, characterized, and further used to study the kinetics of water adsorption and desorption. It has been shown that LTA zeolite in a static mode provides adsorption of water vapor at the level of ~30 wt % for LTA and ~20 wt % for SOD. It has been found that during water adsorption from the gas phase on the LTA or SOD zeolite in a flow-through unit, the dew point reaches –50 or –9°С, respectively. The kinetics of adsorption of water vapor on zeolite granules has been studied; the values of apparent activation energy of the adsorption process have been calculated, which amount to about 50 kJ mol–1; and the rate order of the process has been determined (0.2 for LTA and 0.9 for SOD). The apparent activation energies for water desorption from the zeolites have been calculated by isoconversional analysis in terms of the Friedman, Ozawa–Flynn–Wall, and Kissinger–Akahira–Sunose models. It has been shown that all three models give similar results. It has been found that at given degree of conversion, the activation energies are not higher than 60 kJ mol–1, a value that corresponds to desorption of physically bound water. The increase in activation energy to 110 kJ mol–1 (for SOD) or 80 kJ mol–1 (for LTA) is associated with the removal of water from the α- and β-cages of zeolites.

Application of Acrylate Latex Emulsion as the Binder for Coating Aluminum Substrate by Silica-Gel Powder

The adsorbent coated exchangers are the main part of adsorption refrigeration systems. Although coated exchangers are commercially available, the coating technique and the binder used are seldom revealed and left as a challenge for researchers. Dip-coating is the most commonly used coating technique. However, the variety of binders used indicates that choosing the appropriate binder is still a matter of trial-and-error. A series of experiments were performed to introduce acrylic latex emulsion (ALE) and bitumen emulsion as the new binder for coating silica-gel powder on aluminum. The results indicate coats created by both emulsion binders are stable but the bitumen emulsion keeps its stability for about 10[Formula: see text]min after mixing with water and silica-gel powder. The effect of ALE binder and water concentrations on water vapor equilibrium and desorption kinetics was investigated. The outcomes indicated that the sample containing 0.8[Formula: see text]g water/g silica-gel, 0.08[Formula: see text]g ALE binder/g silica-gel shows the fastest desorption kinetic and the minimum capacity loss. The mechanical stability of this sample was evaluated by the shear test and the pull-off test. The measured values show that the prepared laminate withstands up to 27[Formula: see text]N/cm2 shear stress and 18[Formula: see text]N/cm2 tensile stress.

Study of the kinetics of water desorption on binder-free pellets of SOD and LTA zeolites using model-free isoconversion analyzes

Abstract The moulded binder-free pellets of SOD (Sodalite) and LTA (Linde Type A) zeolites have been prepared from mixtures based on kaolin and metakaolin, respectively, which have been confirmed by X-ray diffraction and IR spectroscopy. Using the SEM and XRD methods, it was determined that the SOD particles was irregular in shape with a size of 0.5–1 μm and a dimension of coherent scattering region of 453 nm; the LTA particles have a shape close to a cube and a size of about 2 μm, and a dimension of coherent scattering region is 760 nm. According to BET measurements, the surface area of SOD (141 m2 g−1) and LTA (115 m2 g−1) zeolites have been determined. The amounts of absorbed water vapor for SOD were about 20 wt%, and for LTA were about 30 wt%. By synchronous thermal analysis, it was shown that desorption of water occurs in two stages. The first stage is the removal of capillary water: for SOD zeolite it is a temperature of up to 95 °C, for LTA zeolite it is about 50 °C. It is found that further desorption of water from SOD and LTA zeolites occur from α- and β-cages of zeolites. By employing Friedman, Ozawa-Flynn-Wall, and Kissinger–Akahira–Sunose analyzes, the apparent activation energy was calculated for water desorption on the zeolites. The advantage of these analyzes is that it is not necessary to have a kinetic model of the interface reaction. This allows to significantly simplifying the calculation of the activation energy. It is demonstrated that all three analyzes yielded close results. It was found that at a conversion (desorption) extent of about 0.2–0.3, the apparent activation energy values are not more than 60 kJ mol−1. The increase in apparent activation energy values up to 110 kJ mol−1 (for SOD) and up to 80 kJ mol−1 (for LTA) is associated with removal of water from α- and β-cages of zeolites.

Kinetics of Water Vapor Adsorption and Desorption in MIL-101 Metal–Organic Frameworks

The adsorption–desorption isotherms and relaxation curves of water in chromium terephthalate metal–organic frameworks (MOFs), MIL-101, were measured by the gravimetric method at 298 K and 1 atm. Th...

Water desorption from rapidly-heated metal oxide surfaces—first principles, molecular dynamics, and the Temkin isotherm

Quantitative understanding and control of water and impurity desorption from steel surfaces are crucial for high-voltage, pulsed power, vacuum technology, catalysis, and environmental applications. We apply a suite of modeling techniques, ranging from electronic density functional theory, to classical molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) methods to study the thermodynamics and kinetics of fast water desorption from different surfaces of hematite Fe2O3 and Cr2O3. Water binding energies on chromium oxide are found to be higher than iron oxide at zero temperature. MD simulations are conducted on Fe2O3 surfaces using thermodynamically consistent initial water inventory deduced with GCMC. The resulting time- and temperature-dependent desorption profiles on the Fe2O3 surfaces show multi-water cooperative behavior which cannot be deduced from zero temperature predictions, but which are in reasonable agreement with simple Temkin isotherm model estimates if finite temperature effects are incorporated into the Temkin binding energy parameter. Qualitatively different desorption behaviors associated with the and facets are discussed.

Water diffusion with temperature enabling predictions for sorption and transport behavior in thermoset materials

Water desorption kinetics for a number of epoxy materials (five amine and one anhydride cured), with glass transitions from below room temperature to 245 °C, were studied using thermogravimetry and near-infrared spectroscopy between ambient and 200 °C. Computational models based on 1D finite difference or 3D finite element Fickian diffusion processes were then applied to determine the underlying diffusivity. Classical Fickian diffusion with a constant D was sufficient to describe the water desorption behavior for all evaluated materials and conditions, with water induced swelling affecting the diffusion process no more than through small dimensional changes. The temperature dependence for diffusivity displayed mostly a single activation energy (Ea) between 44 and 62 kJ mol−1 for all materials except one, which showed a change from 75 kJ mol−1 below Tg (∼65 °C), to 53 kJ mol−1 above. The obtained diffusivities and their Ea were then used to predict and illustrate the sorption behavior for other geometries and temperatures. The trends for these materials were discussed within the existing theories for fractional free volume, effective crosslink density and chemical composition. Unexpectedly, this study shows that Tg has no or only limited influence on water diffusivity in contrast with the Cohen-Turnbull model. Water sorption (solubility in the material) is of similar magnitude independent of temperature (i.e. low Ea) as anticipated. Only a fraction of the water uptake was found to be associated with free volume utilization, with the majority of water resulting in material volume changes, which as a consequence means that dynamic water uptake and drying will result in changing stress conditions (expansion and contraction) for glassy thermosets even under ambient conditions.

Equilibrium and Kinetics of Water Vapor Adsorption on Shale

Water vapor adsorption and desorption isotherms and kinetics studies on three Sichuan Basin shale samples were performed at 298 K by an accurate gravimetric method. The adsorption equilibrium data were fitted using both Dent model and Modified Dent model to estimate the adsorption characteristic of water on the primary and secondary sites. The primary site adsorption is restricted to a monolayer while the secondary site adsorption is associated with multilayer sorption. A positive correlation was found between clay mineral content and monolayer sorption content. The isosteric heats of sorption of water were determined from the equilibrium data and they decreased with the increase of adsorption amount. The adsorption/desorption hysteresis were studied with the pore structure. The kinetics of water vapor adsorption was studied with the unipore model and linear driving force mass transfer (LDF) model. The effective diffusivity and kinetic rate constant varied with the increase of relative pressure, which suggested diffusion of water vapor on shale corresponding to a combination of adsorption on primary sites, adsorption on secondary sites, formation of water clusters, and capillary condensation.

Nanocomposite Cryogels Based on Poly (Vinyl Alcohol)/Unmodified Na+-Montmorillonite Suitable for Wound Dressing Application: Optimizing Nanoclay Content

A new type of nanocomposite cryogels containing polyvinyl alcohol and 0–10% of hydrophilic natural Na-montmorillonite (Na+-MMT), free from any modification, were prepared with a freeze–thaw process. The effects of nanoclay content and the sonication process on the morphology and thermomechanical properties, equilibrium water content (EWC), and the water vapor transmission rate (WVTR) of nanocomposite films were investigated at 37°C, and the amount of optimized nanocaly content was found. The kinetics of water sorption and desorption of the nanocomposites were also studied. The results showed that (Na+-MMT) may act as a co-crosslinker and improve the water vapor transmission rate and the swelling characteristics of the nanocomposite cryogels. They also showed the optimized critical concentration of nanoclay in achievement of the required sorption and desorption characteristics as well as WVTR and EWC were within the acceptable range for wound dressing and skin treatment.