Water Adsorption Kinetics Research Articles

Use of Zeolites in the Capture and Storage of Thermal Energy by Water Desorption-Adsorption Cycles.

In this work, four zeolite-bearing materials (three naturally occurring and one of synthetic origin) were considered for thermal energy capture and storage. Such materials can store thermal energy as heat of desorption of the water present therein, heat that is given back when water vapor is allowed to be re-adsorbed by zeolites. This study was carried out by determining the loss of water after different activation thermal treatments, the water adsorption kinetics and isotherm after an activation step of the zeolites, the intergranular and intragranular porosity, and the thermal conductivity of the zeolite-bearing materials. Moreover, the thermal stability of the framework of the zeolites of the four materials tested was investigated over a large number of thermal cycles. The results indicate that zeolite 13X was the most suitable material for thermal energy storage and suggest its use in the capture and storage of thermal energy that derives from thermal energy waste.

Passive rapid-cycling atmospheric water generator

Rapid water adsorption-desorption kinetics are the key to realizing exceptional yield in passive atmospheric water harvesting (PAWH). Recently in Nature Nanotechnology, Jia Zhu et al. developed a nanoporous carbon with rapid water adsorption kinetics and excellent photothermal properties to achieve PAWH with high yield. Herein, this facile method can kill two birds with one stone. Rapid water adsorption-desorption kinetics are the key to realizing exceptional yield in passive atmospheric water harvesting (PAWH). Recently in Nature Nanotechnology, Jia Zhu et al. developed a nanoporous carbon with rapid water adsorption kinetics and excellent photothermal properties to achieve PAWH with high yield. Herein, this facile method can kill two birds with one stone.

Experimental investigation of sodium polyacrylate-based innovative adsorbent material for higher desalination and cooling effects

This study explores enhancing adsorption system’s performance utilizing sodium polyacrylate (SP) as an adsorbent for the first time. Four innovated SP samples are explored: raw SP, SP/HCl, SP/(NH4)2CO3), and SP/CaCl2 composite for adsorption desalination and cooling applications. Different characterization methods, including X-ray diffraction, nitrogen adsorption isotherm, and water adsorption (isotherms and kinetics) of SP samples, are investigated. Water adsorption experimental results onto SP samples and their numerical fitting with the Dubinin-Astakhov equilibrium model for isotherms and linear driving force model for kinetics have been expressed. The composite SP/CaCl2 had the highest experimental adsorption uptake of 1.26 kgH2O/kg among the studied samples. At 85 °C regeneration temperature, water desalination production per day (SDWP) achieves 15 m3/ton, with a cooling power of 425 W/kg. SDWP could reach 41 m3/ton of SP/CaCl2 per day with heat recovery. The system can obtain an SDWP of 45 m3/ton per day at a regeneration temperature of 95 °C. The findings show that the system can run efficiently using renewable energy, waste heat, or geothermal energy as heat sources.

Experimental and Theoretical Assessment of Water Sorbent Kinetics.

The kinetics of water adsorption in powder sorbent layers are important to design a scaled-up atmospheric water capture device. Herein, the adsorption kinetics of three sorbents, a chromium (Cr)-based metal-organic framework (Cr-MIL-101), a carbon-based material (nanoporous sponges/NPS), and silica gel, have been tested experimentally, using powder layers ranging from ∼0 to 7.5 mm in thickness, in a custom-made calibrated environmental chamber cycling from 5 to 95% RH at 30 °C. A mass and energy transfer model was applied onto the experimental curves to better understand the contribution of key parameters (maximum water uptake, kinetics of single particles, layer open porosity, and particle size distribution). Open porosity (i.e., the void-to-particle ratio in the sorbent layer) shows the highest influence to improve the kinetics. Converting the sorbent kinetics data into a daily yield of captured water demonstrated (i) the existence of an optimal open porosity for each sorbent, (ii) that thinner layers with moderate open porosity performed respectively better than thicker layers with high open porosity, and (iii) that high maximum water uptake and fast single-particle kinetics are not necessarily predictive of high daily water yield.

Pt-Co single atom alloy catalysts: Accelerated water dissociation and hydrogen evolution by strain regulation

The alkaline hydrogen evolution reaction (HER) on Pt-based catalysts is largely limited by the slow water dissociation kinetics. Pt-based single atom alloy catalysts (SAAC) with water dissociation sites have been demonstrated as excellent alkaline HER catalysts. However, the regulation of their activity and stability at the atomic scale is still a great challenge. Herein, the kinetic and stability issues are successfully resolved via engineering the electronic structure of Pt-Co SAAC by Au-induced tensile strain. The atomic dispersion of Co into the Pt shell was confirmed by extended X-ray absorption fine structure and the electronic structure and catalytic HER performance was modulated by the tensile strain induced by the Pt shell thickness. An inverse volcano-type relation between HER activity and surface strain was found. Density functional theory (DFT) calculations reveal that the Au-induced tensile strain on Pt-Co shell can not only boost the adsorption and dissociation kinetics of water at Co site by upshifting the d-band and promoting the electron transfer, but also downshift the d-band center of Pt in Pt-Co shell, leading to optimized H* adsorption/desorption. The champion catalyst provides an overpotential of only 14 mV at the current density of 10 mA cm−2. This work not only provides an effective strategy for the construction of single-atom alloy electrocatalysts for high performance toward alkaline HER but also sheds light on the understanding of the reaction mechanism at the atomic level.

Experimental investigation for water adsorption characteristics on functionalized MIL-125 (Ti) MOFs: Enhanced water transfer and kinetics for heat transformation systems

Employing adsorption technology, metal organic frameworks (MOFs) are found promising to generate cooling, heating, and desalinated water with zero or negligible carbon footprint. In this article, we present various functional groups namely hydroxyl (-OH), amino (-NH2), nitro (-NO2), bromo (-Br) and pyridine (-C5H5N) assisted MIL-125 (Ti) MOFs to control water adsorption/ desorption capacity under the working domain of adsorption heat transformation (A-HT) process. The MOFs are at first synthesized, and later these are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-gravimetric analyzer (TGA) and nitrogen (N2) adsorption techniques. The water adsorption isotherms and kinetics are measured by gravimetric methods. Using isotherms data in pressure-temperature coordinate system, the isosteric adsorption-heat (Qst) is evaluated. The experimental results show that the functional group not only influences the hydrophobic and hydrophilic behaviors of MIL-125 (Ti) MOFs but also controls the water transfer per adsorption-desorption cycle with variable uptake/offtake rates (kinetics). Employing isotherms and kinetics data of functionalized (MOFs + water) systems plus the thermodynamic modeling of A-HT cycle, the performance parameters such as cooling, heating and desalination capacities are estimated for various cycle times and heat inputs. The mass and heat transfer processes involved in each component of A-HT system are presented. It is found that OH-MIL-125 (Ti) provides 3 times faster kinetics as compared with the parent MIL-125 (Ti) MOFs. Hence the cooling/heating and water production of A-HT are improved significantly with the addition of functional group, and NH2-MIL-125 (Ti) shows the best cooling and water production performances.

Ab initio insight into the electrolysis of water on basal and edge (fullerene C20) surfaces of 4 Å single-walled carbon nanotubes.

The extreme surface reactivity of 4 Å single-walled carbon nanotubes (SWCNTs) makes for a very promising catalytic material, however, controlling it experimentally has been found to be challenging. Here, we employ ab initio calculations to investigate the extent of surface reactivity and functionalization of 4 Å SWCNTs. We study the kinetics of water dissociation and adsorption on the surface of 4 Å SWCNTs with three different configurations: armchair (3,3), chiral (4,2) and zigzag (5,0). We reveal that out of three different configurations of 4 Å SWCNTs, the surface of tube (5,0) is the most reactive due to its small HOMO-LUMO gap. The dissociation of 1 H2O molecule into an OH/H pair on the surface of tube (5,0) has an adsorption energy of -0.43 eV and an activation energy barrier of 0.66 eV at 298.15 K in pure aqueous solution, which is less than 10% of the activation energy barrier of the same reaction without the catalyst present. The four steps of H+/e- transfer in the oxygen evolution reaction have also been studied on the surface of tube (5,0). The low overpotential of 0.38 V indicates that tube (5,0) has the highest potential efficiency among all studied carbon-based catalysts. We also reveal that the armchair edge of tube (5,0) is reconstructed into fullerene C20. The dangling bonds on the surface of fullerene C20 result in a more reactive surface than the basal surface of tube (5,0), however the catalytic ability was also inhibited in the later oxygen reduction processes.

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.

Water desalination by silica supported ionic liquid: Adsorption kinetics and system modeling

Significant efforts have been done in order to improve adsorption desalination systems by developing advanced adsorbents. Silica-supported ionic liquid (SIL) has been recently proposed as a promising adsorption material for water desalination due to its relatively high adsorption capacity around 1 kgwater.kgSIL−1. Such achieved performance can be considered as an initial cornerstone that requires further important additional data before reaching a successful practical application. In this paper, experimental measurements of water adsorption kinetics in the SIL named EMIM-AC/Syloid 72FP are presented. The kinetics is interpreted using a linear driving force (LDF) model that shows good harmony with experimental data. Depending on a former study on adsorption isotherms and the current kinetics data, the performance of an adsorption water desalination system (ADS) is predicted using a dynamic lumped parameter model. The results show a bright future for this SIL material in water desalination application with high theoretical pure water production achieving 47 m3 day−1ton−1, 0.85 coefficient of performance with 600 W kgSIL−1 specific cooling power. Furthermore, system working with the EMIM-AC/Syloid 72FP can theoretically be powered by as low as 40 °C heat source.

TGA investigation of water and ethanol adsorption over LTA zeolites

In absolute ethanol production, LTA zeolites (3A and 4A) are industrially used because of their selectivity and affinity to water. Despite the numerous studies performed on these materials, a lack of data is encountered, particularly at the gaseous phase. This study contributes to the understanding and elucidation of the behavior of water and ethanol adsorbed separately over 3A, 4A and 5A zeolites. Using TGA measurements in dynamic mode, this study focuses on the investigation of temperature effect (T = 20–45 °C) on the adsorption kinetics of water and ethanol. The comparison of the adsorption properties of the three zeolites shows a particular behavior of the 3A, which is characterized by both the higher water uptake and the specific affinity reflected by the initial adsorption rate and the diffusion coefficient. Based on some previous studies, which point out that ethanol may be adsorbed on 3A, this investigation shows the role of water traces in the “ethanol” uptake. The comparison of the water and ethanol kinetics at various temperatures leads to estimate the optimal selectivity temperature. On the other hand, the modeling study using four kinetic models highlights the good fitting of pseudo‒first order from which the adsorption activation energies are deduced.

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.

Sensitivity Analysis and Effective Parametrization of PEM Fuel Cell Models

The cost of proton-exchange-membrane fuel cells (PEMFCs) remains a major hurdle in large-scale commercialization of this technology. To improve their performance and reduce cost, novel materials and electrode designs are continuously envisioned, e.g., non-PGM catalyst layers, ultra-thin Pt/Pt-Ni based catalyst layers, structured ionomer arrays or NSTF catalyst layers.1 Understanding the impact of these improvement strategies can be extremely time and cost intensive due to complex physical phenomena and large design space. We have previously developed a PEMFC modeling framework2 which has been a time and cost effective tool for understanding and optimizing the complex multi-physics phenomena within PEMFCs; however, several of the cell parameters used in the modeling have large spread in measured data.3 Furthermore, several transport parameters such as water adsorption kinetics have not been accurately measured and the approximations are spread over several orders of magnitude. These uncertainties cause problems in ascertaining accuracy of the modeling approach and they reduce the predictive power of the numerical models.The aim of this work is to identify the sensitivity of PEFC numerical model outputs to various input parameters. The previously in-house developed MEA modeling framework2 is used for PEMFC modeling. The sensitivity of the model outputs with respect to inputs parameters is obtained by analyzing the condition numbers for different output-input pairs at varying operating conditions. An example of the sensitivity analysis is shown in Figure 1. The condition numbers are obtained for the entire possible range of input parameters at varying operating conditions to identify the most crucial parameters of the PEMFC model. Based on our preliminary analysis, parameters related to kinetics (exchange current density and ECSA) and heat/water management in electrodes and ionomer (ionomer fraction, thermal conductivity) are most crucial.One of the major goals of this work is to identify the most crucial set of parameters towards which the model shows maximum sensitivity. This will guide future experimentalists to measure these properties with higher accuracy. Furthermore, the sensitivity analysis will also enable us to optimize the PEMFC performance by selectively targeting the most sensitive parameters and thereby making the largest impact. Acknowledgements The work is funded under the Fuel Cell Performance and Durability Consortium (FC-PAD), by the Fuel Cell Technologies Office (FCTO), Office of Energy Efficiency and Renewable Energy (EERE), of the U.S. Department of Energy under contract number DE-AC02-05CH11231. The authors would like to thank Nathan Craig at Robert Bosch LLC for his valuable input in designing the sensitivity analysis. The authors would also like to thank Giovanna Bucci and Matthias Hanauer at Robert Bosch for their valuable inputs and discussion. References P. K. Sinha, W. Gu, A. Kongkanand and E. Thompson, J. Electrochem. Soc., 158, B831 (2011).L. M. Pant, M. R. Gerhardt, N. Macauley, R. Mukundan, R. L. Borup and A. Z. Weber, Electrochim. Acta, 326, 134963 (2019).R. Vetter and J. O. Schumacher, ArXiv181110091 Phys. (2018). Figure 1

Camphor leaf-derived activated carbon prepared by conventional physical activation and its water adsorption profile

Preparation of activated carbon from biomass residue with conventional steam activation was conducted to find the alternative raw materials for meeting the high demand for low-cost porous material in the desiccant application. In this study, activated carbons were produced from dead camphor leaves using two-step methods at different preparation temperatures. The characterization results revealed that the prepared activated carbons have a surface area of 700 m2/g, with 75% of microporosity. The water vapor sorption study reported that the water uptake of camphor leaf-based activated carbons was strongly affected by the pore properties of the materials. Moreover, from the water adsorption kinetics, it was observed that the rate constant of adsorption was varied at each relative pressure, which can be assumed that the water adsorption mechanism is different at each relative pressure. From these results, it was revealed that the prepared camphor leaf-based activated carbons have a promising ability to adsorb water vapor from humid air.

Ambient aging effects on the effective energy gap of ZnO thin films

Using photoconductance spectroscopy, we have studied the influence of different types of thermal annealing on epitaxial ZnO thin films where band bending effects play a major role. Once the film is exposed to ambient air conditions after a simple thermal annealing in oxygen at 600°C, the effective energy gap is stable with a value of ≃3.15 eV, while after a corresponding annealing in vacuum and subsequent air exposure, it starts at ≃3.24 eV, and then it evolves along the days until it reaches the bulk energy gap value of ZnO. By means of valence band x-ray photoemission spectroscopy (XPS), we have confirmed that these phenomena are related via the Franz–Keldysh effect to a downward band bending in the former case and a time dependent upward band bending in the latter one that slowly tends to a flat band condition, tracking the behavior observed in the effective energy gap. Core level XPS measurements suggest that for each type of thermal annealing, a different adsorption kinetics of water and hydrogen take place.

Problem Solving of Isopropyl Alcohol – Water Azeotropic Characteristics Using Packed (Natural Zeolite) Bed Adsorber

The adsorption kinetics of water from an azeotropic mixture of isopropyl alcohol and water using chemically activated natural zeolites with and without a binder (starch) was investigated. In addition, an investigation of the compressive strength of zeolite pellets was conducted to ascertain the performance of the adsorbent for long-term operation. Three parameters were applied in the zeolite-making process: the particle size of zeolite (20, 30, 50, and 80 mesh), the sintering temperature (550, 750, and 1,000°C), the compaction pressure (2, 4, and 6 tonnes), and the starch-to-zeolite weight ratio (0, 1:3, 1:5, and 1:7). Initial screenings indicated that the strongest zeolite pellet was 80-mesh zeolite powder (without starch addition) that was compacted using 6 tonnes pressure and was sintered at 750°C. The adsorption tests using the strongest zeolite were conducted in a packed-bed column for three cycles, followed by compressive strength tests on the zeolite pellets after each cycle. According to the experimental data, zeolite pellets made without the addition of starch could adsorb up to 98.4% of the initial water in the mixture. From the four models proposed to describe the kinetics of adsorption of water from the mixture, the Freundlich model turned out to be the best model.

Stability of camu‐camu encapsulated with different prebiotic biopolymers

A viable possibility for the best use of bioactive compounds present in camu-camu, fruit native to the Amazonian rainforest, is the preparation of microcapsules using different biopolymers by the spray-drying technique, which would increase the possibilities for innovation in the food industry, as well as facilitate the application in different food matrices. In this context, the chemical, physicochemical, and morphological properties and stability of camu-camu extract (peel and pulp) spray-dried using maltodextrin, inulin, and oligofructose as encapsulating agents were investigated, as well as lyophilized camu-camu extract (CEL). Different relative humidities (22%, 51%, and 75%) and temperatures (25 °C and 45 °C) were evaluated. The moisture, water activity, and solubility values varied from 18.4 to 107.9 g water per kilogram dry powder, 0.06 to 0.27, and 950.80 to 920.28 g microparticles per kilogram of water respectively. Retention of the bioactive compounds varied in the ranges 5.5-7.1 g per kilogram ascorbic acid fresh weight and 7.2-9.0 g per kilogram anthocyanins fresh weight. The increase in temperature and relative humidity during storage provided a significant decrease in the stability of the bioactive compounds for all treatments. However, the CEL presented higher water adsorption kinetics and degradation under all storage conditions, indicating the importance of the use of encapsulating agents. In general, the prebiotic biopolymers used as encapsulating agents in the microencapsulation of extracts of camu-camu by spray-drying presented satisfactory results, suggesting that this technique is an effective strategy to increase the stability of bioactive compounds contained in fruits and vegetables. © 2020 Society of Chemical Industry.

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.

Synthesis and Characterization of Alginate–Silica Gel Composites for Adsorption Dehumidification

Desiccant coated heat exchanger (DCHE)-based adsorption dehumidification systems have great potential for energy conservation and emission reduction. The selection of desiccant materials can greatly impact the overall performance of DCHE systems. However, the unsatisfied adsorption quantity of widely used silica gel at middle relative humidity range and the possible corrosion problem of salt-supported silica gel are bottlenecks for the engineering application. A strategy for synthesizing novel alginate–silica gel composites that have fair adsorption quantity without corrosion is demonstrated. Textural properties suggested that silica gel particles can be well distributed in the surface of composite samples with the liquid–solid mixing and post cross-linking method. Dynamic water adsorption test showed that the composite with a sodium alginate-to-silica gel mass ratio of 5:1 possessed the best water adsorption kinetics. Water adsorption quantity difference of the composite between a typical adsorption condition (80% RH) and a regeneration condition (30% RH) is more than twice that of silica gel. Dehumidification capacities of the composite-coated DCHE were 34–60% higher than those of a silica gel-coated DCHE under set simulation conditions. This method offers a promising way of material synthesis for researchers who are interested in the area of coatings, separations, dehumidification, etc.

Reaction-diffusion approach to modeling water diffusion in glutinous rice flour particles during dynamic vapor adsorption.

Dynamic vapor sorption (DVS) method is now widely adopted to determine water diffusion properties in food materials using a sheet or bulk particles as test samples. The Fickian second law with an instant equilibrium boundary condition, although commonly used, can not accurately model the water adsorption kinetics during DVS tests. Dynamic water adsorption of glutinous rice flour was measured at 30°C and eleven relative humidity steps, and modeled using the Fickian second law with three kinds of boundary condition. Results indicated that the boundary conditions had great impacts on the predicted values especially for the initial section in the DVS curves, and that modifying boundary conditions could not improve the fitness of the final section which characterized a continuing slight increase of water concentration. A reaction-diffusion model, which assumes two diffusible water populations and describes water transport as a competition between diffusion and reversible adsorption on solid matrix, was developed and found to be able to capture the features of water diffusion in the whole adsorption duration. Implementation of the reaction-diffusion approach to glutinous rice flour indicated that diffusion of the Langmuir water became very slow when its adsorption reached equilibrium, while the diffusion of the non-Langmuir water slowed down when water clustering occurred, at the same time the rates of the surface adsorption and bulk adsorption began to decrease. The model developed in this work would help to deepen our mechanistic understanding of water diffusion during a isothermal adsorption.

Water adsorption on Al doped silicatene films grown on Mo(112)

At ultrahigh vacuum (UHV), clean and Al doped SiO2 films were epitaxially grown on Mo(112). The pristine films are often denoted as silicatene, whereas the doping should result in two-dimensional zeolitelike films. The films were prepared by vapor deposition of Al on silicatene, followed by postannealing in UHV. The films were characterized by Auger electron spectroscopy and thermal desorption spectroscopy (TDS). Whereas the first synthesis of these films was reported earlier [Stacchiola et al., Angew. Chem. Int. Ed. Engl. 45, 7636 (2006); Gründling et al., Surf. Sci. 318, 97 (1994)], we discuss another variation of the film preparation. Moreover, water adsorption kinetics was studied by TDS. Accordingly, Al doped silica exhibits hydrophilic characteristics compared to hydrophobic silicatene, which reflects the enhanced chemical reactivity due to the doping induced polarity of the zeolite film.