Dynamics Of Water Adsorption Research Articles

A two-stage sorption strategy to improve heat storage performance of salt/porous matrix composites

Composites combining salt hydrates and porous matrix like metal–organic frameworks (MOFs) are used to enhance the performance of thermochemical storage materials. However, the mechanism for the enhancement and the strategy for the selection of salt hydrates and porous matrix are not clear. The heat storage performance is determined by water adsorption dynamics, capacity and their sorption energy of the single components. The single components (salts or matrix) normally have either fast water adsorption dynamics or high-water uptake capacity, but not both of them. In this study, we investigate the enhancement of adsorption in composite materials, and a novel strategy is then proposed to combine the advantages from adsorbents with higher adsorption dynamics at low water partial pressure with those with a high capacity at high water partial pressure to promote the water adsorption capacity and kinetics, hence efficient energy storage. Two types of composites have been used to demonstrate the two-stage strategy developed in this study, in which SrCl2 and SrBr2 are incorporated into MOF MIL-101(Cr) to enhance adsorption and heat storage. In these composites, SrCl2 and SrBr2 can be regarded as the moisture pumps, capturing water vapour from air to improve the adsorption dynamics, while MIL-101(Cr) with high adsorption capacity functions as a water reservoir to take the water accumulated by the salts. Through this two-stage design, the water sorption capacity of the composites is 2–3 times higher than the water uptake of either salts or MOF within 120 min. As SrCl2 has a faster water adsorption kinetics than SrBr2, SrCl2/MIL-101(Cr) reaches an uptake of 0.73 g/g, however, the water sorption capacity of SrBr2/MIL-101(Cr) is 0.54 g/g. The composite samples also present good heat storage capacities of 1462 J/g for SrCl2/MIL-101(Cr) and 1526 J/g for SrBr2/MIL-101(Cr), and good cycling stability after 15 repeating adsorption/desorption cycles.

Dynamics of water adsorption on SAPO-34: Comparison of three adsorbent bed configurations of adsorption chillers

Intensification of the adsorption dynamics is a strategic way to make adsorption chillers and heat pumps more competitive with conventional vapour compression systems. This can be achieved by consolidating the adsorbent bed with a heat exchanger to enhance heat transfer. This work investigates the dynamics of water adsorption on a commercial adsorbent SAPO-34 for three bed configurations, namely, a reference bed consisting of a monolayer of loose beads located on an aluminium plate, and two consolidated beds – a monolayer of beads glued to the plate, and a homogeneous coating of the plate prepared with binder. The morphology and texture of the prepared beds were studied by optical and scanning electron microscope techniques as well as by low temperature nitrogen adsorption. Six binders involved, both organic (hydroxyethyl cellulose, polyvinylpyrrolidone, polyaniline) and inorganic (heat-conductive compound CPTD, bentonite clay, colloidal silica sol), produced varying effects. It was found that the most preferred configuration involves SAPO beads glued to the plate with bentonite for which the heat transfer was enhanced by a factor of 1.2–1.7 while maintaining sufficient mass transfer. The effective heat transfer coefficient was measured for the most promising binders and selected configurations, and varied between 120 and 248 W/(m2 K). The heat transfer acceleration permitted the specific cooling power (at a conversion of 0.8) to increase from 2.7 kW/kg for loose beads of 0.8–0.9 mm size to 3.5 kW/kg for the same beads bound with bentonite. Thus, gluing pre-made commercial adsorbent beads with heat-exchanger with suitable binders presents a simple and promising method to enhance the adsorption dynamics, resulting in a more compact design of adsorption chillers.

Insight into in situ enzymatic transesterification modification of polyethylene terephthalate fibers with polyethylene glycol

Polyethylene terephthalate (PET) fabric was enzymatically modified with polyethylene glycol (PEG). Lipase from Aspergillus oryzae was used as a catalyst. The wetting behavior of the modified PET fabric was characterized by the water contact angle, water adsorption dynamics and moisture regain. The initial water contact angle of the modified fabric decreased from 129.3° to 74.9°. The water absorption dynamics results indicated that the equilibrium water absorption amount of the modified fabric was approximately 10 times greater than that of the untreated sample. The initial absorption rate (Vinit) of the modified fabric was almost 30 times higher than that of the untreated fabric. The moisture regain reached 3.52 % after modification. Scanning electron microscopy revealed granular and sheet coatings on the surface of the modified fabric. Chemical linkage of PEG onto the PET fibers was confirmed by attenuated total reflection–Fourier transform infrared spectroscopy. The modification had no significant effect on the thermal properties of the PET fabrics according to the thermogravimetric curve and differential scanning calorimetry results. The mechanical properties of the modified fabric were slightly improved. Therefore, in situ enzymatic transesterification between PET and PEG could be a potential novel modification approach for adding value to PET fiber textiles.

Effects of the combination of phenolic-resin impregnation and heat treatment on physical, mechanical and decay resistance of Taxodium hybrid “Zhongshanshan” wood

ABSTRACT This study aimed to evaluate the influence of cooperative modification treatments and treatment sequencing on the properties of treated fast-growing wood. Two integrated treatment methods including, impregnation with Phenol-Formaldehyde resin followed by heat treatment (PF-HT), and heat treatment antecedent to impregnation with Phenol-Formaldehyde resin (HT-PF) were applied on Taxodium hybrid “Zhongshanshan” wood. Comprehensive characterization was undertaken, investigating micro-morphology, chemical structure, mechanical properties, shrinkage and expansion properties, and decay resistance before and after treatment. Results indicated that the weight percentage gain (WPG) of the HT-PF wood exceeded that of the PF-HT wood, and the WPG of the former displayed an ascending tendency with increasing heating temperature, reaching a final difference of 10%. For instance, the modulus of elasticity of the HT-PF wood was 18% higher than that of the PF-HT wood in the bending test at a temperature of 215°C. Throughout the dynamic water adsorption test, both the hydrated water percentage and the dissolved water percentage of PF-HT wood were lower than those of PF-HT wood. After 3 months of exposure to brown-rot fungi, both HT-PF wood and PF-HT wood achieved a high level of decay resistance.

Smart hydrogel composite for microenvironmental humidity regulation in cigar storage.

Environmental humidity profoundly influences various life activities, especially for plants that depend heavily on optimal humidity for growth. The humidity index is particularly crucial for preserving the functionality of plant leaves, notably in economically valuable plants such as cigar tobacco. This paper introduces a novel dual-layer moisturizing material, a PAS-PDMS composite, based on polyacrylamide/solketal (PAS) hydrogel and polydimethylsiloxane (PDMS). This material features a unique hierarchical water release mechanism. Comprehensive analyses, including thermogravimetric analysis, Fourier-transform infrared spectroscopy, low-field nuclear magnetic resonance, and dynamic water adsorption studies, confirm the water migration and humidity control mechanisms of the PAS-PDMS composite. This smart hydrogel composite regulates microenvironmental humidity bidirectionally. When applied to cigar boxes for storage, it stabilizes internal humidity at approximately 65%, maintaining this level for over 20 days. Furthermore, the PAS-PDMS composite exhibits superior mechanical properties and light transmittance, achieving an exceptional transmittance of 84%. In conclusion, the PAS-PDMS composite offers intelligent humidity control, providing a novel approach to the storage and preservation of cigars.

Water Adsorption Dynamics on Metal-Organic Framework MOF-801: Comparative Study of Loose and Glued Grains, and Coatings.

Adsorption heat transformation and storage (AHTS) is an environmentally benign and energy-saving alternative to common compression chillers and heat pumps. The low specific power (SP) of adsorption systems is a key drawback that hinders their broader dissemination. The optimization of adsorption dynamics is a prerequisite for SP enhancement. In this work, we studied the dynamics of water vapor adsorption on MOF-801-a promising adsorbent for AHTS. For the first time, two configurations of compact MOF-801 bed, namely, grains glued to the surface of a metal support and thin adsorbent coatings, are prepared, and their porous structure is characterized. The water adsorption dynamics is compared with a common loose grains configuration. The main findings are: (a) the binder can both accelerate and decelerate the water adsorption, and its chemical nature is subject to careful selection; (b) at the initial time, heat transfer between the support and adsorbent bed controls the adsorption rate, and, at a longer time, mass transfer starts to affect it; (c) polyvinylpyrrolidone, bentonite, thermal grease, and hydroxyethylcellulose increase the heat transfer coefficients and accelerate adsorption; polyvinyl alcohol and polyaniline slow it down; and (d) for the coatings prepared with polyvinylpyrrolidone, an SP of 1.6-5.1 kW/kg can be achieved, which is about twice that for the loose grains. The new configurations can be recommended for effective but expensive adsorbents such as MOFs, and their implementation will contribute to the further spread of AHTS technology.

Humidity sensing based strategy for in situ probing and manipulating electrified interfacial water adsorption dynamics

Understanding and manipulating the ubiquitous electrified interfacial water adsorption dynamics are highly important in surface science, sensing, catalysis and energy storage. However, the interfacial water is extremely hard to probe due to the interference from bulk water and complex interfacial environments. Herein we report a strategy to explore the adsorption dynamics of electrified interfacial water through combing a dynamic humidity sensing system, the in situ diffuse reflectance infrared Fourier transform spectroscopy, and the density functional theory calculations. By atomically engineering the Ti3C2Tx with atomic Mo substitution of Ti, the water adsorption dynamics on the obtained Mo2TiC2Tx were dramatically enhanced. The Mo2TiC2Tx was demonstrated as an excellent humidity-sensing material with an ultrahigh sensitivity of 1.75 ± 0.06, fast response (35.9 s), and hysteresis-free properties in 2.7–93 % relative humidity range. This work provides universal strategies to in situ probe and manipulate the electrified interfacial water adsorption dynamics.

Pressure- and temperature-initiated adsorption of water vapour in a finned flat-tube adsorber

Adsorption heat transformation is an environmentally friendly and effective method of using low-temperature heat from renewable, industrial and domestic sources. The transformation can be initiated by changing either adsorptive pressure (pressure-initiated, PI) or adsorbent temperature (temperature-initiated, TI). This work aims to elucidate how the initiation pathway affects the dynamics of water adsorption for silicoaluminophosphate AQSOA-FAM-Z02 loaded inside a commercial finned flat-tube heat exchanger. The main findings of this study are as follows: (a) all kinetic curves can be represented as a superposition of fast and slow exponentials associated with the process rate limitation by vapour transfer or heat transfer, respectively; (b) at a short time (<150–200 s), the PI adsorption is faster than the TI one by a factor of 3; (c) at a long time (>100–150 s), the PI desorption is slower than the TI one. From the practical point of view, the revealed differences between the PI and TI dynamics could allow the specific power of adsorption heat transformers to be improved through a better organization of the working cycle.

Controlling the thermal switching in upconverting nanoparticles through surface chemistry.

Photon upconversion taking place in small rare-earth-doped nanoparticles has been recently observed to be thermally modulated in an anomalous manner, showing thermal enhancement of the emission intensity. This effect was proved to be linked to the role of adsorbed water molecules as surface quenchers. The surface capping of the particles has a direct influence on the thermal dynamics of water adsorption and desorption, and therefore on the optical properties. Here, we show that the upconversion intensity of small-size (<25 nm) nanoparticles co-doped with Yb3+ and Er3+ ions, and functionalized with different capping molecules, presents clear irreversibility patterns upon thermal cycling that strongly depend on the chemical nature of the nanoparticle surface. By performing temperature-controlled luminescence measurements we observed the formation of a thermal hysteresis loop, resembling an optical switching phenomenon, whose shape and trajectory depend on the hydrophilicity of the surface. Additionally, an intensity overshoot takes place immediately after turning off the heating source, affecting each radiative transition differently. We performed numerical modelling to understand this effect considering non-radiative energy transfer from the surface defect states to the Er3+ ions. These findings are relevant for the comprehension of nanoparticle-based luminescence and the interplay between the surface and volume effects, and more generally, for applications involving UCNPs such as nanothermometry and bioimaging, and the development of optical encoding systems.

Establishment of Lower Hygroscopicity and Adhesion Strategy for Infrared-Freeze-Dried Blueberries Based on Pretreatments Using CO2 Laser in Combination with Ultrasound

The present study aimed at solving industrial problems of hygroscopicity and adhesion of freeze-dried crisp-texture blueberries without adversely affecting the other properties. CO2-based laser in combination with ultrasound-assisted infusion of soybean protein isolate (SPI) prior to pulse-spouted infrared freeze drying (PSIRFD) was noted to be effective in solving this major problem through the results of dynamic water adsorption analyzer. The main reason why this approach worked was that laser pretreatment reduced the exposure of fruit contents (e.g., sugar, organic acid) outside the epidermis. Also, SPI interacted with the fruit contents to reduce the number of hydrophilic points under the synergistic effect of laser and ultrasound by differential scanning calorimetry, Fourier-transform infrared spectroscopy, and X-ray diffraction analysis. What is more, the sample prepared by this method possessed the better physicochemical properties and lower energy consumption. So, CO2-based laser in combination with ultrasound along with PSIRFD represents an attractive alternative for producing high-quality dried blueberries.

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.

Dynamics of Water Adsorption from Butanol–Water Vapor in a Biosorbent Packed Column

Drying is essential in the production of biobutanol. In this work, the dynamics of water adsorption from butanol–water vapor mixtures in a fixed bed column were investigated. The biosorbent used in this system was derived from a cellulosic material oat hull. Water adsorption breakthrough curves obtained from the biosorbent packed column were simulated by the Bohart–Adams model and Klinkenberg model. The Klinkenberg model provided a better simulation of the experimental data in comparison with the Bohart–Adams model. The mass transfer coefficient and mass transfer resistances were investigated from the modeling results. The results indicated that the rate of water adsorption was controlled by internal mass transfer resistance. The water adsorption on the biosorbent was visualized with the aid of microscope imaging. This study reveals that water saturated oat hull based biosorbent was regenerated and reused successfully.

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.

MOF-801 as a promising material for adsorption cooling: Equilibrium and dynamics of water adsorption

With exhausting fossil fuels and increasing demand for heating and cooling, the effective utilization of renewable and waste energy sources becomes of increasing importance. Adsorption cooling driven by low temperature heat is an energy and environment saving alternative to the common compression systems. The performance of adsorption chillers strongly depends on the compliance of the adsorbent properties with the cycle operating conditions. In this paper, the comprehensive study of equilibrium and dynamics of water adsorption on a new efficient adsorbent of water vapour MOF-801 is performed to evaluate its feasibility for adsorption cooling. It was shown that at the adsorption temperature of 30 °C the MOF-801 provides the cooling effect at the evaporation temperature as low as 5 °C that indicates significant affinity to water vapour. On the other hand, it can be regenerated by low temperature heat at 80–85 °C. The uptake variation under the conditions of a typical adsorption cooling cycle reaches 0.21 g/g. Water adsorption on loose grains of MOF-801 occurs under grain-size insensitive mode when the adsorption rate is proportional to the (S/m)-ratio of the heat transfer surface S to the adsorbent mass m. The Specific Cooling Power equal to 2 kW/kg is measured at S/m = 6 m2/kg and 80% of reaching the equilibrium conversion, which is of high practical interest. Thus, the results obtained demonstrate the high potential of the working pair “MOF-801 – water” for adsorption cooling.

Angle-Independent Optical Moisture Sensors Based on Hydrogel-Coated Plasmonic Lattice Arrays

Plasmonic nanostructures provide excellent platforms for colorimetric sensors in chemical, biological, and environmental applications. In contrast to the existing library of plasmonic sensors, we report an angle-independent optical sensor that is designed for monitoring soil moisture and operating on rough surfaces. The optical moisture sensor is constructed by coating hydrogel on top of an ultrathin, plasmonic Au nanorod lattice array, where the refractive index changes of the hydrogel upon exposure to moisture are transduced into spectral shifts of the resonances of the array. A modified Langmuir adsorption isotherm model is used to capture the dynamics of water adsorption and desorption at the interface between the sensor and the ambient environment. The nanorod length and the nanorod array pitch are systematically tuned to decouple the localized surface plasmon resonance of the nanorods and the Rayleigh anomalies of the nanorod array, creating sensors with angle-independent resonances (∼0.2 nm/deg). As a proof of concept, we place the sensor on uneven soil surfaces and demonstrate the consistent sensor resonance shift that only depends on the soil wetness. Robust, eco-friendly optical moisture sensors with angle-independent resonances provide a promising sensing platform for smart soil moisture monitoring important to tackle the challenge of water scarcity in agriculture.

NH2-MIL-125 as promising adsorbent for adsorptive cooling: Water adsorption dynamics

Adsorption heat transformation (AHT) has attracted an increasing research interest as energy saving and environmentally benign alternative to vapor compression systems. Novel adsorbent NH2-MIL-125 could be promising for AHT owing to its high water adsorption capacity and good hydrothermal stability, although its dynamic properties have not been tested yet. In this paper the results of dynamic study of water adsorption on loose grains of NH2-MIL-125 are presented. The adsorption dynamics is studied by a Large Temperature Jump method under typical operating conditions of isobaric stages of adsorptive cooling cycle. The effects of the adsorption/ desorption temperature, adsorbent grain size and number of the grain layers are explored. The water adsorption on the grains of 0.2–1.8mm size are shown to occur under at “grain size insensitive” mode as the adsorption rate is determined by the ratio S/m of the heat transfer area to the adsorbent mass regardless the grain size. Indeed, the ad/desorpion rate and the Specific Cooling Power (SCP) are proportional to the (S/m)-ratio. Quite high SCP-values of 0.4–2.8kW/kg can be obtained in adsorption chillers having a large (S/m)-ratio of 1.6–6.9m2/kg, which is of high practical interest.

Pre-treating biosorbents for purification of bioethanol from aqueous solution

ABSTRACTCost-effective biosorbents made from the byproducts of agriculture, forest, and related industries, such as barley straw, canola meal, and wood sawdust, have significant water adsorption capacity, showing a great potential for selective water removal from bioalcohols to produce fuel grade products. However, there is a challenge that the biosorbents are not stable when they come in contact with aqueous solution. There are organic carbons released from biosorbents to liquid phase, which needs to be addressed before this technology is applied in the industrial purification of bioalcohols. In this work, raw barley straw representing an abundant group of cellulosic materials in the above-mentioned industries was used as a model material. A methodology of chemical and physical treatment was developed to treat barley straw which successfully enhanced the stability and reduced the total organic carbon release from the material into the aqueous solution. In addition, the pre-treated barley straw biosorbent had significantly increased micropores, and the Brunauer--Emmett--Teller surface area favored by water adsorption compared with raw barley straw. It also had higher water uptake and dynamic water adsorption selectivity. The pre-treated barley straw was able to selectively remove water and generate concentrated ethanol.

“Water - Silica Siogel” working pair for adsorption chillers: Adsorption equilibrium and dynamics

The aim of this paper is to study the equilibrium and dynamics of water adsorption on a commercial silica gel Siogel. This adsorbent has recently been suggested and tested for adsorptive transformation and storage of low temperature heat. The original data on the water vapour equilibrium and dynamics are compared with those earlier reported for the Fuji silica RD. This database can be used for theoretical analysis, mathematical modeling and evaluation of adsorptive cycles based on the working pair “water – Siogel” and driven by heat from renewable heat sources.

A review on the buffering capacity of earth building materials

Unfired clay building materials are recognised for their ability to regulate indoor humidity levels through their moisture buffering capacity. Research is being conducted on the moisture buffering capacity of a variety of building materials with natural materials, such as clay, and organic materials, such as hemp or straw, presenting a greater potential to regulate indoor humidity than industrial building materials. Due to their high affinity to water, which is usually regarded as detrimental, clay materials present complex hygrothermal coupling phenomena, which are still under investigation. This paper summarises some recent investigations into the dynamic water adsorption process within clay materials in relation to their ability to regulate indoor air humidity levels. First, a review of the experimental methods to characterise this behaviour is provided. A review of experimentally measured results on the material scale using compressed earth block, rammed earth or plaster samples is then provided, followed by some larger and whole building measurements.

From single molecules to water networks: Dynamics of water adsorption on Pt(111).

The adsorption dynamics of water on Pt(111) was studied using ab initio molecular dynamics simulations based on density functional theory calculations including dispersion corrections. Sticking probabilities were derived as a function of initial kinetic energy and water coverage. In addition, the energy distribution upon adsorption was monitored in order to analyze the energy dissipation process. We find that on the water pre-covered surface the sticking probability is enhanced because of the attractive water-water interaction and the additional effective energy dissipation channels to the adsorbed water molecules. The water structures forming directly after the adsorption on the pre-covered surfaces do not necessarily correspond to energy minimum structures.