Sorption Hysteresis Research Articles

Size and shape dependence of hydrogen-induced phase transformation and sorption hysteresis in palladium nanoparticles

Abstract Phase transitions of metals in hydrogen environments are critically important for applications in energy storage, catalysis, and sensing. Nanostructured metallic particles can lead to faster charging and discharging kinetics, increased lifespan, and enhanced catalytic activities. However, establishing a direct causal link between nanoparticle structure and function remains challenging. In this work, we establish a computational framework to explore the atomic configuration of a metal-hydrogen (M-H) system when in equilibrium with a H environment. This approach combines Diffusive Molecular Dynamics with an iteration strategy, aiming to minimize the system's free energy and ensure uniform chemical potential across the system that matches that of the H environment. Applying this framework, we investigate H chemical potential-composition isotherms during the hydrogenation and dehydrogenation of palladium nanoparticles, ranging in size from $3.9$ nm to $15.6$ nm and featuring various shapes including cube, rhombic dodecahedron, octahedron, and sphere. Our findings reveal an abrupt phase transformation in all examined particles during both H loading and unloading processes, accompanied by a distinct hysteresis gap between absorption and desorption chemical potentials. Notably, as particle size increases, absorption chemical potential rises while desorption chemical potential declines, consequently widening the hysteresis gap across all shapes. Regarding shape effects, we observe that, at a given size, cubic particles exhibit the lowest absorption chemical potentials during H loading, whereas octahedral particles demonstrate the highest. Moreover, octahedral particles also exhibit the highest desorption chemical potentials during H unloading. These size and shape effects are elucidated by statistics of atomic volumetric strains resulting from specific facet orientations and inhomogeneous H distributions. Prior to phase transformation in absorption, a H-rich surface shell induces lattice expansion in the H-poor core, while before phase transformation in desorption, surface stress promotes lattice compression in the H-rich core. The magnitude of the volumetric strains correlates well with the size and shape dependence, underlining their pivotal role in the observed phenomena.

Modelling of water sorption hysteresis of cement-based materials based on pore microstructure

This paper presents a model for predicting water sorption isotherms of cement-based materials. In our model, hysteresis contributions of interlayer pores and gel/capillary pores are calculated separately. The hysteresis model of gel/capillary pores is achieved in four steps: (i) quantification of the pore network, (ii) determination of the criterion of saturation/desaturation of pores, (iii) derivation of the two-dimensional volumetric density distribution function, (iv) calculation of the real-time water content of gel/capillary pores. The hysteresis of interlayer pores is represented by an empirical model based on experiments. The reliability of the model is verified by comparing the model predictions and the experimental data in the literatures. Furthermore, three subjects were discussed: the influence of pore network on hysteresis, the hysteretic behavior of water in pores, the interaction of hysteresis mechanisms.

Effect of temperature-dependent and hysteretic sorption in computational mould risk analyses of wood fibreboard sheathing

Wood is known for its complex hygroscopic properties. Previous studies show that both the temperature-dependency and the hysteresis in sorption should be included in the physical models, if the most accurate results are desired from simulations of building assemblies with wood-based materials. Literature is scarce on the topic, where the significance of these aspects on the reliability of mould-risk assessments is inspected. Exterior walls with glass wool insulation and LDF-sheathing were studied by using two different models with previously measured material data. Over 300 hygrothermal simulations were carried out, where mould-indices were computed on the warm side of the sheathing. According to both conventional and more sophisticated model, the studied walls perform well in cold climate if no driving rain leaks in. Temperature-dependent and hysteretic model yields slightly smaller mould-indices in general, but for certain leaky cases the difference is significant, which indicates the importance of sophisticated sorption-properties in modelling.

Why sorption hysteresis in tobermorite is limited

Molecular simulations are performed to decipher the nanoscale processes associated with water sorption in tobermorite, a microporous phase that functions as the binder in autoclaved aerated cement composites. Merlino’s cross-linked tobermorite 11 Å is studied. We show that there is no hysteresis in bulk tobermorite at the molecular scale because the zeolitic cavities occupied by water are smaller than the critical pore size for hysteresis disappearance, and upon sorption, tobermorite 11 Å shows virtually no volume change. These effects combined explain why hysteresis under sorption in tobermorite is limited. Similar explanation could also explain absence of significant hysteresis in some layered double hydroxides present in cement systems.

Sorption Hysteresis: A Statistical Thermodynamic Fluctuation Theory.

Hysteresis is observed commonly in sorption isotherms of porous materials. Still, there has so far been no unified approach that can both model hysteresis and assess its underlying energetics. Standard approaches, such as capillary condensation and isotherms based on interfacial equations of state, have not proved to be up to the task. Here, we show that a statistical thermodynamic approach can achieve the following needs simultaneously: (i) showing why adsorption and desorption transitions may be sharp yet continuous; (ii) providing a simple (analytic) isotherm equation for hysteresis branches; (iii) clarifying the energetics underlying sorption hysteresis; and (iv) providing macroscopic and nanoscopic perspectives to understanding hysteresis. This approach identifies the two pairs of parameters (determinable by fitting experimental data) that are required to describe the hysteresis: the free energy per molecule within the pore clusters and the cluster size in the pores. The present paper focuses on providing mechanistic insights to IUPAC hysteresis types H1, H2(a), and H2(b) and can also be applied to the isotherm types IV and V.

A chemo-mechanical model for describing sorption hysteresis in a glassy polyurethane

Hysteretic sorption and desorption of water is observed from 0 to 95% relative humidity and 298–333 K on a glassy polyurethane foam. It is postulated that sorption-induced swelling of the glassy polyurethane increases the concentration of accessible hydrogen-bonding adsorption sites for water. The accessibility of sites is kinetically controlled due to the restricted thermal motions of chains in the glassy polymer, causing a difference in accessible site concentrations during sorption and desorption. This discrepancy leads to hysteresis in the sorbed concentrations of water. A coupled chemo-mechanical model relating volumetric strain, adsorption site concentration, and sorbed water concentration is employed to describe water sorption hysteresis in the glassy polyurethane. This model not only describes the final mass uptake for each relative humidity step, but also captures the dynamics of water uptake, which exhibit diffusion and relaxation rate-controlled regimes.

Investigating the Sorption Isotherms and Hysteresis of a Round Perforated Brick Using Newly Developed Models

This article deals with the hygrothermal behavior of round perforated brick including hysteresis effects. It aims at examining the effect of temperature on sorption isotherms and hysteresis of this product, reducing the energy consumption of the buildings, reinforcing the constructional economy and the inhabitant’s comfort as well as offering a hygrothermal description of this product that has never been previously investigated. To achieve this, we have carried out an experimental study to determine the sorption isotherms and the hysteresis in five different temperatures (10, 23, 30, 40, and 50 °C). Twelve equations have been tested against the experimental isotherms in order to find the optimal one. After that, three models were tested in order to develop a personal model; the latter explains the real effect of the hysteresis phenomenon on hygrothermal behavior of the studied product. To validate the mathematical model, two methods were applied to calculate the isosteric heat. The obtained results revealed a significant influence of the increase in temperature on the hygrothermal behavior in which a decrease in the equivalent water content was found. Moreover, the developed experimental model is based on Oswin’s model describing the dependence of temperature on the sorption characteristics of round perforated bricks. Furthermore, the Huang model was found to be the best compared with the other models with a regression factor (R2) of 0.990. The validation of the results using the isosteric heat parameter has confirmed that the suggested models demonstrated a perfect presentation of the sorption isotherms and the hysteresis phenomenon of the round perforated brick.

Properties of Catalpa bungei (Bignoniaceae) earlywood and latewood in the same growth ring during moisture adsorption/desorption: swelling and shrinkage at the cell level

Summary In this study, Dynamic Vapor Sorption Resolution combined with a Dino-Lite Edge Digital Microscope was used to document in real-time the swelling/shrinkage behavior of earlywood and latewood cells (wood fiber and vessel) on homogeneous samples of Catalpa bungei C.A.Mey. at the microscopic scale. The results showed that the lumen and cell wall of wood fibers swelled with the increase of relative humidity and shrank with the decrease of relative humidity in the sorption cycle of 0∼95% relative humidity condition. However, vessels showed an opposite trend to the behaviors mentioned above. In any region of both types of cells, latewood cell size (area and diameter) changed more significantly. For diameter change, the change of tangential diameter was larger than that of radial diameter. In addition, in the sorption cycle, the size (area and diameter) change of any region of wood fiber and vessel showed swelling hysteresis. Compared with earlywood cells, latewood cells had a more pronounced swelling hysteretic value, and the swelling hysteretic value in the tangential direction was higher than that in the radial direction in terms of diameter. Sorption hysteresis might be one of the contributing factors to swelling hysteresis. Finally, it was found that under any relative humidity, the dimensional changes of the wood fibers and the vessels were immediately stabilized when the moisture content reached its equilibrium.

Porous Core-membrane Microstructured Nanomaterial Composed of Deep Eutectic Solvents and MOF-808 for CO2 Capture.

A series of porous core-membrane microstructured nanomaterials, constructed of a deep eutectic solvent (DES) membrane and porous MOF-808 core via liquid surface tensions and electrostatic interactions, are introduced for carbon dioxide capture with the sorption mechanism coupling diffusion, physisorption, and chemisorption. MOF-808 as the porous core considerably improves the diffusion interactions for DES membranes, hence significantly enhancing the sorption performance of DESs. Although the DES consisted by monoethanolamine and tetrapropylammonium chloride (MEA-TPAC-7) has the highest sorption capacity among all DESs, it is only 4.39 mmol g-1 at 2.4 bar and further attenuates by fastidious diffusion interactions when increasing viscosity or dose. The sorption capacities of DES@MOF-120 are 5.18 mmol g-1 at 3.0 bar and 4.78 mmol g-1 at 2.4 bar without apparent sorption hysteresis in pressure swing sorption, which are substantially improved contrasted to MEA-TPAC-7. The sorption isotherms are reconstructed via Sips models considering surface heterogeneity with regression correlation coefficients over 0.9454 to forecast maximum sorption capacity over 6.33 mmol g-1 .

Water Vapor Sorption Kinetics of Beech Wood Modified with Phenol Formaldehyde Resin Oligomers

Beech is an important tree species in Europe. This study aimed to elucidate the influence of four molecular weights of phenol formaldehyde (PF) resin (266, 286, 387, and 410 g/mol) on the sorption behavior of unmodified and modified beech wood samples using a dynamic vapor sorption (DVS) apparatus. The variations in the environmental relative humidity and moisture content (MC) of the samples were recorded, and the DVS isotherms were plotted from the equipment. During the sorption process, the MC of the modified samples decreased in comparison to that of the unmodified samples, and both apparently decreased with the increasing molecular weight of the PF resin. The DVS isotherm hysteresis plot illustrated a reduction in sorption hysteresis for the modified wood with varying PF resins compared to the unmodified samples. Based on the DVS isotherm adsorption and desorption plots, the decrease in the equilibrium of the MC can be attributed to there being fewer sorption sites in the modified samples, which exhibited the lowest hygroscopicity. Overall, the moisture sorption mechanism for both types of samples was clarified, highlighting a clear correlation between the molecular weight of the applied PF resin and its influence on moisture sorption behavior.

In-situ gas contents of a multi-section coal seam in Sydney basin for coal and gas outburst management

The gas content is crucial for evaluating coal and gas outburst potential in underground coal mining. This study focuses on investigating the in-situ coal seam gas content and gas sorption capacity in a representative coal seam with multiple sections (A1, A2, and A3) in the Sydney basin, where the CO2 composition exceeds 90%. The fast direct desorption method and associated devices were described in detail and employed to measure the in-situ gas components (Q1, Q2, and Q3) of the coal seam. The results show that in-situ total gas content (QT) ranges from 9.48 m3/t for the A2 section to 14.80 m3/t for the A3 section, surpassing the Level 2 outburst threshold limit value, thereby necessitating gas drainage measures. Among the gas components, Q2 demonstrates the highest contribution to QT, ranging between 55% and 70%. Furthermore, high-pressure isothermal gas sorption experiments were conducted on coal samples from each seam section to explore their gas sorption capacity. The Langmuir model accurately characterizes CO2 sorption behavior, with fit coefficients (R2) greater than 0.99. Strong positive correlations are observed between in-situ gas content and Langmuir volume, as well as between residual gas content (Q3) and sorption hysteresis. Notably, the A3 seam section is proved to have a higher outburst propensity due to its higher Q1 and Q2 gas contents, lower sorption hysteresis, and reduced coal toughness f value. The insights derived from the study can contribute to the development of effective gas management strategies and enhance the safety and efficiency of coal mining operations.

Effect of soil organic matter on sorption of water vapor and associated hysteresis

AbstractIn‐depth knowledge about the impact of organic matter (OM) on soil water vapor sorption (SWVS) and associated hysteresis related to various water activity (aw) levels is limited. The objective of this study was to elucidate the effect of OM on SWVS and sorption hysteresis for different aw levels. We measured water sorption isotherms and physicochemical properties of eight soils with varying clay (6%–47%) and OM (2.0%–7.8%) contents before and after OM removal. In general, OM increased SWVS, but the effect of OM on SWVS varied for different aw ranges. The presence of OM generally increased water vapor sorption during the adsorption process. For soils with OM content above 4.6%, the presence of OM decreased water vapor sorption during the condensation process. The local hysteresis (Hw) of soils with OM was higher than that of soils without OM for soils with OM contents above 3.4%. For aw < ∼0.75, the water vapor sorption hysteresis of soils with and without OM showed a significant correlation with cation exchange capacity (CEC), and the Hw values of soils with OM were lower than that of soils without OM for the same CEC. The OM can affect water vapor sorption and the associated hysteresis at low aw levels through adsorbed cations and organic functional groups, and at high aw levels through the structures of pores and OM.

Cover Crop Straw Interferes in the Retention and Availability of Diclosulam and Diuron in the Environment

Pre-emergent herbicides are applied directly in the soil or over the straw in no-till systems and can be retained, reducing the product’s availability. The current study characterizes the retention of diclosulam and diuron in forage turnip (FT), buckwheat (BW), and black oat (BO) straws. Radiometric techniques evaluated the sorption–desorption and leaching processes. Spectroscopic and microscopic methods characterized chemical and morphological alterations in the straw. Sorption rates (Kf) of diclosulam and diuron followed the order BO > BW > FT. Irreversible sorption (hysteresis < 0.7) occurs to diclosulam applied to BO straw. The BO straw showed porous structures, indicating physical entrapment of the herbicides. Straw fragments (<1 mm) increased the sorption of herbicides. The increase in straw amount (2.5 to 5 t ha−1) reduced herbicide leaching to 18.8%. Interactions between chemical groups (C-Cl, C-F, and C-N) from herbicides with straw characterize a chemical barrier. The present research suggests that entrapment and chemical interaction are involved in the sorption–desorption process of herbicides, such as diclosulam and diuron, in the straw matrix, directly interfering with their availability in the environment. This process can reduce the herbicide environmental risk but can decrease weed control efficiency.

Ultrafast Water H-Bond Rearrangement in a Metal–Organic Framework Probed by Femtosecond Time-Resolved Infrared Spectroscopy

We investigated the water H-bond network and its dynamics in Ni2Cl2BTDD, a prototypical MOF for atmospheric water harvesting, using linear and ultrafast IR spectroscopy. Utilizing isotopic labeling and infrared spectroscopy, we found that water forms an extensive H-bonding network in Ni2Cl2BTDD. Further investigation with ultrafast spectroscopy revealed that water can reorient in a confined cone up to ∼50° within 1.3 ps. This large angle reorientation indicates H-bond rearrangement, similar to bulk water. Thus, although the water H-bond network is confined in Ni2Cl2BTDD, different from other confined systems, H-bond rearrangement is not hindered. The picosecond H-bond rearrangement in Ni2Cl2BTDD corroborates its reversibility with minimal hysteresis in water sorption.

Quantitative evaluation of pore connectivity of shales with a type H3 sorption hysteresis loop

Pore connectivity is a key parameter affecting the hydrocarbon yield of shale reservoirs, and a quantitative study on it is helpful to evaluate the exploration and development potential of shale gas. In this paper, the shales from the Jurassic Yangxia and Kezilenur Formations in the Kuqa Depression, Tarim Basin, China, were taken as an example, and organic petrography analysis, X-ray diffraction analysis, field emission scanning electron microscope (FE-SEM), gas adsorption and helium pycnometry were carried out to determine their petrological, organic geochemical characteristics and pore distribution features. A method for estimating the connectivity of shale with isotherm adsorption curves of a H3 hysteresis loop was established and used to characterize the connectivity of shale pores. The results show that the total pore volume of shale ranges from 2.479 × 10-3 to 20.379 × 10-3 cm3/g, and the specific surface area (SSA) ranges from 1.222 cm2/g to 12.668 cm2/g. The samples’ coordination number (Z) is between 1.215 and 3.064, and the percolation cluster length (L) is between 2.429 and 3.859. Shale with more micropores or higher TOC has a larger Z value, indicating that organic matter pores and micropores have better connectivity. There is no correlation between Z and Tmax, meaning that the effect of maturity on Z is insignificant. The impact of TOC on the L value is also not substantial. Besides, Tmax and illite content show a negative correlation with L, indicating that the high maturity and illite content impede the development of the percolation cluster.

Investigation of methane mass transfer and sorption in Marcellus shale under variable net-stress

Natural gas in shale exists as free and adsorbed gas, subject to prevailing pore pressures and stress conditions. Accordingly, to accurately estimate/predict the shale gas recovery potential, a central requirement is to represent gas transport and sorption behavior under varying stress conditions. The objective of this work is to facilitate the interpretation of laboratory-scale experiments, at relevant conditions, in an attempt to bridge the gap in scales between laboratory- and field-scale observations.We have conducted a series of high-pressure experiments on a full-diameter core sample from the Marcellus shale. These include gas loading (pressure-decay) and depletion (production) experiments with pure methane (CH4) at variable stress conditions to characterize transport and sorption behavior under reservoir-relevant conditions. We have formulated and applied a novel integral model for mass transfer and storage in multi-porosity shale systems that allows us to effectively investigate transport and sorption phenomena: We delineate gas transport by interpreting helium (He) pressure-decay experiments and demonstrate how to use the information gained to calculate the relevant transport coefficients of CH4 and other gases. A separate measurement of the CH4 sorption isotherm on a smaller sample (a shale cube) was interpreted and combined with the transport description to predict the production behavior of CH4 from the experiments with the full-diameter core.Our experiments demonstrate that the representation of sorption hysteresis is crucial for predicting and guiding shale gas production: At the end of both gas production experiments, approximately 20% of the initial gas in place remained in the core. Without accounting for sorption hysteresis, our modeling demonstrates that the CH4 production could be overestimated by 10%. We demonstrate that our integral, triple-porosity model provides an effective approach for the interpretation and prediction of gas transport and sorption behavior during loading and production experiments on shale cores under variable net-stress conditions.In summary, our work combines measurements and modeling of mass transfer and sorption in shales at different scales to validate a characterization approach that facilitates an improved understanding of shale gas production. Furthermore, the triple-porosity model utilized in our work defines a potential pathway for the translation of laboratory-scale experimentation to larger-scale applications.

Influence of Natural Aging on the Moisture Sorption Behaviour of Wooden Structural Components

A greater understanding of moisture sorption behaviour of aged wooden structural components, which has a close relationship with dimensional stability, is required to effectively evaluate and preserve historical artefacts. This study focused on the effects of aging on Baotou beam samples from a Chinese historical wooden building. An analysis of the sorption isotherms and hysteresis loops of a naturally aged, decayed sample (AOS), an aged sound sample (AIS), and a reference sample (RS), using classical sorption isotherm models revealed that the moisture sorption behaviour of samples from the same growth ring in a Baotou beam can differ significantly. AOS showed higher hygroscopicity than AIS, and both these samples were more hygroscopic than RS. Furthermore, the mono/multilayer moisture contents of AOS were always higher than those of AIS and RS. In addition, Fourier transform infrared, second-derivative infrared, and two-dimensional correlation infrared spectroscopy were used to investigate chemical changes in the samples. The relative hemicellulose and lignin contents of the samples changed significantly with wood aging. Furthermore, AOS exhibited the highest calcium oxalate content, which may be associated with fungal infections. Overall, these results provide valuable insights into the effects of aging on wood samples and the dimensional stability of timber structures, which could inform future research on methods for the preservation or restoration of aging timber structures.

Measuring Water Vapor Sorption Hysteresis of Cement Paste through an Optical Fiber Sensor

Water vapor sorption is a powerful tool for the analysis of cement paste, one of the most used substances by mankind. The monitoring of cementitious materials is fundamental for the improvement of infrastructure resilience, which has a deep impact on the economy, the environment, and on society. In this work, a multimode fiber was embedded in cement paste for real-time monitoring of cement paste water vapor sorption. Changes in the reflected light intensity due to the build-up of water in the cement paste’s pores were exploited for this purpose. The sample was 7-day moist cured, and the relative humidity was controlled between 8.9% and 97.6%. Reflected light intensity was converted into a specific surface area of cement paste (133 m2/g) and thickness of water through the Brunauer-Emmett-Teller (BET) method and into a pore size distribution through the Barret-Joyner-Halenda (BJH) method. The results achieved through reflected light intensity agree with those found in the literature, validating the usage of this setup for the monitoring of water vapor sorption, breaking away from standard gravimetric measurements.

Water vapor sorption characteristics and hysteresis of earlywood and latewood within the same growth ring of Catalpa bungei

Water vapor sorption characteristics and hysteresis of earlywood and latewood within the same growth ring of Catalpa bungei

Effects of viscoelasticity on moisture sorption of maltodextrins

By means of a physically-based drying model we argue that hysteresis in moisture sorption of food materials can be explained by viscoelastic relaxation effects. The model is applied to maltodextrins, for which we have recently determined their rheology for conditions approaching the glassy state, as well as their moisture diffusion coefficients (which is shown to follow our earlier model for moisture diffusion). For these maltodextrins moisture sorption has been performed using the Dynamic Vapour Sorption (DVS) method. After an update of the earlier (sub)model for moisture diffusion with insights from aerosol drying, the model is shown to give reasonable predictions of the DVS experiments, which clearly exhibit the hysteresis in moisture sorption. The model was fitted to DVS data of four maltodextrins, differing in their DE-values. The independently determined fitting parameters showed a high degree consistency amongst the four maltodextrins, and they were close to some parameter values determined experimentally with rheology measurements. Via a parameter study we have performed a rough sensitivity study, showing significant effects of all model parameter. All the results of this study together makes us quite confident that viscoelastic relaxation effects is indeed the cause of hysteresis in moisture sorption, as has been argued earlier for solvent sorption of synthetic polymers.