Slope Of Isotherm Research Articles

Facile preparation and study of supramolecular architecture of an efficient nanocomposite LB film AHSM/SA based on azo-functionalized hockey stick-shaped mesogen at air-water and air-solid interface

Facile preparation and study of supramolecular architecture of an efficient nanocomposite LB film AHSM/SA based on azo-functionalized hockey stick-shaped mesogen at air-water and air-solid interface

Coverage, repulsion, and reactivity of hydrogen on High-Entropy alloys

Coverage, repulsion, and reactivity of hydrogen on High-Entropy alloys

Adsorption of Diffusing Tracers, Apparent Tortuosity, and Application to Mesoporous Silica.

The apparent tortuosity due to adsorption of diffusing tracers in a porous material is determined by a scaling approach and is used to analyze recent data on LiCl and alkane diffusion in mesoporous silica. The slope of the adsorption isotherm at small loadings is written as β = qA/qG, where qA is the adsorption-desorption ratio and qG = ϵ/(as) - 1 is a geometrical factor depending on the range a of the tracer-wall interaction, the porosity ϵ, and the specific surface area s. The adsorption leads to a decrease of effective diffusion coefficient, which is quantified by multiplying the geometrical tortuosity factor τgeom by an apparent tortuosity factor τapp. In wide pores or when the adsorption barrier is high, τapp = β + 1, as obtained in previous works, but in narrow pores there is an additional contribution from frequent adsorption-desorption transitions. These results are obtained in media with parallel pores of constant cross sections, where the ratio between the effective pore width ϵ/s and the actual width is ≈0.25. Applications to mesoporous silica samples are justified by the small deviations from this ideal ratio. In the analysis of alkane self-diffusion data, the fractions of adsorbed molecules predicted in a recent theoretical work are used to estimate τgeom of the silica samples, which is ≫1 only in the sample with the narrowest pores (nominal 3 nm). The application of the model to Li+ ion diffusion leads to similar values of τgeom and to a difference of energy barriers of desorption and adsorption for those ions of ∼0.06 eV. Comparatively, alkane self-diffusion provides the correct order of magnitude of τgeom, with adsorption playing a less important role, whereas adsorption effects on Li+ diffusion are much more important.

A novel bidentate diamide ligand DODQ for the separation of uranium and rare earth ions in nitric acid medium

A novel bidentate diamide ligand DODQ for the separation of uranium and rare earth ions in nitric acid medium

Energetic and exergetic analysis of a transcritical CO2 air-source heat pump water heating system in the cold region

Energetic and exergetic analysis of a transcritical CO2 air-source heat pump water heating system in the cold region

Isothermal Dual-Phase Flow Modeling to Assess the Impact of Gas Collection on Geotechnical and Hydraulic Performance of Landfills.

Liquid addition to landfilled municipal solid waste (MSW) is a practice employed to accelerate the biodegradation of the organic fraction of MSW and ensuing gas generation. Pore landfill gas (LFG) and leachate pressure from the added moisture and enhanced gas generation are expected to impact the geotechnical stability of landfill slopes. The impact of moisture addition and gas collection on the stability of landfills was numerically modeled using transient isothermal dual-phase flow and slope stability modeling. The temporal variation in the factor of safety (FS) for slope stability analysis was estimated for the simultaneous flow of LFG and leachate with and without gas collection and leachate recirculation for varying LFG generation rates and waste moisture contents. A significant decline in the FS for landfill slope stability was observed when recirculating leachate without active gas collection. Even without pressurized leachate recirculation, a significant decline in the FS value was observed for landfills with relatively high in situ moisture content without active gas collection. In some modeled scenarios without LFG collection, the FS value was lower than 1. The analysis suggests that the landfill side slope stability analysis should incorporate LFG generation and the resultant pressure for landfills containing high-moisture-content waste and for the landfill with pressurized leachate recirculation. The analysis suggests that an efficient gas collection system plays a critical role in the geotechnical stability of the slope of wet landfills and the performance of leachate recirculation trenches.

Surrounding water vapor induced diffusion and physisorption of water within thermoplastic polyurethane TPU samples: A critical analysis of DVS data

In this paper, experimental characterization by dynamic vapor sorption (DVS) experiments on thermoplastic polyurethane (TPU) samples is presented. Experiments were conducted at different constant temperatures – at 15, 25, and 35 degrees C – giving access to the sorption isotherm showing almost no temperature dependency. As the specimens were prepared with a defined geometry (disc’ with different thicknesses from 600 to 1600 μm and a diameter of 30 mm), the recorded mass history in response to a quasi-instantaneous change of the sample-enclosing humidity was employed to backcalculate diffusivity in narrow ranges for the prescribed externally assigned relative humidities, with a step-wise increase (or decrease) of ten percent. The backcalculated diffusion coefficients show dependency on (i) the temperature what is well described in Arrhenius plots and (ii) the relative humidity range. The influence of sample thickness is marginal, indicating that the surface resistance to mass transfer, as quantified by the Biot number, is negligible when interpreting DVS data presented in this paper. Furthermore, the order of magnitude of the backcalculated diffusion coefficients and their temperature dependency in terms of determined activation energies is discussed, depending on whether the physi-sorbed water content within the polymer network or the (externally) assigned water vapor content is employed as potential/state variable for the mathematical description of the diffusion process (gradients of the state variable represent the driving force of the diffusion process). When water vapor content is employed, the slope of the sorption isotherm has to be considered in the diffusion analysis.

Sorption Characteristic of Thermally Modified Wood at Varying Relative Humidity

Thermal modification (TM) is commonly used for improving the performance of wood under varying environmental conditions. The effect of TM on the hygroscopic properties of wood has been studied extensively; however, the sorption mechanism and the states of water of thermally modified wood (TMW) at varying relative humidity (RH) is limited. In this work, Douglas fir was modified at 180 °C, 200 °C and 220 °C for a duration of 2 h and the Hailwood–Horrobin model and NMR relaxometry were used after specimens were conditioned at eight different RHs. The results showed that TM inhibited monolayer and polylayer moisture sorption with increasing modification temperatures in all RHs. The lower slope of the sorption isotherms in TMW decreased compared with the control, indicating that the TM increased the hygroscopical stability of wood. The T2 distribution indicated that no free water was observed in the hygroscopic moisture range. The mobility of water molecules in the cell walls was decreased by TM intensity and increased by increasing RH.

Modeling of type II high-resolution sorption isotherms: Evaluation of different approaches

Several classical sorption isotherm equations were fitted to experimental high-resolution data for type II multilayer isotherms. Both the models and the experimental data (sorption of Ar (87 K), N2 (77 K), H2O (303 K), n-pentane (298 K), neopentane (273 K) on macroporous silica are taken from the literature. Further data include N2 sorption on nonporous functionalized silica and α-alumina. The following equations are tested: Brunauer-Emmett-Teller (BET), its modification by Anderson, Aranovich, the ζ-isotherm, Harkins-Jura, Frenkel-Halsey-Hill (FHH), that of de Boer and Zwikker manifesting itself in later work of Fuller, Condon, and Adolphs, the dual-site Langmuir equation with monolayer clustering recently presented by Calzaferri et al., and at last the general cluster sorption isotherm (GCSI, Micropor. Mesopor. Mater. 316 (2021) 110909). The GCSI describes all experimental data with high accuracy, not only for homogeneous but also for heterogeneous surfaces with a Gaussian energy distribution. All other models fail more or less, depending on the initial slope of the experimental isotherm. Besides theoretical considerations, the quality of each isotherm modeling is evaluated by the pure statistical Akaike criterion.

Thermodynamics of grain boundary adsorption in binary systems with limited solubility

Abstract A thermodynamic analysis of grain boundary adsorption is presented. From the thermodynamic model developed it follows that in binary polycrystals with identical grain boundaries at some conditions three phases can coexist in equilibrium below the solidus temperature. The model predicts that two solid solutions in the grain and in the grain boundaries coexist below some critical value, X 2 * $X_2^*$ , of solute concentration in the grain. At X 2 * $X_2^*$ , a compositional phase transition occurs in the GB which is accompanied by a gap in the adsorption isotherm, a change of the slope of the GB tension isotherm, and the formation of a new 2D grain boundary phase. It is shown for three systems (Cu–Sb, Fe –P, and Sn–Bi) that the compositions of the GB phase and the phase in the grain are in close agreement with the predictions.

Adsorption, separation, and purification of cyclosporine A using reversed-phase liquid chromatography

环孢素A(cyclosporine A, CsA)是由11个氨基酸组成的中性环状多肽,是临床拮抗器官和组织移植后排异反应的首选药物。高效液相色谱法广泛应用于CsA的分离分析,开展CsA色谱行为的研究是使用制备高效液相色谱纯化CsA的关键。该文首先在C18固定相上比较了CsA在甲醇-水和乙腈-水两种流动相体系中的保留行为,结果表明其保留时间对有机相比例变化比较敏感。控制甲醇比例在84%~88%,或者乙腈比例在75%~85%, CsA的保留因子(k)在3~7范围内。考察了上样量对CsA峰形的影响。随着上样量增加,在两种流动相体系中,CsA的峰形都由对称开始变得拖尾,保留时间前移。因此在进行CsA纯化时,需要特别注意前杂的去除情况。然后采用吸附等温线描述CsA的保留行为,当流动相中CsA的质量浓度较低时,有机相比例对溶质在固定相上的吸附量影响并不明显。随着溶质的质量浓度增加至0.5 g/L以上,有机相比例降低有助于提高CsA在固定相上的吸附量。和甲醇-水体系相比,在乙腈-水体系中固定相对溶质有更大的吸附容量。用模型对CsA的等温吸附曲线拟合,在甲醇-水体系中符合Langmuir模型,在乙腈-水体系中为Moreau模型。由模型参数可知在两种体系下,CsA在C18固定相上均为单层吸附,区别在于乙腈-水体系中CsA会产生较大的分子间作用力。最后,实验采用0~60 min 65%~75%乙腈、60~80 min 75%乙腈的条件开展了环孢素A纯化的探索实验,可将CsA的杂质控制在0.2%以下。本研究结果对采用制备高效液相色谱纯化CsA具有指导意义。

Desorption Isotherms for Poly- and Perfluoroalkyl Substances in Soil Collected from an Aqueous Film-Forming Foam Source Area

Bench-scale experiments were performed to evaluate poly- and perfluoroalkyl substance (PFAS) desorption from vadose zone soils collected at a site historically impacted with aqueous film-forming foam (AFFF). A sequential dilution batch method was employed to obtain PFAS desorption isotherms from a shallow surface soil [0.03 to 0.9 m below ground surface (bgs)] and from a deep soil (0.9–2.4 m bgs). Results showed that the desorption isotherms were reasonably described by a linear model, and that a fraction of the soil-bound PFAS mass was not readily desorbed (or, non-labile); the recalcitrance of this non-labile fraction was evaluated on a subset of samples and shown to persist for up to 9 months. The non-labile fraction of PFAS mass sorbed to the soil (non-labile PFAS sorbed mass divided by the total PFAS sorbed mass) ranged from 0.17 g g−1 for perfluorohexane sulfonamide in the deep soil to 0.87 g g−1 for 8∶2 fluorotelomer sulfonate in the shallow soil, and generally increased with the PFAS organic carbon:water partitioning coefficient (Koc). The fraction of the PFAS within the non-labile fraction was generally greater in the shallow soil than in the deep soil, likely due to the elevated organic carbon content of the shallow soil. The slopes of the desorption isotherms associated with the readily-desorbable (labile) PFAS fraction for the shallow soil were within the ranges predicted by Koc-based models derived from adsorption data. Overall, results for the soils studied herein suggest that much of the PFAS mass present in the soil likely is not readily available for leaching into infiltrating waters. Such information could provide useful insight for developing PFAS soil cleanup standards.

Effects of increasing water activity on the relationship between water vapor sorption and clay content

AbstractThe dependence of the relationship between hygroscopic water content (θh) and clay content on water activity is not well understood. Here, we determined the correlation coefficients between θh (or the slope of soil water vapor adsorption isotherms, Svai) and clay content at nine water activity levels (i.e., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9) and investigated the evolution of correlation coefficients with increasing water activity for 65 soils with mixed and illitic clay mineralogy. The correlation coefficient between θh0.1 (water content at a water activity of 0.1) and clay content was the lowest (.82) due to the differences in soil‐specific hydration processes. At the water activity range from 0.1 to 0.6, the Svai showed stronger correlations (r = .91–.93) with clay content than θh0.1 because the multilayer sorption controlled by van der Waals force is related to clay content. When water activity increased from 0.1 to 0.6, the observed strong correlation between Svai and clay content resulted in an increase of correlation coefficient between θh and clay content from .82 to .96. Compared with the correlation (r = .96) between θh and clay content at the beginning of condensation process, a weaker correlation (r = .87–.92) between Svai and clay content was observed during condensation process, which led to a slight strengthening of the correlation between θh and clay content at high water activities (>0.6). This was explained by the different clay particle properties and water activity thresholds for initiation of condensation.

Estimation of soil specific surface area from adsorbed soil water content

AbstractThe adsorbed water content is an attractive predictor for estimation of soil specific surface area (SSA) as its measurement is less laborious and more cost effective than standard laboratory techniques. We analysed the effects of total specific surface area (SSAtot), external specific surface area (SSAex) and internal specific surface area (SSAin) on water vapour sorption on 21 soil samples, and proposed models for estimating SSAex, SSAtot and SSAin from organic carbon content and the slope of soil water vapour sorption isotherm (SL0.5) and water content (WC0.5) at a water activity of 0.5. The results indicated that the variation of correlation coefficients between water content change at 0.05 water activity interval (WCC0.05) and SSAtot with water activity was mainly due to the differences in water vapour adsorption in interlayer spaces at different water activity levels. Furthermore, in the soil water content range from ~0.001 to ~0.03 g g−1 (within the water activity range from ~0.45 to ~0.75), water vapour adsorption was related closely to SSAex. Cross‐validation results on estimated SSAex, SSAtot and SSAin of the 21 samples produced root mean square error (RMSE) values less than 9.39 m2 g−1 and Nash‐Sutcliffe model efficiency coefficients (E) greater than 0.93, suggesting that the proposed models provided reasonable estimates of SSA components. Thus, soil water vapour adsorption data can be applied to simultaneously estimate SSAex, SSAtot and SSAin. Variation of correlation between WCC0.05 and SSAtot with water activity depended on SSAin. Soil water vapour sorption is related closely to SSAex at water activities from ~0.45 to ~0.75. The proposed models yield reasonable estimates of SSAtot, SSAex and SSAin. Adsorbed water content can be used as a predictor for SSA estimation.Highlights Variation of correlation between WCC0.05 and SSAtot with water activity depended on SSAin. Soil water vapor sorption relates closely to SSAex at water activities from ~0.45 to ~0.75. The proposed models yield reasonable estimates of SSAtot, SSAex, and SSAin. Adsorbed water content can be used as a predictor for SSA estimation.

Adsorption-Induced and Thermal Deformation of Microporous Carbon Adsorbent upon n-Octane Adsorption

Relative linear adsorption-induced deformation of granules of AR-V microporous carbon adsorbent has been measured upon n-octane adsorption at pressures p of 1 Pa to 1.6 kPa and temperatures T = 273, 293, 313, 353, and 393 K. At p > 200 Pa, the adsorption-induced deformation is positive and grows with p throughout the considered temperature range. Under isobaric conditions, the adsorption-induced deformation and the slope of deformation isotherms increase as T decreases. At p 350 K, the adsorbent expands throughout the pressure range. Molecular dynamics simulation has been employed to study the structure of n-octane adsorption associates in model slit-like micropores having a width corresponding to the effective size of micropores in AR-V adsorbent calculated in terms of the theory of volume filling of micropores. The structure of the adsorption associates has been related to the characteristic features of the adsorption-induced deformation of AR-V adsorbent.

Selective adsorption of soil humic acid on binary systems containing kaolinite and goethite: Assessment of sorbent interactions

Inorganic colloids are ubiquitous in soils and coexist as simple mixtures or as strong associations of particles. The coexisting inorganic colloids with a variety of active sites can selectively adsorb humic substances and thus affect the availability and mobility of organic matter. To investigate the selective adsorption of organic matter by coexisting inorganic colloids, humic acid (JGHA) extracted from soil, a kaolinite and goethite synthetic association (KGA) and a kaolinite and goethite mixture (KGM) were prepared and studied. With the adsorption expressed in μmol m−2, the adsorption affinity of JGHA on KGA (initial slope of isotherms) was slightly higher than that on KGM, although KGM could adsorb more JGHA molecules at larger JGHA concentrations. At pH 4, JGHA was adsorbed on the kaolinite edges and goethite through electrostatic attraction and ligand exchange, and on the kaolinite siloxane plates through hydrophobic interaction. At pH 6 and 8, the adsorption occurred only on the kaolinite siloxane plates and goethite. The overall average adsorption Gibbs energies were moderately negative, and comprised a strongly negative average overall molar entropy and a negative average overall molar entropy contribution. Thus, overall JGHA adsorption on KGA and KGM was enthalpy controlled. The large exothermic enthalpy gains and entropy losses were a result of electrostatic attraction and ligand exchange. The entropy gains because of hydrophobic attraction between JGHA and the kaolinite siloxane plates are masked by the larger entropy loss of adsorption on the hydrophilic surfaces. The fractions of JGHA with molar mass >~12.9 kDa (1 Da = 1 g mol−1) were adsorbed selectively by KGM, whereas the fractions <~12.9 kDa were selectively adsorbed by KGA. High molar mass and hydrophobic fractions adsorb selectively on the kaolinite siloxane plates, whereas low molar mass fractions with hydrophilic groups adsorb selectively on goethite and the kaolinite edges.Highlights Selective adsorption behaviour of HA on binary systems containing kaolinite and goethite. High molar mass and hydrophobic HA fractions selectively adsorb on kaolinite siloxane plates. Low molar mass and hydrophilic HA fractions selectively adsorb on kaolinite edges and goethite. Binding affinity of HA to KGA is stronger than to KGM; mineral associations are more beneficial for fixing OM in soil.

Comparative Analysis of Sorption Isotherms for Wood Pellets and Solid Wood

Abstract.The published data on equilibrium moisture content vs. equilibrium relative humidity (EMC-ERH) for wood pellet do not cover the range of temperature and relative humidity to which a pellet is exposed to during its storage and handling. A few published EMC-ERH relations covering a wider range of temperatures and relative humidity are available for solid wood (lumber) and wood chips. The question is whether the data for solid wood is applicable to wood pellets. For this research, we examined the sorption isotherms of wood pellets and solid wood. The analysis shows that EMC for solid wood is higher than the EMC for wood pellet for a relative humidity larger than 30%. The slope of EMC-ERH isotherm for solid wood in the range of 30%-70% is slightly steeper than the slope of isotherm for wood pellet, indicating the pellet’s EMC is less sensitive to ERH when compared to EMC-ERH for solid wood. Keywords: EMC, ERH, Densified biomass, Equilibrium moisture content, Equilibrium relative humidity, Solid wood, Wood pellets.

Intrinsic relationship between Langmuir sorption volume and pressure for coal: Experimental and thermodynamic modeling study

Gas adsorption volume has long been recognized as an important parameter for coalbed methane (CBM) resource assessment as it determines the overall gas capacity of coal. As the industrial standard practice, Langmuir volume (VL) is used to describe the gas adsorption volume. Another important parameter, Langmuir pressure (PL), is typically overlooked because it does not directly relate to the resource estimation. However, PL defines the slope of the adsorption isotherm and the ability of a well to attain the critical desorption pressure in a significant reservoir volume, which is critical to plan the initial water depletion rate for a CBM well. Qualitatively, both VL and PL are related to the fractal pore structure of coal, but the intrinsic relationships among fractal pore structure, VL, and PL are not well studied and quantified due to the complex pore structure of coal. In this study, a series of experiments were conducted to measure the fractal dimensions of coal and their relationship to methane adsorption capacity. The thermodynamic model of the gas adsorption on heterogonous surfaces was revisited, and the theoretical models that correlate the fractal dimensions with the Langmuir constants were proposed. Applying the fractal theory, adsorption capacity (VL) is proportional to a power function of specific surface area and fractal dimension, and the slope of the regression line contains information on the molecular size of the adsorbed gas. We also found that PL is linearly correlated with sorption capacity, which is defined as a power function of total adsorption capacity (VL) and a heterogeneity factor (ν). This implies that PL is not independent of VL, instead, a positive correlation between VL and PL has been noted elsewhere (e.g., Pashin [1]). In the Black Warrior Basin, Langmuir volume is positively related to coal rank (Pashin, 2010; Kim, 1977) [1,2], and Langmuir pressure is inversely related to coal rank. It was also found that PL is negatively correlated with adsorption capacity and fractal dimension. A complex surface corresponds to a more energetic system, which results in an increase in the number of available adsorption sites and adsorption potential, which raises the value of VL and reduces the value of PL.

The effect of activation time on water sorption behavior of nitrogen-doped, physically activated, monolithic carbon for adsorption cooling

Abstract Monolithic, nitrogen-doped carbon sorbents were prepared from resorcinol-urea-formaldehyde resins and physically activated with CO2 for different activation times. The effect of the activation time on the water sorption behavior and the physicochemical properties were investigated. Longer activation times lead to a steeper slope of the water sorption isotherm and, due to a higher specific surface area and micropore volume, an increased water sorption capacity. It was found that, after physical activation for 3 h at 800 °C, the physically activated, nitrogen-doped carbon has a high surface area (>1000 m2/g) and a high water sorption capacity (50 wt%). In a miniaturized adsorption heat pump test stand, the best candidate material was assessed alongside commercial silica gel for reference. At a temperature swing from 90 °C → 50 °C, the CO2-activated carbon exhibits a maximal specific cooling power which is a factor of 1.7 higher in comparison with the reference silica gel (429 W/kg versus 255 W/kg). At a more applicable temperature swing, 60 °C → 30 °C, the CO2-activated carbon yields a specific cooling power 3.8 times higher than that of the silica gel reference (932 W/kg versus 240 W/kg).

Griffith’s postulate: Grand Canonical Monte Carlo approach for fracture mechanics of solids

Abstract A Grand Canonical Monte Carlo Approach (GCMC) is proposed for the fracture analysis of solids discretized as mass points and bond interactions. In contrast to classical load-driven fracture processes, the GCMC approach introduces an auxiliary field, the bond rupture potential μ , to which the system is subjected; in addition to changes in volume V and temperature T. In this μ VT-ensemble, bond isotherms that link the average number of bonds to the bond rupture potential ( N k - μ ) are obtained that carry critical information for fracture analysis. Specifically, the slope of the bond isotherm reflects bond fluctuations, permitting identification of (1) a fluctuation-based damage variable, and (2) the competition in energy fluctuations between the redistribution of strain energy induced by bond rupture, and the dissipation of the groundstate energy. Based on these fluctuations, it is shown that the GCMC-approach allows the identification of a critical bond energy release rate of material samples, when strain energy fluctuations equal groundstate energy fluctuations – much akin to Griffith’s 1921 stationarity postulate to “predicting the breaking loads of elastic solids”. This is illustrated by means of thermodynamic integration of bond isotherms to determine force-displacement curves, for both notched and unnotched homogeneous samples discretized by regular 2-D lattices with bonds exhibiting harmonic potentials.