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Coal-water interactions have profound influences on gas extraction from coal and coal utilization. Experimental measurements on three coals using X-ray photoelectron spectroscopy (XPS), low-temperature nitrogen adsorption and dynamic water vapor sorption (DVS) were conducted. A mechanism-based isotherm model was proposed to estimate the water vapor uptake at various relative humidities, which is well validated with the DVS data. The validated isotherm model of sorption was further used to derive the isosteric heat of water vapor sorption. The specific surface area of coal pores is not the determining parameter that controls water vapor sorption at least during the primary adsorption stage. Oxidation degree dominates the primary adsorption, and which togethering with the cumulative pore volume determine the secondary adsorption. Higher temperature has limited effects on primary adsorption process.The isosteric heat of water adsorption decreases as water vapor uptake increases, which is found to be close to the latent heat of bulk water condensation at higher relative humidity. The results confirmed that the primary adsorption is controlled by the stronger bonding energy while the interaction energy between water molecules during secondary adsorption stage is relatively weak. However, the thermodynamics of coal-water interactions are complicated since the internal bonding interactions within the coal are disrupted at the same time as new bonding interactions take place within water molecules. Coal has a shrinkage/swelling colloidal structure with moisture loss/gain and it may exhibit collapse behavior with some collapses irreversible as a function of relative humidity, which further plays a significant role in determining moisture retention.

Clarification of the molecular mechanism underlying the interaction of coal with CH4, CO2, and H2 O molecules is the basis for an in-depth understanding of the states of fluid in coal and fluid-induced coal swelling/contraction. In terms of instrumental analysis, molecular simulation technology based on molecular mechanics/dynamics and quantum chemistry is a powerful tool for revealing the relationship between the structure and properties of a substance and understanding the interaction mechanisms of physical-chemical systems. In this study, the giant canonical ensemble Monte Carlo（GCMC） and molecular dynamics（MD） methods were applied to investigate the adsorption behavior of a Yanzhou coal model（C222H185N3O17S5）. We explored the adsorption amounts of CH4, CO2, and H2 O onto Yanzhou coal, the adsorption conformation, and the impact of oxygen-containing functional groups. Furthermore, we revealed the different adsorption mechanisms of the three substances using isosteric heat of adsorption and energy change data.（1） The adsorption isotherms of the mono-component CH4, CO2, and H2 O were consistent with the Langmuir model, and their adsorption amounts showed an order of CH4CO2〉CH4. In addition, at higher temperatures, the isosteric heat of adsorption decreased; pressure had no significant effect on the heat of adsorption.（3） CH4 molecules displayed an aggregated distribution in the pores, whereas CO2 molecules were cross arranged in pairs. Regarding H2 O molecules, under the influence of hydrogen bonds, the O atom pointed to surrounding H2 O molecules or the H atoms of coal molecules in a regular pattern. The intermolecular distances of the three substances were 0.421, 0.553, and 0.290 nm, respectively. The radial distribution function（RDF） analysis showed that H2 O molecules were arranged in the most compact fashion, forming a tight molecular layer.（4） H2 O molecules showed a significantly stratified distribution around oxygen-containing functional groups on the coal surface, and the bonding strength showed a descending order of hydroxyl〉 carboxyl〉carbonyl. In contrast, CO2 and CH4 showed only slightly stratified distributions.（5） After the adsorption of CH4, CO2, and H2 O, the total energy, the energy of valence electrons, and the non-bonding interaction of the system in the Yanzhou coal model all decreased. The results regarding the decrease in the total energy of the system indicated an order of H2O〉CO2〉CH4 in terms of the adsorption priority of the Yanzhou coal model. The results regarding the decrease in the energy of valence electrons showed that under certain geological conditions, a pressure-induced “coal strain” could lead to a structural rearrangement during the interaction of coal with fluid to form a more stable conformation, which might be the molecular mechanism of coal swelling resulting from the interaction between fluid and coal. An analysis of the contribution of Van der Waals forces, electrostatic interactions and hydrogen bonds to the decrease in non-bonding interactions revealed the mechanism underlying the interactions between coal molecules and the three substances. The interaction between coal molecules and CH4 consisted of typical physical adsorption, whereas that between coal molecules and CO2 consisted mainly of physical adsorption combined with weak chemical adsorption. The interaction between coal molecules and H2 O is physical and chemical.

Simulation and design of adsorptive separation units demand accurate estimation of thermodynamic properties. Isosteric heat of adsorption as calculated from generalized Langmuir (gL) isotherm coupled with Clausius–Clapeyron expression for pure component and mixed-gas adsorption equilibria is presented in this work. The estimated isosteric heat of adsorption as functions of surface loading and composition is validated against the experimental data for various adsorption systems. Furthermore, the gL results are compared against classical Langmuir (cL) and Toth isotherm for pure components and with Ideal Adsorbed Solution Theory (IAST) for mixed-gas adsorption equilibria. The comparison highlights that gL outperforms cL and Toth for pure component adsorption and IAST for mixed-gas adsorption, and gL reliably captures the loading dependence and the composition dependence for isosteric heat of adsorption.

Heterosubstitution is widely used to control the surface properties of graphene materials. The knowledge of the mechanism of organic solvent vapour sorption on doped graphene materials is necessary for development of air purification technologies, volatile organic compounds sensors, metal-free catalysis and for many other applications. The effect of N, S and Si doping and oxidative functionalization of few-layer graphene nanoflakes on the adsorption of organic solvent vapours was measured. The nanoflakes were also analyzed by TEM, XPS, Raman spectroscopy and low-temperature nitrogen physisorption. Special attention was paid to the dependence of the isosteric heat of adsorption on the surface coverage for various adsorbate-adsorbent pairs, which carry information about the energy inhomogeneity of the surface, the hierarchy of adsorbate-adsorbate, adsorbate-basal plane and adsorbate-functional groups interactions, and the mechanism of adsorption. This dependence for the hexane sorption can be used to detect hydrophilic groups on the surface, and to compare the degree of curvature of graphene layers in different heterosubstituted graphene materials. Graphical Abstract

Metal-organic frameworks (MOFs) are a class of porous coordination polymers constructed from co-ordinately binding metals and organic linkers. Aluminium fumarate, a microporous MOF composed of aluminium and fumaric acid, has a high affinity toward water vapor adsorption. The adsorption process in such porous materials could be featured for cooling by harnessing thermal energy, reducing the need for an energy-intensive vapor compression refrigeration system. The thermodynamic property field analysis is crucial for calculating the adsorption cooling system’s energetic performance. In this work, the thermodynamic property fields of pristine aluminium fumarate and nickel and cobalt-doped aluminium fumarates were analyzed, and the results were compared from the viewpoint of adsorption cooling application. The water adsorption isotherms on these samples were correlated with the Sun and Chakraborty and the Universal models. Thermodynamic properties, isosteric heat of adsorption, and specific heat capacity of the MOF/water pairs were investigated, and results were analyzed with respect to the adsorbate uptake. The performance parameters, specific cooling effect, and coefficient of performance were studied and compared for the samples. Nickle and cobalt-doped aluminium fumarates have presented a higher specific cooling effect than the pristine MOF. This analysis provides crucial findings contributing to design practical MOF/water-based adsorption cooling systems.

To evaluate the storage stability of flours from Rhynchophorus phoenicis and Imbrasia truncata larvae obtained by freeze-drying, their moisture adsorption isotherms have been determined at 20, 30 and 40 °C and their thermal properties explored by differential scanning calorimetry (DSC). DSC evidenced reversible transitions attributed to lipid melting/crystallization between − 60 and 90 °C. The GAB model was chosen to model adsorption isotherms. It evidenced 2 and 3 water compartments in R. phoenicis and I. truncata flours, respectively. Adsorption isotherm of R. phoenicis is type III at 20 and 30 °C, while that of I. truncata is type II at 20, 30 and 40 °C. GAB model also allowed calculating flour monolayer moisture contents (Mo ≤ 5.6 g/100 g dry matter (DM)). Net isosteric heat (qst) was evaluated. q st decreases with increase of water content and was higher for the flour of I. truncata larvae (from 8571 to 503 J/mol; 2,5 to 20 g/100 g DM) than that of R. phoenicis larvae (from 1750 to 124 J/mol; 5 to 30 g/100 g DM). Finally, the maximum storage times of the insect flours under typical packaging and storage conditions were estimated according to the Heiss and Eichner model. Highest for the flour of I. truncata , q st remained however moderate indicating that the insects can be dried without important energy supply. The estimated storage time of R. phoenicis larvae and I. truncata flours (3 g/100 g DM), stored at 20 °C in polyethylene bags, could reach 263 (8 months and 19 days) and 116 days (3 months and 24 days), respectively. These results provide valuable insights into the stability and potential applications insect flour in the food processing industry. This information could help in determining suitable packaging methods and storage conditions to maintain the quality and shelf life of products containing these flours to set safety and quality standards for such products.

The stoichiometry of the components of hexacyanoferrate materials affecting their final porosity properties and applications in CO2 capture is an issue that is rarely studied. In this work, the effect that stoichiometry of all element components and oxidation states of transition metals has on the structures of mesoporous K or Na-cobalt hexacyanoferrates (CoHCFs) and CO2 removal is reported. A series of CoHCFs model systems are synthesized using the co-precipitation method with varying amounts of Co ions. CoHCFs are characterized by N2 adsorption, TGA, FTIR-ATR, XRD, and XPS. N2 adsorption results reveal a more developed external surface area (72.69–172.18 m2/g) generated in samples containing mixtures of K+/Fe2+/Fe3+ ions (system III) compared to samples with Na+/Fe2+ ions (systems I, II). TGA results show that the porous structure of CoHCFs is affected by Fe and Co ions oxidation states, the number of water molecules, and alkali ions. The formation of two crystalline cells (FCC and triclinic) is confirmed by XRD results. Fe and Co oxidation states are authenticated by XPS and allow for the confirmation of charges involved in the stabilization of CoCHFs. CO2 removal capacities (3.04 mmol/g) are comparable with other materials reported. CO2 adsorption kinetics is fast (3–6 s), making CoHCFs attractive for continuous operations. Qst (24.3 kJ/mol) reveals a physical adsorption process. Regeneration effectiveness for adsorption/desorption cycles indicates ~1.6% loss and selectivity (~47) for gas mixtures (CO2:N2 = 15:85). The results of this study demonstrate that the CoHCFs have practical implications in the potential use of CO2 capture and flue gas separations.

The isosteric heat of adsorption (IHA) is one of the key thermodynamic variables for evaluating the interaction between shale and methane, which is rarely studied especially under high pressure. In this work, we conducted methane adsorption experiments at pressures up to 30 MPa and different temperatures on shale samples collected from Longmaxi formation in Sichuan Basin, China. Based on the definition of IHA and Langmuir adsorption model, we proposed a new method to analyze the IHA of methane on shale under four conditions. The calculated results show that the commonly used Clausius–Clapeyron equation overestimates the true isosteric heat of shale, especially under high pressure. IHA under four conditions yield a fixed order as qst,i-va > qst,r-va > qst,i+va > qst,r+va, indicating both the real gas behavior and the adsorbed-phase volume have a negative influence on it, and the effect of adsorbed-phase volume is dominant. Moreover, IHA at zero coverage ( q st 0 ) in Henry region determined by linear fitting can be regarded as a maximum value in the above four cases, which is independent of pressure and temperature. Therefore, q st 0 can be used as a unique descriptor to evaluate the adsorption affinity of the shale. This work modified the method to obtain the true IHA of supercritical methane on shale more accurately, which lays the foundation for future investigations of the thermodynamics and heat transfer characteristics of the interaction between high pressure methane and shale.

Thermal effects accompanying gas sorption on micro- and mesoporous materials provide unique insights into the type, course, and efficiency of sorption. In this study, metal-organic frameworks (MOFs) with different topologies and chemical structures were synthesized and investigated: HKUST-1, Ni-MOF-74, UiO-66, and MIL-140A. These MOFs were characterized structurally and sorptively with respect to selected greenhouse gases (GHGs). Sorption capacities for CO2 and CH4 were determined at several temperatures and measurement pressures, and the maximum sorption capacity was determined using the Langmuir-Freundlich model. Thermal effects accompanying adsorption were quantified through the isosteric heat of adsorption parameter. For each MOF, the values of isosteric heat of adsorption were higher for CO2 than for CH4. The values of this parameter was determined in the following order: HKUST-1 > Ni-MOF-74 > UiO-66 > MIL-140A. Energy homogeneity of the adsorbent surface was observed in nearly all cases, except for UiO-66 during CO2 adsorption. Changes in the determined isosteric heat of adsorption of CO2 with increasing sorption capacity were in the range of 5-15 kJ/mol, while for CH4 they ranged from 1.4 to 17 kJ/mol, respectively. The level of thermal selectivity of CO2 over CH4 was determined in the following order: UiO-66 (1.9) > Ni-MOF-64 (1.7) > MIL-140A (1.5) > HKUST-1 (1.1).

Groundwater with increased ammonia concentration is a constant concern regarding the preparation of drinking water. The affinity of ammonia to be adsorbed on the surface of different solid materials significantly influences the selection of its removal process and has been the motivation for this investigation. Crystal-Right(TM) (CR-100) was used for the removal of ammonia from aqueous solution in batch adsorption procedure. The kinetics of adsorption followed the pseudo-second-order model. The Elovich model suggested that chemisorption rate decreased with the temperature increase. The liquid film diffusion and intra-particle diffusion models revealed that heterogeneous adsorbent surface energy had a particularly pronounced impact on the overall mass transfer rate. The Arrhenius and Eyring's equations suggested spontaneous and endothermic nature of complex adsorption/ion exchange removal process. The isosteric heat of adsorption revealed that with the increase in surface loading lateral interactions between the adsorbed molecules occurred. Keywords: groundwater treatment, synthetic mesoporous adsorbent, adsorption, isosteric heat of adsorption.