Isosteric Heat Of Adsorption Research Articles

CO2 adsorption on carbonaceous materials obtained from forestry and urban waste materials: a comparative study.

The increasing emissions of gaseous pollutants of anthropogenic origin, such as carbon dioxide (CO2), which causes global warming, have raised great interest in developing and improving processes that allow their mitigation. Among them, adsorption on porous materials has been proposed as a sustainable alternative. This work presents a study of CO2 equilibrium adsorption at low temperatures (0, 10, and 20°C) over a wide range of low pressures, on activated carbon derived from Eucalyptus (ES) and Patula pine (PP) forest waste, and carbonaceous material derived from waste tires (WT). The precursors of these materials were previously prepared, and their physicochemical properties were characterized. ES and PP were thermochemically treated with phosphoric acid, and WT was oxidized with nitric acid. Additionally, these materials were used to obtain monoliths using uniaxial compaction techniques and different binding agents, with better results obtained with montmorillonite. A total of six adsorbent solids had their textural and chemical properties characterized and were tested for CO2 adsorption. The highest specific surface area (1405 m2g-1), and micropore properties were found for activated carbon derived from Eucalyptus whose highest adsorption capacity ranged from 2.27mmolg-1 (at 0°C and 100kPa) to 1.60mmolg-1 (at 20°C and 100kPa). The activated carbon monoliths presented the lowest CO2 adsorption capacities; however, the studied materials showed high potential for CO2 capture and storage applications at high pressures. The isosteric heats of adsorption were also estimated for all the materials and ranged from 16 to 45kJmol-1 at very low coverage explained by the energetic heterogeneity and weak repulsive interactions among adsorbed CO2 molecules.

A developed dual-site Langmuir model to represent the high-pressure methane adsorption and thermodynamic parameters in shale

Comprehending the mechanism of methane adsorption in shales is a crucial step towards optimizing the development of deep-buried shale gas. This is because the methane adsorbed in shale represents a significant proportion of the subsurface shale gas resource. To properly characterize the methane adsorption on shale, which exhibits diverse mineral compositions and multi-scale pore sizes, it is crucial to capture the energy heterogeneity of the adsorption sites. In this paper, a dual-site Langmuir model is proposed, which accounts for the temperature and pressure dependence of the density of the adsorbed phase. The model is applied to the isothermals of methane adsorption on shale, at pressures of up to 30 MPa and temperatures ranging from 40 to 100 °C. The results show that the proposed model can describe the adsorption behavior of methane on shale more accurately than conventional models, which assume a constant value for the density of adsorbed phase. Furthermore, the proposed model can be extrapolated to higher temperatures and pressures. Thermodynamic parameters were analyzed using correctly derived equations. The results indicate that the widely used, but incorrect, equation would underestimate the isosteric heat of adsorption. Neglecting the real gas behavior, volume of the adsorbed phase, and energy heterogeneity of the adsorption sites can lead to overestimation of the isosteric heat of adsorption. Furthermore, the isosteric heat evaluated from excess adsorption data can only be used to make a rough estimate of the real isosteric heat at very low pressure.

Prominent COF, g-C3N4, and Their Heterojunction Materials for Selective Photocatalytic CO2 Reduction

New heterojunction materials (HJs) were synthesized in-situ by molecularly bonding the monomers of a triazine-based covalent organic framework (bulk COF) on the template of exfoliated carbon nitride (g-C3N4). The photocatalysts reduced carbon dioxide to carbon monoxide in aqueous dispersions under UV irradiation. The g-C3N4 showed production of 6.50 μmol CO g−1 h−1 and the bulk COF of 2.77 μmol CO g−1 h−1. The CO yield was evaluated in sustainability photoreduction cycles and their CO2 uptake capacity and isosteric heat of adsorption were estimated. All the heterojunction photocatalysts obtained ameliorated CO production rates compared to the bulk COF. Finally, the influence of the Pt co-catalyst on the photocatalytic activities was determined without the addition of any sacrificial agent, and the COF:g-C3N4 heterojunction with the ratio of 1:10 was proven to be a photocatalytic system with an optimum and selective, CO yield of 7.56 μmol g−1 h−1.

Molecular Simulation of Adsorption and Diffusion of Methane and Ethane in Kaolinite Clay under Supercritical Conditions: Effects of Water and Temperature

Grand Canonical Monte Carlo (GCMC) simulation and Molecular Dynamics (MD) simulations were used to study the effects of temperature (310 K to 400 K), pressure (≤30 MPa) and water content (0 molecule/nm3 to 9 molecule/nm3) on the adsorption and diffusion behavior of CH4 and C2H6 in 3 nm kaolinite slit under supercritical conditions. The obtained adsorption capacity, isosteric adsorption heat, concentration distribution and diffusion coefficient were analyzed and compared. The simulation results show that the adsorption capacity of C2H6 is higher under low pressure conditions, and the adsorption capacity of CH4 is higher under high pressure conditions due to the small molecular radius and increased adsorption space. The addition of water molecules and the increase in temperature will reduce the adsorption capacity and isosteric adsorption heat of the two gases. We analyzed the changes in Langmuir volume and Langmuir pressure of the two gases under different temperature and water content conditions. The addition of water molecules and the increase in temperature will reduce the saturation adsorption capacity (which has a greater effect on C2H6) and the adsorption rate of the two gases in the kaolinite slit. The water molecules occupy the adsorption site of the gas molecules (limiting the diffusion of the gas molecules), which reduces the interaction between gas molecules and the wall surface, thus altering the distribution of the two gases in the slit. The increase in temperature will accelerate the oscillation of the gas molecules, increasing diffusion, and also leads to a reduction in the peak value of the adsorption peaks of the two gases.

Hydrocarbons (C8–C12) separation in porous metallocavitand M-PPX (M = Cu, Ag, Au): From computational insight

High throughput computational approach has been employed to investigate the adsorption and separation of C8–C12 hydrocarbons (HCs) on a tube-shaped metallocavitand, pillarplex (PPX). The Cu (I), Ag (I), and Au (I) seamed PPX and their HC complexes has been examined using density functional theory (DFT), proclaiming Cu-PPX has a higher binding affinity with the HCs whereas Ag-PPX is lower. The thermodynamic properties reveal the host–guest complex is stable at ambient condition. Noncovalent interaction (NCI) analysis shows the interaction of guests within the cavity of PPX is mainly attributed by Van der Waals type. The energy decomposition analysis (EDA) enunciates the percentage contribution of dispersion interaction (ΔEdisp) is 59–62%, the electrostatic (ΔEelct) and orbital (ΔEorb) terms have a moderate contribution towards the total binding energy. The Grand canonical Monte Carlo (GCMC) simulation manifests the Cu-PPX and Au-PPX are the ideal hosts with the optimum capacity to store HCs at ambient conditions. The octane uptake is 18.01, 17.50, and 25.31 cm3STP/g in Cu, Ag and Au-PPX and the uptake reduces upon increasing the HC chain length. The isosteric heat of adsorption (Qst) is corroborated with the computed DFT data at ambient setup. The ideal adsorption solution theory (IAST) claims the C8 selectivity in Cu, Ag and Au-PPX is optimum at 298 K and the increasing temperature from 298 K to 323 K, the selectivity of the C9 and C12 in Cu-PPX and Au-PPX, respectively is remarkable after the complete separation of C8. Hence Cu-PPX and Au-PPX is the potential candidate for industrial use to separate the heavy HCs.

Microstructure changes induced by adsorption/desorption of low rank coals and its desorption hysteresis mechanism

Adsorption/desorption behavior and its hysteresis phenomenon of coalbed methane (CBM) make a critical contribution to estimate CBM recovery. Hence, to investigate the adsorption/desorption mechanism of low rank coals, this study compared the adsorption/desorption characteristics of methane in different rank coals through isotherm adsorption/desorption experiments and then analyzed the changes in microstructure before and after adsorption/desorption. Thus, the coupling relationship among chemical structure, nanopores and gas adsorption/desorption and the desorption hysteresis mechanism for low rank coals were revealed. Results show that the isosteric adsorption heat and desorption hysteresis coefficient present a decreasing first and then increasing trend with coalification from isotherm adsorption/desorption curves and thermodynamic characteristics. Specially, for low rank coals, as the degree of thermal evolution increases, the desorption hysteresis coefficient increases from 0.27 to 0.39 during low metamorphism stage. Then, compared the nanopore structure distribution and microcrystalline structure characteristics before and after adsorption/desorption, methane adsorption/desorption behavior not only promotes the pore expansion effect of ultra-micropores, but also leads to a swelling effect of basic structure unit (BSU). Furthermore, it can be found that as the BSU increases, the specific surface area (SSA) and pore volume (PV) of nanopores in coal increase, which directly controls the adsorption space. Meanwhile, the adsorption/desorption behavior can also induce the BSU swelling to change nanopore structure distribution, especially micropores and ultra-micropores. Finally, concerning desorption hysteresis effect, its esssence can actually be explained by the energy difference and microstructure. All these findings would provide the theorical guidance for CBM development in low rank coals.

Adsorptive separation of CH4, H2, CO2, and N2 using fullerene pillared graphene nanocomposites: Insights from molecular simulations.

The adsorptive separation performances of fullerene pillared graphene nanocomposites (FPGNs) with tunable micro and meso porous morphology are investigated for the binary mixtures of CH4, H2, CO2 and N2 by using grand canonical Monte Carlo (GCMC) simulations. Different fullerene types are considered in designs as pillar to investigate the effects of porosity on the gas separation performances of FPGNs, and the GCMC simulations are performed for an equimolar binary mixture of CO2/H2, CO2/CH4, CO2/N2 and CH4/H2 inspired by industrial gas mixtures. It is found that CO2/N2, CO2/H2 and CH4/H2 selectivity of FPGNs are about 72, 410 and 145 at 298K and 1bar, which are higher than those for several adsorbent materials reported. Five different FPGN models which contain covalently bonded periodical fullerene and graphene units were constructed using C60, C180, C320, C540 and C720 fullerenes, followed by geometry optimization using Open Babel. All GCMC simulations of adsorption were performed in the RASPA. The adsorption isotherms of FPGNs for pure gases are comparatively examined, and their performances are discussed based on the pore structure and isosteric heat of adsorption. Then, the separation factors of FPGNs for equimolar binary mixtures of these gases are elucidated from the difference in the heat of adsorption and the adsorption selectivity.

Molecular Simulation Study Based on Adsorption of Gas (CO2,O2,CH4) on Coal

This study aimed to further explore the adsorption properties of different gases (CO2, O2, and CH4) on the coking coal surface by establishing a molecular model. Changes in the absolute adsorption capacity and the isosteric heat of adsorption of gases under different temperatures, pressures, and compositions were simulated using grand canonical Monte Carlo (GCMC) and molecular dynamics simulations. Interaction energy and energy distribution were used to analyze the adsorption behavior of gases, and the diffusion properties were investigated using the diffusion coefficient and diffusion activation energy. The absolute adsorption results fit well with the Langmuir–Freundlich model. The absolute adsorption capacity had a significant positive correlation with pressure and the corresponding mole fraction, and a significant negative correlation with temperature. The competitiveness, based on binary adsorption selectivity, was in the order of CO2 > O2 > CH4. The isosteric heat of adsorption of CH4 was slightly higher than that of O2, and that of CO2 was 1.49–1.64 times that of O2 and CH4. The isosteric heat of the adsorption of gases was also barely influenced by temperature and pressure. The interaction energy between CO2 and coal was greater than that of O2 or CH4, but the high pressure and high content were not conducive to the adsorption of O2 by CO2. The preferred adsorption site for CO2 was stronger than that for O2 and CH4, and its peak value negatively correlated with the molar fraction. The diffusion coefficient for single component gases initially increased and then decreased with increased pressure, showing a positive correlation with temperature. A close inverse correlation existed between diffusion activation energy and pressure. These results revealed the microscopic adsorption and diffusion regularities of CO2, O2, and CH4 in the coal model, indicating great significance in accurately predicting coal fires.

Air-Stable Cu(I) Metal-Organic Framework for Hydrogen Storage.

Metal-organic frameworks (MOFs) that contain open metal sites have the potential for storing hydrogen (H2) at ambient temperatures. In particular, Cu(I)-based MOFs demonstrate very high isosteric heats of adsorption for hydrogen relative to other reported MOFs with open metal sites. However, most of these Cu(I)-based MOFs are not stable in ambient conditions since the Cu(I) species display sensitivity toward moisture and can rapidly oxidize in air. As a result, researchers have focused on the synthesis of new air-stable Cu(I)-based materials for H2 storage. Here, we have developed a de novo synthetic strategy to generate a robust Cu(I)-based MOF, denoted as NU-2100, using a mixture of Cu/Zn precursors in which zinc acts as a catalyst to transform an intermediate MOF into NU-2100 without getting incorporated into the final MOF structure. NU-2100 is air-stable and displays one of the initial highest isosteric heats of adsorption (32 kJ/mol) with good hydrogen storage capability under ambient conditions (10.4 g/L, 233 K/100 bar to 296 K/5 bar). We further elucidated the H2 storage performance of NU-2100 using a combination of spectroscopic analysis and computational modeling studies. Overall, this new synthetic route may enable the design of additional stable Cu(I)-MOFs for next-generation hydrogen storage adsorbents at ambient temperatures.

Shaping of HKUST-1 via Extrusion for the Separation of CO2/CH4 in Biogas

HKUST-1 is a metal-organic framework (MOF) that is widely studied as an adsorbent for CO2 capture because of its high adsorption capacity and good CO2/CH4 selectivity. However, the numerous synthesis routes for HKUST-1 often result in the obtention of MOF in powder form, which limits its application in industry. Here, we report the shaping of HKUST-1 powder via the extrusion method with the usage of bio-sourced polylactic acid (PLA) as a binder. The characterization of the composite was determined by XRD, FTIR, TGA and SEM analyses. The specific surface area was determined from the N2 adsorption isotherm, whereas the gas adsorption capacities were investigated via measurements of CO2 and CH4 isotherms of up to 10 bar at ambient temperature. The material characterization reveals that the composite preserves HKUST-1’s crystalline structure, morphology and textural properties. Furthermore, CO2 and CH4 adsorption isotherms show that there is no degradation of gravimetric gas adsorption capacity after shaping and the composite yields a similar isosteric adsorption heat as pristine HKUST-1 powder. However, some trade-offs could be observed, as the composite exhibits a lower bulk density than pristine HKUST-1 powder and PLA has no impact on pristine HKUST-1’s moisture stability. Overall, this study demonstrates the possibility of shaping commercial HKUST-1 powder, using PLA as a binder, into a larger solid-state-form adsorbent that is suitable for the separation of CO2 from CH4 with a well-preserved pristine MOF gas-adsorption performance.

A computational investigation on the roles of binding affinity and pore size on CO2/N2 overall adsorption process performance of MOFs through modifying MIL-101 structure

To develop an appropriate metal-organic framework to capture CO2 from dry flue gas, understanding the roles of structural modifications, location of primary adsorption sites and underlying adsorption mechanisms is crucial. Herein, effects of type, position and concentration of nitrogen-containing functional groups and C/N-substituted ligands are investigated on overall CO2/N2 adsorption process performance and mechanism of pristine and metal-substituted MIL-101 MOFs. In this investigation, density functional theory computations, grand-canonical Monte-Carlo, and molecular dynamics simulations are applied. Taguchi-based overall evaluation criteria objective function is also used to assess the overall adsorption performances of these MIL-101 MOFs in terms of CO2 uptake capacity, CO2/N2 selectivity, isosteric heat of adsorption and mass transfer resistance. The PBE/DZVP computations resulted in the CO2-framework binding energies ranging from −3.85 to −21.01 kJ/mol implying an acid-base type of physisorption. A correlation is introduced to estimate the CO2 uptake capacity from binding affinity and pore diameter of these MIL-101 MOFs. Mechanistic investigations show that to enhance CO2 uptake capacity and CO2/N2 selectivity, functionalization of the linker ligands is more successful than functionalization of the open metal sites having strong interactions with CO2 molecules. Results also showed that the best possible scenario to improve the overall adsorption process performance of MIL-101 is to substitute the C atom(s) of the BDC ligands with the N atom(s), regardless of the central metal atom type. The comprehensive molecular design approach introduced in this work can be used as a methodology by scientists for the development of new MOFs for practical CO2 capture applications.

Analysis and Refinement of Host-Guest Interactions in Metal-Organic Frameworks.

ConspectusMetal-organic frameworks (MOFs) are a class of hybrid porous materials characterized by their periodic assembly using metal ions and organic ligands through coordination bonds. Their high crystallinity, extensive surface area, and adjustable pore sizes make them promising candidates for a wide array of applications. These include gas adsorption and separation, substrate binding, and catalysis, of relevance to tackling pressing global issues such as climate change, energy challenges, and pollution. In comparison to traditional porous materials such as zeolites and activated carbons, the design flexibility of organic ligands in MOFs, coupled with their orderly arrangement with associated metal centers, allows for the precise engineering of uniform pore environments. This unique feature enables a rich variety of interactions between the MOF host and adsorbed gas molecules, which are fundamental to understanding the observed uptake capacity and selectivity for target gas molecules and thus the overall performance of the material.In this Account, a data set for three-dimensional MOFs has been constructed based upon the structural analysis of host-guest interactions using the largest experimental database, the Cambridge Structural Database (CSD). A full screening was performed on structures with guest molecules of H2, C2H2, CO2, and SO2, and the relationship between the primary binding site, the isosteric heats of adsorption (Qst), and the adsorption uptake was extracted and established. We review the methodologies to refine host-guest interactions based primarily on our studies on the host-guest chemistry of MOFs. The methods include ligand functionalization, variation of metal centers, formation of defects, addition of single atom sites, and control of pore size and structure. In situ structural and dynamic investigations using diffraction and spectroscopic techniques are powerful tools to visualize the details of host-guest interactions upon the above modifications, affording key insights into functional performance at a molecular level. Finally, we give an outlook of future research priorities in the study of host-guest chemistry in MOF materials. We hope this Account will encourage the rational development and improvement of future MOF-based sorbents for applications in challenging gas adsorption, separations, and catalysis.

Controllable C2H2/CO2 inverse adsorption and separation in pillar-layered Zn-1,2,4-triazolate-dicarboxylate frameworks induced by the ligand aromaticity

Acetylene (C2H2) and carbon dioxide (CO2) both are linear molecules and the similarity in size and physical properties makes their separation very challenging. Compared to the C2H2-selective C2H2/CO2 separation, the inscrutable CO2-selective capture (also called inverse C2H2/CO2 separation) process is ideal as it enables one-step production of high-purity C2H2. Herein, we demonstrate the controllable C2H2/CO2 inverse adsorption and separation in a series of isomorphic Zn-1,2,4-triazolate-dicarboxylate pillar-layered frameworks (Zn-FA-TRZ, Zn-MUC-TRZ, and Zn-BDC-TRZ) based on the aromaticity modulation strategy. Compared with Zn-MUC-TRZ, the utilization of shorter FA linker only with one double bond leads to an intersection point between the isothermal adsorption curves. After the intersection points, Zn-FA-TRZ showed higher CO2 uptakes than C2H2 (thermodynamic inversion) and the intersection point moving towards the high-pressure region with the increasing temperature. When BDC involved, the enhanced ligand aromaticity enables a complete thermodynamic inversion for C2H2 and CO2 adsorption due to the much stronger interactions between the aromatic ring and CO2 molecules. The isosteric heats of adsorption for CO2 and C2H2 clearly support such inverse adsorption induced by the ligand aromaticity. Furthermore, the fixed-bed dynamic breakthrough experiments indicate that Zn-FA-TRZ and Zn-MUC-TRZ both have common C2H2-selective separation process, but Zn-BDC-TRZ adsorbent shows a prominent CO2-selective inverse C2H2/CO2 separation. Specially, with temperature increased, the inverse separation performance enhanced, and high purity C2H2 (>99.99 %) can be obtained via one-step separation from C2H2/CO2 (50/50) mixture at room temperature. Overall, inverse C2H2/CO2 separation was successfully achieved in pillar-layered metal–organic frameworks, which is helpful for the exploration of practical acetylene adsorbents.

Engineered cellulose-based porous carbon adsorbents for superior gas adsorption and selective separation of CH4/H2 and CH4/N2

Adsorption and separation of methane from turquoise hydrogen and coalbed methane is becoming an important method for using unconventional natural gas. Adsorbent performance determines this technique. In this regard, the cellulose-based (Cell-PC) adsorbents were engineered by a facile process with a one-pot calcination method without solvent and an activating reagent-free like KOH with an economical and green approach for CH4/H2 and CH4/N2 separation. The series of adsorbents were synthesized, such as Cell-100, U-Cell-111, O-Cell-111, O-Cell-112, O-Cell-113, and O-Cell-113-a, from cellulose with urea/oxalic acid and sodium hydrogen carbonate, which helps to create pore structure. All adsorbents were characterized by several techniques, including XRD, SEM, XPS, and BET. All Cell-PC adsorbents were used to systematically investigate adsorption studies for CH4, N2, and H2. The O-Cell-113-a adsorbent demonstrated a superior CH4 uptake capacity of 52.75 cm3/g at 273 K and 37.92 cm3/g at 298 K under 100 kPa. It was attributed to the synergistic role of high surface area, mesopore volume, micropore volume, morphology, and surface functional group. However, the O-Cell-113-a showed lower adsorption for N2 and was unable to adsorb H2 at 298 K, indicating the adsorbent has selective adsorption properties for CH4. Furthermore, the ideal adsorbed solution theory (IAST) model was used to calculate the selectivity of CH4/N2, which was found to be around 13.78 at 273 K and 12.64 at 298 K, which is higher than most previously reported porous carbon. The isosteric heat of adsorption of O-Cell-113-a adsorbent was further calculated for CH4 and N2.

Computational Study of Metal‐Organic Frameworks for Hydrogen Sulfide Adsorption: Grand Canonical Monte Carlo and Molecular Dynamics Simulations

AbstractHydrogen sulfide (H2S) is a highly toxic, and flammable acid gas that is widely present in confined spaces. However, conventional adsorption materials are inefficient and have poor reuse properties. Metal‐organic frameworks (MOFs) show potential viability as novel materials in gas adsorption. Herein, mainstream MOFs were investigated based on molecular simulation techniques to explore the differences contributing to H2S adsorption. The adsorption process of H2S in MOFs was simulated by Grand Canonical Monte Carlo (GCMC) method, and the diffusion behavior was investigated based on molecular dynamics (MD) simulations. The results showed that the interaction energy and isosteric heat of adsorption were important criteria for determining the adsorption performance of H2S. The regulation of open metal sites could help to further enhance the adsorption of H2S, and the pore structure of MOFs affected the capture of H2S. A higher self‐diffusion rate implies faster H2S capture. Hydrogen bonds affect the trapping efficiency of MOFs for H2S and the relative positions of ligands in the benzene ring cause subtle differences in adsorption. This study provides design strategies for the improvement of new high‐performing MOFs for H2S adsorption in confined spaces.

Experimental Studies of Methane Adsorption on Activated Carbon and 3D Graphene Materials

Two kinds of slit pore carbon materials, namely activated carbon (AC) and 3D graphene materials (3D-GS), were purchased to examine their methane storage capabilities. The structural analysis and characterization of AC and 3D-GS were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), the X-ray energy dispersive spectrum (EDS), and N2 adsorption/desorption isotherms. Additionally, a thermodynamic framework was employed in the Henry’s law region to evaluate the potential well between the adsorbed fluid and adsorbent. The adsorption behavior of methane on two materials at room temperature and high pressure was also investigated. The results show that the Toth equation is the most suitable model for predicting adsorption isotherms than the Langmuir and L-F equations and determines that the absolute uptake of methane storage on AC and 3D-GS are, respectively, 7.86 mmol·g−1 and 8.9 mmol·g−1 at 298 K and 35 bar. In the Henry’s law region, the isosteric heat of methane adsorption on 3D-GS is larger than that of AC. Meanwhile, the potential well between methane and carbon-based materials decreases as the temperature increases. This indicates that the capacity of methane uptake is enhanced at lower temperatures, which is consistent with the measurements of adsorption isotherms. The research concludes that the 3D-GS is more suitable as a material storage medium than AC. This study provides valuable theoretical guidance for exploring the potential of methane storage on slit pore carbon-based material.

Synthesis and spectroscopic characteristics of chitosan composite of zinc-based metal-organic framework for rapid adsorption of organic pollutants from aqueous media

ABSTRACT The efficiency of the metal-organic framework of zinc (MOF-74) and its chitosan composite (CS/MOF-74) as a potential sorbent for the elimination of azo in addition to thiazine-type dyes from water by subsequent adsorption was studied. The synthesized adsorbents were characterized by various characterization techniques. The chitosan composite exhibited tremendous adsorption properties toward methyl orange (MO) and methylene blue (MB) at pH < 5.5 and pH > 5.5, respectively. The equilibrium data were evaluated by Dubinin-Radushkevich, Langmuir, Freundlich, and Tempkin isotherm models where the Langmuir model was best fitted to the adsorption data. The mono-layer sorption capacity values were found to be in the order 2047 mg/g and 1363 mg/g for MO and MB respectively onto CS/MOF-74 which are almost 6–8 epochs superior to MOF-74 and CS. In addition, pseudo-first, pseudo-second, intraparticle diffusion and Richenberg kinetic models were assessed to the kinetic data where the pseudo-second-order fitted very well to the adsorption data. The higher values of diffusion coefficient confirmed the greater involvement of the film diffusion than the pore and surface diffusion for the elimination of basic as well as acidic dyes onto CS/mOF-74. Thermodynamically, the negative value of isosteric heat of adsorption (Δ H ˉ ) concluded that the current study was found exothermic in nature. Moreover, electrostatic interactions, hydrogen bonding, and electron donor–acceptor interactions were suggested as probable mechanisms in the current adsorption process. The current study estimates the industrial importance of a chitosan composite of MOF-74 as it requires a short adsorption equilibrium time for the removal of the dyes and is satisfactorily reusable.

Design of carbonized unidirectional polyimide aerogel for CO2 capture: Effect of pore morphology/topology on CO2 capture

Design of efficient CO2 adsorbent is an effective way to capture CO2. Bamboo-derived activated carbon is a promising CO2 adsorbent. Inspired by this, carbonized unidirectional polyimide (CUPI) aerogels were newly designed by the ice templating method using directional freezing technology. The pore property of CUPI aerogel can be tuned by changing the solidification velocity, and a series of CUPI aerogels were designed to explore the CO2 capture performance in view of pore morphology/topology. As a result, the obtained CUPI-8 exhibits higher CO2 adsorption capacity compared to carbonized polyimide aerogels due to the synergistic effect of micropores and lamellar pores. Specially, the CO2 adsorption capacity over CUPI-8 can be up to 5.75 mmol/g at 20 bar and 298 K. Furthermore, the adsorption isotherm of CUPI-8 still shows an upward trend even nearly 20 bar. The isosteric adsorption heat (Qst) value of CUPI-8 is nearly in the ideal scope of 30–50 kJ mol−1. The efficient CO2 adsorption performance and good chemical stability of CUPI aerogel makes it a promising absorbent for practical application. This work provides a new opportunity for researching the effect of pore morphology/topology and the synergistic effect of hierarchical pores on CO2 capture.

A Microporous Zn(bdc)(ted)0.5 with Super High Ethane Uptake for Efficient Selective Adsorption and Separation of Light Hydrocarbons.

Separating light hydrocarbons (C2H6, C3H8, and C4H10) from CH4 is challenging but important for natural gas upgrading. A microporous metal-organic framework, Zn(bdc)(ted)0.5, based on terephthalic acid (bdc) and 1,4-diazabicyclo[2.2.2]octane (ted) ligands, is synthesized and characterized through various techniques, including powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and porosity analysis. The adsorption isotherms of light hydrocarbons on the material are measured and the isosteric adsorption heats of CH4, C2H6, C3H8, and C4H10 are calculated. The prediction of C2-4/C1 adsorption selectivities is accomplished using ideal adsorbed solution theory (IAST). The results indicate that the material exhibits exceptional characteristics, including a Brunauer-Emmett-Teller (BET) surface area of 1904 m2/g and a pore volume of 0.73 cm3/g. Notably, the material demonstrates remarkable C2H6 adsorption capacities (4.9 mmol/g), while CH4 uptake remains minimal at 0.4 mmol/g at 298 K and 100 kPa. These findings surpass those of most reported MOFs, highlighting the material's outstanding performance. The isosteric adsorption heats of C2H6, C3H8, and C4H10 on the Zn(bdc)(ted)0.5 are higher than CH4, suggesting a stronger interaction between C2H6, C3H8, and C4H10 molecules and Zn(bdc)(ted)0.5. The molecular simulation reveals that Zn(bdc)(ted)0.5 prefers to adsorb hydrocarbon molecules with richer C-H bonds and larger polarizability, which results in a stronger dispersion force generated by an adsorbent-adsorbate induced polarization effect. Therefore, the selectivity of C4H10/CH4 is up to 180 at 100 kPa, C3H8/CH4 selectivity is 67, and the selectivity of C2H6/CH4 is 13, showing a great potential for separating C2-4 over methane.

Molecular Simulations of the Chain Length Dependent Adsorption of C7‐C14 n‐Alkanes in ZIF‐8

AbstractRecent experiments show that the diffusivities of C8 and C10 n‐alkanes in ZIF‐8 are higher than those of C7 and C9, respectively. We investigated this unusual ‘odd‐even' effect by simulating the adsorption of C7‐C14 n‐alkanes in ZIF‐8 using hybrid Monte Carlo molecular simulations. The resultant adsorption isotherms, guest‐host energies, isosteric heats, and chain length distributions are analyzed for trends among the n‐alkanes. ZIF‐8 cages filled with n‐alkanes are characterized using a combination of image processing and data science to quantify the differences in packing that occur with chain length. Results indicate that packing changes drastically from C7 to C8 and from C9 to C10, which is consistent with the diffusion trends previously reported in experiments.