Ideal Adsorbed Solution Theory Research Articles

Three Robust Isoreticular Metal-Organic Frameworks with High-Performance Selective CO2 Capture and Separation.

Based on the hard-soft acid base (HSAB) theory, three robust isoreticular metal-organic frameworks (MOFs) with nia topology were successfully synthesized by solvothermal reaction {[In3O(BHB)(H2O)3]NO3·3DMA (JLU-MOF110(In)), [Fe3O(BHB)(H2O)3]NO3 (JLU-MOF110(Fe)), and [Fe2NiO(BHB)(H2O)3] (JLU-MOF110(FeNi)) (DMA = N,N-dimethylacetamide, H6BHB = 4,4″-benzene-1,3,5-triyl-hexabenzoic acid)}. Both JLU-MOF110(In) and JLU-MOF110(Fe) are cationic frameworks, and their BET surface areas are 301 and 446 m2/g, respectively. By modification of the components of metal clusters, JLU-MOF110(FeNi) features a neutral framework, and the BET surface area is increased up to 808 m2/g. All three MOF materials exhibit high chemical and thermal stability. JLU-MOF110(In) remains stable for 24 h at pH values ranging from 1 to 11, while JLU-MOF110(Fe) and JLU-MOF110(FeNi) persist to be stable for 24 h at pH from 1 to 12. JLU-MOF110(In) exhibits thermal stability up to 350 °C, whereas JLU-MOF110(Fe) and JLU-MOF(FeNi) can be stable up to 300 °C. Thanks to the microporous cage-based structure and abundant open metal sites, JLU-MOF110(In), JLU-MOF110(Fe), and JLU-MOF110(FeNi) have excellent CO2 capture capacity (28.0, 51.5, and 99.6 cm3/g, respectively, under 298 K and 1 bar). Interestingly, the ideal adsorption solution theory results show that all three MOFs exhibit high separation selectivity toward CO2 over N2 (35.2, 43.2, and 43.2 for CO2/N2 = 0.15/0.85) and CO2 over CH4 (14.4, 11.5, and 10.1 for CO2/CH4 = 0.5/0.5) at 298 K and 1 bar. Thus, all three MOFs are potential candidates for CO2 capture and separation. Among them, JLU-MOF110(FeNi) displays the best separation potential, as revealed by dynamic column breakthrough experiments.

Computing Mixture Adsorption in Porous Materials through Flat Histogram Monte Carlo Methods.

Mixture adsorption properties of porous materials are critical to determine their potential as adsorbents in separation applications. Toward the discovery of optimal adsorbents, in silico screening studies typically employ the grand canonical Monte Carlo (GCMC) technique to compute adsorption properties of gas mixtures in materials of interest at a given condition (i.e., composition, total pressure, and temperature) or to compute their adsorption properties for each component, followed by utilizing methods to predict mixture adsorption isotherms. However, the former approach results in the need for repeated calculations when different conditions such as compositions are considered. For the latter, the predictions may involve uncertainties, sometimes originating from the fitting quality to the pure component isotherms, and repeated simulations may also be needed for different temperatures. To this end, this study demonstrates the potential of flat histogram Monte Carlo methods in addressing the abovementioned shortfalls. Specifically, the so-called NVT + W method, first reported by Smit and co-workers, is extended herein to determine the macrostate probability distribution (MPD) of binary mixtures in porous materials. The obtained MPD can be reweighted to any conditions, yielding accurate adsorption isotherms of any desired compositions and temperatures. This approach, denoted as 2D NVT + W, is also compared with the widely adopted ideal adsorbed solution theory (IAST) method, and the former is found to offer more reliable predictions. Overall, the 2D NVT + W approach represents an efficient and effective alternative to compute mixture adsorption isotherms for porous materials, and the obtained MPD can be conveniently reused by peer researchers. A user-friendly Python code is also provided along with this article to employ this method.

Simultaneous extraction of C3H8 and C2H6 from ternary C3H8/C2H6/CH4 mixtures in an ultra-microporous metal–organic framework

The efficient purification of methane from other light hydrocarbons is of prime importance in natural gas purification. However, the exploitation of stable adsorbents with both high selectivity and high adsorption capacity remains a challenge. Herein, an ultra-microporous Co-based metal–organic framework (Co-MOF) with abundant selective binding sites decorating the pore wall was applied for the highly efficient separation of ternary C3H8/C2H6/CH4 mixtures. The Co-MOF shows remarkable C3H8 and C2H6 adsorption capacities with uptakes of 59.4 cm3/g and 58.6 cm3/g, respectively, while only adsorbing a low amount of CH4 with an uptake of 16.6 cm3/g at 298 K and 100 kPa. The ideal adsorbed solution theory selectivities for C2H6/CH4 (v/v = 50/50) and C3H8/CH4 (v/v = 50/50) reach 26.0 and 290.0 at 298 K, respectively, surpassing most of the state-of-the-art MOF materials. The molecular simulation reveals that the excellent adsorption and separation performance of Co-MOF derives from its suitable pore size and functional pore surfaces. Furthermore, the breakthrough experiments reveal that the Co-MOF exhibits excellent separation performance of C3H8 and C2H6 from natural gas. Notably, the dynamic separation performance of Co-MOF can be well-maintained after five cycles, demonstrating its excellent cycling stability. The high stability and excellent separation performance make Co-MOF a promising adsorbent for natural gas purification.

Interpreting gas sorption isotherms in glassy polymers using a Bayesian framework: A view on parameter uncertainty propagation into mixture sorption predictions

Investigation of mixed-gas sorption is necessary for robust design and optimization of membrane-based processes. While sorption models for glassy polymers are well-established, they often deviate from observed mixture data. In doing so, however, parameters of these models are typically estimated via traditional least-squares optimization methods, and so parametric uncertainty is often ignored in mixture sorption predictions. As an alternative, we use Bayesian Inference (BI) to estimate probability distributions for sorption models' parameters and thus provide statistically meaningful mixture sorption forecasts that reflect parameter uncertainty rigorously. To this end, we exploit molecular sorption simulations, combining Grand Canonical Monte Carlo (GCMC) and Equilibrium Molecular Dynamics (EMD), to focus on two different glassy polymer systems (i.e., single- and mixed-gas sorption of CO2/CH4 in a fluorinated polyimide and CH4/H2 in a polymer of intrinsic microporosity) and three popular mixture sorption models (the Dual-Mode Sorption model, Non-Equilibrium Thermodynamics for Glassy Polymers model, and the Ideal Adsorbed Solution Theory) to demonstrate the benefits of this technique for uncertainty quantification and propagation in membrane applications. We show that observed sorption data at typical working pressures (e.g., 0−25atm) are often insufficient to accurately estimate model parameters, and consequently, these models often fail to represent observed mixture data adequately. Furthermore, we show that sorption data (e.g., high-pressure data), able to capture intrinsic isotherm nonlinearities of sorption models, are critical to considerably improve parameter inference from collective model-data fits and thus accurately predict mixture sorption.

A Route to Understanding the Ethane Adsorption Selectivity of the Zeolitic Imidazolate Framework-8 in Ethane-Ethylene Mixtures.

Ethylene production has a negative environmental impact, with its separation step being one of the major contributors of pollution. This has encouraged the search for energy-efficient alternatives, among which the adsorptive separation of ethane and ethylene stands out. ZIF-8 is a molecular sieve that is potentially useful for this purpose. It is selective to ethane, an exceptional property that remains unexplained. Furthermore, the adsorption of ethane and ethylene above room temperature, such as at steam cracking process outlet temperatures, has not been addressed either. This work aims to fill this knowledge gap by combining experiments at very low volumetric fillings with density-functional theory modelling methods. Adsorption isotherms of ethane and ethylene on ZIF-8 at pressures below 0.3 bar and 311 K, 333 K, and 363 K were measured using zero-length column chromatography. The low-pressure domain of the isotherms contains information on the interactions between the adsorbate molecules and the adsorbent. This favors the understanding of their macroscopic behavior from simulations at the atomic level. The isosteric enthalpy of adsorption of ethane remained constant at approximately -10 kJ/mol. In contrast, the isosteric enthalpy of adsorption of ethylene decreased from -4 kJ/mol to values akin to those of ethane as temperature increased. ZIF-8 selectivity to ethane, estimated from ideal adsorbed solution theory, decreased from 2.8 to 2.0 with increasing pressure up to 0.19 bar. Quantum mechanical modelling suggested that ethylene had minimal interactions with ZIF-8, while ethane formed hydrogen bonds with nitrogen atoms within its structure. The findings of this research are a platform for designing new systems for the adsorptive separation of ethane and ethylene and thus, reducing the environmental impact of ethylene production.

Binary carbon dioxide and nitrogen adsorption on pomelo peel-derived porous sorbent

The rising concern regarding CO2 emission from fossil fueled-power plants, along with the heightened interest in repurposing biowaste has necessitated the utilization of biowaste as an adsorbent for CO2 capture. In this study, the pomelo peel-derived activated carbon (POM-AC) was investigated as a potential adsorbent for post-combustion CO2 capture application, which involves capturing CO2 from the CO2 and N2 gas mixture. The POM-AC was characterized, revealing a microporous-mesoporous structure that contains various surface functional groups including hydroxyl, carbonyl, carboxyl, and alkene groups. The strong affinity of POM-AC towards CO2 over N2 was demonstrated from the increment in the CO2 and N2 gas mixture uptake with the increase in CO2 gas compositions. The total adsorption capacity of POM-AC at ambient conditions for 100% CO2, 15% CO2, 10% CO2, and 5% CO2 is 127.8 mg/g, 55.7 mg/g, 49.1 mg/g, and 38.3 mg/g, respectively. Notably, POM-AC outperformed the commercial activated carbon (Chemiz-AC) at simulated post-combustion conditions due to POM-AC having smaller pores than Chemiz-AC. The Ideal Adsorbed Solution Theory (IAST) prediction of binary CO2 and N2 adsorption equilibria showed higher CO2 adsorption capacity than N2 at post-combustion gas compositions (5–15% CO2), which further suggests its stronger preferential of CO2 over N2. Furthermore, a relatively high CO2/N2 selectivity of 23.9 was predicted for 15% CO2 gas composition. The adsorption isotherm and kinetic analysis revealed that the surface of POM-AC is heterogenous, and the rate-controlling step of CO2 and N2 adsorption is physisorption. Coupled with the utilization of a zero-cost biowaste as an activated carbon precursor, these findings showed that POM-AC could be a promising adsorbent for post-combustion CO2 capture application.

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.

Efficient Exploration of Adsorption Space for Separations in Metal-Organic Frameworks Combining the Use of Molecular Simulations, Machine Learning, and Ideal Adsorbed Solution Theory.

Adsorption-based separations using metal-organic frameworks (MOFs) are promising candidates for replacing common energy-intensive separation processes. The so-called adsorption space formed by the combination of billions of possible molecules and thousands of reported MOFs is vast. It is very challenging to comprehensively evaluate the performance of MOFs for chemical separation through experiments. Molecular simulations and machine learning (ML) have been widely applied to make predictions for adsorption-based separations. Previous ML approaches to these issues were typically limited to smaller molecules and often had poor accuracy in the dilute limit. To enable exploration of a wider adsorption space, we carefully selected a diverse set of 45 molecules and 335 MOFs and generated single-component isotherms of 15,075 MOF-molecule pairs by grand canonical Monte Carlo. Using this database, we successfully developed accurate (r2 > 0.9) machine learning models predicting adsorption isotherms of diverse molecules in large libraries of MOFs. With this approach, we can efficiently make predictions of large collections of MOFs for arbitrary mixture separations. By combining molecular simulation data and ML predictions with Ideal Adsorbed Solution Theory, we tested the ability of these approaches to make predictions of adsorption selectivity and loading for challenging near-azeotropic mixtures.

High-Pressure Gravimetric Measurements for Binary Gas Adsorption Equilibria and Comparisons with Ideal Adsorbed Solution Theory (IAST).

Measurements of gas mixture adsorption equilibria at high pressures are important for assessing actual adsorbent selectivities but are often out of reach, given the challenging nature of the required experiments. Here, we report a high-pressure gravimetric binary gas adsorption equilibrium measurement system based on simultaneous gas density and mixture adsorption measurements in a single gas cell coupled to a magnetic-suspension balance. Compared to traditional techniques which rely on analytical measurements of gas composition, this approach does not require any sampling. Adsorption measurements of two gas mixtures (0.500 N2 + 0.500 CH4 and 0.400 N2 + 0.600 CO2, mole fraction) on a commercially available molecular sieve (NaY, sodium molecular sieve type Y) were carried out in the temperature range 282 to 325 K with a pressure up to 10 MPa. A prediction method for the gas mixture adsorption equilibria in a closed system using the ideal adsorbed solution theory (IAST) model was used to compare the experimental results. For binary mixtures of components with similar adsorption capacities (here N2 and CH4), the system can measure the adsorption equilibria at pressures higher than 1.0 MPa and the result agrees well with the IAST model prediction. For two gases with very different adsorption capacities, the uncertainty in the adsorption equilibrium measurement is much larger. The dominant uncertainty source is the gas density measurement, whose uncertainty could potentially be cut to half if the current titanium sinker is replaced with a sinker made of single-crystal silicon and with a larger volume.

Optimization performance of viscose rayon derived flexible porous carbon cloths in relation to their CO2 capture, CO2/CH4 separation and methanol adsorption

From the practical perspective, innovative porous carbon material is needed for gas adsorption and separation. Here, flexible porous carbon cloths are successfully prepared from viscose rayon cloth via controllable adjusted KOH activation. In order to optimize such flexible porous carbon cloths, the relationship between KOH activation condition and the porous carbon cloths property have been systematically studied. The effect factors on CO2 capture, CO2/CH4 separation and methanol adsorption have been analyzed in depth. Due to the largest narrow micropore volume (PV1 nm), ACC-240–800 exhibits the best CO2 uptake capacity of 4.11 mmol g−1 under ambient condition. Based on the ideal adsorbed solution theory model, the ACC-240–700 exhibits the highest selectivity of 3.73, 3.13 and 2.65 for CO2/CH4 mixing proportion of 30/70, 46/60 and 50/50, respectively, at 25 °C and 1 bar, owing to the synergetic result of O&N content and PV1 nm. The CO2/CH4 separation performance on ACC-240–700 is analyzed and confirmed by Qst calculation for CO2 and CH4, and dynamic breakthrough experiments with equimolar binary CO2/CH4 (50/50) mixture. The determining factors on methanol adsorption is mainly the porosity structure. The best methanol adsorption uptake of 12.87 mmol g−1 is observed on ACC-240–800 at 25 °C and 95 mbar, because of the largest values of SBET, Vmicro and PV1mn. The flexible porous carbon cloths provided in this work can act as effective adsorbent for carbon capture, low-quality nature gas upgrading and methanol adsorption in the industrial processes.

An anionic MOF as a multifunctional platform for selective adsorption of CO2, separation of organic dyes and ionic conductivity

It is a very effective strategy to capture and separate carbon dioxide by incorporation of alkali cations into MOFs. Presented here is an anionic metal-organic framework (MOF) (Me2NH2)2Co(tpta)·2H2O (1), in which the exchange of alkali ions (Li+ and Na+) took place with H2N(Me)2+ cations. As expected, CO2/N2 selectivity of the framework was improved significantly and reached 61.6 due to the inclusion of Li + using the ideal adsorbed solution theory (IAST) model. The enhancement of its CO2 uptake capability and selectivity has been mainly attributed to the charge-quadrupole interaction. For the CO2/N2 system, it is found that the inclusion of Li+ rather than Na+ favors higher selectivity. Additionally, it successfully separated cationic dye crystal violet (CV+) from anionic dye methyl orange (MO−) by the column-chromatography. Evidently, the enhancement of the electrostatic interaction greatly improves the separation performance of the framework.

Development of a Mixed Multinuclear Cluster Strategy in Metal-Organic Frameworks for Methane Purification and Storage.

Metal-organic frameworks (MOFs) have attracted extensive attention in methane (CH4) purification and storage. Specially, multinuclear cluster-based MOFs usually have prominent performance because of large cluster size and abundant open metal sites. However, compared to diverse combinations of organic linkers, one MOF with two or more multinuclear clusters is difficult to achieve. In this paper, we demonstrate a mixed multinuclear cluster strategy, which successfully led to three new heterometallic MOFs (SNNU-328-330) with the same common H3TATB [2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine] tritopic linker and six types of multinuclear clusters ([YCd(COO)4(μ2-H2O)], [YCd2(COO)8], [In3(COO)6(μ3-OH)], [In3Eu2(COO)9(μ3-OH)3(μ4-O)], [Y9(COO)12(μ3-OH)14] and [Y2Cd8(COO)16(μ2-H2O)4(μ3-OH)8]). Three MOF adsorbents all show great potentials to remove the impurities (CO2 and C2-hydrocarbons) in natural gas and show prominent high-pressure methane storage capacity. Among them, the ideal adsorbed solution theory separation ratios of equimolar C2H2/CH4, C2H4/CH4, C2H6/CH4, and CO2/CH4 at 298 K for SNNU-328 reach to 29.7-16.0, 19.1-8.2, 33.2-10.3, and 74.3-8.5, which have surpassed many famous MOF adsorbents. Dynamic breakthrough experiments conducted at 273 and 298 K showed that SNNU-330 can separate CH4 from C2H2/CH4, C2H4/CH4, C2H6/CH4, and CO2/CH4 mixtures with the breakthrough interval times of about 48.2, 17.9, 37.2, and 17.1 min g-1 (273 K, 1 bar, v/v = 50/50, 2 mL min-1), respectively. Remarkably, SNNU-329 exhibits extremely high methane storage performance at 298 K with the total uptake and working capacity of 192 cm3 cm-3 (95 bar) and 171 cm3 cm-3 (65 bar) due to the synergistic effects of high surface area, suitable pore sizes, and multiple open metal sites.

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.

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.

Two metal-organic frameworks based on tetracarboxylic ligand exhibiting high performance for gas adsorption and separation

Developing porous materials for purification of acetylene is of great significance, but remains challenging. Currently, the use of metal-organic frameworks (MOFs) for gas adsorption separation has received substantial research interest. Herein, based on the tetracarboxylic acid ligand H4TPTA ([1,1':3′,1″-terphenyl]-4,4′,4″,6′-tetracarboxylic acid), two MOFs (ErTPTA and CdTPTA) constructed by trinuclear cluster secondly building units (SBUs) have been successfully synthesized. They are three dimensional (3D) framework with 1D rhomboid channels, demonstrating a (4,8)-connected scu network. A series of gas adsorption tests were performed and the both compounds exhibited outstanding gas selective adsorption performance. Accordingly, the ideal adsorption solution theory (IAST) is used to simulate the adsorption selectivity, the selectivity of CdTPTA for CO2/CH4 is 11.85 (0.5:0.5) and 17.02 (0.05:0.95), and for C2H2/CH4 is 11.81 (0.5:0.5); the selectivity of ErTPTA for C2H2/CO2 is 4.45 (0.5:0.5).

CO2-Induced Gate-Opening Adsorption on a Chabazite/Phillipsite Composite Zeolite Transformed from a Faujasite Zeolite Using Organic Structure-Directing Agent-Free Steam-Assisted Conversion.

Organic structure-directing agent-free steam-assisted conversion and Cs+ ion exchange were used to transform the faujasite (FAU)-type zeolite to the Cs+-type chabazite/phillipsite (CHA/PHI) composite zeolite. Compared with the pure PHI-type zeolite, the Cs+-type CHA/PHI zeolite showed gate-opening CO2 adsorption behavior and good thermal stability. In situ powder X-ray diffraction (PXRD) of the CO2 adsorption was measured to elucidate the mechanism for the gate-opening adsorption on the CHA/PHI zeolite. The Na+-type CHA/PHI zeolite did not show such adsorption behavior, and the PXRD pattern of the Na+-type CHA/PHI zeolite did not change with increasing CO2 partial pressure, which suggests that this unique adsorption behavior was caused by the PHI framework transition or Cs+ ions moving in both the CHA and PHI frameworks. Furthermore, in situ Fourier-transform infrared spectra of CO2 adsorption and CO2 breakthrough measurement on the Cs+-type CHA/PHI zeolite suggest that the CHA and PHI frameworks in the CHA/PHI zeolite shared eight-membered-ring windows and that CO2 molecules could easily diffuse from a CHA cage to a PHI framework. The ideal adsorbed solution theory was used to calculate the CO2/N2 separation selectivity for the Cs+-type CHA/PHI zeolite. At 298 and 318 K, the Cs+-type CHA/PHI composite zeolite showed a high CO2/N2 separation coefficient of >10,000 compared with other zeolites with high CO2 adsorption capacity. Furthermore, the CO2 working capacity was calculated for the Cs+-type CHA/PHI zeolite in both the pressure- and temperature-swing processes, and the results showed that the CHA/PHI composite zeolite could selectively separate CO2 from the CO2/N2 gas mixtures released from power generation plants operating using these processes.

Pore engineering in cost-effective and stable Al-MOFs for efficient capture of the greenhouse gas SF6

The capture and separation of the greenhouse gas sulfur hexafluoride (SF6) from nitrogen (N2) holds significant potential for mitigating the greenhouse effect and yielding economic advantages for the semiconductor industry. In this study, a pair of isoreticular cost-effective and stable metal–organic frameworks (MOFs) with slightly different pore environments (CAU-10-H and CAU-10-Py) were prepared at >10 g scale for SF6/N2 separation. CAU-10-Py exhibited a remarkable improvement in SF6 uptake capacity at both low pressure (1.13 mmol/g at 0.1 bar and 298 K, compared to 0.68 mmol/g) and elevated pressure (2.11 mmol/g at 1 bar and 278 K, compared to 1.07 mmol/g). The ideal adsorbed solution theory (IAST) selectivity of SF6/N2 (10/90) was found to be 204 for CAU-10-Py and 123 for CAU-10-H. These enhanced capacities and selectivity endow CAU-10-Py a highly promising candidate for SF6 capture. Single crystal structural analysis, 77 K N2 adsorption data and theoretical calculations indicated that the substitution of benzene by pyridine slightly expand the pore diameter, facilitating more efficient accommodation of SF6 within the channel pores. The SF6 molecule is adsorbed around four benzene rings in CAU-10-H but trapped by two pyridine rings in CAU-10-py, resulting in one fold increase in adsorption capacity. Intriguingly, time-dependant adsorption experiments revealed that CAU-10-Py exhibited a higher SF6 adsorption rate and a lower N2 adsorption rate compared to CAU-10-H, further highlighting the benefit of CAU-10-Py for SF6/N2 separation. Dynamic breakthrough experiments conducted under simulated working conditions further confirmed the outstanding SF6/N2 separation performance of CAU-10-Py. Considering its excellent regeneration ability and cycling performance, this cost-effective and easily scalable MOF demonstrates great promise for SF6/N2 separation.

Effect of Carbon Nanoparticles on the Porous Texture of ι-Carrageenan-Based N-Doped Nanostructured Porous Carbons and Implications for Gas Phase Applications

S and N double-doped high surface area biomass-derived carbons were obtained from marine biomass-derived ι-carrageenan. Adding carbon nanoparticles (CNPs), namely graphene oxide (GO) or carbon nanotubes (CNTs), in the early stage of the synthesis leads to a modified porous texture and surface chemistry. The porous textures were characterized by N2 (−196.15 °C) and CO2 (0 °C) isotherms. The best GO- and CNT-added carbons had an apparent surface area of 1780 m2/g and 1170 m2/g, respectively, compared to 1070 m2/g for the CNP-free matrix. Analysis of the Raman spectra revealed that CNT was more efficient in introducing new defects than GO. Based on XPS, the carbon samples contain 2–4.5 at% nitrogen and 1.1 at% sulfur. The Dubinin–Radushkevich (DR) and Henry models were used to assess the strength of the interactions between various gases and the surface. The N2/H2 and CO2/CH4 selectivities were estimated with ideal adsorbed solution theory (IAST). While the CNPs, particularly GO, had a remarkable influence on the porous texture and affected the surface chemistry, their influence on the separation selectivity of these gases was more modest.

Robust Fluorine-Functionalized {Ln5}-Organic Frameworks for Excellent Catalytic Performance on Cycloaddition of CO2 with Epoxides and Knoevenagel Condensation.

Lanthanide-organic frameworks (LnOFs) are a class of promising catalysts on a large number of organic reactions because of the higher coordination number of Ln3+ ions, inspired by which exploratory preparation of cluster-based LnOFs was carried out by us. Herein, the exquisite combination of spindly [Ln5(μ3-OH)6(CO2)6(H2O)6] clusters (abbreviated as {Ln5}) and fluorine-functionalized tetratopic ligand of 2',3'-difluoro-[p-terphenyl]-3,3″,5,5″-tetracarboxylic acid (F-H4PTTA) engendered two highly robust isomorphic nanoporous frameworks of {[Ln5(FPTTA)2(μ3-OH)6(H2O)6](NO3)}n (NUC-61, Ln = Ho and Dy). NUC-61 compounds are rarely reported {Ln5}-based 3D frameworks with nano-caged voids (19 Å × 17 Å), which are shaped by twelve [Ln5(μ3-OH)6(COO)8] clusters and eight completely deprotonated F-PTTA4- ligands. Activated NUC-61a compounds are characterized by plentiful coexisted Lewis acid-base sites of open LnIII sites, capped μ3-OH, and -F. Judged by the ideal adsorbed solution theory (IAST), activated NUC-61Ho-a had a high CO2/CH4 adsorptive selectivity with the value of 12.7 (CO2/CH4 = 50/50) and 9.1 (CO2/CH4 = 5/95) at 298 K, which could lead to high-purity CH4 (≥99.9996%). Furthermore, catalytic experiments exhibited that NUC-61Ho-a, as a representative, could efficiently catalyze the cycloaddition reactions of CO2 with epoxides as well as the Knoevenagel condensation reactions of aldehydes and malononitrile. This work proves that the {Ln5}-based skeletons of NUC-61 with chemical stability, heterogeneity, and recyclability are an excellent acid-base bifunctional catalyst for some organic reactions.

Preparation of Cu-BTC MOF extrudates for CH4 separation from CH4/N2 gas mixture

Metal-Organic Frameworks (MOF) are promising materials for gas separation and storage. The shaping of MOFs is an essential step for their practical industrial application. In this work, Cu-BTC MOF extrudates (B-5, B-10, and B-15) were prepared by using 5, 10, and 15 wt% of carboxymethyl cellulose as a binder and well characterized by powder X-ray diffraction (PXRD), N2 adsorption-desorption at 77 K, FTIR, TGA, and Scanning Electron Microscopy (SEM). The equilibrium adsorption isotherms of CH4 and N2 with Cu-BTC extrudates were measured at 298, 313, and 328 K and up to 10 bar pressure and compared with zeolite 13X and 5A. The isotherm data of both adsorbates were fitted in Dual Site Langmuir equations, and adsorption selectivity of methane over nitrogen was predicted using Ideal Adsorbed Solution Theory (IAST) method for 20:80, 30:70, and 50:50 (mol%/mol%) CH4/N2 feed gas mixtures representing nitrogen bearing coal bed methane. The CH4/N2 selectivity of Cu-BTC extrudates B-5, B-10, and B-15 was higher than commercial zeolite 13X and 5A. For example, for the 20:80 CH4/N2 feed mixture, the CH4/N2 selectivity of Cu-BTC extrudates B-5, B-10, and B-15 was 3.21, 3.24, and 3.25, respectively, which are about 38 & 34% higher than zeolite 13X and 5A which makes them potential adsorbent for further dynamic studies for the said separation application.