Microporous Adsorbents for CH4 Capture and Separation from Coalbed Methane with Low CH4 Concentration: Review

A rapid increase in natural gas consumption has resulted in a shortage of conventional natural gas resources, while an increasing concentration of CH4 in the atmosphere has intensified the greenhouse effect. The exploration and utilization of coalbed methane (CBM) resources not only has the potential to fill the gap in natural gas supply and promote the development of green energy, but could also reduce CH4 emissions into the atmosphere and alleviate global warming. However, the efficient separation of CH4 and N2 has become a significant challenge in the utilization of CBM, which has attracted significant attention from researchers in recent years. The development of efficient CH4/N2 separation technologies is crucial for enhancing the exploitation and utilization of low-concentration CBM and is of great significance for sustainable development. In this paper, we provide an overview of the current methods for CH4/N2 separation, summarizing their respective advantages and limitations. Subsequently, we focus on reviewing research advancements in adsorbents for CH4/N2 separation, including zeolites, metal-organic frameworks (MOFs), and porous carbon materials. We also analyze the relationship between the pore structure and surface properties of these adsorbents and their adsorption separation performances, and summarize the challenges and difficulties that different types of adsorbents face in their future development. In addition, we also highlight that matching the properties of adsorbents and adsorbates, controlling pore structures, and tuning surface properties on an atomic scale will significantly increase the potential of adsorbents for CH4 capture and separation from CBM.

Pore Chemical Modification of Bimetallic Coordination Networks for Coal-Bed Methane Purification under Humid Conditions

The recycling of low-concentration coal-bed methane (CBM) is environmentally beneficial and plays a crucial role in optimizing the energy mix. In this work, we present a strategy involving pore chemical modification to synthesize a series of bimetallic diamond coordination networks, namely CuIn(ina)4, CuIn(3-ain)4, and CuIn(3-Fina)4 (where ina = isonicotinic acid, 3-ain = 3-amino-isonicotinic acid, and 3-Fina = 3-fluoroisonicotinic acid). Among these, the amino-functionalized CuIn(3-ain)4 exhibits excellent CH4 adsorption capacity (1.71 mmol g-1) and CH4/N2 selectivity (7.5) due to its optimal pore size and chemical environment, establishing it as a new benchmark material for CBM separation. Dynamic breakthrough experiments confirm the exceptional CH4/N2 separation performance of CuIn(3-ain)4. Notably, CuIn(3-ain)4 demonstrates excellent stability under wet conditions and maintains outstanding separation performance even in high-humidity environments. Additionally, theoretical simulations provide valuable insights into how selective adsorption performance can be fine-tuned by manipulating the pore size and geometry. Regeneration tests and cycling evaluations further underscore the remarkable potential of CuIn(3-ain)4 as a highly efficient adsorbent for the separation of CBM.

An efficient Ni-based adsorbent for selective removal of 85Kr and 14CH4 in radioactive contaminants from nuclear process off-gas stream

Efficient adsorbents for radioactive gas treatment in nuclear energy cycle is crucial for eliminating negative environmental impacts caused by wide nuclear applications. A Ni-based MOF material called JUC-86(Ni) which is based on 1-H-benzimidazole-5-carboxylic acid (HBIC) linker was synthesized for adsorbing the 85Kr, 14CH4 from off-gas stream. It was disclosed that there is a suitable pore environment for 85Kr and 14CH4 preferred adsorption in JUC-86 and the adsorption capacity could even reach 2.79 mmol/g (85Kr) and 2.54 mmol/g (14CH4) which are almost higher than all the adsorbents. The 85Kr/N2 and 14CH4/N2 IAST selectivities of the resulting sample are satisfactory (11.63 and 9.43) and well matched with the breakthrough experiments where the breakthrough times of 85Kr and 14CH4 are much longer than N2. What's more, the adsorption heats of 85Kr and 14CH4 are less than 30 kJ/mol which indicated a stronger affinity than N2 and a low-energy regeneration. As simulation results showed that the adsorption distribution follows a-spiral-pattern which could be attributed to the N atom in the CN, this is also the dominant factor of the 85Kr and 14CH4 preferable adsorption.

Fabricating a Robust Ultramicroporous Metal-Organic Framework for Purifying Natural Gas and Coal Mine Methane

Purifying methane (CH4) from natural gas and coal mine methane (CMM) is of great significance but challenging in the chemical industry. Herein, a robust ultramicroporous metal-organic framework (MOF) is reported, which can be synthesized on a gram scale by stirring under room temperature. Single-component adsorption isotherms of gases (CH4, ethane (C2H6), propane (C3H8), nitrogen (N2)) and breakthrough experiments indicate that the MOF can separate CH4 efficiently from CH4/C2H6/C3H8 ternary mixture, with super high purity-CH4 production of 154.7 cm3 g-1. Additionally, the MOF shows higher CH4 capacity than N2, resulting in excellent separation performance for the CH4/N2 mixture. Notably, the binding sites of gases can be precisely determined by single-crystal X-ray data, further confirmed by molecular simulation. It is found that there are multiple hydrogen bonds and C─H···π interactions between the gases and the framework. This work offers an excellent candidate material for CH4 purification with both high capacity and separation efficiency.

Non-CO2 greenhouse gas separation using advanced porous materials

Global warming has become a growing concern over decades, prompting numerous research endeavours to reduce the carbon dioxide (CO2) emission, the major greenhouse gas (GHG). However, the contribution of other non-CO2 GHGs including methane (CH4), nitrous oxide (N2O), fluorocarbons, perfluorinated gases, etc. should not be overlooked, due to their high global warming potential and environmental hazards. In order to reduce the emission of non-CO2 GHGs, advanced separation technologies with high efficiency and low energy consumption such as adsorptive separation or membrane separation are highly desirable. Advanced porous materials (APMs) including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs), porous organic polymers (POPs), etc. have been developed to boost the adsorptive and membrane separation, due to their tunable pore structure and surface functionality. This review summarizes the progress of APM adsorbents and membranes for non-CO2 GHG separation. The material design and fabrication strategies, along with the molecular-level separation mechanisms are discussed. Besides, the state-of-the-art separation performance and challenges of various APM materials towards each type of non-CO2 GHG are analyzed, offering insightful guidance for future research. Moreover, practical industrial challenges and opportunities from the aspect of engineering are also discussed, to facilitate the industrial implementation of APMs for non-CO2 GHG separation.

Influence of ligands within Al-based metal-organic frameworks for selective separation of methane from unconventional natural gas

Efficient CH₄/N₂ separation from unconventional natural gas is vital for both energy recycling and climate change control. Figuring out the reason for the disparity between ligands in the framework and CH₄ is the crucial problem for developing adsorbents in PSA progress. In this study, a series of eco-friendly Al-based MOFs, including Al-CDC, Al-BDC, CAU-10, and MIL-160, were synthesized to investigate the influence of ligands on CH₄ separation through experimental and theoretical analyses. The hydrothermal stability and water affinity of synthetic MOFs were explored through experimental characterization. The active adsorption sites and adsorption mechanisms were investigated via quantum calculation. The results manifested that the interactions between CH₄ and MOFs materials were affected by the synergetic effects of pore structure and ligand polarities, and the disparities of ligands within MOFs determined the separation efficiency of CH₄. Especially, the CH₄ separation performance of Al-CDC with high sorbent selection (68.56), moderate isosteric adsorption heat for CH₄ (26.3 kJ/mol), and low water affinity (0.1 g/g at 40% RH) was superior to most porous adsorbents, which was attributed to its nanosheet structure, proper polarity, reduced local steric hindrance, and extra functional groups. The analysis of active adsorption sites indicated that hydrophilic carboxyl groups and hydrophobic aromatic ring were the dominant CH₄ adsorption sites for liner ligands and bent ligands, respectively. The methylene groups with saturated C-H bonds enhanced the wdV interaction between ligands and CH₄, resulting in the highest binding energy of CH₄ for Al-CDC. The results provided valuable guidance for the design and optimization of high-performance adsorbents for CH₄ separation from unconventional natural gas.

Highly fluorescent nickel based metal organic framework for enhanced sensing of Fe3+ and Cr2O72- ions

Heavy metal contamination has sparked widespread concern among the populace. The significant issues necessitate the creation of high-performance fluorescent pigments that can identify harmful elements in water. The present study deals with metal organic framework [MOF] based on nickel [Ni-BDC MOF]. The Ni-BDC MOF was prepared by facile solvothermal method using nickel nitrate hexahydrate and terephthalic acid ligand as precursors. The MOF was characterized by various techniques in order to examine the crystal, morphological, structural, composition, thermal and optical properties. The detailed characterizations revealed that the synthesized Ni-BDC MOF are well-crystalline with high purity and possessing 3D rhombohedral microcrystals with rough surface. The MOF demonstrate good luminescence performance and excellent water stability. According to the Stern Volmer plot, the tests set up under optimized conditions demonstrate a linear correlation between the fluorescence intensity and concentration of both ions, i.e. Fe³⁺, and Cr₂O₇^2- ions. The linear range and detection limit for Fe³⁺ and Cr₂O₇^2- were found to be 0-1.4 nM and 0.159 nM, and 0-1 nM and 0.120 nM, respectively. The mechanisms for the selective detection of cations and anions were also explored. The recyclability for the prepared MOF was checked up to five cycles which showed excellent stability with just a slight reduction in efficiency. The constructed sensor was also used to assess the presence of Fe³⁺ and Cr₂O₇^2- ions in actual water samples. The results of the different experiments revealed that the prepared MOF is a good material for detecting Fe³⁺ and Cr₂O₇^2- ions.

Computational investigation of multifunctional MOFs for adsorption and membrane-based separation of CF4/CH4, CH4/H2, CH4/N2, and N2/H2 mixtures

The ease of functionalization of metal-organic frameworks (MOFs) can unlock unprecedented opportunities for gas adsorption and separation applications as the functional groups can impart favorable/unfavorable regions/interactions for the desired/undesired adsorbates. In this study, the effects of the presence of multiple functional groups in MOFs on their CF₄/CH₄, CH₄/H₂, CH₄/N₂, and N₂/H₂ separation performances were computationally investigated combining grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The most promising adsorbents showing the best combinations of selectivity, working capacity, and regenerability were identified for each gas separation. 15, 13, and 16 out of the top 20 MOFs identified for the CH₄/H₂, CH₄/N₂, and N₂/H₂ adsorption-based separation, respectively, were found to have -OCH₃ groups as one of the functional groups. The biggest improvements in CF₄/CH₄, CH₄/H₂, CH₄/N₂, and N₂/H₂ selectivities were found to be induced by the presence of -OCH₃-OCH₃ groups in MOFs. For CH₄/H₂ separation, MOFs with two and three functionalized linkers were the best adsorbent candidates while for N₂/H₂ separation, all the top 20 materials involve two functional groups. Membrane performances of the MOFs were also studied for CH₄/H₂ and CH₄/N₂ separation and the results showed that MOFs having -F-NH₂ and -F-OCH₃ functional groups present the highest separation performances considering both the membrane selectivity and permeability.

Enhancing CH4 Capture from Coalbed Methane through Tuning van der Waals Affinity within Isoreticular Al-Based Metal-Organic Frameworks

Efficient separation of the CH₄/N₂ mixture is of great significance for coalbed methane purification. It is an effective strategy to separate this mixture by tuning the van der Waals interaction due to the nonpolar properties of CH₄ and N₂ molecules. Herein, we prepared several isoreticular Al-based metal-organic frameworks (MOFs) with different ligand sizes and polarities because of their high structural stability and low cost/toxicity feature of Al metal. Adsorption experiments indicated that the CH₄ uptake, Q_st of CH₄, and CH₄/N₂ selectivity are in the order of Al-FUM-Me (27.19 cm³(STP) g^-1, 24.06 kJ mol^-1 and 8.6) > Al-FUM (20.44 cm³(STP) g^-1, 20.60 kJ mol^-1 and 5.1) > Al-BDC (15.98 cm³(STP) g^-1, 18.81 kJ mol^-1 and 3.4) > Al-NDC (10.86 cm³(STP) g^-1, 14.89 kJ mol^-1 and 3.1) > Al-BPDC (5.90 cm³(STP) g^-1, 11.75 kJ mol^-1 and 2.2), confirming the synergetic effects of pore sizes and pore surface polarities. Exhilaratingly, the ideal adsorbed solution theory selectivity of Al-FUM-Me is higher than those of all zeolites, carbon materials, and most water-stable MOF materials (except Al-CDC and Co₃(C₄O₄)₂(OH)₂), which is comparable to MIL-160. Breakthrough results demonstrate its excellent separation performance for the CH₄/N₂ mixture with good regenerability. The separation mechanism of Al-FUM-Me for the CH₄/N₂ mixture was elucidated by theoretical calculations, showing that the stronger affinity of CH₄ can be attributed to its relatively shorter interaction distance with adsorption binding sites. Therefore, this work not only offers a promising candidate for CH₄/N₂ separation but also provides valuable guidance for the design of high-performance adsorbents.

Valorization of spent disposable wooden chopstick as the CO2 adsorbent for a CO2/H2 mixed gas purification

A series of activated carbons (ACs) derived from spent disposable wooden chopsticks was prepared via steam activation and used to separate carbon dioxide (CO₂) from a CO₂/hydrogen (H₂) mixed gas at atmospheric pressure. A factorial design was employed to investigate the effects of the activation temperature and time as well as their interactions on the production yield of ACs and their CO₂ adsorption capacity. The activation temperature exhibited a much higher impact on both the production yield and the CO₂ adsorption capacity of ACs than the activation time. The interaction of both parameters did not significantly affect the yield of ACs, but did affect the CO₂ adsorption capacity. The optimal preparation condition provided ACs with a desirable yield of around 23.18% and a CO₂ adsorption capacity of 85.19 mg/g at 25 °C and 1 atm and consumed the total energy of 225.28 MJ/kg AC or 116.4 MJ/g-mol CO₂. A H₂ purity of greater than 96.8 mol% was achieved from a mixed gas with low CO₂ concentration (< 20 mol%) during the first 3 min of adsorption and likewise around 90 mol% from a mixed gas with a high CO₂ concentration (> 30 mol%) during the first 2 min. The CO₂ adsorption on the as-prepared ACs proceeded dominantly via multilayer physical adsorption and was affected by both the surface area and micropore volume of the ACs. The adsorption capacity was diminished by around 18% after six adsorption/desorption cycles. The regeneration of the as-prepared chopstick-derived ACs can be easily performed via heating at a low temperature and ambient pressure, suggesting their potential application in the temperature swing adsorption process.

Tuning the Pore Environment of MOFs toward Efficient CH4/N2 Separation under Humid Conditions

Adsorption separation technology using adsorbents is promising as an alternative to the energy-demanding cryogenic distillation of natural gas (CH₄/N₂) separation. Although a few adsorbents, such as metal-organic frameworks (MOFs), with high performance for CH₄/N₂ separation, have been reported, it is still challenging to target the desired adsorbents for the actual CH₄/N₂ separation under humid conditions because the adsorption capacity and selectivity of the adsorbents might be mainly dampened by water vapor. Except for the high CH₄ uptake and CH₄/N₂ selectivity, the adsorption material should simultaneously have excellent stability against moisture and relatively low-water absorption affinity. Here, we tuned the ligands and metal sites of reticular MOFs, Zn-benzene-1,4-dicarboxylic acid-1,4-diazabicyclo[2.2.2]octane (Zn-BDC-DABCO) (DMOF), affording a series of isostructural MOFs (DMOF-N, DMOF-A₁, DMOF-A₂, and DMOF-A₃). Because of the finely engineered pore size and introduced aromatic rings in the functional DMOF, gas sorption results reveal that the materials show improved performance with a benchmark CH₄ uptake of 37 cm³/g and a high CH₄/N₂ adsorption selectivity of 7.2 for DMOF-A₂ at 298 K and 1.0 bar. Moisture stability experiments show that DMOF-A₂ is a robust MOF with low water vapor capacity even at ∼40% relative humidity (RH) because of the presence of more hydrophobic aromatic rings. Breakthrough experiments verify the excellent CH₄/N₂ separation performances of DMOF-A₂ under high humidity.

Nickel-Based Metal-Organic Frameworks for Coal-Bed Methane Purification with Record CH4 /N2 Selectivity

The enrichment and purification of coal-bed methane provides a source of energy and helps offset global warming. In this work, we demonstrate a strategy involving the regulation of the pore size and pore chemistry to promote the separation of CH₄ /N₂ mixtures in four nickel-based coordination networks, named Ni(ina)₂ , Ni(3-ain)₂ , Ni(2-ain)₂ , and Ni(pba)₂ , (where ina=isonicotinic acid, 3-ain=3-aminoisonicotinic acid, 2-ain=2-aminoisonicotinic acid, and pba=4-(4-pyridyl)benzoic acid). Among them, Ni(ina)₂ and Ni(3-ain)₂ can effectively separate CH₄ from N₂ with top-performing performance because of the suitable pore size (≈0.6 and 0.5 nm) and pore environment. Explicitly, Ni(ina)₂ exhibits the highest ever reported CH₄ /N₂ selectivity of 15.8 and excellent CH₄ uptake (40.8 cm³  g^-1 ) at ambient conditions, thus setting new benchmarks for all reported MOFs and traditional adsorbents. The exceptional CH₄ /N₂ separation performance of Ni(ina)₂ is confirmed by dynamic breakthrough experiments. Under different CH₄ /N₂ ratios, Ni(ina)₂ selectively extracts methane from the gaseous blend and produces a high purity of CH₄ (99 %). Theoretical calculations and CH₄ -loading single-crystal structure analysis provide critical insight into the adsorption/separation mechanism. Ni(ina)₂ and Ni(3-ain)₂ can form rich intermolecular interactions with methane, indicating a strong adsorption affinity between pore walls and CH₄ molecules. Importantly, Ni(ina)₂ has good thermal and moisture stability and can easily be scaled up at a low cost ($25 per kilogram), which will be valuable for potential industrial applications. Overall, this work provides a powerful approach for the selective adsorption of CH₄ from coal-bed methane.

Metal-Organic Frameworks (MOFs) as methane adsorbents: From storage to diluted coal mining streams concentration

Ventilation Air Methane emissions (VAM) from coal mines lead to environmental concern because their high global warming potential and the loss of methane resources. VAM upgrading requires pre-concentration processes dealing with high flow rates of very diluted streams (<1% methane). Therefore, methane separation and concentration is technically challenging and has important environmental and safety concerns. Among the alternatives, adsorption on Metal-Organic Frameworks (MOFs) could be an interesting option to methane selective separation, due to its tuneable character and outstanding physical properties. Most of the works devoted to the methane adsorption on MOFs deal with methane storage. Therefore, these works were reviewed to determine the properties governing methane-MOF interactions. In addition, the metallic ions and organic linkers roles have been identified. With these premises, decisive effects in the methane adsorption selectivity in nitrogen/methane lean mixtures have been discussed, since nitrogen is the most concentrated gas in the VAM stream, and it is very similar to methane molecule. In order to fulfill this overview, the effect of other aspects, such as the presence of polar compounds (moisture and carbon dioxide), was also considered. In addition, engineering considerations in the operation of fixed bed adsorption units and the main challenges associated to MOFs as adsorbents were also discussed.

Separation and Purification of Hydrocarbons with Porous Materials

This Minireview focuses on the developments of the adsorptive separation of methane/nitrogen, ethene/ethane, propene/propane mixtures as well as on the separation of C8 aromatics (i.e. xylene isomers) with a wide variety of materials, including carbonaceous materials, zeolites, metal-organic frameworks, and porous organic frameworks. Some recent important developments for these adsorptive separations are also highlighted. The advantages and disadvantages of each material category are discussed and guidelines for the design of improved materials are proposed. Furthermore, challenges and future developments of each material type and separation processes are discussed.

Deep learning combined with IAST to screen thermodynamically feasible MOFs for adsorption-based separation of multiple binary mixtures

The structures of metal-organic frameworks (MOFs) can be tuned to reproducibly create adsorption properties that enable the use of these materials in fixed-adsorption beds for non-thermal separations. However, with millions of possible MOF structures, the challenge is to find the MOF with the best adsorption properties to separate a given mixture. Thus, computational, rather than experimental, screening is necessary to identify promising MOF structures that merit further examination, a process traditionally done using molecular simulation. However, even molecular simulation can become intractable when screening an expansive MOF database for their separation properties at more than a few composition, temperature, and pressure combinations. Here, we illustrate progress toward an alternative computational framework that can efficiently identify the highest-performing MOFs for separating various gas mixtures at a variety of conditions and at a fraction of the computational cost of molecular simulation. This framework uses a "multipurpose" multilayer perceptron (MLP) model that can predict single component adsorption of various small adsorbates, which, upon coupling with ideal adsorbed solution theory (IAST), can predict binary adsorption for mixtures such as Xe/Kr, CH₄/CH₆, N₂/CH₄, and Ar/Kr at multiple compositions and pressures. For this MLP+IAST framework to work with sufficient accuracy, we found it critical for the MLP to make accurate predictions at low pressures (0.01-0.1 bar). After training a model with this capability, we found that MOFs in the 95th and 90th percentiles of separation performance determined from MLP+IAST calculations were 65% and 87%, respectively, the same as MOFs in the simulation-predicted 95th percentile across several mixtures at diverse conditions (on average). After validating our MLP+IAST framework, we used a clustering algorithm to identify "privileged" MOFs that are high performing for multiple separations at multiple conditions. As an example, we focused on MOFs that were high performing for the industrially relevant separations 80/20 Xe/Kr at 1 bar and 80/20 N₂/CH₄ at 5 bars. Finally, we used the MOF free energies (calculated on our entire database) to identify privileged MOFs that were also likely synthetically accessible, at least from a thermodynamic perspective.

Nanoscale nickel metal organic framework decorated over graphene oxide and carbon nanotubes for water remediation

In this report, highly crystalline and well-dispersed nano-sized nickel metal organic framework (MOFs) was decorated over graphene oxide (GO) and carbon nanotubes (CNTs) platforms to form hybrid nanocomposites. These as-synthesized hybrid nanocomposites were synthesized through a one-pot green solvothermal method. The prepared nanocomposites were characterized by SEM, TEM, EDS, XRD, FT-IR, Raman and TGA techniques. XRD analysis revealed the crystalline structure of the hybrid nanocomposites. Morphological and elemental studies also verified successful decoration of nickel-benzene dicarboxylate (Ni-BDC) MOFs over GO and CNT platforms. Chemical analysis collected through IR, and thermal analysis collected through TGA technique, illustrated the presence of all the components in the hybrid nanomaterials. Methylene blue (MB) was used as a model organic pollutant to analyze the adsorption capacity of the prepared nanocomposites. According to the findings, a strong interaction exists between the MB molecule and the developed adsorbents at which due to the synergistic effect, the hybrid nanocomposites show several times higher adsorption capacity compared to that of parent materials. This improvement can be due to several reasons: high surface area of the MOFs in the composites resulting from the smaller size of MOFs, presence of the pores formed between the MOFs and the platforms and different morphological characteristic of Ni-BDC MOFs in hybrid nanocomposites, compared to bare Ni-BDC MOFs. Furthermore, the isotherm and kinetic studies revealed that the adsorption of MB onto the newly prepared adsorbents could best be explained by the Langmuir and Pseudo-second order kinetic models. A regeneration study demonstrated the highly stable nature of the hybrid nanocomposites.

Selective CO2 or CH4 adsorption of two anionic bcu-MOFs with two different counterions: experimental and simulation studies

Two new bcu-MOFs with counterions tuned from Li(H₂O)₄⁺ to DMA⁺ have been successfully synthesized and their selective CO₂ or CH₄ adsorption over N₂ gas has been systematically investigated in-depth by both experimental and simulation studies.

Microporous Metal-Organic Frameworks with Hydrophilic and Hydrophobic Pores for Efficient Separation of CH4/N2 Mixture

Highly selective removal of N₂ from unconventional natural gas is considered as a viable way to increase the heat value of CH₄ and reduce the greenhouse effect caused by the direct emission of CH₄/N₂ mixture. In this work, a three-dimensional Cu-MOF with two different types of micropores was synthesized, exhibiting a high selectivity for CH₄/N₂ (10.00-12.67) and the highest sorbent selection parameter value (65.73) among the reported materials. The CH₄ molecule interacts with the framework to form multiple van der Waals interactions both in hydrophilic and hydrophobic pores, indicated by density functional theory calculations to gain a deep insight into the adsorption binding sites. In contrast, the weak polarity feature of the hydrophobic pore and the occupied open-metal sites in the hydrophilic pore result in a very low adsorption uptake of N₂. The excellent separation performance combining the good stability and regenerability guarantees this Cu-MOF to be a promising adsorbent for an efficient separation of the CH₄/N₂ mixture.

Large-Scale Screening and Design of Metal-Organic Frameworks for CH4 /N2 Separation

CH₄ /N₂ separation is one of the great challenges in gas separation, which is of scientific and practical importance, such as in the upgrading of unconventional natural gas. Unfortunately, the separation performance is still quite low so far mainly due to their very close physical properties. In this work, a high-throughput computational screening method was performed to develop metal-organic frameworks (MOFs) for efficient CH₄ /N₂ separation. General designing rules as well as the correlation between selectivity and our proposed adsorbility (AD) parameter were obtained by carrying out systematic GCMC simulations of the existing 5109 CoRE MOFs. With the aid of this information, five virtual MOFs were screened out from the large database with 303 991 generated MOFs constructed in our previous work, exhibiting much higher selectivities than all the reported values. Among them, the selectivity of Zn-PYZ-BPY-1 can reach over 29.0, about 2.4 times of the highest value reported in the literature. These results may not only suggest promising candidates for CH₄ /N₂ separation but also provide useful information for large screening of MOFs for other specific separation mixtures.

A Metal-Organic Framework Based Methane Nano-trap for the Capture of Coal-Mine Methane

As a major greenhouse gas, methane, which is directly vented from the coal-mine to the atmosphere, has not yet drawn sufficient attention. To address this problem, we report a methane nano-trap that features oppositely adjacent open metal sites and dense alkyl groups in a metal-organic framework (MOF). The alkyl MOF-based methane nano-trap exhibits a record-high methane uptake and CH₄ /N₂ selectivity at 298 K and 1 bar. The methane molecules trapped within the alkyl MOF were crystalographically identified by single-crystal X-ray diffraction experiments, which in combination with molecular simulation studies unveiled the methane adsorption mechanism within the MOF-based nano-trap. The IAST calculations and the breakthrough experiments revealed that the alkyl MOF-based methane nano-trap is a new benchmark for CH₄ /N₂ separation, thereby providing a new perspective for capturing methane from coal-mine methane to recover fuel and reduce greenhouse gas emissions.

3D porous metal-organic framework for selective adsorption of methane over dinitrogen under ambient pressure

We report a highly porous 3D metal-organic framework (MOF) that shows potential for coal mine methane (CMM) capture.

Role of porosity and polarity of nanoporous carbon spheres in adsorption applications

Structure-properties (i.e., porosity and polarity) of carbons are judiciously considered for the specific adsorption applications.

Highly efficient adsorbent design using a Cu-BTC/CuO/carbon fiber paper composite for high CH4/N2 selectivity

Cu-BTC/CuO/CFP, which was obtained via atomic layer deposition, has higher selectivity for CH₄/N₂, temperature uniformity, and lower pressure drop compared to Cu-BTC.