Dynamic Breakthrough Research Articles

Modulation of pore chemistry through fluorinated anions exchange in a metal–organic framework for C2H4 purification

Modulating the pore chemistry and introducing ideal binding sites in MOFs to achieve one-step purification of C2H4 from ternary C2H2/C2H4/C2H6 mixture is promising but challenging. Herein, we report a post-synthetic fluorinated anions exchange strategy to access C2H4 adsorbents from a stable metal–organic framework (MOF) Fe-BDC-TPT-Cl of the acs topology (H2BDC=terephthalic acid; TPT=2,4,6-tri(4-pyridyl)-1,3,5-triazine). Introduction of BF4− and SiF62− anions gave rise to two new MOFs, Fe-BDC-TPT-BF4 and Fe-BDC-TPT-SiF6 with retained topology but different pore chemistry. Fe-BDC-TPT-BF4 exhibits the highest C2H2 uptake of 210.1 cm3 g−1 at 298 K and 100 kPa among porous adsorbents reported by now. Strong BF4−/SiF62−…HC affinity enhances host–guest interaction, enabling high separation potential (ΔQ) for C2H2/C2H4 and C2H6/C2H4. Both static sorption isotherms and dynamic breakthrough experiments revealed good performance of Fe-BDC-TPT-BF4 and Fe-BDC-TPT-SiF6 for the C2H2/C2H4/C2H6 separation. The productivity of C2H4 (purity > 99.95 %) recovered from (1/92/7) C2H2/C2H4/C2H6 over Fe-BDC-TPT-SiF6 outperforms that of Fe-BDC-TPT-Cl by more than two times. This work demonstrates that fluorinated anions exchange is an efficient strategy to regulate the pore chemistry of MOF adsorbents for one-step purification of C2H4.

Breakthrough curves of H2/CO2 adsorptions on CuBTC and MIL-125(Ti)_NH2 predicted by empirical correlations and deep neural networks

With the continuous emergence of new materials, efficiently screening suitable materials for hydrogen purification by pressure swing adsorption (PSA) technology has become a hot topic. Metal-organic frameworks (MOFs) hold significant promise in gas adsorption and separation due to their unique structure and versatility. Breakthrough curves depict the dynamic adsorption kinetics of multi-components in fixed-bed columns, offering a means to screen adsorbents. In this study, a deep neural network (DNN) model comprising 11 hidden layers is developed to predict the dynamic breakthrough behavior of MOF CuBTC and MIL-125(Ti)_NH2 adsorbents. The training data for the DNN were generated from a non-isothermal model established using Aspen Adsorption software. Results demonstrate that the DNN model effectively predicts the H2/CO2 breakthrough behavior on CuBTC and MIL-125(Ti)_NH2 adsorbents. Compared with empirical mathematical correlation models, the DNN can predict breakthrough profiles under varying operating conditions, exhibiting superior adaptability. Furthermore, parametric studies based on the DNN model reveal that initial temperature, adsorption pressure and feed flow rate play important roles in the dynamic adsorption process, significantly influencing the position and shape of the breakthrough curve. Decreasing the feed flow rate and initial temperature while increasing adsorption pressure can enhance breakthrough times and hydrogen purity. By comparing the breakthrough curves of the two adsorbents under different operating conditions for H2/CO2, the dimensionless breakthrough time of CO2 on the CuBTC adsorbent was longer. Additionally, simulation results of the PSA cycle suggest that CuBTC yields higher hydrogen purity than MIL-125(Ti)_NH2. Consequently, CuBTC is deemed more suitable for hydrogen purification of binary H2/CO2 mixtures than MIL-125(Ti)_NH2.

Three-dimensional linker-promoted hierarchical porous metal–organic framework for natural gas purification

The purification of methane from natural gas is extremely important for industrial applications. In this study, hierarchical porous material LIFM-Z1 with microporous cages and mesoporous hexagonal one-dimensional channels was successfully synthesized and evaluated. The results show that LIFM-Z1 can effectively separate CH4 from the mixed gas containing CH4, C2H6, C3H8 and n-C4H10. Single-component adsorption experiments revealed the selective adsorption ability of LIFM-Z1 for C2H6, C3H8, and n-C4H10, enabling a clear distinction between these components and CH4. This selectivity was further verified by dynamic breakthrough experiments. Theoretical analysis shows that the interaction between LIFM-Z1 and gas molecules mainly depends on the synergistic effect of C–H⋯O hydrogen bond and C–H⋯C van der Waals force. The results highlight the potential of utilizing 3D linkers to enhance the inner wall interaction with CH4 and its related gases in MOF construction. These characteristics of LIFM-Z1 not only successfully demonstrate the potential of separation and purification of natural gas with high efficiency, but also show its broad application prospects in the actual natural gas processing.

Ultramicroporous zinc-aminotriazole MOF with customized alkaline pore environments for highly efficient capture of CO2 from flue gas

CO2 capture from natural gas and N2-rich flue gas is essential for improving the utilization of natural resource gases reducing CO2 emission, thereby alleviating the greenhouse effect. However, achieving effective Adsorptive separation of CO2 from CH4, N2, and O2 based on molecular sieving is still challenging and rarely reported, but selectively capturing CO2 places high desires on maximizing separation efficiency. Here, we report a zinc-aminotriazole ultramicroporous metal–organic framework (ZnATZoxH2O), constructed from zinc carbonate, 3-amino-1,2,4-triazole (ATZ), and oxalic acid with water as the only solvent. ZnATZoxH2O features NH2-functionalized and pore channels around 3.6 Å, which preferentially adsorb CO2. This material exhibits high CO2 uptake of 61.9 cm3 g−1 at 298 K and 1 bar and significantly high IAST selectivity for CO2/N2 (>103) and CO2/CH4 (>105) and CO2/O2 (>104). Theoretical GCMC simulations reveal that negatively charged amino groups decorated on the pore channel surface and carboxylic acid in the pore environment enhance the binding affinity over CO2 through electrostatic interactions for preferential capture of CO2. Single-component adsorption experiments and dynamic breakthrough experiments mutually validated the superior separation performance of this material and dynamic column breakthrough tests to produce high dynamic CO2 separation productivity of 2.017 mmol g−1 and 3.4 mmol g−1 for CO2/N2 (15/85), CO2/CH4 (50/50), and 2.26mmol g−1 CO2/N2/O2 (15/80/5). Non-hazardous water as a synthetic solvent to assemble highly stable and efficient CO2-selective materials makes it promising for practical industrial applications.

Asymmetrical Modification of Cyclopentadienyl Cobalt in Eu-MOF for C2H2/CO2 Separation.

The development of novel adsorption materials is of significance for the efficient and low-energy purification of acetylene (C2H2). Emerging metal-organic framework (MOF) adsorbents demonstrate great application prospects in the field of gas adsorption and separation. Herein, we synthesized a Eu-MOF asymmetrically modified with cyclopentadienyl cobalt exhibiting two different types of cages, denoted as UPC-119. Adsorption isotherms and dynamic breakthrough curves confirm its potential in C2H2/CO2 separation, which is further evidenced by theoretical simulations. The high adsorption capacity and low adsorption enthalpy render UPC-119 as a promising adsorbent for C2H2/CO2 separation with ease of regeneration.

Construction of Coordination Spaces with Narrow Pore Windows in Co-Based Metal-Organic Frameworks toward CO2/N2 Separation.

Carbon emission reduction is an important measure to mitigate the greenhouse effect, which has become a hotspot in global climate change research. To contribute to this, here, we fabricated two Co-based metal-organic frameworks (Co-MOFs), namely, {[Co3(NTB)2(bib)]·(DMA)2·(H2O)4}n (DZU-211) and {[Co3(NTB)2(bmip)]·(DMA)2}n (DZU-212) (H3NTB = 4,4',4″-nitrilotribenzoic acid, bib = 1,4-bis(imidazol-1-yl)-butane, bmip = 1,3-bis(2-methyl-1H-imidazol-1-yl)propane) to realize efficient CO2/N2 separation by dividing coordination spaces into suitable pores with narrow windows. DZU-211 reveals a 3D open porous framework, while DZU-212 exhibits a 3D double-fold interpenetrated structure. The two MOFs both possess large coordination spaces and small open pore sizes, via the bib ligand insertion and framework interpenetration, respectively. Comparatively, DZU-211 reveals superior selective CO2 uptake properties due to its more suitable pore characteristics. Gas sorption experiments show that DZU-211 has a CO2 uptake of 52.6 cm3 g-1 with a high simulated CO2/N2 selectivity of 101.7 (298 K, 1 atm) and a moderate initial adsorption heat of 38.1 kJ mol-1. Moreover, dynamic breakthrough experiments confirm the potential application of DZU-211 as a CO2 separation material from postcombustion flue gases.

Leveraging synergistic polar and nonpolar binding sites in a fluorinated metal–organic framework for efficient ethane/ethylene separation

Constructing favorable C2H6-selective adsorbents for one-step C2H4 purification from C2H6/C2H4 mixtures is a matter of considerable significance, but is still a very challenging task in the field of petrochemical industry. Herein, we report a well-designed ant-type metal–organic framework (NUM-16) with appropriate pore size and pore environment for preferential trapping C2H6. NUM-16a (activated NUM-16) performs a high C2H6 uptake of 4.39 mmol/g and a good adsorption selectivity for C2H6/C2H4 (10:90, v/v) mixture at 298 K and 1 bar. The separation mechanism, as unveiled by the grand canonical Monte Carlo simulations and density functional theory calculations, is mainly attributed to synergistic polar and nonpolar binding sites on the pore surface of NUM-16a, which provide stronger affinities to C2H6 than C2H4. Under ambient conditions, dynamic breakthrough experiments revealed that NUM-16a demonstrates the enormous potential for actual C2H6/C2H4 separation and is expected to be applied to the correlative industrial process. Both experiments and theoretical calculations distinctly demonstrated that the reasonable integration of polar and nonpolar binding sites in C2H6-preferred MOFs is a feasible strategy for efficient C2H6/C2H4 separation. This work afforded some useful insights into designing and developing high-powered MOF adsorbents to solve tricky industrial separation challenges.

3D-printed zeolite 13X gyroid monolith adsorbents for CO2 capture

Self-standing 3D-printed gyroid monoliths of zeolite 13X were fabricated for the first time for carbon dioxide adsorption. Gyroid sheet-based triply periodic minimal surface (TPMS) lattices provide high surface area per unit volume, smooth surfaces with no discontinuities, and low pressure drop compared to powder and beads, which are essential in gas adsorption. A photopolymer resin and zeolite 13X powder slurry was 3D-printed by digital light processing followed by debinding to remove the polymer and sintering to diffuse and consolidate the zeolite 13X particles. The sintered adsorbents were mechanically stable, and structural and morphological analyses revealed the interconnected nature of the gyroid cells permitting CO2 molecules to easily diffuse into the printed structure, thus ensuring sufficient adsorbent/adsorbate contact. The gyroid zeolite monoliths reached an equilibrium adsorption capacity of 3.5 mmol g−1 in 77 min at 25 °C and 1 bar, whereas the beads and powder required 96 and 100 min, respectively, while after 20 pressure swing adsorption (PSA) cycles, the zeolite monolith showed sustainable performance compared to the powder. The CO2/N2 selectivity ranged from 328 (at 50 mbar) to 51 (at 1 bar) at 25 °C for the zeolite monolith, whereas the powder exhibited selectivity values in the range of 294 (at 50 mbar) to 33 (at 1 bar). Dynamic breakthrough experiments using CO2/N2 mixtures confirmed the fast kinetics and separation performance of the monoliths, while the pressure drop was also significantly lower than the powder and the beads. The novel topology of the developed self-standing gyroid zeolite monoliths eliminate the need for structuring of powdered adsorbents and exhibit competitive performance, enhanced kinetics and cyclability, and reduced pressure drop toward large-scale carbon capture application.

Efficient adsorptive separation of nitrotoluene isomers via a stable and low-cost metal–organic framework with descending affinity order of meta-/ortho-/para-isomers

Obtaining purified nitrotoluenes from their mixture is significant but challenging due to their similar molecular sizes and physical properties. To overcome this challenge, here we report a stable, inexpensive and green-synthesized aluminium-based metal–organic framework (MIL-160) to separate the nitrotoluene mixtures. The appropriate pore size and pore environment permitted MIL-160 to exhibit a rare meta-nitrotoluene (m-NT) preference and always maintain the meta- > ortho- > para-nitrotoluene (m- > o- > p-NT) adsorption order in dynamic breakthrough and pulse modes as well as batch-mode adsorption. Theoretical calculations revealed that the abundant H/O atoms in the confined nanospace provided strong binding sites for selectively capturing nitrotoluene isomers. Specifically, due to difference in shape matching, the strongest host–guest interactions occurred in m-NT@MIL-160, followed by o-NT@MIL-160, and last p-NT@MIL-160. Notably, breakthrough experiments confirmed that a variety of binary and ternary mixtures can be separated via continuous adsorption. The dynamic adsorption stage of ternary mixture directly produced 0.33 mmol g−1 of pure p-NT, and the eluent in the desorption stage contained a high content of m-NT. Additional dynamic adsorption model fitting results indicated that the outstanding dynamic separation performance was also achieved from kinetic factors. These results lay the foundation for the effective separation of nitrotoluene mixtures.

Triple Templates Directed Synthesis of Nitrogen-Doped Hierarchically Porous Carbons from Pyridine Rich Monomer as Efficient and Reversible SO2 Adsorbents.

Herein, a variety of 2,6-diaminopyridine (DAP) derived nitrogen-doped hierarchically porous carbon (DAP-NHPC-T) prepared from carbonization-induced structure transformation of DAP-Zn-SiO2-P123 nanocomposites are reported, which are facilely prepared from solvent-free co-assembly of block copolymer templates P123 with pyridine-rich monomer of DAP, Zn(NO3)2 and tetramethoxysilane. In the pyrolysis process, P123 and SiO2 templates promote the formation of mesoporous and supermicroporous structures in the DAP-NHPC-T, while high-temperature volatilization of Zn contributed to generation of micropores. The DAP-NHPC-T possess large BET surface areas (≈956-1126 m2g-1), hierarchical porosity with micro-supermicro-mesoporous feature and high nitrogen contents (≈10.44-5.99 at%) with tunable density of pyridine-based nitrogen sites (≈5.99-3.32 at%), exhibiting good accessibility and reinforced interaction with SO2. Consequently, the DAP-NHPC-T show high SO2 capacity (14.7mmolg-1, 25°C and 1.0bar) and SO2/CO2/N2 IAST selectivities, extraordinary dynamic breakthrough separation efficiency and cycling stability, far beyond any other reported nitrogen-doped metal-free carbon. As verified by in situ spectroscopy and theoretical calculations, the pyridine-based nitrogen sites of the DAP-NHPC-T boost SO2 adsorption via the unique charge transfer, the adsorption mechanism and reaction model have been finally clarified.

Highly Selective SO2 Capture by Triazine-Functionalized Triphenylamine-Based Nanoporous Organic Polymers.

The emissions of sulfur dioxide (SO2) from combustion exhaust gases pose significant risks to public health and the environment due to their harmful effects. Therefore, the development of highly efficient adsorbent polymers capable of capturing SO2 with high capacity and selectivity has emerged as a critical challenge in recent years. However, existing polymers often exhibit poor SO2/CO2 and SO2/N2 selectivity. Herein, we report two triazine-functionalized triphenylamine-based nanoporous organic polymers (ANOP-6 and ANOP-7) that demonstrate both good SO2 uptake and high SO2/CO2 and SO2/N2 selectivity. These polymers were synthesized through cost-effective Friedel-Crafts reactions using cyanuric chloride, 3,6-diphenylaminecarbazole, and 2,2',7,7'-tetrakis(diphenylamino)-9,9'-spirobifluorene. The resultant ANOPs are composed of triazine and triphenylamine units and feature an ultramicroporous structure. Remarkably, ANOPs exhibit impressive adsorption capacities for SO2, with uptakes of approximately 3.31-3.72 mmol·g-1 at 0.1 bar, increasing to 9.52-9.94 mmol·g-1 at 1 bar. The static adsorption isotherms effectively illustrate the ability of ANOPs to separate SO2 from SO2/CO2 and SO2/N2 mixtures. At 298 K and 1 bar, ANOP-6 shows outstanding selectivity toward SO2/CO2 (248) and SO2/N2 (13146), surpassing all previously reported triazine-based nanoporous organic polymers. Additionally, dynamic breakthrough tests demonstrate the superior separation properties of ANOPs for SO2 from an SO2/CO2/N2 mixture. ANOPs exhibit a breakthrough time of 73.1 min·g-1 and a saturated SO2 capacity of 0.53 mmol·g-1. These results highlight the exceptional adsorption properties of ANOPs for SO2, indicating their promising potential for the highly efficient capture of SO2 from flue gas.

Pore engineering in highly stable hydrogen-bonded organic frameworks for efficient CH4 purification

The unsatisfactory stability of hydrogen-bonded organic frameworks (HOFs) arising from the weakness and flexibility of hydrogen-bonding (H-bonding) has generally hindered their practical applications. By synergistically employing three key strategies: (Ⅰ) introducing charge-assisted H-bonding to increase the polarity of the framework, (Ⅱ) optimizing the length of the building unit by extending the core structure of the linker molecule, and (III) incorporating functional sites containing methoxy and trifluoromethyl, to increase the stability of HOFs and the adsorption affinity for gas molecules, we successfully synthesized three charge-assisted hydrogen-bonded HOFs (NKM-HOF-3, NKM-HOF-4, and NKM-HOF-5; NKM = Nankai Materials). These HOFs exhibit distinct space configurations of nonporous packing, discrete cavities or continuous one-dimensional channels. Notably, NKM-HOF-5 exhibits commendable thermal and chemical stability and can be readily regenerated by re-solvothermal reaction. The activated NKM-HOF-5a exhibits a low affinity for CH4 but captures C2H6 and C3H8 with a relatively high affinity. According to theoretical calculations, the suitable pore size, together with functionalized and polarized surface environments in NKM-HOF-5a contribute to the excellent selective gas adsorption performance of NKM-HOF-5a. Furthermore, the dynamic breakthrough experiments demonstrate the highly efficient separation performance of NKM-HOF-5a for C2H6/CH4, C3H8/CH4, and C3H8/C2H6/CH4.

Green and Scalable Preparation of an Isomeric CALF-20 Adsorbent with Tailored Pore Size for Molecular Sieving of Propylene from Propane.

Molecular sieving of propylene (C3H6) from propane (C3H8) is highly demanded for C3H6 purification. However, delicate control over aperture size to achieve both high C3H6 uptake and C3H6/C3H8 selectivity with low cost remains a significant challenge. Herein, a green and scalable approach is reported for preparing an isomeric CALF-20 adsorbent, termed as NCU-20, using water as the only solvent with a cost of $10 per kilogram. NCU-20 features a contracted pore size (4.2×4.7Å2) compared to CALF-20 (5.2×5.7Å2), which enables molecular sieving of C3H6 (4.16×4.65Å2) from C3H8 (4.20×4.80Å2). Notably, NCU-20 exhibits record-high C3H6 adsorption capacity (94.41 cm3cm-3) at 298K and 1.0bar, outperforming all C3H6/C3H8 molecular sieving adsorbents. The sieving performances of C3H6/C3H8 are well maintained at elevated temperatures. Therefore, a delicate balance between C3H6 adsorption capacity (91.62 cm3cm-3) and C3H6/C3H8 selectivity (uptake ratio of 22.2) is obtained on NCU-20 at 298K and 0.5bar. Furthermore, dynamic breakthrough experiments demonstrate a high productivity of 65.39 cm3cm-3 for high-purity C3H6 (>99.5%) from an equimolar C3H6/C3H8 gas-mixture.

A large-scale synthesizable superhydrophobic C2H6- selective MOF for C2H6/C2H4 separation

Developing C2H6-selective adsorbents for efficient separation of C2H6/C2H4 is of great significance for the petrochemical industry. Numerous C2H6-selective adsorbents have been created, but their applicability in real-world industrial settings is severely constrained by their unscalable production and generally low stability (particularly water resistance). Herein, we proposed a series of C2H6-selective adsorbents CUPMOF-2-M (M = Zn, Mn, Cu, Mg), in which CUPMOF-2-Zn (also termed MET-6) not only possesses good C2H6-selective separation effect but super-hydrophobicity and low cost. At 298 K and 80 % relative humidity, CUPMOF-2-Zn only adsorbs 0.4 mmol·g−1 of water, outperforming all previously reported C2H6-selective materials in terms of hydrophobicity. Moreover, dynamic breakthrough experiments solidly demonstrated that CUPMOF-2-Zn can efficiently separate C2H6/C2H4 in high humidity conditions. More importantly, CUPMOF-2-Zn can be synthesized in a large-scale at room temperature (one batch 10 kg), which is essential to industrial implementation for separation of C2H6/C2H4.

Highly efficient separation of CO2/N2 and CO2/CH4 via metal-ion regulation in ultra-microporous metal-organic frameworks

Efficient separation of CO2 from CH4 and N2 is crucial for industrial processes. This study presents a novel approach to enhance CO2/N2 and CO2/CH4 separation using metal-ion regulation in ultra-microporous metal–organic frameworks (MOFs). Specifically, we synthesized ZSTU-8-M (M=Cd, Zn) by coordinating norfloxacin ligands with different metal ions, achieving precise modulation of the pore structure. Ideal adsorption solution theory (IAST) calculations demonstrated that ZSTU-8-Cd exhibited superior selectivity for CO2/N2 (952) and CO2/CH4 (369) mixtures compared to ZSTU-8-Zn. Grand canonical Monte Carlo (GCMC) simulations and in situ single-crystal X-ray diffraction (SCXRD) confirmed the presence of specific CO2 binding sites within the pore channels. The CO2 molecule shows a unique strong adsorption mechanism of hydrogen bonding sites in this structure, and thus achieves high adsorption capacity at low pressure. Dynamic breakthrough experiments further validated the practical separation efficiency of ZSTU-8-Cd, with high retention times and saturated adsorption capacities for CO2. These findings highlight the ability of metal-ion modulation to achieve simultaneous improvement in adsorption capacity and selectivity, demonstrating the potential of MOFs for advanced gas separation applications.

Ultramicroporous metal-organic framework for efficient carbon dioxide capture from flue gas and natural gas

Carbon dioxide capture from flue gas (CO2/N2) and natural gas (CO2/CH4) is a challenging and cost-effective task. In this paper, ultramicroporous metal-organic frameworks (MOFs) (Co-norf and Ni-norf) are synthesized to realize the efficient separation of CO2/N2 and CO2/CH4 by metal ion regulation. The Ideal Adsorption Solution Theory (IAST) was calculated to evaluate the adsorption selectivity of activated Co-norf and Ni-norf for CO2/N2 (v/v = 15/85) mixtures and CO2/CH4 mixtures. The CO2/N2 selectivity of Co-norf and Ni-norf at 100 kPa was 734 and 96, respectively, which corresponds to an almost 7.6-fold increase by metal ion modulation. The specific binding sites of CO2 molecules within the pore channels were obtained by grand canonical Monte Carlo simulation (GCMC). Dynamic breakthrough experiments respond to the actual separation in systems simulating flue gas and natural gas, where the higher saturation adsorption and longer retention time proved that Co-norf is an ideal material for CO2 capture and separation. The present work provides a feasible approach for the application of MOF in gas separation.

Three-way ROD metal-organic frameworks for natural gas upgrading

The reticular chemistry of rod MOFs has attracted increasing attention from structures to applications. Herein, a series of MOF materials along with unique 3-way rod secondary building units were thoroughly prepared according to our previous work (3W-ROD-2-OH, 3W-ROD-2-F, 3W-ROD-2-CH3). Thanks to their unique structural features, 3W-ROD-2-X exhibited relatively high adsorption capacities for C3H8 (8.53∼8.74 mmol/g), C2H6 (3.40∼3.69 mmol/g), and CO2 (1.94∼2.15 mmol/g), over CH4 (0.42∼0.45 mmol/g) at 298 K and 1 bar. The adsorption selectivities of C3H8/CH4, C2H6/CH4, and CO2/CH4 were calculated by IAST. The selectivities were 53.7∼70.9 (C3H8/CH4 = 15:85), 8.9∼11 (C2H6/CH4 = 15:85) and 5.3∼7.0 (CO2/CH4 = 15:85), respectively. Meanwhile, dynamic breakthrough experiments proved that 3W-ROD-2-CH3 showed separation property toward C3H8/CH4, C2H6/CH4, and CO2/CH4. The results indicate that the materials have the potential for natural gas upgrading.

An adenine-based metal-organic framework with tailored pore environment for adsorption separation of C2H2 from C2H4 and CO2

The separation of acetylene (C2H2) from mixtures with ethylene (C2H4) and carbon dioxide (CO2) is crucial yet challenging in the chemical industry. Based on the adsorption separation technology, it is desirable to design and develop efficient adsorbents for C2H2 separation. In this work, we present an adenine-based metal-organic framework (Cu-AD-HEA), which features tailored pore environment with Lewis basic sites within the specific intersecting channels for the separation of C2H2 from mixtures with C2H4 and CO2. The obtained Cu-AD-HEA exhibits exceptional adsorption capacity for C2H2 and demonstrates competitive adsorption selectivity for C2H2/C2H4 and C2H2/CO2. Furthermore, dynamic breakthrough results further illustrate the superior dynamic separation of C2H2 over C2H4 and CO2. Moreover, detailed molecular simulations and density functional theory (DFT) calculations elucidate that C2H2 is preferentially captured in a tailored pore environment of Cu-AD-HEA with stronger binding affinity through CH⋯N/O hydrogen bonds and C–H⋯π or π⋯π interactions. This work offers an effective MOF-based adsorbent for the separation of C2H2 from mixtures with C2H4 and CO2.

Electrostatically driven kinetic inverse CO2/C2H2 separation in LTA-type zeolites

The identical molecular size and similar physical properties of carbon dioxide (CO2) and acetylene (C2H2) make their adsorptive separation extremely challenging to achieve with most adsorbents. Reports on the separation of CO2 and C2H2 mixtures by zeolites are even rarer with the mechanism of adsorptive separation requiring further exploration. In this paper, we report that ion modulation of zeolite 5A promotes the difference in kinetic diffusion of CO2 and C2H2, realizing the inverse separation of zeolite from selective adsorption of C2H2 to selective adsorption of CO2. Creating a compact pore space restricting the orientation of gas molecules enables charge recognition. The positive electrostatic potential at the pore openings was utilized to hinder the diffusion of C2H2 between the cages while ensuring the transfer of CO2, increasing their diffusion differences in pore channels and leading to the CO2/C2H2 kinetic selectivity of 31.97. Grand canonical Monte Carlo (GCMC) simulation demonstrates that the CO2 distribution in K-5A-β is significantly higher than that of C2H2. Dynamic breakthrough experiments verify the excellent performance of material in practical CO2/C2H2 separation, for CO2/C2H2 (50/50 and 1/99, V/V) mixtures can be separated in one step, thus directly generating high purity C2H2 (> 99.95%), which provides a promising thought for the zeolite-based separation of CO2 and C2H2.

Preparation and characterization of UiO-66-(OH)2/MWCNTs composites for CO2/N2 adsorption separation

The increasing CO2 concentration in the atmosphere can lead to climate change, and CO2 capture technology is one of the most direct and effective means of reducing carbon emissions. In this study, a new composite was prepared in situ by loading multi-walled carbon nanotubes (MWCNTs) onto metal–organic frameworks (MOFs) to efficiently capture CO2 in flue gas. The morphological states and pore structures of the composites were analyzed using characterization methods. The CO2 adsorption properties of the composites were tested at 273 K and 298 K with different MWCNTs loadings. The optimal CO2 adsorption quantities of the composite material were measured to be 4.4 and 5.75 mmol/g, respectively, which increased the adsorption capacity by 66.7 % and 55 %, respectively, compared with the parent material at a pressure of 1 bar. The CO2/N2 separation performance of the composites was examined using ideal adsorption solution theory calculations and dynamic adsorption breakthrough experiments. The stability of the composites was investigated by thermogravimetric analysis, acidification experiments, and cyclical adsorption–desorption experimentation. The UiO-66-(OH)2/MWCNTs composites exhibited superior CO2 adsorption–separation performance, thermal stability, acid resistance, and cycling stability. Therefore, the composite has potential applications in CO2 capture separation technology.