Topological Design of Unprecedented Metal-Organic Frameworks Featuring Multiple Anion Functionalities and Hierarchical Porosity for Benchmark Acetylene Separation

Multifunctional and Ultrastable Co-MOF Effectively Separates Various Different Component Gas Mixtures

Developing low-cost and multifunctional adsorbents for adsorption separation to obtain high-purity (>99.9%) gases is intriguing yet challenging. Notably, the ongoing trade-off between adsorption capacity and selectivity in separating multicomponent mixed gases still persists as a pressing scientific challenge requiring urgent attention. Herein, the ultrastable TJT-100 exhibits unique structural characteristics including uncoordinated carboxylate oxygen atoms, coordinated water molecules directed toward the pore surface, and sufficient Me2NH2+ cations in channels. TJT-100 exhibits a high adsorption capacity and exceptional separation performance, particularly notable for its high C2H2 capacity of 127.7 cm3/g and remarkable C2H2 selectivity over CO2 (5.4) and CH4 (19.8), which makes it a standout material for various separation applications. In a breakthrough experiment with a C2H2/CO2 mixture (v/v = 50/50), TJT-100 achieved a record-high C2H2 productivity of 69.33 L/kg with a purity of 99.9%. Additionally, TJT-100 demonstrates its effectiveness in separating CO2 from natural gas and flue gas. Its exceptional selectivity for CO2/CH4 (10.7) and CO2/N2 (11.9) results in a high CO2 productivity of 21.23 and 22.93 L/kg with 99.9% purity from CO2/CH4 (v/v = 50/50) and CO2/N2 (v/v = 15/85) mixtures, respectively.

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.

Single-Molecule Traps in Covalent Organic Frameworks for Selective Capture of C2H2 from C2H4-Rich Gas Mixtures

Removing trace amounts of acetylene (C2H2) from ethylene (C2H4)-rich gas mixtures is vital for the supply of high-purity C2H4 to the chemical industry and plastics sector. However, selective removal of C2H2 is challenging due to the similar physical and chemical properties of C2H2 and C2H4. Here, we report a "single-molecule trap" strategy that utilizes electrostatic interactions between the one-dimensional (1D) channel of a covalent organic framework (denoted as COF-1) and C2H2 molecules to massively enhance the adsorption selectivity toward C2H2 over C2H4. C2H2 molecules are immobilized via interactions with the O atom of C=O groups, the N atom of C≡N groups, and the H atom of phenyl groups in 1D channels of COF-1. Due to its exceptionally high affinity for C2H2, COF-1 delivered a remarkable C2H2 uptake of 7.97 cm3/g at 298 K and 0.01 bar, surpassing all reported COFs and many other state-of-the-art adsorbents under similar conditions. Further, COF-1 demonstrated outstanding performance for the separation of C2H2 and C2H4 in breakthrough experiments under dynamic conditions. COF-1 adsorbed C2H2 at a capacity of 0.17 cm3/g at 2,000 s/g when exposed to 0.5 ml/min C2H4-rich gas mixture (99% C2H4) at 298 K, directly producing high-purity C2H4 gas at a rate of 3.95 cm3/g. Computational simulations showed that the strong affinity between C2H2 and the single-molecule traps of COF-1 were responsible for the excellent separation performance. COF-1 is also robust, providing a promising new strategy for the efficient removal of trace amounts of C2H2 in practical C2H4 purification.

Pore Environmental Modification by Amino Groups in Robust Microporous MOFs for SF6 Capturing and SF6/N2 Separation

Capturing and separating the greenhouse gas SF6 from nitrogen N2 have significant greenhouse mitigation potential and economic benefits. We used a pore engineering strategy to manipulate the pore environment of the metal-organic framework (MOF) by incorporating organic functional groups (-NH2). This resulted in an enhanced adsorption of SF6 and separation of the SF6/N2 mixture in the MOF. The introduction of amino (-NH2) groups into YTU-29 resulted in a reduction of the Brunauer-Emmett-Teller surface but an increase in interactions with SF6 within the confined pores. Water-stable YTU-29-NH2 showed a significantly higher SF6 uptake (95.5 cm3/g) than YTU-29 (77.4 cm3/g). The results of the breakthrough experiments show that YTU-29-NH2 has a significantly improved separation performance for SF6/N2 mixtures, with a high SF6 capture of 0.88 mmol/g compared to 0.56 mmol/g by YTU-29. This improvement is due to the suitable pore confinement and accessible -NH2 groups on pore surfaces. Considering its excellent regeneration ability and cycling performance, ultrastable YTU-29-NH2 demonstrates great potential for SF6 capturing and SF6/N2 separation.

Exhaled Anesthetic Xenon Regeneration by Gas Separation Using a Metal-Organic Framework with Sorbent-Sorbate Induced-Fit

Noble gas xenon (Xe) is an excellent anesthetic gas, but its rarity, high cost and constrained production prohibits wide use in medicine. Here, we have developed a closed-circuit anesthetic Xe recovery and reusage process with highly effective CO2-specific adsorbent CUPMOF-5 that is promising to solve the anesthetic Xe supply problem. CUPMOF-5 possesses spacious cage cavities interconnected in four directions by confinement throat apertures of ~3.4 Å, which makes it an ideal molecular sieving of CO2 from Xe, O2, N2 with the benchmark selectivity and high uptake capacity of CO2. In situ single-crystal X-ray diffraction (SCXRD) and computational simulation solidly revealed the vital sieving role of the confined throat and the sorbent-sorbate induced-fit strengthening binding interaction to CO2. CUPMOF-5 can remove 5 % CO2 even from actual moist exhaled anesthetic gases, and achieves the highest Xe recovery rate (99.8 %) so far, as verified by breakthrough experiments. This endows CUPMOF-5 great potential for the on-line CO2 removal and Xe recovery from anesthetic closed-circuits.

Ideal Cage-like Pores for Molecular Sieving of Butane Isomers with High Purity and Record Productivity

n-C4H10 and iso-C4H10 are both important petrochemical raw materials. Considering the coexistence of the isomers in the production process, it is necessary to achieve their efficient separation through an economical way. However, to obtain high-purity n-C4H10 and iso-C4H10 in one-step separation process, developing iso-C4H10-exclusion adsorbents with high n-C4H10 adsorption capacity is crucial. Herein, we report a cage-like MOF (SIFSIX-Cu-TPA) with small windows and large cavities which can selectively allow smaller n-C4H10 enter the pore and accommodate a large amount of n-C4H10 simultaneously. Adsorption isotherms reveal that SIFSIX-Cu-TPA not only completely excludes iso-C4H10 in a wide temperature range, but also exhibits a very high n-C4H10 adsorption capacity of 94.2 cm3 g-1 at 100 kPa and 298 K, which is the highest value among iso-C4H10-exclusion-type adsorbents. Breakthrough experiments show that SIFSIX-Cu-TPA has excellent n/iso-C4H10 separation performance and can achieve a record-high productivity of iso-C4H10 (3.2 mol kg-1) with high purity (>99.95 %) as well as 3.0 mol kg-1 of n-C4H10 (>99 %) in one separation circle. More importantly, SIFSIX-Cu-TPA can realize the efficient separation of butanes at different flow rates, temperatures, as well as under high humid condition, which indicates that SIFSIX-Cu-TPA can be deemed as an ideal platform for industrial butane isomers separation.

Metal-Organic Framework with Space-Partition Pores by Fluorinated Anions for Benchmark C2H2/CO2 Separation

The efficient separation of C2H2 from C2H2/CO2 or C2H2/CO2/CH4 mixtures is crucial for achieving high-purity C2H2 (>99%), essential in producing contemporary commodity chemicals. In this report, we present ZNU-12, a metal-organic framework with space-partitioned pores formed by inorganic fluorinated anions, for highly efficient C2H2/CO2 and C2H2/CO2/CH4 separation. The framework, partitioned by fluorinated SiF62- anions into three distinct cages, enables both a high C2H2 capacity (176.5 cm3/g at 298 K and 1.0 bar) and outstanding C2H2 selectivity over CO2 (13.4) and CH4 (233.5) simultaneously. Notably, we achieve a record-high C2H2 productivity (132.7, 105.9, 98.8, and 80.0 L/kg with 99.5% purity) from C2H2/CO2 (v/v = 50/50) and C2H2/CO2/CH4 (v/v = 1/1/1, 1/1/2, or 1/1/8) mixtures through a cycle of adsorption-desorption breakthrough experiments with high recovery rates. Theoretical calculations suggest the presence of potent "2 + 2" collaborative hydrogen bonds between C2H2 and two hexafluorosilicate (SiF62-) anions in the confined cavities.

A microporous bismuth-based MOF for efficient separation of acetylene from carbon dioxide

The separation of acetylene from carbon dioxide is challenging due to their almost identical molecular sizes and volatilities. Metal-organic frameworks (MOFs) in general are strong candidates for the separation of gas mixtures owing to the presence of functional pore surfaces that can selectively capture specific target molecules. Herein, we report a stable and easily synthesized bismuth-based MOF, Bi-BTC, which can achieve the separation of acetylene and carbon dioxide. We performed a detailed analysis of the sorption properties of the Bi-MOF. Bi-BTC shows good adsorption capacities for C2H2 with a capacity of 53.8 cm3 g-1 at 298 K and 1.0 bar, and C2H2/CO2 selectivity of 5.14/7.69 at 298 K and 1.0/0.1 bar. IAST selectivity calculations indicate that Bi-BTC possesses good separation capacity, and dynamic breakthrough experiments were performed to prove the separation of C2H2 and CO2. Bi-MOFs as a group of relatively less studied types of MOFs have interesting adsorption characteristics, and this study on Bi-based MOF will enrich three-dimensional Bi-MOF adsorbents for gas adsorption and separation applications.

A novel hydrophobic carborane-hybrid microporous material for reversed C2H6 adsorption and efficient C2H4/C2H6 separation under humid conditions

Since ethylene (C2H4) is important feedstock in the chemical industry, developing economical and energy-efficient adsorption separation techniques based on ethane (C2H6)-selective adsorbents to replace the energy-intensive cryogenic distillation is highly demanded, which however remains a daunting challenge. While previous anionic boron cluster hybrid microporous materials display C2H4-selective features, we herein reported that the incorporation of a neutral para-carborane backbone and aliphatic 1,4-diazabicyclo[2.2.2]octane (DABCO) enables the reversed adsorption of C2H6 over C2H4. The generated carborane-hybrid microporous material ZNU-10 (ZNU = Zhejiang Normal University) is highly stable in humid air and maintains good C2H6/C2H4 separation performance under high humidity. Gas loaded single crystal structure and density-functional theory (DFT) calculations revealed that the weakly polarized carborane and DABCO within ZNU-10 induce more specific C-Hδ+⋯Hδ--B dihydrogen bonds and other van der Waals interactions with C2H6, while the suitable pore space allows the high C2H6 uptake. Approximately 14.5 L kg-1 of polymer grade C2H4 can be produced from simulated C2H6/C2H4 (v/v 10/90) mixtures under ambient conditions in a single step, comparable to those of many popular materials.

Multimodal Engineering of Catalytic Interfaces Confers Multi-Site Metal-Organic Framework for Internal Preconcentration and Accelerating Redox Kinetics in Lithium-Sulfur Batteries

The development of highly efficient catalysts to address the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) in lithium-sulfur batteries (LSBs) remains a formidable challenge. In this study, a series of multi-site catalytic metal-organic frameworks (MSC-MOFs) were elaborated through multimodal molecular engineering to regulate both the reactant diffusion and catalysis processes. MSC-MOFs were crafted with nanocages featuring collaborative specific adsorption/catalytic interfaces formed by exposed mixed-valence metal sites and surrounding adsorption sites. This design facilitates internal preconcentration, a coadsorption mechanism, and continuous efficient catalytic conversion toward polysulfides concurrently. Leveraging these attributes, LSBs with an MSC-MOF-Ti catalytic interlayer demonstrated a 62 % improvement in discharge capacity and cycling stability. This resulted in achieving a high areal capacity (11.57 mAh cm-2 ) at a high sulfur loading (9.32 mg cm-2 ) under lean electrolyte conditions, along with a pouch cell exhibiting an ultra-high gravimetric energy density of 350.8 Wh kg-1 . Lastly, this work introduces a universal strategy for the development of a new class of efficient catalytic MOFs, promoting SRR and suppressing the shuttle effect at the molecular level. The findings shed light on the design of advanced porous catalytic materials for application in high-energy LSBs.

Thiadiazole-Functionalized Th/Zr-UiO-66 for Efficient C2H2/CO2 Separation

Adsorptive separation technology provides an effective approach for separating gases with similar physicochemical properties, such as the purification of acetylene (C2H2) from carbon dioxide (CO2). The high designability and tunability of metal-organic framework (MOF) adsorbents make them ideal design platforms for this challenging separation. Herein, we employ an isoreticular functionalization strategy to fine-tune the pore environment of Zr- and Th-based UiO-66 by the immobilization of the benzothiadiazole group via bottom-up synthesis. The functionalized UPC-120 exhibits an enhanced C2H2/CO2 separation performance, which is confirmed by adsorption isotherms, dynamic breakthrough curves, and theoretical simulations. The synergy of ligand functionalization and metal ion fine-tuning guided by isoreticular chemistry provides a new perspective for the design and development of adsorbents for challenging gas separation processes.

One Scalable and Stable Metal-Organic Framework for Efficient Separation of CH4/N2 Mixture

Separating CH4 from coal bed methane is of great importance but challenging. Adsorption-based separation often suffers from low selectivity, poor stability, and difficulty to scale up. Herein, a stable and scalable metal-organic framework [MOF, CoNi(pyz-NH2)] with multiple CH4 binding sites was reported to efficiently separate the CH4/N2 mixture. Due to its suitable pore size and multiple CH4 binding sites, it exhibits excellent CH4/N2 selectivity (16.5) and CH4 uptake (35.9 cm3/g) at 273 K and 1 bar, which is comparable to that of the state-of-the-art MOFs. Theoretical calculations reveal that the high density of open metal sites and polar functional groups in the pores provide strong affinity to CH4 than to N2. Moreover, CoNi(pyz-NH2) displays excellent structural stability and can be scale-up synthesized (22.7 g). This work not only provides an excellent adsorbent but also provides important inspiration for the future design and preparation of porous adsorbents for separations.

Crystal Engineering of a New Hexafluorogermanate Pillared Hybrid Ultramicroporous Material Delivers Enhanced Acetylene Selectivity

Hybrid ultramicroporous materials (HUMs), metal-organic platforms that incorporate inorganic pillars, are a promising class of porous solids. A key area of interest for such materials is gas separation, where HUMs have already established benchmark performances. Thanks to their ready compositional modularity, we report the design and synthesis of a new HUM, GEFSIX-21-Cu, incorporating the ligand pypz (4-(3,5-dimethyl-1H-pyrazol-4-yl)pyridine, 21) and GeF62- pillaring anions. GEFSIX-21-Cu delivers on two fronts: first, it displays an exceptionally high C2H2 adsorption capacity (≥5 mmol g-1) which is paired with low uptake of CO2 (<2 mmol g-1), and, second, a low enthalpy of adsorption for C2H2 (ca. 32 kJ mol-1). This combination is rarely seen in the C2H2 selective physisorbents reported thus far, and not observed in related isostructural HUMs featuring pypz and other pillaring anions. Dynamic column breakthrough experiments for 1:1 and 2:1 C2H2/CO2 mixtures revealed GEFSIX-21-Cu to selectively separate C2H2 from CO2, yielding ≥99.99% CO2 effluent purities. Temperature-programmed desorption experiments revealed full sorbent regeneration in <35 min at 60 °C, reinforcing HUMs as potentially technologically relevant materials for strategic gas separations.