Efficient CO 2 Removal for Ultra ‐ Pure CO Production by Two Hybrid Ultramicroporous Materials

Quasi-open Cu(I) sites for efficient CO separation with high O2/H2O tolerance

Carbon monoxide (CO) separation relies on chemical adsorption but suffers from the difficulty of desorption and instability of open metal sites against O2, H2O and so on. Here we demonstrate quasi-open metal sites with hidden or shielded coordination sites as a promising solution. Possessing the trigonal coordination geometry (sp2), Cu(I) ions in porous frameworks show weak physical adsorption for non-target guests. Rational regulation of framework flexibility enables geometry transformation to tetrahedral geometry (sp3), generating a fourth coordination site for the chemical adsorption of CO. Quantitative breakthrough experiments at ambient conditions show CO uptakes up to 4.1 mmol g-1 and CO selectivity up to 347 against CO2, CH4, O2, N2 and H2. The adsorbents can be completely regenerated at 333-373 K to recover CO with a purity of >99.99%, and the separation performances are stable in high-concentration O2 and H2O. Although CO leakage concentration generally follows the structural transition pressure, large amounts (>3 mmol g-1) of ultrahigh-purity (99.9999999%, 9N; CO concentration < 1 part per billion) gases can be produced in a single adsorption process, demonstrating the usefulness of this approach for separation applications.

Optimizing Sieving Effect for CO2 Capture from Humid Air Using an Adaptive Ultramicroporous Framework

Excessive CO2 in the air can not only lead to serious climate problems but also cause serious damage to humans in confined spaces. Here, a novel metal-organic framework (FJI-H38) with adaptive ultramicropores and multiple active sites is prepared. It can sieve CO2 from air with the very high adsorption capacity/selectivity but the lowest adsorption enthalpy among the reported physical adsorbents. Such excellent adsorption performances can be retained even at high humidity. Mechanistic studies show that the polar ultramicropore is very suitable for molecular sieving of CO2 from N2 , and the distinguishable adsorption sites for H2 O and CO2 enable them to be co-adsorbed. Notably, the adsorbed-CO2 -driven pore shrinkage can further promote CO2 capture while the adsorbed-H2 O-induced phase transitions in turn inhibit H2 O adsorption. Moreover, FJI-H38 has excellent stability and recyclability and can be synthesized on a large scale, making it a practical trace CO2 adsorbent. This will provide a new strategy for developing practical adsorbents for CO2 capture from the air.

Induced-Fit-Identification in a Rigid Metal-Organic Framework for ppm-Level CO2 Removal and Ultra-Pure CO Enrichment

Removing CO2 from crude syngas via physical adsorption is an effective method to yield eligible syngas. However, the bottleneck in trapping ppm-level CO2 and improving CO purity at higher working temperatures are major challenges. Here we report a thermoresponsive metal-organic framework (1 a-apz), assembled by rigid Mg2 (dobdc) (1 a) and aminopyrazine (apz), which not only affords an ultra-high CO2 capacity (145.0/197.6 cm3  g-1 (0.01/0.1 bar) at 298 K) but also produces ultra-pure CO (purity ≥99.99 %) at a practical ambient temperature (TA ). Several characterization results, including variable-temperature tests, in situ high-resolution synchrotron X-ray diffraction (HR-SXRD), and simulations, explicitly unravel that the excellent property is attributed to the induced-fit-identification in 1 a-apz that comprises self-adaption of apz, multiple binding sites, and complementary electrostatic potential (ESP). Breakthrough tests suggest that 1 a-apz can remove CO2 from 1/99 CO2 /CO mixtures at practical 348 K, yielding 70.5 L kg-1 of CO with ultra-high purity of ≥99.99 %. The excellent separation performance is also revealed by separating crude syngas that contains quinary mixtures of H2 /N2 /CH4 /CO/CO2 (46/18.3/2.4/32.3/1, v/v/v/v/v).

Fluorinated metal-organic frameworks for gas separation

Fluorinated metal-organic frameworks (F-MOFs) as fast-growing porous materials have revolutionized the field of gas separation due to their tunable pore apertures, appealing chemical features, and excellent stability. A deep understanding of their structure-performance relationships is critical for the synthesis and development of new F-MOFs. This critical review has focused on several strategies for the precise design and synthesis of new F-MOFs with structures tuned for specific gas separation purposes. First, the basic principles and concepts of F-MOFs as well as their structure, synthesis and modification and their structure to property relationships are studied. Then, applications of F-MOFs in adsorption and membrane gas separation are discussed. A detailed account of the design and capabilities of F-MOFs for the adsorption of various gases and the governing principles is provided. In addition, the exceptional characteristics of highly stable F-MOFs with engineered pore size and tuned structures are put into perspective to fabricate selective membranes for gas separation. Systematic analysis of the position of F-MOFs in gas separation revealed that F-MOFs are benchmark materials in most of the challenging gas separations. The outlook and future directions of the science and engineering of F-MOFs and their challenges are highlighted to tackle the issues of overcoming the trade-off between capacity/permeability and selectivity for a serious move towards industrialization.

Efficient CO2/CO separation in a stable microporous hydrogen-bonded organic framework

We herein realize the first example of using a microporous HOF material (ZJU-HOF-1) with suitable pore cavities for highly efficient CO₂/CO separation under dry and humid conditions.

A Thermally and Chemically Stable Copper(II) Metal-Organic Framework with High Performance for Gas Adsorption and Separation

A versatile microporous metal-organic framework (MOF), {[Cu(TIA)]·1.5CH₃OH}_n (Cu-1), was successfully obtained via the solvothermal reaction of cuprous(II) salt with the bifunctional ligand 3-(1H-1,2,4-triazol-1-yl)isophthalic acid. Single-crystal X-ray diffraction studies indicate that Cu-1 contains an apo three-dimensional skeleton and two types of one-dimensional channels. The framework of Cu-1 has excellent acid-alkali resistance and thermal stability, which is stable in a pH = 2-13 aqueous solution and an 260 °C air environment. In addition, the microporous copper MOF shows very high uptakes of CO₂ (180 cm³·g^-1) and C₂H₂ (113 cm³·g^-1) at 273 K and displays excellent adsorption selectivity for small molecular gases. The ideal adsorbed solution theory selectivity values for C₂H₂/C₂H₄, CO₂/CH₄, and CO₂/N₂ are 2, 9, and 22 at 298 K, respectively. At the same time, breakthrough experiments for CO₂/CH₄, CO₂/N₂, and C₂H₂/C₂H₄ were further conducted to verify the efficient separation performances.

An Unprecedented Pillar-Cage Fluorinated Hybrid Porous Framework with Highly Efficient Acetylene Storage and Separation

Despite much intense investigation on the C₂ H₂ /CO₂ separation, the trade-off between the adsorption capacity and separation selectivity is still tricky. To overcome the dilemma, we have rationally synthesized an ultra-stable fluorinated hybrid porous material SIFSIX-Cu-TPA with the ith-d topology. Completely differing from the famous pillar-layer fluorinated materials, SIFSIX-Cu-TPA possesses a unique pillar-cage structure, in which the SiF₆ ^2- anions cross-link two adjacent metal nodes as pillars to stabilize the three-dimensional framework constructed by icosahedral and tetrahedral cages. As anticipated, SIFSIX-Cu-TPA has high BET surface area (1330 m²  g^-1 ) as well as high C₂ H₂ uptake (185 cm³  g^-1 at 298 K and 1 bar). At the same time, due to the obvious difference in the adsorption performance of CO₂ and C₂ H₂ especially in the low pressure area, SIFSIX-Cu-TPA also exhibits an excellent C₂ H₂ /CO₂ separation performance (breakthrough time up to 68 min g^-1 at 298 K and 1 bar).

Tunable Selectivity and High Efficiency of CO2 Electroreduction via Borate-Enhanced Molten Salt Electrolysis

Converting CO₂ into value-added chemical fuels and functional materials by CO₂ reduction reaction (CO₂RR) is conducive to achieving a carbon-neutral energy cycle. However, it is still challenging to efficiently navigate CO₂RR toward desirable products. Herein, we report a facile strategy to extend product species in borate-containing molten electrolyte at a positively shifted cathodic potential with a high current density (e.g. 100 mA/cm²), which can selectively electro-transform CO₂ into desired products (either CO or solid carbon nanofibers, respectively reaching a high selectivity of ∼90%). The borates can act as a controller of electrolyte alkalinity to buffer the concentration of sequentially generated O²⁻ during CO₂RR, positively shifting the reduction potential of the captured CO₂ and concurrently extending the product species. The sustainable buffering effect is available under CO₂ atmosphere. Compared with borate-free electrolyte, the CO₂ conversion efficiency is over three times higher, while the electrolysis energy consumption is decreased by over 40%.

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The product selectivity of CO₂ reduction reaction was highly tunable

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Extending product species via regulating electrolyte alkalinity was achieved

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Borate-assisted oxygen removal was conducive to produce CO₂-derived CNFs

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Lower energy consumption and higher CO₂ conversion efficiency were achieved

Acid-Base-Resistant Metal-Organic Framework for Size-Selective Carbon Dioxide Capture

The development of practical porous materials for the selective capture of CO₂ from flue gas and crude biogas is highly critical for both environment protection and energy safety. Here, a novel metal-organic framework (FJI-H29) has been prepared, which not only has excellent acid-base resistance but also possesses polar micropores (3.4-4.3 Å) that can match CO₂ molecules well. FJI-H29 can selectively capture CO₂ from N₂ and CH₄ with excellent separation efficiency and suitable adsorption enthalpy under ambient conditions. Breakthrough experiments further confirm its practicability for both CO₂/N₂ and CO₂/CH₄ separation. All of these confirm FJI-H29 is a practical CO₂ adsorbent. Modeling calculations reveal that the confinement effect of micropores and the polar environment synergistically promotes the selective adsorption of CO₂, which will provide a potential strategy for the synthesis of a practical metal-organic framework for CO₂ capture.

Realization of an Ultrasensitive and Highly Selective OFET NO2 Sensor: The Synergistic Combination of PDVT-10 Polymer and Porphyrin-MOF

Organic field-effect transistors (OFETs) are emerging as competitive candidates for gas sensing applications due to the ease of their fabrication process combined with the ability to readily fine-tune the properties of organic semiconductors. Nevertheless, some key challenges remain to be addressed, such as material degradation, low sensitivity, and poor selectivity toward toxic gases. Appropriately, a heterojunction combination of different sensing layers with multifunctional capabilities offers great potential to overcome these problems. Here, a novel and highly sensitive receptor layer is proposed encompassing a porous 3D metal-organic framework (MOF) based on isostructural-fluorinated MOFs acting as an NO₂ specific preconcentrator, on the surface of a stable and ultrathin PDVT-10 organic semiconductor on an OFET platform. Here, with this proposed combination we have unveiled an unprecedented 700% increase in sensitivity toward NO₂ analyte in contrast to the pristine PDVT-10. The resultant combination for this OFET device exhibits a remarkable lowest detection limit of 8.25 ppb, a sensitivity of 680 nA/ppb, and good stability over a period of 6 months under normal laboratory conditions. Further, a negligible response (4.232 nA/%RH) toward humidity in the range of 5%-90% relative humidity was demonstrated using this combination. Markedly, the obtained results support the use of the proposed novel strategy to achieve an excellent sensing performance with an OFET platform.

Optimized trimetallic benzotriazole-5-carboxylate MOFs with coordinately unsaturated active sites as an efficient electrocatalyst for the oxygen evolution reaction

Enhanced OER performance of bimetallic and trimetallic MOFs were gained through synergistic effect in Fe/Co/Ni unsaturated coordination sites.

Assembly of Metal-Organic Frameworks of SiF62- in Situ Formed from Borosilicate Glass

The SiF₆^2- anions are in situ formed in the reactions of MF₂ (M = Cu²⁺, Zn²⁺, Ni²⁺, and Co²⁺) salts and nitrogen-containing ligands in borosilicate glass tubes under solvothermal conditions and then used to further construct a family of metal-organic frameworks (MOFs). This in situ reaction demonstrates a new and facile strategy for the fabrication of MOFs based on SiF₆^2-.

Crystalline Anionic Germanate Covalent Organic Framework for High CO2 Selectivity and Fast Li Ion Conduction

The metalloid-centered covalent organic framework has attracted great interest from both its structure and application. Heavier elements have seldomly been incorporated in the covalent organic frameworks, even if they exhibit special structural features and properties. Herein, we reported the first crystalline germanate covalent organic framework with hexacoordinated germanate linked by an anthracene linker. The existence of counterion lithium ions in the framework provides a high CO₂ uptake of 88.5 cm³  g^-1 at 273 K and a high CO₂ /N₂ selectivity of 101. A significantly improved lithium ion conductivity of 0.25 mS cm^-1 at room temperature was observed due to the soft germanium center.

Porous metal-organic frameworks for gas storage and separation: Status and challenges

Gases are widely used as energy resources for industry and our daily life. Developing energy cost efficient porous materials for gas storage and separation is of fundamentally and industrially important, and is one of the most important aspects of energy chemistry and materials. Metal-organic frameworks (MOFs), representing a novel class of porous materials, feature unique pore structure, such as exceptional porosity, tunable pore structures, ready functionalization, which not only enables high density energy storage of clean fuel gas in MOF adsorbents, but also facilitates distinct host-guest interactions and/or sieving effects to differentiate different molecules for energy-efficient separation economy. In this review, we summarize and highlight the recent advances in the arena of gas storage and separation using MOFs as adsorbents, including progresses in MOF-based membranes for gas separation, which could afford broader concepts to the current status and challenges in this field.

Selective Adsorption of Water, Methanol, and Ethanol by Naphthalene Diimide-Based Coordination Polymers with Constructed Open Cu2+ Metal Sites and Separation of Ethanol/Acetonitrile

The selective separation of ethanol/acetonitrile by porous materials has rarely been observed owing to their similar physicochemical properties. In this work, we report a new coordination network, [Cu₂(4-pmntd)₂(opd)₂](4-pmntd = N,N'-bis(4-pyridymethy)naphthalene diimide, opd = disodium 1,2-benzenedicarboxylate), which exhibits selective separation of ethanol over acetonitrile. The weak coordination bonds formed by unsaturated Cu²⁺ sites and hydroxyl groups are the key to such performance.

A metal-organic framework based on a custom-designed diisophthalate ligand exhibiting excellent hydrostability and highly selective adsorption of C2H2 and CO2 over CH4

The ligand truncation strategy provides facile access to a wide variety of linkers for the construction of MOFs bearing diverse structures and intriguing properties. In this work, we employed this strategy to design and prepare a novel bent diisophthalate ligand, and used it to successfully construct a copper-based MOF ZJNU-51 with the formula of [Cu2L(H2O)2]·5DMF (H4L = 5,5'-(triphenylamine-4,4'-diyl) diisophthalic acid), which was thoroughly characterized by various techniques including FTIR, TGA, PXRD and single-crystal X-ray diffraction. ZJNU-51 is a two-fold interpenetrated network in which the single network consists of dicopper paddlewheel units connected by the organic ligands and contains open channels as well as six distinct types of metal-organic cages. Furthermore, gas adsorption properties with respect to C2H2, CO2, and CH4 were systematically investigated, demonstrating that ZJNU-51 is a highly promising material for C2H2/CH4 and CO2/CH4 separations. Specifically, the IAST adsorption selectivity at 298 K and 1 atm reaches 35.6 and 5.4 for the equimolar C2H2/CH4 and CO2/CH4 gas mixtures, respectively. More significantly, as revealed by PXRD and N2 adsorption measurements, ZJNU-51 exhibits excellent chemical stability, which lays a good foundation for its practical application.

Nanospace within metal-organic frameworks for gas storage and separation

Porous metal-organic frameworks (MOFs), also known as porous coordination polymers, represent a new class of porous materials, and one of their striking features lies in their tunable, designable, and functionalizable nanospace. This nanospace within MOFs provides virtually plenty of room for imagination, allowing designed incorporation of different size, shape, and functionalities for targeted gas storage and separation applications. Furthermore, the features of high porosities, tunable framework structures and pore sizes, and immobilized functional sites enable MOF materials to fully make use of their nanopore space for gas storage, to optimize their sieving effects, and to differentiate their interactions with gas molecules for gas separation. In this review article, we highlight some recent significant advances in developing microporous MOFs for some of the most important gas storage and separation applications.

Diverse cobalt(ii) coordination polymers for water/ethanol separation and luminescence for water sensing applications

N,N′-Bis(3-pyridylmethyl)pyromellitic diimide has four conformations, which lead to four types of cobalt(ii) coordination polymers. Such coordination networks can be used for luminescent water sensing and water/ethanol separation.

Potential of ultramicroporous metal–organic frameworks in CO2 clean-up

This article explains the need for energy-efficient large-scale CO₂ capture and briefly mentions the requirements for optimal solid sorbents for this application.