Fine pore engineering in a series of isoreticular metal-organic frameworks for efficient C2H2/CO2 separation

Extra-High CO2 Adsorption and Controllable C2H2/CO2 Separation Regulated by the Interlayer Stacking in Pillar-Layered Metal-Organic Frameworks

Pillar-layered metal-organic frameworks (PLMOFs) are promising gas adsorbents due to their high designability. In this work, high CO2 storage capacity as well as controllable C2H2/CO2 separation ability are acquired by rationally manipulating the interlayer stacking in pillar-layered MOF materials. The rational construction of pillar-layered MOFs started from the 2D Ni-BTC-pyridine layer, an isomorphic structure of pioneering MOF-1 reported in 1995. The replacement of terminal pyridine groups by bridging pyrazine linkers under optimized solvothermal conditions led to three 3D PLMOFs with different stacking types between adjacent Ni-BTC layers, named PLMOF 1 (ABAB stacking), PLMOF 2 (AABB stacking), and PLMOF 3 (AAAA stacking). Regulated by the layer arrangements, CO2 and C2H2 adsorption capacities (273 K and 1 bar) of PLMOFs 1-3 vary from 173.0/153.3, 185.0/162.4, to 203.5/159.5 cm3 g-1, respectively, which surpass the values of most MOF adsorbents. Dynamic breakthrough experiments further indicate that PLMOFs 1-3 have controllable C2H2/CO2 separation performance, which can successfully overcome the C2H2/CO2 separation challenge. Specially, PLMOFs 1-3 can remove trace CO2 (3%) from the C2H2/CO2 mixture and produce high-purity ethylene (99.9%) in one step with the C2H2 productivities of 1.68, 2.45, and 3.30 mmol g-1, respectively. GCMC simulations indicate that the superior CO2 adsorption and unique C2H2/CO2 separation performance are mainly ascribed to different degrees of CO2 agglomeration in the ultramicropores of these PLMOFs.

Topology Reconfiguration of Anion-Pillared Metal-Organic Framework from Flexibility to Rigidity for Enhanced Acetylene Separation

Flexible metal-organic framework (MOF) adsorbents commonly encounter limitations in removing trace impurities below gate-opening threshold pressures. Topology reconfiguration can fundamentally eliminate intrinsic structural flexibility, yet remains a formidable challenge and is rarely achieved in practical applications. Herein, a solvent-mediated approach is presented to regulate the flexible CuSnF6-dpds-sql (dpds = 4,4''-dipyridyldisulfide) with sql topology into rigid CuSnF6-dpds-cds with cds topology. Notably, the cds topology is unprecedented and first obtained in anion-pillared MOF materials. As a result, rigid CuSnF6-dpds-cds exhibits enhanced C2H2 adsorption capacity of 48.61 cm3 g-1 at 0.01 bar compared to flexible CuSnF6-dpds-sql (21.06 cm3 g-1). The topology transformation also facilitates the adsorption kinetics for C2H2, exhibiting a 6.5-fold enhanced diffusion time constant (D/r2) of 1.71 × 10-3 s-1 on CuSnF6-dpds-cds than that of CuSnF6-dpds-sql (2.64 × 10-4 s-1). Multiple computational simulations reveal the structural transformations and guest-host interactions in both adsorbents. Furthermore, dynamic breakthrough experiments demonstrate that high-purity C2H4 (>99.996%) effluent with a productivity of 93.9 mmol g-1 can be directly collected from C2H2/C2H4 (1/99, v/v) gas-mixture in a single CuSnF6-dpds-cds column.

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.

Advancements and Challenges in the Application of Metal-Organic Framework (MOF) Nanocomposites for Tumor Diagnosis and Treatment

Nanoscale metal-organic frameworks (MOFs) offer high biocompatibility, nanomaterial permeability, substantial specific surface area, and well-defined pores. These properties make MOFs valuable in biomedical applications, including biological targeting and drug delivery. They also play a critical role in tumor diagnosis and treatment, including tumor cell targeting, identification, imaging, and therapeutic methods such as drug delivery, photothermal effects, photodynamic therapy, and immunogenic cell death. The diversity of MOFs with different metal centers, organics, and surface modifications underscores their multifaceted contributions to tumor research and treatment. This review is a summary of these roles and mechanisms. The final section of this review summarizes the current state of the field and discusses prospects that may bring MOFs closer to pharmaceutical applications.

Measuring Mass Transfer of n-Hexane and 2-Chloroethyl Ethyl Sulfide in Sorbent/Polymer Fiber Composites Using a Volumetric Adsorption Apparatus

The integration of metal-organic frameworks (MOFs) into composite systems serves as an effective strategy to increase the processability of these materials. Notably, MOF/fiber composites have shown much promise as protective equipment for the capture and remediation of chemical warfare agents. However, the practical application of these composites requires an understanding of their mass transport properties, as both mass transfer resistance at the surface and diffusion within the materials can impact the efficacy of these materials. In this work, we synthesized composite fibers of MOF-808 and amidoxime-functionalized polymers of intrinsic microporosity (PIM-1-AX) and measured the adsorption and mass transport behavior of n-hexane and 2-chloroethyl ethyl sulfide (CEES), a sulfur mustard simulant. We developed a new Fickian diffusion model for cylindrical shapes to fit the dynamic adsorption data obtained from a commercial volumetric adsorption apparatus and found that mass transport behavior in composite fibers closely resembled that in the pure PIM fibers, regardless of MOF loading. Moreover, we found that n-hexane adsorption mirrors that of CEES, indicating that it could be used as a structural mimic for future adsorption studies of the sulfur mustard simulant. These preliminary insights and the new model introduced in this work lay the groundwork for the design of next-generation composite materials for practical applications.

Enhanced Co-Adsorption of Alcohols and Amines for Visible Light Driven Oxidative Condensation Using Iron-Based MOF

Imines are essential intermediates in organic transformations, and is generally produced by dehydrogenative condensation of alcohols and amines with the assist of specialized catalysts and additives. Heterogeneous photocatalysis provides a sustainable platform for such process without the using of toxic oxidants, yet a functionalized photocatalyst with optimized co-adsorption of reactants needs to be developed to promote the stoichiometric oxidative condensation under ambient conditions. Here, we show that benzyl alcohol and aniline adsorb non-interferingly on the Fe node and the linker sites of the MIL-53(Fe) metal organic frameworks (MOFs), respectively. The co-adsorption of both reactants barely influences the reduction of molecular oxygen to generate oxygen radicals, resulting in efficient formation of benzaldehyde under visible light. Additionally, the weak adsorption of water together with surface acidity of the MIL-53(Fe) promote a rapid condensation of benzaldehyde with aniline and the depletion of generated water, achieving an efficient C-N bond creation for a wide range of substrates.

An adsorbate biased dynamic 3D porous framework for inverse CO2 sieving over C2H2

Separating carbon dioxide (CO2) from acetylene (C2H2) is one of the most critical and complex industrial separations due to similarities in physicochemical properties and molecular dimensions. Herein, we report a novel Ni-based three-dimensional framework {[Ni4(μ3-OH)2(μ2-OH2)2(1,4-ndc)3](3H2O)}n (1,4-ndc = 1,4-naphthalenedicarboxylate) with a one-dimensional pore channel (3.05 × 3.57 Å2), that perfectly matches with the molecular size of CO2 and C2H2. The dehydrated framework shows structural transformation, decorated with an unsaturated Ni(ii) centre and pendant oxygen atoms. The dynamic nature of the framework is evident by displaying a multistep gate opening type CO2 adsorption at 195, 273, and 298 K, but not for C2H2. The real time breakthrough gas separation experiments reveal a rarely attempted inverse CO2 selectivity over C2H2, attributed to open metal sites with a perfect pore aperture. This is supported by crystallographic analysis, in situ spectroscopic inspection, and selectivity approximations. In situ DRIFTS measurements and DFT-based theoretical calculations confirm CO2 binding sites are coordinatively unsaturated Ni(ii) and carboxylate oxygen atoms, and highlight the influence of multiple adsorption sites.

Optical Phenomena in Molecule-Based Magnetic Materials

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

Effect of Polymorphism on the Sorption Properties of a Flexible Square-Lattice Topology Coordination Network

The stimulus-responsive behavior of coordination networks (CNs), which switch between closed (nonporous) and open (porous) phases, is of interest because of its potential utility in gas storage and separation. Herein, we report two polymorphs of a new square-lattice (sql) topology CN, X-sql-1-Cu, of formula [Cu(Imibz)2]n (HImibz = {[4-(1H-imidazol-1-yl)phenylimino]methyl}benzoic acid), isolated from the as-synthesized CN X-sql-1-Cu-(MeOH)2·2MeOH, which subsequently transformed to a narrow pore solvate, X-sql-1-Cu-A·MeOH, upon mild activation (drying in air or heating at 333 K under nitrogen). X-sql-1-Cu-A·MeOH contains MeOH in cavities, which was removed through exposure to vacuum for 2 h, yielding the nonporous (closed) phase X-sql-1-Cu-A. In contrast, a more dense polymorph, X-sql-1-Cu-B, was obtained by exposing X-sql-1-Cu-(MeOH)2·2MeOH directly to vacuum for 2 h. Gas sorption studies conducted on X-sql-1-Cu-A and X-sql-1-Cu-B revealed different switching behaviors to two open phases (X-sql-1-Cu·CO2 and X-sql-1-Cu·C2H2), with different gate-opening threshold pressures for CO2 at 195 K and C2H2 at 278 K. Coincident CO2 sorption and in situ powder X-ray diffraction studies at 195 K revealed that X-sql-1-Cu-A transformed to X-sql-1-Cu-B after the first sorption cycle and that the CO2-induced switching transformation was thereafter reversible. The results presented herein provide insights into the relationship between two polymorphs of a CN and the effect of polymorphism upon gas sorption properties. To the best of our knowledge, whereas sql networks such as X-sql-1-Cu are widely studied in terms of their structural and sorption properties, this study represents only the second example of an in-depth study of the sorption properties of polymorphic sql networks.

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.

Electrochemical coupling in subnanometer pores/channels for rechargeable batteries

Subnanometer pores/channels (SNPCs) play crucial roles in regulating electrochemical redox reactions for rechargeable batteries. The delicately designed and tailored porous structure of SNPCs not only provides ample space for ion storage but also facilitates efficient ion diffusion within the electrodes in batteries, which can greatly improve the electrochemical performance. However, due to current technological limitations, it is challenging to synthesize and control the quality, storage, and transport of nanopores at the subnanometer scale, as well as to understand the relationship between SNPCs and performances. In this review, we systematically classify and summarize materials with SNPCs from a structural perspective, dividing them into one-dimensional (1D) SNPCs, two-dimensional (2D) SNPCs, and three-dimensional (3D) SNPCs. We also unveil the unique physicochemical properties of SNPCs and analyse electrochemical couplings in SNPCs for rechargeable batteries, including cathodes, anodes, electrolytes, and functional materials. Finally, we discuss the challenges that SNPCs may face in electrochemical reactions in batteries and propose future research directions.

Supramolecular Interactions Induce Dynamics in Metal-Organic Layers to Selectively Separate Acetylene from Carbon Dioxide

We report the synthesis and structural characterization of a 2D metal-organic framework with AB-packing layers, [Co2(pybz)2(CH3COO)2]·DMF (Co2, pybz= 4-(4-pyridyl)benzoate), containing a stable (4,4)-grid network fabricated by paddle-wheel nodes, ditopic pybz, and acetate ligands. After removal of the guest, the layer structure is retained but reorganized into an ABCD packing mode in the activated phase (Co2a). Consequently, the intralayer square windows (7.2 × 5.0 Å2) close, while the interlayer separation is decreased slightly from 3.69 to 3.45 Å, leaving a narrow gap. Importantly, the dangling methyl group of the acetate with H-bonds to the adjacent layers and also the well-distributed π-π interactions between the aromatic rings of neighboring layers facilitate the structural stability. These weak supramolecular interactions further allow for favorable dynamic exfoliation of the layers, which promotes efficient adsorption of C2H2 (41.6 cm3 g-1) over CO2 with an adsorption ratio of 6.3 (0.5 bar, 298 K). The effective separation performance of equimolar C2H2/CO2 was verified by cycling breakthrough experiments and was even tolerable to moisture (R.H = 52%). DFT calculations, in situ PXRD, and PDF characterization reveal that the favorable retention of C2H2 rather than that of CO2 is due to its H-bond formation with the paddle-wheel oxygen atoms that triggers the increase in interlayer separation during C2H2 adsorption.

Molecular sieving of iso-butene from C4 olefins with simultaneous high 1,3-butadiene and n-butene uptakes

Iso-butene (iso-C4H8) is an important raw material in chemical industry, whereas its efficient separation remains challenging due to similar molecular properties of C4 olefins. The ideal adsorbent should possess simultaneous high uptakes for 1,3-butadiene (C4H6) and n-butene (n-C4H8) counterparts, endowing high efficiency for iso-C4H8 separation in adsorption columns. Herein, a sulfate-pillared adsorbent, SOFOUR-DPDS-Ni (DPDS = 4,4'-dipyridyldisulfide), is reported for the efficient iso-C4H8 separation from binary and ternary C4 olefin mixtures. The rigidity in pore sizes and shapes of SOFOUR-DPDS-Ni exerts the molecular sieving of iso-C4H8, while exhibiting high C4H6 and n-C4H8 uptakes. The benchmark Henry's selectivity for C4H6/iso-C4H8 (2321.8) and n-C4H8/iso-C4H8 (233.5) outperforms most reported adsorbents. Computational simulations reveal the strong interactions for C4H6 and n-C4H8. Furthermore, dynamic breakthrough experiments demonstrate the direct production of high-purity iso-C4H8 (>99.9%) from C4H6/iso-C4H8 (50/50, v/v), n-C4H8/iso-C4H8 (50/50, v/v), and C4H6/n-C4H8/iso-C4H8 (50/15/35, v/v/v) gas-mixtures.

Construction of Multifunctional Luminescent Lanthanide MOFs for Luminescent Sensing of Temperature, Trifluoroacetic Acid Vapor and Explosives

Metal-organic frameworks (MOFs) with multifunctional and tunable optical properties have unique advantages in the field of sensing, and the structure and properties of MOFs are significantly influenced by the ligands. In this study, a Y-type tricarboxylic acid ligand containing amide bonds was synthesized through functional guidance, and three isomorphic and heterogeneous three-dimensional MOFs (Eu-MOF, Tb-MOF, and Gd-MOF) were obtained by solvothermal reaction. Further studies revealed that both the Tb-MOF and Eu-MOF could selectively detect picric acid (PA). The luminescence quenching of the two MOFs by PA was attributed to competing absorption and photoelectron energy transfer mechanisms. In addition, due to the energy transfer between Tb and Rhodamine B, Rhodamine B was encapsulated into Tb-MOF. The obtained material exhibited a linear relationship between the temperature parameters I544/I584 and temperature within the range of 280-400 K, the correlation coefficient (R2) reached an impressive value of 0.999, and the absolute sensitivity of the sample used for temperature sensing was 1.534% K-1. What is more, the material exhibited a good response to trifluoroacetic acid vapor, which suggests the potential of the material for temperature sensing and detection of trifluoroacetic acid vapor. The designed and investigated strategy can also serve as a reference for further research on excellent multifunctional sensors.

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.

Interaction-selective molecular sieving adsorbent for direct separation of ethylene from senary C2-C4 olefin/paraffin mixture

Olefin/paraffin separations are among the most energy-intensive processes in the petrochemical industry, with ethylene being the most widely consumed chemical feedstock. Adsorptive separation utilizing molecular sieving adsorbents can optimize energy efficiency, whereas the size-exclusive mechanism alone cannot achieve multiple olefin/paraffin sieving in a single adsorbent. Herein, an unprecedented sieving adsorbent, BFFOUR-Cu-dpds (BFFOUR = BF4-, dpds = 4,4'-bipyridinedisulfide), is reported for simultaneous sieving of C2-C4 olefins from their corresponding paraffins. The interlayer spaces can be selectively opened through stronger guest-host interactions induced by unsaturated C = C bonds in olefins, as opposed to saturated paraffins. In equimolar six-component breakthrough experiments (C2H4/C2H6/C3H6/C3H8/n-C4H8/n-C4H10), BFFOUR-Cu-dpds can simultaneously divide olefins from paraffins in the first column, while high-purity ethylene ( > 99.99%) can be directly obtained through the subsequent column using granular porous carbons. Moreover, gas-loaded single-crystal analysis, in-situ infrared spectroscopy measurements, and computational simulations demonstrate the accommodation patterns, interaction bonds, and energy pathways for olefin/paraffin separations.

Quasi-Discrete Pore Engineering via Ligand Racemization in Metal-Organic Frameworks for Thermodynamic-Kinetic Synergistic Separation of Propylene and Propane

The adsorptive separation of propylene and propane offers an energy-efficient alternative to the conventional cryogenic distillation technology. However, developing porous adsorbents with both high equilibrium and kinetic selectivity remains extremely challenging due to the similar size and physical properties of these gases. Herein, this work reports a ligand racemization strategy to construct quasi-discrete pores in MOFs for a synergistically enhanced thermodynamic and kinetic separation performance. The use of enantiopure l-malic acid versus racemic dl-malic acid as ligands afforded isoreticular Ni-based MOFs with contrasting one-dimensional channels (l-mal-MOF) and quasi-discrete cavities connected by small windows (dl-mal-MOF). The periodic pore constrictions in dl-mal-MOF significantly increased the differentiation in diffusion rates and binding energies between propylene and propane. dl-mal-MOF exhibited an exceptional propylene uptake of 1.82 mmol/g at 0.05 bar and 298 K along with an ultrahigh equilibrium-kinetic combined selectivity of 62.6. DFT calculations and MD simulations provided insights into the synergistic mechanism of preferential propylene adsorption and diffusion. Breakthrough column experiments demonstrated the excellent separation and high-purity recovery of propylene over propane on dl-mal-MOF. The robust stability and facile regeneration highlight its potential for propylene purification applications.

Separation of High-Purity C2H2 from Binary C2H2/CO2 Using Robust Al-Based MOFs Comprising Nitrogen-Containing Heterocyclic Dicarboxylate

In this study, three nitrogen-containing aluminum-based metal-organic frameworks (Al-MOFs), namely, CAU-10pydc, MOF-303, and KMF-1, were investigated for the efficient separation of a C2H2/CO2 gas mixture. Among these three Al-MOFs, KMF-1 demonstrated the highest selectivity for C2H2/CO2 separation (6.31), primarily owing to its superior C2H2 uptake (7.90 mmol g-1) and lower CO2 uptake (2.82 mmol g-1) compared to that of the other two Al-MOFs. Dynamic breakthrough experiments, using an equimolar binary C2H2/CO2 gas mixture, demonstrated that KMF-1 achieved the highest separation performance. It yielded 3.42 mmol g-1 of high-purity C2H2 (>99.95%) through a straightforward desorption process under He purging at 298 K and 1 bar. To gain insights into the distinctive characteristics of the pore surfaces of structurally similar CAU-10pydc and KMF-1, we conducted computational simulations using canonical Monte Carlo and dispersion-corrected density functional theory methods. These simulations revealed that the secondary amine (C2N-H) groups in KMF-1 played a more significant role in differentiating between C2H2 and CO2 compared to that of the N atoms in CAU-10pydc and MOF-303. Consequently, KMF-1 emerged as a promising adsorbent for the separation of high-purity C2H2 from binary C2H2/CO2 gas mixtures.

Metal Ion-controlled Growth of Different Metal-Organic Framework Micro/nanostructures for Enhanced Supercapacitor Performance

We report a metal ion-modulated effective strategy to achieve different metal-organic framework (MOF) micro/nanostructures using different metal precursors like CoCl2  ⋅ 6H2 O, CoCl2  ⋅ 6H2 O and NiCl2  ⋅ 6H2 O, and NiCl2  ⋅ 6H2 O with pyridine-3,5-dicarboxylate (3,5-pdc). The structural characterizations confirm that different morphological structures, hollow microsphere, hierarchical nanoflower, and solid nanosphere are for Co-(3,5-pdc), Co0.19 Ni0.81 -(3,5-pdc), and Ni-(3,5-pdc), respectively. These different MOF micro/nanostructures correlate with the coordination ability of Co and Ni with 3,5-pdc. Benefitting from the synergistic effect of the alloying metal nodes of Co and Ni producing rapid and rich redox reactions and the hierarchical nanoflower with higher surface area enabling excellent ion kinetics, the Co0.19 Ni0.81 -(3,5-pdc) exhibits higher specific capacitance of 515 F g-1 /273 C g-1 at 0.5 A g-1 than that of Ni-(3,5-pdc) (290 F g-1 /153.7 C g-1 ) and Co-(3,5-pdc) (132 F g-1 /67 C g-1 ), good rate capability and cycling stability. Moreover, the asymmetric supercapacitor device (Co0.19 Ni0.81 -(3,5-pdc)//AC) assembled from Co0.19 Ni0.81 -(3,5-pdc) and activated carbon (AC) achieves a maximum energy density of 42.6 Wh kg-1 at a power density of 277.3 W kg-1 .

Water vapour induced structural flexibility in a square lattice coordination network

Herein, we introduce a new square lattice topology coordination network, sql-(1,3-bib)(ndc)-Ni, with three types of connection and detail its gas and vapour induced phase transformations. Exposure to humidity resulted in an S-shaped isotherm profile, suggesting potential utility of such materials as desiccants.

Multivariate Hydrogen-Bonded Organic Frameworks with Tunable Permanent Porosities for Capture of a Mustard Gas Simulant

Precise synthesis of topologically predictable and discrete molecular crystals with permanent porosities remains a long-term challenge. Here, we report the first successful synthesis of a series of 11 isoreticular multivariate hydrogen-bonded organic frameworks (MTV-HOFs) from pyrene-based derivatives bearing -H, -CH3 , -NH2 and -F groups achieved by a shape-fitted, π-π stacking self-assembly strategy. These MTV-HOFs are single-crystalline materials composed of tecton, as verified by single-crystal diffraction, nuclear magnetic resonance (NMR) spectra, Raman spectra, water sorption isotherms and density functional theory (DFT) calculations. These MTV-HOFs exhibit tunable hydrophobicity with water uptake starting from 50 to 80 % relative humidity, by adjusting the combinations and ratios of functional groups. As a proof of application, the resulting MTV-HOFs were shown to be capable of capturing a mustard gas simulant, 2-chloroethyl ethyl sulfide (CEES) from moisture. The location of different functional groups within the pores of the MTV-HOFs leads to a synergistic effect, which resulted in a superior CEES/H2 O selectivity (up to 94 %) compared to that of the HOFs with only pure component and enhanced breakthrough performance (up to 4000 min/g) when compared to benchmark MOF materials. This work is an important advance in the synthesis of MTV-HOFs, and provides a platform for the development of porous molecular materials for numerous applications.

"Photochemical Surgery" of 1D Metal-Organic Frameworks with a Site-Selective Solubilization/Crystallization Strategy

One-dimensional (1D) hybrid MOFs are attractive if they consist of different MOF blocks with interconnected channels. However, the precision synthesis of such 1D multiblock MOFs with the desired block lengths and sequences remains a formidable challenge. Herein we propose the "photochemical surgery" method, which combines top-down and bottom-up approaches to enable the site-selective solubilization (removal)/crystallization (reconstruction) of 1D MOFs. We employed photoreactive MOFs, which were prepared by complexing either Cd2+ or Zn2+ with a mixture containing a photochromic bispyridyl ligand (PyDTEopen or PyDTZEopen) and an isophthalate (5-nitroisophthalate (nip2-) or 5-bromoisophthalate (bip2-)). These MOFs were obtained as high-aspect-ratio, needlelike, colorless crystals that bore 1D channels oriented parallel to the long needle axis. When photoreactive DTECdMOFNO2 ([Cd(nip)(PyDTEopen)(H2O)]n), for example, was immobilized at both ends with a metal alloy on a glass substrate and exposed to UV light through a photomask for 60 min in N,N-dimethylformamide/methanol (DMF/MeOH), the unmasked part was removed via solubilization to produce a 50 μm gap. The resulting specimen was immersed for 24 h at 25 °C in DMF/MeOH containing the necessary components for the construction of DTZECdMOFNO2 ([Cd(nip)(PyDTZEopen)(H2O)]n). Eventually, the gap was filled with DTZECdMOFNO2 to produce a triblock hybrid MOF (DTECdMOFNO2-DTZECdMOFNO2-DTECdMOFNO2). The result of a guest diffusion experiment confirmed that the newly formed DTZECdMOFNO2 block shared its 1D channels with the host DTECdMOFNO2 blocks. "Photochemical surgery" can be applied to synthesize 1D hybrid MOFs bearing unconventional sequences and morphologies, e.g., honeycomb- and inverted-honeycomb-patterned hybrids.

An aliphatic MOF with a molecular sieving effect for efficient C2H2/C2H4 separation

A metal-organic framework, SDMOF-1, with rigid pores of about 3.4 Å, which is appropriate for accommodating C2H2 molecules, exhibits high C2H2 adsorption capacity and great separation capability of the C2H2/C2H4 mixture. This work provides a new method to design aliphatic MOFs with a molecular sieving effect to realize efficient gas separation.

A Microporous Hydrogen Bonded Organic Framework for Highly Selective Separation of Carbon Dioxide over Acetylene

The separation of acetylene (C2 H2 ) from carbon dioxide (CO2 ) is a very important but challenging task due to their similar molecular dimensions and physical properties. In terms of porous adsorbents for this separation, the CO2 -selective porous materials are superior to the C2 H2 -selective ones because of the cost- and energy-efficiency but have been rarely achieved. Herein we report our unexpected discovery of the first hydrogen bonded organic framework (HOF) constructed from a simple organic linker 2,4,6-tri(1H-pyrazol-4-yl)pyridine (PYTPZ) (termed as HOF-FJU-88) as the highly CO2 -selective porous material. HOF-FJU-88 is a two-dimensional HOFs with a pore pocket of about 7.6 Å. The activated HOF-FJU-88 takes up a high amount of CO2 (59.6 cm3  g-1 ) at ambient conditions with the record IAST selectivity of 1894. Its high performance for the CO2 /C2 H2 separation has been further confirmed through breakthrough experiments, in situ diffuse reflectance infrared spectroscopy and molecular simulations.

Engineering of Stable Anionic/Neutral MOFs with Zinc-Adeninate Building Units for Efficient C2H2/CO2 Separation

Using adenine and metal ions to form secondary building units (SBUs), further connected by a highly symmetrical multicarboxylic linker to construct an amino-modified porous framework with high porosity, is an effective strategy. By regulating the deprotonation and hydrolysis capacity of the synthesized solvent, it is possible to obtain different charged frameworks. In this work, two stable anionic/neutral MOFs, (Et2NH2)[Zn3(TCPE)(adenine)2CH3COO]·DEF·3H2O (1) and [Zn3.5(adenine)(TCPE)1.5(DMA)(H2O)0.5]·2DMA·2H2O (2), have been synthesized based on zinc-adeninate building units and symmetric tetrakis(4-carboxyphenyl)ethylene (H4TCPE) in N,N-diethylformamide (DEF) and N,N-dimethylacetamide (DMA) reaction systems, respectively. 1 is an anionic framework based on 1D rod zinc-adeninate SBU, containing 1D rectangular (14.3 × 6.3 Å2) and square (14.3 × 14.3 Å2) channels. While 2 is a neutral framework built from isolated zinc-adeninate SBU, it contains hexagonal cages with a dimension of 5.5 Å in the structure. Both of them have high porosity (61.6% for 1 and 46.3% for 2) and high stability in a wide range of pH. 1 and 2 show high C2H2 adsorption capacity at 298 K (48.1 and 70.1 cm3 g-1, respectively) and selective capacity for C2H2/CO2 mixtures, which was confirmed by the breakthrough experiments. Furthermore, the interaction between the frameworks and gas molecules has also been explained by theoretical calculation. This work provides a good example of the design and regulation of porous structures for adsorption and separation functions.

Inverse CO2/C2H2 separation assisted by coordinated water in a dysprosium(III) metal-organic framework

An ultramicroporous metal-organic framework (MOF) constructed from dysprosium(III) and oxalate, termed Dy-F-oxa, is carefully studied for inverse separation of CO2 from C2H2. Adsorption experiments and modeling studies reveal that the high CO2 adsorption is attributed to the preferential sites for CO2 by coordinated water. After the equimolar gas mixture breakthrough experiment, C2H2 can be directly produced as a pure effluent.

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

Separation of acetylene (C2 H2 ) from carbon dioxide (CO2 ) or ethylene (C2 H4 ) is industrially important but still challenging so far. Herein, we developed two novel robust metal organic frameworks AlFSIX-Cu-TPBDA (ZNU-8) with znv topology and SIFSIX-Cu-TPBDA (ZNU-9) with wly topology for efficient capture of C2 H2 from CO2 and C2 H4 . Both ZNU-8 and ZNU-9 feature multiple anion functionalities and hierarchical porosity. Notably, ZNU-9 with more anionic binding sites and three distinct cages displays both an extremely large C2 H2 capacity (7.94 mmol/g) and a high C2 H2 /CO2 (10.3) or C2 H2 /C2 H4 (11.6) selectivity. The calculated capacity of C2 H2 per anion (4.94 mol/mol at 1 bar) is the highest among all the anion pillared metal organic frameworks. Theoretical calculation indicated that the strong cooperative hydrogen bonds exist between acetylene and the pillared SiF6 2- anions in the confined cavity, which is further confirmed by in situ IR spectra. The practical separation performance was explicitly demonstrated by dynamic breakthrough experiments with equimolar C2 H2 /CO2 mixtures and 1/99 C2 H2 /C2 H4 mixtures under various conditions with excellent recyclability and benchmark productivity of pure C2 H2 (5.13 mmol/g) or C2 H4 (48.57 mmol/g).

Closo-[B12 H12 ]2- Derivatives with Polar Groups As Promising Building Blocks in Metal-Organic Frameworks for Gas Separation

Engineering design of metal organic frameworks (MOFs) for gas separation applications is nowadays a thriving field of investigation. Based on the recent experimental studies of dodecaborate-hybrid MOFs as potential materials to separate industry-relevant gas mixtures, we herein present a systematic theoretical study on the derivatives of the closo-dodecaborate anion [B12 H12 ]2- , which can serve as building blocks for MOFs. We discover that amino functionalization can impart a greater ability to selectively capture carbon dioxide from its mixtures with other gases such as nitrogen, ethylene and acetylene. The main advantage lies in the polarization effect induced by amino group, which favors the localization of the negative charges on the boron-cluster anion and offers a nucleophilic anchoring site to accommodate the carbon atom in carbon dioxide. This work suggests an appealing strategy of polar functionalization to optimize the molecule discrimination ability via preferential adsorption.

A cage-on-MOF strategy to coordinatively functionalize mesoporous MOFs for manipulating selectivity in adsorption and catalysis

Functionalizing porous materials with capping agents generates hybrid materials with enhanced properties, while the challenge is how to improve the selectivity and maintain the porosity of the parent framework. Herein, we developed a "Cage-on-MOF" strategy to tune the recognition and catalytic properties of MOFs without impairing their porosity. Two types of porous coordination cages (PCCs) of opposite charges containing secondary binding groups were developed to coordinatively functionalize two distinct porous MOFs, namely MOF@PCC nanocomposites. We demonstrated that the surface-capped PCCs can act as "modulators" to effectively tune the surface charge, stability, and adsorption behavior of different host MOF particles. More importantly, the MOF@PCCs can serve as selective heterogeneous catalysts for condensation reactions to achieve reversed product selectivity and excellent recyclability. This work sets the foundation for using molecular cages as porous surface-capping agents to functionalize and manipulate another porous material, without affecting the intrinsic properties of the parent framework.

Cyclobutanedicarboxylate Metal-Organic Frameworks as a Platform for Dramatic Amplification of Pore Partition Effect

Ultrafine tuning of MOF structures at subangstrom or picometer levels can help improve separation selectivity for gases with subtle differences. However, for MOFs with a large enough pore size, the effect from ultrafine tuning on sorption can be muted. Here we show an integrative strategy that couples extreme pore compression with ultrafine pore tuning. This strategy is made possible by unique combination of two features of the partitioned acs (pacs) platform: multimodular framework and exceptional tolerance toward isoreticular replacement. Specifically, we use one module (ligand 1, L1) to shrink the pore size to an extreme minimum on pacs. A compression ratio of about 30% was achieved (based on the unit cell c/a ratio) from prototypical 1,4-benzenedicarboxylate-pacs to trans-1,3-cyclobutanedicarboxylate-pacs. This is followed by using another module (ligand 2, L2) for ultrafine pore tuning (<3% compression). This L1-L2 strategy increases the C2H2/CO2 selectivity from 2.6 to 20.8 and gives rise to an excellent experimental breakthrough performance. As the shortest cyclic dicarboxylate that mimics p-benzene-based moieties using a bioisosteric (BIS) strategy on pacs, trans-1,3-cyclobutanedicarboxylate offers new opportunities in MOF chemistry.

Yolk-Shell and Hollow Zr/Ce-UiO-66 for Manipulating Selectivity in Tandem Reactions and Photoreactions

One of the hallmarks of multicomponent metal-organic frameworks (MOFs) is to finely tune their active centers to achieve product selectivity. In particular, obtaining bimetallic MOF hollow structures with precisely tailored redox centers under the same topology is still challenging despite a recent surge of such efforts. Herein, we present an engineering strategy named "cluster labilization" to generate hierarchically porous MOF composites with hollow structures and tunable active centers. By partially replacing zirconium with cerium in the hexanuclear clusters of UiO-66, unevenly distributed yolk-shell structures (YSS) were formed. Through acid treatment or annealing of the YSS precursor, single-shell hollow structures (SSHS) or double-shell hollow structures (DSHS) can be obtained, respectively. The active centers in SSHS and DSHS differ in their species, valence, and spatial locations. More importantly, YSS, SSHS, and DSHS with distinct active centers and microenvironments exhibit tunable catalytic activity, reversed selectivity, and high stability in the tandem reaction and the photoreaction.

Highly Efficient CO2/C2H2 Separation by Porous Graphene via Quadrupole Gating Mechanism

Acetylene (C₂H₂) is an important and widely used raw material in various industries (such as petrochemical). Generally, a product yield is proportional to the purity of C₂H₂; however, C₂H₂ from a typical industrial gas-production process is commonly contaminated by CO₂. So far, the achievement of high-purity C₂H₂ separated from a CO₂/C₂H₂ mixture is still challenging due to their very close molecular dimensions and boiling temperatures. Taking advantage of their quadrupoles with opposite signs, here, we show that the graphene membrane embedded with crown ether nanopores can achieve an unprecedented separation efficiency of CO₂/C₂H₂. Combining the molecular dynamics simulation and the density functional theory (DFT) approaches, we discovered that the electrostatic gas-pore interaction favorably allows the fast transport of CO₂ through crown ether nanopores while completely prohibiting C₂H₂ transport, which yields a remarkable permeation selectivity. In particular, the utilized crown ether pore is capable of allowing the individual transport of CO₂ while completely rejecting the passage of C₂H₂, independent of the applied pressures, fed gases ratios, and exerted temperatures, featuring the superiority and robustness of the crown pore in CO₂/C₂H₂ separation. Further, DFT and PMF calculations demonstrate that the transport of CO₂ through the crown pore is energetically more favorable than the transport of C₂H₂. Our findings reveal the potential application of graphene crown pore for CO₂ separation with outstanding performance.

Immobilization of the Polar Group into an Ultramicroporous Metal-Organic Framework Enabling Benchmark Inverse Selective CO2/C2H2 Separation with Record C2H2 Production

One-step harvest of high-purity light hydrocarbons without the desorption process represents an advanced and highly efficient strategy for the purification of target substances. The separation and purification of acetylene (C₂H₂) from carbon dioxide (CO₂) by CO₂-selective adsorbents are urgently demanded yet are very challenging owing to their similar physicochemical properties. Here, we employ the pore chemistry strategy to adjust the pore environment by immobilizing polar groups into an ultramicroporous metal-organic framework (MOF), achieving one-step manufacture of high-purity C₂H₂ from CO₂/C₂H₂ mixtures. Embedding methyl groups into prototype stable MOF (Zn-ox-trz) not only changes the pore environment but also improves the discrimination of guest molecules. The methyl-functionalized Zn-ox-mtz thus exhibits the benchmark reverse CO₂/C₂H₂ uptake ratio of 12.6 (123.32/9.79 cm³ cm^-3) and an exceptionally high equimolar CO₂/C₂H₂ selectivity of 1064.9 at ambient conditions. Molecular simulations reveal that the synergetic effect of pore confinement and surfaces decorated with methyl groups provides high recognition of CO₂ molecules through multiple van der Waals interactions. The column breakthrough experiments suggest that Zn-ox-mtz dramatically achieved the one-step purification capacity of C₂H₂ from the CO₂/C₂H₂ mixture with a record C₂H₂ productivity of 2091 mmol kg^-1, surpassing all of the CO₂-selective adsorbents reported so far. In addition, Zn-ox-mtz exhibits excellent chemical stability under different pH values of aqueous solutions (pH = 1-12). Moreover, the highly stable framework and excellent inverse selective CO₂/C₂H₂ separation performance showcase its promising application as a C₂H₂ splitter for industrial manufacture. This work paves the way to developing reverse-selective adsorbents for the challenging gas separation process.

Nanopolyhybrids: Materials, Engineering Designs, and Advances in Thermal Management

The fundamental requirements for thermal comfort along with the unbalanced growth in the energy demand and consumption worldwide have triggered the development and innovation of advanced materials for high thermal-management capabilities. However, continuous development remains a significant challenge in designing thermally robust materials for the efficient thermal management of industrial devices and manufacturing technologies. The notable achievements thus far in nanopolyhybrid design technologies include multiresponsive energy harvesting/conversion (e.g., light, magnetic, and electric), thermoregulation (including microclimate), energy saving in construction, as well as the miniaturization, integration, and intelligentization of electronic systems. These are achieved by integrating nanomaterials and polymers with desired engineering strategies. Herein, fundamental design approaches that consider diverse nanomaterials and the properties of nanopolyhybrids are introduced, and the emerging applications of hybrid composites such as personal and electronic thermal management and advanced medical applications are highlighted. Finally, current challenges and outlook for future trends and prospects are summarized to develop nanopolyhybrid materials.

Highly Productive C3H4/C3H6 Trace Separation by a Packing Polymorph of a Layered Hybrid Ultramicroporous Material

Ultramicroporous materials can be highly effective at trace gas separations when they offer a high density of selective binding sites. Herein, we report that sql-NbOFFIVE-bpe-Cu, a new variant of a previously reported ultramicroporous square lattice, sql, topology material, sql-SIFSIX-bpe-Zn, can exist in two polymorphs. These polymorphs, sql-NbOFFIVE-bpe-Cu-AA (AA) and sql-NbOFFIVE-bpe-Cu-AB (AB), exhibit AAAA and ABAB packing of the sql layers, respectively. Whereas NbOFFIVE-bpe-Cu-AA (AA) is isostructural with sql-SIFSIX-bpe-Zn, each exhibiting intrinsic 1D channels, sql-NbOFFIVE-bpe-Cu-AB (AB) has two types of channels, the intrinsic channels and extrinsic channels between the sql networks. Gas and temperature induced transformations of the two polymorphs of sql-NbOFFIVE-bpe-Cu were investigated by pure gas sorption, single-crystal X-ray diffraction (SCXRD), variable temperature powder X-ray diffraction (VT-PXRD), and synchrotron PXRD. We observed that the extrinsic pore structure of AB resulted in properties with potential for selective C₃H₄/C₃H₆ separation. Subsequent dynamic gas breakthrough measurements revealed exceptional experimental C₃H₄/C₃H₆ selectivity (270) and a new benchmark for productivity (118 mmol g^-1) of polymer grade C₃H₆ (purity >99.99%) from a 1:99 C₃H₄/C₃H₆ mixture. Structural analysis, gas sorption studies, and gas adsorption kinetics enabled us to determine that a binding "sweet spot" for C₃H₄ in the extrinsic pores is behind the benchmark separation performance. Density-functional theory (DFT) calculations and Canonical Monte Carlo (CMC) simulations provided further insight into the binding sites of C₃H₄ and C₃H₆ molecules within these two hybrid ultramicroporous materials, HUMs. These results highlight, to our knowledge for the first time, how pore engineering through the study of packing polymorphism in layered materials can dramatically change the separation performance of a physisorbent.

Control over Phase Transformations in a Family of Flexible Double Diamondoid Coordination Networks through Linker Ligand Substitution

In this work, we present the first metal-organic framework (MOF) platform with a self-penetrated double diamondoid (ddi) topology that exhibits switching between closed (nonporous) and open (porous) phases induced by exposure to gases. A crystal engineering strategy, linker ligand substitution, was used to control gas sorption properties for CO₂ and C3 gases. Specifically, bimbz (1,4-bis(imidazol-1-yl)benzene) in the coordination network X-ddi-1-Ni ([Ni₂(bimbz)₂(bdc)₂(H₂O)]_n, H₂bdc = 1,4-benzenedicarboxylic acid) was replaced by bimpz (3,6-bis(imidazol-1-yl)pyridazine) in X-ddi-2-Ni ([Ni₂(bimpz)₂(bdc)₂(H₂O)]_n). In addition, the 1:1 mixed crystal X-ddi-1,2-Ni ([Ni₂(bimbz)(bimpz)(bdc)₂(H₂O)]_n) was prepared and studied. All three variants form isostructural closed (β) phases upon activation which each exhibited different reversible properties upon exposure to CO₂ at 195 K and C3 gases at 273 K. For CO₂, X-ddi-1-Ni revealed incomplete gate-opening, X-ddi-2-Ni exhibited a stepped isotherm with saturation uptake of 3.92 mol·mol^-1, and X-ddi-1,2-Ni achieved up to 62% more gas uptake and a distinct isotherm shape vs the parent materials. Single-crystal X-ray diffraction (SCXRD) and in situ powder X-ray diffraction (PXRD) experiments provided insight into the mechanisms of phase transformation and revealed that the β phases are nonporous with unit cell volumes 39.9, 40.8, and 41.0% lower than the corresponding as-synthesized α phases, X-ddi-1-Ni-α, X-ddi-2-Ni-α, and X-ddi-1,2-Ni-α, respectively. The results presented herein represent the first report of reversible switching between closed and open phases in ddi topology coordination networks and further highlight how ligand substitution can profoundly impact the gas sorption properties of switching sorbents.

Molecular Mechanisms behind Acetylene Adsorption and Selectivity in Functional Porous Materials

Since its first industrial production in 1890s, acetylene has played a vital role in manufacturing a wide spectrum of materials. Although current methods and infrastructures for various segments of acetylene industries are well-established, with emerging functional porous materials that enabled desired selectivity toward target molecules, it is of timely interest to develop new efficient technologies to promote safer acetylene processes with a higher energy efficiency and lower carbon footprint. In this Minireview, we, from the perspective of materials chemistry, review state-of-the-art examples of advanced porous materials, namely metal-organic frameworks and decorated zeolites, that have been applied to the purification and storage of acetylene. We also discuss the challenges on the roadmap of translational research in the development of new solid sorbent-based separation technologies and highlight areas which require future research efforts.

Engineering Pore Environments of Sulfate-Pillared Metal-Organic Framework for Efficient C2 H2 /CO2 Separation with Record Selectivity

Engineering pore environments exhibit great potential in improving gas adsorption and separation performances but require specific means for acetylene/carbon dioxide (C₂ H₂ /CO₂ ) separation due to their identical dynamic diameters and similar properties. Herein, a novel sulfate-pillared MOF adsorbent (SOFOUR-TEPE-Zn) using 1,1,2,2-tetra(pyridin-4-yl) ethene (TEPE) ligand with dense electronegative pore surfaces is reported. Compared to the prototype SOFOUR-1-Zn, SOFOUR-TEPE-Zn exhibits a higher C₂ H₂ uptake (89.1 cm³ g^-1 ), meanwhile the CO₂ uptake reduces to 14.1 cm³ g^-1 , only 17.4% of that on SOFOUR-1-Zn (81.0 cm³ g^-1 ). The high affinity toward C₂ H₂ than CO₂ is demonstrated by the benchmark C₂ H₂ /CO₂ selectivity (16 833). Furthermore, dynamic breakthrough experiments confirm its application feasibility and good cyclability at various flow rates. During the desorption cycle, 60.1 cm³ g^-1 C₂ H₂ of 99.5% purity or 33.2 cm³ g^-1 C₂ H₂ of 99.99% purity can be recovered by stepped purging and mild heating. The simulated pressure swing adsorption processes reveal that 75.5 cm³ g^-1 C₂ H₂ of 99.5+% purity with a high gas recovery of 99.82% can be produced in a counter-current blowdown process. Modeling studies disclose four favorable adsorption sites and dense packing for C₂ H₂ .

One Atom Can Make All the Difference: Gas-Induced Phase Transformations in Bisimidazole-Linked Diamondoid Coordination Networks

Coordination networks (CNs) that undergo gas-induced transformation from closed (nonporous) to open (porous) structures are of potential utility in gas storage applications, but their development is hindered by limited control over their switching mechanisms and pressures. In this work, we report two CNs, [Co(bimpy)(bdc)]_n (X-dia-4-Co) and [Co(bimbz)(bdc)]_n (X-dia-5-Co) (H₂bdc = 1,4-benzendicarboxylic acid; bimpy = 2,5-bis(1H-imidazole-1-yl)pyridine; bimbz = 1,4-bis(1H-imidazole-1-yl)benzene), that both undergo transformation from closed to isostructural open phases involving at least a 27% increase in cell volume. Although X-dia-4-Co and X-dia-5-Co only differ from one another by one atom in their N-donor linkers (bimpy = pyridine, and bimbz = benzene), this results in different pore chemistry and switching mechanisms. Specifically, X-dia-4-Co exhibited a gradual phase transformation with a steady increase in the uptake when exposed to CO₂, whereas X-dia-5-Co exhibited a sharp step (type F-IV isotherm) at P/P₀ ≈ 0.008 or P ≈ 3 bar (195 or 298 K, respectively). Single-crystal X-ray diffraction, in situ powder XRD, in situ IR, and modeling (density functional theory calculations, and canonical Monte Carlo simulations) studies provide insights into the nature of the switching mechanisms and enable attribution of pronounced differences in sorption properties to the changed pore chemistry.

Vertex Strategy in Layered 2D MOFs: Simultaneous Improvement of Thermodynamics and Kinetics for Record C2H2/CO2 Separation Performance

Developing adsorbents with multiple merits in capacity, selectivity, mass transfer, and stability toward C₂H₂/CO₂ separation is crucial and challenging for producing high-purity C₂H₂ for advanced polymers and the electronic industry. Here, we demonstrate a vertex strategy to create adsorbents combining these merits through rationally designing the vertex groups of a wavy-shaped framework in layered 2D metal-organic frameworks (MOFs) to finely regulate the local conformation and stacking interactions, which creates the optimal inter- and intralayer space to realize simultaneous improvement of adsorption thermodynamics and kinetics. Two new hydrolytically stable MOFs, ZUL-330 and ZUL-430, were prepared, and diverse experiments and modeling on both adsorption equilibrium and diffusion were performed. Record separation selectivities coupled with extraordinary dynamic C₂H₂ capacities were achieved for C₂H₂/CO₂ mixtures with different proportions (50/50 or 10/5, v/v), along with a small diffusion barrier and fast mass transfer. Consequently, polymer-grade (99.9%) and electronic-grade (99.99%) C₂H₂ were obtained with excellent productivities of up to ∼6 mmol cm^-3.

Tetranuclear CuII Cluster as the Ten Node Building Unit for the Construction of a Metal-Organic Framework for Efficient C2 H2 /CO2 Separation

Rational design of high nuclear copper cluster-based metal-organic frameworks has not been established yet. Herein, we report a novel MOF (FJU-112) with the ten-connected tetranuclear copper cluster [Cu₄ (PO₃ )₂ (μ₂ -H₂ O)₂ (CO₂ )₄ ] as the node which was capped by the deprotonated organic ligand of H₄ L (3,5-Dicarboxyphenylphosphonic acid). With BPE (1,2-Bis(4-pyridyl)ethane) as the pore partitioner, the pore spaces in the structure of FJU-112 were divided into several smaller cages and smaller windows for efficient gas adsorption and separation. FJU-112 exhibits a high separation performance for the C₂ H₂ /CO₂ separation, which were established by the temperature-dependent sorption isotherms and further confirmed by the lab-scale dynamic breakthrough experiments. The grand canonical Monte Carlo simulations (GCMC) studies show that its high C₂ H₂ /CO₂ separation performance is contributed to the strong π-complexation interactions between the C₂ H₂ molecules and framework pore surfaces, leading to its more C₂ H₂ uptakes over CO₂ molecules.

Quantitatively Visualizing the Thermal Dehydration Process and Isotope Effect in Single HKUST-1 Metal-Organic Framework Particles

Quantitatively visualizing the thermal dehydration in metal-organic frameworks (MOFs), especially at the single-particle level, is still challenging, hindering a deeper understanding of the reaction dynamics. Using in situ dark-field microscopy (DFM), we image the thermal dehydration process of single water-containing HKUST-1 (H₂O-HKUST-1) metal-organic framework (MOF) particles. DFM maps the color intensity of single H₂O-HKUST-1, which is linearly correlated with the water content in the HKUST-1 framework, enabling a direct quantification of several reaction kinetic parameters of single HKUST-1 particles. Interestingly, when H₂O-HKUST-1 is transformed into deutoxide (D₂O)-containing HKUST-1, the corresponding thermal dehydration reaction displays higher temperature parameters and activation energy but shows a lower rate constant and diffusion coefficient, revealing the isotope effect. The significant variation of the diffusion coefficient is also confirmed by molecular dynamics simulations. The present operando results are anticipated to provide valuable guidelines for the design and development of advanced porous materials.

Probing sub-5 Ångstrom micropores in carbon for precise light olefin/paraffin separation

Olefin/paraffin separation is an important but challenging and energy-intensive process in petrochemical industry. The realization of carbons with size-exclusion capability is highly desirable but rarely reported. Herein, we report polydopamine-derived carbons (PDA-Cx, where x refers to the pyrolysis temperature) with tailorable sub-5 Å micropore orifices together with larger microvoids by one-step pyrolysis. The sub-5 Å micropore orifices centered at 4.1-4.3 Å in PDA-C800 and 3.7-4.0 Å in PDA-C900 allow the entry of olefins while entirely excluding their paraffin counterparts, performing a precise cut-off to discriminate olefin/paraffin with sub-angstrom discrepancy. The larger voids enable high C₂H₄ and C₃H₆ capacities of 2.25 and 1.98 mmol g^-1 under ambient conditions, respectively. Breakthrough experiments confirm that a one-step adsorption-desorption process can obtain high-purity olefins. Inelastic neutron scattering further reveals the host-guest interaction of adsorbed C₂H₄ and C₃H₆ molecules in PDA-Cx. This study opens an avenue to exploit the sub-5 Å micropores in carbon and their desirable size-exclusion effect.

A Robust Molecular Porous Material for C2 H2 /CO2 Separation

A molecular porous material, MPM-2, comprised of cationic [Ni₂ (AlF₆ )(pzH)₈ (H₂ O)₂ ] and anionic [Ni₂ Al₂ F₁₁ (pzH)₈ (H₂ O)₂ ] complexes that generate a charge-assisted hydrogen-bonded network with pcu topology is reported. The packing in MPM-2 is sustained by multiple interionic hydrogen bonding interactions that afford ultramicroporous channels between dense layers of anionic units. MPM-2 is found to exhibit excellent stability in water (>1 year). Unlike most hydrogen-bonded organic frameworks which typically show poor stability in organic solvents, MPM-2 exhibited excellent stability with respect to various organic solvents for at least two days. MPM-2 is found to be permanently porous with gas sorption isotherms at 298 K revealing a strong affinity for C₂ H₂ over CO₂ thanks to a high (ΔQ_st )_AC [Q_st (C₂ H₂ ) - Q_st (CO₂ )] of 13.7 kJ mol^-1 at low coverage. Dynamic column breakthrough experiments on MPM-2 demonstrated the separation of C₂ H₂ from a 1:1 C₂ H₂ /CO₂ mixture at 298 K with effluent CO₂ purity of 99.995% and C₂ H₂ purity of >95% after temperature-programmed desorption. C-H···F interactions between C₂ H₂ molecules and F atoms of AlF₆ ^3- are found to enable high selectivity toward C₂ H₂ , as determined by density functional theory simulations.

De-Linker-Enabled Exceptional Volumetric Acetylene Storage Capacity and Benchmark C2 H2 /C2 H4 and C2 H2 /CO2 Separations in Metal-Organic Frameworks

An ideal adsorbent for separation requires optimizing both storage capacity and selectivity, but maximizing both or achieving a desired balance remain challenging. Herein, a de-linker strategy is proposed to address this issue for metal-organic frameworks (MOFs). Broadly speaking, the de-linker idea targets a class of materials that may be viewed as being intermediate between zeolites and MOFs. Its feasibility is shown here by a series of ultra-microporous MOFs (SNNU-98-M, M=Mn, Co, Ni, Zn). SNNU-98 exhibit high volumetric C₂ H₂ uptake capacity under low and ambient pressures (175.3 cm³  cm^-3 @ 0.1 bar, 222.9 cm³  cm^-3 @ 1 bar, 298 K), as well as extraordinary selectivity (2405.7 for C₂ H₂ /C₂ H₄ , 22.7 for C₂ H₂ /CO₂ ). Remarkably, SNNU-98-Mn can efficiently separate C₂ H₂ from C₂ H₂ /CO₂ and C₂ H₂ /C₂ H₄ mixtures with a benchmark C₂ H₂ /C₂ H₄ (1/99) breakthrough time of 2325 min g^-1 , and produce 99.9999 % C₂ H₄ with a productivity up to 64.6 mmol g^-1 , surpassing values of reported MOF adsorbents.

Redox-Active Mixed-Linker Metal-Organic Frameworks with Switchable Semiconductive Characteristics for Tailorable Chemiresistive Sensing

Metal-organic frameworks (MOFs), with diverse metal nodes and designable organic linkers, offer unique opportunities for the rational engineering of semiconducting properties. In this work, we report a mixed-linker conductive MOF system with both tetrathiafulvalene and Ni-bis(dithiolene) moieties, which allows the fine-tuning of electronic structures and semiconductive characteristics. By continuously increasing the molar ratio between tetrathiafulvalene and Ni-bis(dithiolene), the switching of the semiconducting behaviors from n-type to p-type was observed along with an increase in electrical conductivity by 3 orders of magnitude (from 2.88×10^-7  S m^-1 to 9.26×10^-5  S m^-1 ). Furthermore, mixed-linker MOFs were applied for the chemiresistive detection of volatile organic compounds (VOCs), where the sensing performance was modulated by the corresponding linker ratios, showing synergistic and nonlinear modulation effects.

Fluorido-bridged robust metal-organic frameworks for efficient C2H2/CO2 separation under moist conditions

The modern technology for acetylene production is inevitably accompanied by the contamination of carbon dioxide and moisture impurities. Metal-organic frameworks (MOFs), with rational configurations of fluorine as the hydrogen-bonding acceptor (HBA), exhibit excellent affinities to capture acetylene from the gas mixtures. Currently, most research studies feature anionic fluorine groups as structural pillars (e.g., SiF₆ ^2-, TiF₆ ^2-, NbOF₅ ^2-), whereas in situ insertion of fluorine into metal clusters is rather challenging. Herein, we report a unique fluorine-bridged Fe-MOF, i.e., DNL-9(Fe), which is assembled by mixed-valence Fe^IIFe^III clusters and renewable organic ligands. The fluorine species in the coordination-saturated structure offer superior C₂H₂-favored adsorption sites facilitated by hydrogen bonding, with a lower C₂H₂ adsorption enthalpy than other reported HBA-MOFs, demonstrated by static/dynamic adsorption tests and theoretical calculations. Importantly, DNL-9(Fe) shows exceptional hydrochemical stability under aqueous, acidic, and basic conditions, and its intriguing performance for C₂H₂/CO₂ separation was even maintained at a high relative humidity of 90%.

Reticular Design of Precise Linker Installation into a Zirconium Metal-Organic Framework to Reinforce Hydrolytic Stability

Reticular chemistry allows for the rational assembly of metal-organic frameworks (MOFs) with designed structures and desirable functionalities for advanced applications. However, it remains challenging to construct multi-component MOFs with unprecedented complexity and control through insertion of secondary or ternary linkers. Herein, we demonstrate that a Zr-based MOF, NU-600 with a (4,6)-connected she topology, has been judiciously selected to employ a linker installation strategy to precisely insert two linear linkers with different lengths into two crystallographically distinct pockets in a one-pot, de novo reaction. We reveal that the hydrolytic stability of these linker-inserted MOFs can be remarkably reinforced by increasing the Zr₆ node connectivity, while maintaining comparable water uptake capacity and pore-filling pressure as the pristine NU-600. Furthermore, introducing hydrophilic -OH groups into the linear linker backbones to construct multivariate MOFs can effectively shift the pore-filling step to lower partial pressures. This methodology demonstrates a powerful strategy to reinforce the structural stability of other MOF frameworks by increasing the connectivity of metal nodes, capable of encouraging developments in fundamental sciences and practical applications.

Optimizing Acetylene Sorption through Induced-fit Transformations in a Chemically Stable Microporous Framework

Developing practical storage technologies for acetylene (C₂ H₂ ) is important but challenging because C₂ H₂ is useful but explosive. Here, a novel metal-organic framework (MOF) (FJI-H36) with adaptive channels was prepared. It can effectively capture C₂ H₂ (159.9 cm³  cm^-3 ) at 1 atm and 298 K, possessing a record-high storage density (561 g L^-1 ) but a very low adsorption enthalpy (28 kJ mol^-1 ) among all the reported MOFs. Structural analyses show that such excellent adsorption performance comes from the synergism of active sites, flexible framework, and matched pores; where the adsorbed-C₂ H₂ can drive FJI-H36 to undergo induced-fit transformations step by step, including deformation/reconstruction of channels, contraction of pores, and transformation of active sites, finally leading to dense packing of C₂ H₂ . Moreover, FJI-H36 has excellent chemical stability and recyclability, and can be prepared on a large scale, enabling it as a practical adsorbent for C₂ H₂ . This will provide a useful strategy for developing practical and efficient adsorbents for C₂ H₂ storage.