Partial Linker Substitution Strategy to Construct a Quaternary HKUST-like MOF for Efficient Acetylene Storage and Separation

Copper-Based Metal-Organic Framework as a Potential Therapeutic Gas Carrier: Optimization, Synthesis, Characterization, and Computational Studies

The broad spectrum of health conditions and the global pandemic, leading to inadequate medical oxygen supply and management, has driven interest in developing porous nanocarriers for effective oxygenation strategies. We aim to develop an injectable oxygen carrier with regard to biocompatibility, safety, prehospital availability, and universal applicability. In this study, we have tried to identify important functional sites on metal-organic frameworks (MOFs) for gas binding with the help of Grand canonical Monte Carlo simulation. We have synthesized a copper-based MOF (Cu-BTC) with a 1,3,5-benzenetricarboxylic acid linker through a solvothermal approach as a competent porous adsorbent for oxygen storage and delivery. To optimize process variables, we performed statistical analysis using response surface methodology. A quadratic model was developed to study the interaction between independent variables and the response (i.e., maximizing surface area), whose adequacy is validated by the correlation between experimental and predicted values using the ANOVA method. The synthesized Cu-BTC, before and after oxygen loading, was characterized using X-ray diffraction, surface area, along with pore distribution measurement, particle size analysis, scanning electron microscopy, transmission electron microscopy, and gas adsorption studies. The Cu-BTC MOF exhibited an oxygen uptake of 4.6 mmol g-1, the highest among all the oxygen carriers reported in the literature under the same operating conditions. Overall, our findings suggest that this synthesized Cu-BTC with high surface area (1389 m2 g-1), high porosity, optimum oxygen uptake, and good biocompatibility would show potential toward efficient storage and delivery (direct to the targeted site) of medical oxygen to raise the blood oxygen saturation level.

Boosting Adsorption and Selectivity of Acetylene by Nitro Functionalisation in Copper(II)-Based Metal-Organic Frameworks

Purification and storage of acetylene (C2H2) are important to many industrial processes. The exploitation of metal-organic framework (MOF) materials to address the balance between selectivity for C2H2 vs carbon dioxide (CO2) against maximising uptake of C2H2 has attracted much interest. Herein, we report that the synergy between unsaturated Cu(II) sites and functional groups, fluoro (-F), methyl (-CH3), nitro (-NO2) in a series of isostructural MOF materials MFM-190(R) that show exceptional adsorption and selectivity of C2H2. At 298 K, MFM-190(NO2) exhibits an C2H2 uptake of 216 cm3 g-1 (320 cm3 g-1 at 273 K) at 1.0 bar and a high selectivity for C2H2/CO2 (up to ~150 for v/v = 2/1) relevant to that in the industrial cracking stream. Dynamic breakthrough studies validate and confirm the excellent separation of C2H2/CO2 by MFM-190(NO2) under ambient conditions. In situ neutron powder diffraction reveals the cooperative binding, packing and selectivity of C2H2 by unsaturated Cu(II) sites and free -NO2 groups.

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.

Anchoring ultrasmall Pd nanoparticles by bipyridine functional covalent organic frameworks for semihydrogenation of acetylene

Acetylene hydrogenation is a well-accepted solution to reduce by-products in the ethylene production process, while one of the key technical difficulties lies in developing a catalyst that can provide highly dispersed active sites. In this work, a highly crystalline layered covalent organic framework (COF) material (TbBpy) with excellent thermal stability was synthesized and firstly applied as support for ultrasmall Pd nanoparticles to catalyze acetylene hydrogenation. 100% of C2H2 conversion and 88.2% of C2H4 selectivity can be obtained at 120 °C with the space velocity of 70 000 h-1. The reaction mechanism was elucidated by applying a series of characterization techniques and theoretical calculation. The results indicate that the coordination between Pd and N atom in the bipyridine functional groups of COFs successfully increased the dispersibility and stability of Pd particles, and the introduction of COFs not only improved the adsorption of acetylene and H2 onto catalyst surface, but enhanced the electron transfer process, which can be responsible for the high selectivity and activity of catalyst. This work, for the first time, reported the excellent performance of Pd@TbBpy as a catalyst for acetylene hydrogenation and will facilitate the development and application of COFs materials in the area of petrochemicals.

Cu-MOFs with Rich Open Metal and F Sites for Separation of C2H2 from CO2 and CH4

Herein, we used the 4-fluoro-[1,1'-biphenyl]-3,4',5-tricarboxylic acid (H₃fbptc) ligand to design and construct a new metal-organic framework (MOF), [Cu₃(fbptc)₂(H₂O)₃]·3NMP (1), which possesses rich accessible metal sites and F functional groups in the porous walls and shows high uptake for C₂H₂ (119.3 cm³ g^-1) and significant adsorption selectivity for C₂H₂ over CH₄ (14.4) and CO₂ (3.6) at 298 K and 100 kPa. In particular, for the gas mixtures of C₂H₂-CH₄ and C₂H₂-CO₂, the MOF reveals large breakthrough time ratios (C₂H₂/CH₄ = 13, C₂H₂/CO₂ = 5.9), which are particularly prominent in dynamic breakthrough experiments, also confirming the excellent potential for the practical separation of C₂H₂ from two-component mixtures (C₂H₂-CH₄ and C₂H₂-CO₂) and even three-component mixtures (C₂H₂-CO₂-CH₄).

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.

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.

A highly robust cluster-based indium(III)-organic framework with efficient catalytic activity in cycloaddition of CO2 and Knoevenagel condensation

The efficient catalytic performance displayed by MOFs is decided by an appropriate charge/radius ratio of defect metal sites, large enough solvent-accessible channels and Lewis base sites capable of polarizing substrate molecules. Herein, the solvothermal self-assembly led to a highly robust nanochannel-based framework of {[In₄(CPDD)₂(μ₃-OH)₂(DMF)(H₂O)₂]·2DMF·5H₂O}_n (NUC-66) with a 56.8% void volume, which is a combination of a tetranuclear cluster [In₄(μ₃-OH)₂(COO)₁₀(DMF)(H₂O)₂] (abbreviated as {In₄}) and a conjugated tetracyclic pentacarboxylic acid ligand of 4,4'-(4-(4-carboxyphenyl)pyridine-2,6-diyl)diisophthalic acid (H₅CPDD). To the best of our knowledge, NUC-66 is a rarely reported {In₄}-based 3D framework with embedded hierarchical triangular-microporous (2.9 Å) and hexagonal-nanoporous (12.0 Å) channels, which are shaped by six rows of {In₄} clusters. After solvent exchange and vacuum drying, the surface of nanochannels in desolvated NUC-66a is modified by unsaturated In³⁺ ions, N_pyridine atoms and μ₃-OH groups, all of which display polarization ability towards polar molecules due to their Lewis acidity or basicity. The catalytic experiments performed showed that NUC-66a had high catalytic activity in the cycloaddition reactions of epoxides with CO₂ under mild conditions, which should be ascribed to its structural advantages including nanoscale channels, rich bifunctional active sites, large surface areas and chemical stability. Moreover, NUC-66a, as a heterogeneous catalyst, could greatly accelerate the Knoevenagel condensation reactions of aldehydes and malononitrile. Hence, this work confirms that the development of rigid nanoporous cluster-based MOFs built on metal ions with a high charge and large radius ratio will be more likely to realize practical applications, such as catalysis, adsorption and separation of gas, etc.

Pore Environment Optimization of Microporous Metal-Organic Frameworks with Huddled Pyrazine Pillars for C2H2/CO2 Separation

Metal-organic frameworks (MOFs) have been proven promising in addressing many critical issues related to gas separation and purification. However, it remains a great challenge to optimize the pore environment of MOFs for purification of specific gas mixtures. Herein, we report the rational construction of three isostructural microporous MOFs with the 4,4',4"-tricarboxyltriphenylamine (H₃TCA) ligand, unusual hexaprismane Ni₆O₆ cluster, and functionalized pyrazine pillars [PYZ-x, x = -H (DZU-10), -NH₂ (DZU-11), and -OH (DZU-12)], where the building blocks of Ni₆O₆ clusters and huddled pyrazine pillars are reported in porous MOFs for the first time. These building blocks have enabled the resulting materials to exhibit good chemical stability and variable pore chemistry, which thus contribute to distinct performances toward C₂H₂/CO₂ separation. Both single-component isotherms and dynamic column breakthrough experiments demonstrate that DZU-11 with the PYZ-NH₂ pillar outperforms its hydrogen and hydroxy analogues. Density functional theory calculations reveal that the higher C₂H₂ affinity of DZU-11 over CO₂ is attributed to multiple electrostatic interactions between C₂H₂ and the framework, including strong C≡C···H-N (2.80 Å) interactions. This work highlights the potential of pore environment optimization to construct smart MOF adsorbents for some challenging gas separations.

Substituent Engineering-Enabled Structural Rigidification and Performance Improvement for C2/CO2 Separation in Three Isoreticular Coordination Frameworks

Construction of porous solid materials applied to the adsorptive removal of CO₂ from C₂ hydrocarbons is highly demanded thanks to the important role C₂ hydrocarbons play in the chemical industry but quite challenging owing to the similar physical parameters between C₂ hydrocarbons and CO₂. In particular, the development of synthetic strategies to simultaneously enhance the uptake capacity and adsorption selectivity is very difficult due to the trade-off effect frequently existing between both of them. In this work, a combination of the dicopper paddlewheel unit and 4-pyridylisophthalate derivatives bearing different substituents afforded an isoreticular family of coordination framework compounds as a platform. Their adsorption properties toward C₂ hydrocarbons and CO₂ were systematically investigated, and subsequent IAST and density functional theory calculations combined with column breakthrough experiments verified their promising potential for C₂/CO₂ separations. Furthermore, the substituent engineering endowed the resulting compounds with simultaneous enhancement of uptake capacity and adsorption selectivity and thus better C₂/CO₂ separation performance compared to their parent compound. The substituent introduction not only mitigated the framework distortion via fixing the ligand conformation for establishment of better permanent porosity required for gas adsorption but also polarized the framework surface for host-guest interaction improvement, thus resulting in enhanced separation performance.