Density Gradation of Open Metal Sites in the Mesospace of Porous Coordination Polymers

Tailoring Pore Environments in Metal-Organic Frameworks for Efficient C2H2/CO2 and C2H2/C2H4 Separations

The efficient separation of acetylene (C2H2) from carbon dioxide (CO2) and ethylene (C2H4) is of significant industrial importance but remains highly challenging due to their similar physicochemical properties. In this study, three isostructural metal-organic frameworks, [Co4(µ4-SO4)2(tpim)2(L)2] (tpim = 2,4,5-tri(4-pyridyl)-imidazole, L = dicarboxylate; termed as Co4-L), are constructed from sulfate-capped Co4 clusters extended by N-rich tpim linkers and different-sized dicarboxylate ligands. Among them, the Co₄-1,4-ndc framework, incorporating 1,4-naphthalenedicarboxylic acid (1,4-ndc), offers optimal pore confinement that promotes host-guest interactions between C₂H₂ molecules and framework. This material exhibits high C₂H₂ capture capacities of 4.30 and 3.40 mmol g-¹ from equimolar C₂H₂/CO₂ and C₂H₂/C₂H₄ mixtures, respectively. Theoretical simulations reveal that the enhanced selectivity arises from multiple cooperative hydrogen-bonding interactions between C₂H₂ and the framework Co₄-1,4-ndc, generating strong and preferential binding sites. This study highlights the role of pore-environment engineering of metal-organic frameworks (MOFs) for selective C₂H₂ separation, providing a foundation for the development of advanced adsorbents in industrial gas purification.

A Scalable Pore-space-partitioned Metal-organic Framework Powered by Polycatenation Strategy for Efficient Acetylene Purification

Efficient separation of acetylene (C2H2) from carbon dioxide (CO2) and ethylene (C2H4) is a significant challenge in the petrochemical industry due to their similar physicochemical properties. Pore space partition (PSP) has shown promise in enhancing gas adsorption capacity and selectivity by reducing pore size and increasing the density of guest binding sites. Herein, we firstly employ the 2D→3D polycatenation strategy to construct a PSP metal-organic framework (MOF) Ni-dcpp-bpy, incorporating functional N/O sites to enhance C2H2 purification. The polycatenated framework with optimized pore size and regularity, exhibiting significant improvements over traditional PSP MOFs by resolving the critical contradiction of balancing C2H2 uptake (98.5 cm3 g-1 at 298 K, 100 kPa) and selectivity of C2H2/CO2 (3.4), C2H2/C2H4 (5.9), and C2H2/CH4 (96.4) in a MOF. Breakthrough experiments confirm high-purity C2H4 (>99.9 %) and high C2H2 productivity from binary and ternary mixtures. Notably, Ni-dcpp-bpy exhibits excellent water stability, scalability, and regenerability after 20 cycles for separating C2H2/CO2. Theoretical calculations verify that the strong binding of C2H2 is mainly attributed to the C-H⋅⋅⋅O/N interactions between host Ni-dcpp-bpy and guest C2H2 molecules. The polycatenation strategy not only improved industrial C2H2 purification efficiency but also enriched the design diversity of customized MOFs for other gas separation applications.

Copper-Based Bio-MOF/GO with Lewis Basic Sites for CO2 Fixation into Cyclic Carbonates and C-C Bond-Forming Reactions

Several measures, including crude oil recovery improvement and carbon dioxide (CO2) conversion into valuable chemicals, have been considered to decrease the greenhouse effect and ensure a sustainable low-carbon future. The Knoevenagel condensation and CO2 fixation have been introduced as two principal solutions to these challenges. In the present study for the first time, bio-metal-organic frameworks (MOF)(Cu)/graphene oxide (GO) nanocomposites have been used as catalytic agents for these two reactions. In view of the attendance of amine groups, biological MOFs with NH2 functional groups as Lewis base sites protruding on the channels' internal surface were used. The bio-MOF(Cu)/20%GO performs efficaciously in CO2 fixation, leading to more than 99.9% conversion with TON = 525 via a solvent-free reaction under a 1 bar CO2 atmosphere. It has been shown that these frameworks are highly catalytic due to the Lewis basic sites, i.e., NH2, pyrimidine, and C═O groups. Besides, the Lewis base active sites exert synergistic effects and render bio-MOF(Cu)/10%GO nanostructures as highly efficient catalysts, significantly accelerating Knoevenagel condensation reactions of aldehydes and malononitrile as substrates, thanks to the high TOF (1327 h-1) and acceptable reusability. Bio-MOFs can be stabilized in reactions using GO with oxygen-containing functional groups that contribute as efficient substitutes, leading to an expeditious reaction speed and facilitating substrate absorption.

In situ generated 2,5-pyrazinedicarboxylate and oxalate ligands leading to a Eu-MOF for selective capture of C2H2 from C2H2/CO2

The separation of C2H2/CO2 mixtures is a very important but highly challenging task due to their comparable physical natures and relative sizes. Herein, we report a europium-based 3D microporous MOF with a 4-connected two-nodal net with {4·53·62}2{42·62·82} topology, {[Eu2(pzdc)(ox)2(H2O)4]·5H2O}n (1) (H2pzdc = 2,5-pyrazinedicarboxylic acid, H2ox = oxalic acid), prepared by a hydrothermal method involving in situ generation of 2,5-pyrazinedicarboxylate and oxalate ligands. Two different temperatures were utilized to create two porous materials (1a and 1b) with channels of 4.8 × 5.4 Å and 4.1 × 6.3 Å, and 4.8 × 5.4 and 4.6 × 8.7 Å2, respectively. 1b shows a superior ability to selectively capture C2H2 from C2H2/CO2 as compared with 1a. At 1 bar and 298 K, 1b takes up 4.10 mmol g-1 C2H2 and 1.84 mmol g-1 CO2, respectively. In addition, at 298 K and 1 bar, 1b has a high selectivity for C2H2 over CO2, with an IAST selectivity of 12.7 while the value for 1a is 3.2. The separation of C2H2/CO2 with 1b also exhibits good reusability.

Immobilization of Amino-site into a Pore-Partitioned Metal-Organic Framework for Highly Efficient Separation of Propyne/Propylene

Adsorptive separation of propyne/propylene (C3H4/C3H6) is a crucial yet complex process, however, it remains a great difficulty in developing porous materials that can meet the requirements for practical applications, particularly with an exceptional ability to bind and store trace amounts of C3H4. Functionalization of pore-partitioned metal-organic frameworks (ppMOFs) is methodically suited for this challenge owing to the possibility of dramatically increasing binding sites on highly porous and confined domains. We here immobilized Lewis-basic (-NH2) and Lewis-acidic (-NO2) sites on this platform. Along with an integrated nature of high uptake of C3H4 at 1 kPa, high uptake difference of C3H4-C3H6, moderated binding strength, promoted kinetic selectivity, trapping effect and high stability, the NH2-decorated ppMOF (NTU-100-NH2) can efficiently produce polymer-grade C3H6 (99.95 %, 8.3 mmol ⋅ g-1) at room temperature, which is six times more than the NO2-decorated crystal (NTU-100-NO2). The in situ infrared spectroscopy, crystallographic analysis, and sequential blowing tests showed that the densely packed amino group in this highly porous system has a unique ability to recognize and stabilize C3H4 molecules. Moving forward, the strategy of organic functionalization can be extended to other porous systems, making it a powerful tool to customize advanced materials for challenging tasks.

Pure separation of acetylene based on a sulfonic acid and amino group functionalized Zn-MOF

The dual-ligand strategy was employed to synthesize a new microporous material, [Zn3(SNDC)(AmTAZ)3(H2O)]·H2O·CH3CN (1), incorporating sulfonic acid and amino groups for enhancing gas adsorption and separation. The activated 1 (named 1a) exhibited selective adsorption of acetylene over carbon dioxide and methane. Hence, the dual-ligand strategy optimized the pore environment and provided an effective approach for pure separation of gases.

Boosting Acetylene Packing Density within an Isoreticular Metal-Organic Framework for Efficient C2H2/CO2 Separation

Porous solid adsorbents for C2H2/CO2 separation are generally confronted with poor stability, high cost, or high regeneration energy, which largely inhibit their industrial implementation. A desired adsorbent material for practical implementation should exhibit a good balance between low cost, high stability, scale-up production feasibility, and good separation performance. An effective strategy is herein explored based on reticular chemistry through embedding methyl groups in a prototype microporous metal-organic framework (MOF) featuring low cost and high stability to effectively separate an C2H2/CO2 mixture. The anchored methyl groups on the pore surfaces could strongly boost the C2H2 packing density and specifically enhance the C2H2/CO2 separation performance, as distinctly established by single-component gas sorption isotherms. The CAU-10-CH3 material exhibits an excellent C2H2 packing density of 486 g L-1 and high adsorption differences between C2H2 and CO2 uptake (147%), outperforming the prototype benchmark material CAU-10-H (392 g L-1 and 53%). The highly selective adsorption of C2H2 over CO2 was achieved by a lower C2H2 adsorption enthalpy (25.18 kJ mol-1) compared to that with unfunctionalized CAU-10-H. In addition, dynamic column breakthrough experiments further confirm CAU-10-CH3's efficient separation performance for the C2H2/CO2 mixture. CAU-10-CH3 accomplishes the benchmark balance between cost, stability, scale-up, and separation performance for C2H2/CO2 separation, establishing its promise for industrial implementation. This approach could further facilitate the development of advanced MOF adsorbents to address challenging separation processes. Thus, this study paves the route for the practical implementations of MOF materials in the gas adsorption and separation field.

Size Control of On-Surface Self-Assembled Nanochains Using Soft Building Blocks

Owing to their conformational flexibility, soft molecules with side chains play a crucial role in molecular self-assembly or self-organization processes toward bottom-up building of supramolecular nanostructures. However, the influence of the rotating side chains in the confined space and subsequent surface-confined supramolecular self-assembly remains rarely explored. Herein, using the spatial confinement effect between soft building blocks, we realized size control on surface-confined supramolecular coordination self-assembly through the synergy between the repulsive steric hindrance and the attractive chemical interactions. Combining scanning tunneling microscopy with density functional theory calculations and Monte Carlo simulations, we elucidated the effective repulsive force generated by the thermal wiggling motions of the soft building blocks, allowing length tuning of the self-assembled chain structures. Through a delicate balance between the repulsive interaction induced by the spatial confinement effect and the coordinate chemical interaction, we provide a new strategy for controlling the geometry of the on-surface supramolecular nanostructures.

Direct prediction of gas adsorption via spatial atom interaction learning

Physisorption relying on crystalline porous materials offers prospective avenues for sustainable separation processes, greenhouse gas capture, and energy storage. However, the lack of end-to-end deep learning model for adsorption prediction confines the rapid and precise screen of crystalline porous materials. Here, we present DeepSorption, a spatial atom interaction learning network that realizes accurate, fast, and direct structure-adsorption prediction with only information of atomic coordinate and chemical element types. The breakthrough in prediction is attributed to the awareness of global structure and local spatial atom interactions endowed by the developed Matformer, which provides the intuitive visualization of atomic-level thinking and executing trajectory in crystalline porous materials prediction. Complete adsorption curves prediction could be performed using DeepSorption with a higher accuracy than Grand canonical Monte Carlo simulation and other machine learning models, a 20-35% decline in the mean absolute error compared to graph neural network CGCNN and machine learning models based on descriptors. Since the established direct associations between raw structure and target functions are based on the understanding of the fundamental chemistry of interatomic interactions, the deep learning network is rationally universal in predicting the different physicochemical properties of various crystalline materials.

A Dual-Purpose Ce(III)-Organic Framework with Amine Groups and Open Metal Sites: Third-Order Nonlinear Optical Activity and Catalytic CO2 Fixation

The present work focuses on the synthesis and properties of a novel multifunctional cerium(III) MOF, [Ce2(data)3(DMF)4]·DMF (data2-: 2,5-diaminoterephthalate), abbreviated as NH2-Ce-MUM-2. Its crystal structure reveals an intricate 3D 4,5-connected framework with a xah topology. This MOF features unique properties, such as open metal sites, presence of free amino groups, and high stability. Two main applications of NH2-Ce-MUM-2 were investigated: (i) as a heterogeneous catalyst in the CO2 fixation into cyclic carbonates and (ii) as a material with third-order nonlinear optical activity. As a model reaction, the cycloaddition of CO2 to propylene oxide to give the corresponding cyclic carbonate was explored under mild conditions, at the atmospheric pressure of carbon dioxide and in the absence of cocatalyst and added solvent. Various reaction parameters were investigated toward optimization and exploration of substrate scope, revealing up to 99% product yields of cyclic carbonate products. Besides, the structure of NH2-Ce-MUM-2 is highly stable, permitting its recyclability and reusability in further catalytic experiments. The significant contributions of free amino groups and open metal sites within this catalyst were particularly considered when proposing a potential mechanism for the reaction. Z-Scan measurements were used to evaluate the nonlinear optical (NLO) properties of NH2-Ce-MUM-2 at various laser intensities. A high two-photon absorption (TPA) under greater incident intensities shows that NH2-Ce-MUM-2 might be applicable in optical switching devices. Besides, the self-focusing effects of NH2-Ce-MUM-2 under various incident intensities were highlighted by the nonlinear index of refraction (n2). By reporting the synthesis and characterization of a novel MOF, along with its highly promising catalytic and NLO behavior, the current study introduces an additional example of multifunctional material into a growing family of metal-organic frameworks.

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.

Rational Pore Design of a Cage-like Metal-Organic Framework for Efficient C2H2/CO2 Separation

Considering the importance of C₂H₂ in industry, it is of great significance to develop porous materials for efficient C₂H₂/CO₂ separation. Besides the high selectivity, the C₂H₂ adsorption capacity is another vital factor in C₂H₂/CO₂ separation. However, the "trade-off" between these two factors is still perplexing. Rational pore design of metal-organic frameworks (MOFs) has been proven to be an effective way to solve the above problem. In this work, we have appropriately combined three kinds of strategies in the design of the MOF (FJI-H33), i.e., the introduction of open metal sites, construction of cage-like cavities, and adjustment of moderate pore size. As anticipated, FJI-H33 exhibits both outstanding C₂H₂ adsorption capacity and high C₂H₂/CO₂ selectivity. At 298 K and 100 kPa, the C₂H₂ storage capacity of FJI-H33 is 154 cm³/g, while the CO₂ uptake is only 80 cm³/g. The ideal adsorbed solution theory (IAST) selectivity of C₂H₂/CO₂ (50:50) is calculated as high as 15.5 at 298 K. More importantly, the excellent practical separation performance was verified by breakthrough experiments. In addition, the calculation of adsorption sites and relevant energy by density functional theory (DFT) provides a good explanation for the excellent separation performance and pore design strategy.

Effect of Orbital-Symmetry Matching in a Metal-Organic Framework for Highly Efficient C2H2/C2H4 and C2H2/CO2 Separations

The detailed mechanism of metal-organic-framework (MOF)-based separation materials is still obscure, which obviously hinders their actual application. To address this problem, a trinuclear Cu-cluster-based MOF with a minimum metal-active plane was synthesized for the study of the very challenging C₂H₂/C₂H₄ and C₂H₂/CO₂ separations. Via dispersion-corrected density functional theory calculations, it is indicated that the difference of the adsorption energy accounts for the excellent separation properties toward C₂H₂/C₂H₄ and C₂H₂/CO₂ mixtures, while the frontier molecular orbitals demonstrate that the adsorption-energy difference originates from the orbital-symmetry difference of gas molecules. All of these results provide not only deep insight into the separation mechanism but also an alternative strategy to prepare efficient adsorbents.

Polyoxocationic antimony oxide cluster with acidic protons

The success and continued expansion of research on metal-oxo clusters owe largely to their structural richness and wide range of functions. However, while most of them known to date are negatively charged polyoxometalates, there is only a handful of cationic ones, much less functional ones. Here, we show an all-inorganic hydroxyiodide [H_10.7Sb_32.1O₄₄][H_2.1Sb_2.1I₈O₆][Sb_0.76I₆]₂·25H₂O (HSbOI), forming a face-centered cubic structure with cationic Sb₃₂O₄₄ clusters and two types of anionic clusters in its interstitial spaces. Although it is submicrometer in size, electron diffraction tomography of HSbOI allowed the construction of the initial structural model, followed by powder Rietveld refinement to reach the final structure. The cationic cluster is characterized by the presence of acidic protons on its surface due to substantial Sb³⁺ deficiencies, which enables HSbOI to serve as an excellent solid acid catalyst. These results open up a frontier for the exploration and functionalization of cationic metal-oxo clusters containing heavy main group elements.

Stable Fluorinated Hybrid Microporous Material for the Efficient Separation of C2-C3 Alkyne/Alkene Mixtures

The separation of C₂-C₃ alkyne/alkene mixtures is important but difficult work thanks to their similar physical and chemical properties. Crystalline porous materials with high alkyne adsorption and prominent separation selectivity of alkyne/alkene mixtures have been extensively investigated because of their energy-saving merits. Herein, we report a fluorinated hybrid microporous material (FJI-W1) that exhibits unexpected water and thermal stability. Gas sorption isotherms show that FJI-W1 has ultrahigh C₂H₂ and C₃H₄ adsorption capacities of 150 and 159 cm³/g, respectively. Furthermore, dynamic breakthrough experiments indicate that the intervals of breakthrough time between the two gases for 1:99 (v/v) C₂H₂/C₂H₄ and 1:99 (v/v) C₃H₄/C₃H₆ can be up to 230 and 600 min/g, respectively. Additionally, the tests with different flow rates and three-cycle breakthrough tests demonstrate that FJI-W1 has a remarkable C₂-C₃ alkyne/alkene separation performance.

Anion Regulates Topological Porous Coordination Polymers into the Acetylene Trap

The development of efficient porous absorbents with high uptake and selectivity remains a great challenge, especially for the recovery of acetylene (C₂H₂) from its carbon dioxide (CO₂)-containing mixtures. Here, we propose and report an anion-planting strategy for regulating the scu topological porous coordination polymers (PCPs) into the C₂H₂ trap. The three electronegative anions SiF₆^2-, TiF₆^2-, and ZrF₆^2-, in addition to the ligand of 3,5-di(1H-imidazol-1-yl)benzoic acid (HL) and Cu²⁺ ion, were employed to construct highly porous PCPs (NTU-60, NTU-61, and NTU-62) with varied window aperture. Especially, due to a matching distance (d_F-F) of 5.7 Å along the c-axis, the limited space that can be assigned as a single C₂H₂ trap enables NTU-61 to show optimal ability for C₂H₂ (van der Waals (vdW) parameters of the two H atoms: ∼5.72 Å) recognition, validated by Grand Canonical Monte Carlo (GCMC) calculations and Raman spectra. These characteristics allow the NTU-series to show higher C₂H₂ uptake, as well as excellent C₂H₂/CO₂ separation performance under dynamic conditions. The molecular insight and strategy here not only permit balanced adsorption and separation in a single domain but also exhibit an opportunity to develop advanced adsorbents in nearly all frameworks with lattice or coordinated ions, which may act as the platforms for various selective guest trappings with on-demand time and/or spatial resolution.

A (3,8)-Connected Metal-Organic Framework with Bending Dicarboxylate Linkers for C2H2/CO2 Separation

Herein, by replacement of the linear terephthalate linker with the bending 2,5-thiophenedicarboxylate (tdc^2-) linker in the typical (3,9)-connected metal-organic framework, with a reduced 8-connected hydroxyl-centered trinuclear cluster, a new (3,8)-connected network, [Ni₃(μ₃-OH)(tdc)₃(tpp)] [DZU-1; tpp = 2,4,6-tris(4-pyridyl)pyridine], was synthesized. The modified pore environment enables DZU-1 to selectively adsorb C₂H₂ over CO₂ in an efficient manner.

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

The separation of C₂H₂/CO₂ is not only industrially important for acetylene purification but also scientifically challenging owing to their high similarities in physical properties and molecular sizes. Ultramicroporous metal-organic frameworks (MOFs) can exhibit a pore confinement effect to differentiate gas molecules of similar size. Herein, we report the fine-tuning of pore sizes in sub-nanometer scale on a series of isoreticular MOFs that can realize highly efficient C₂H₂/CO₂ separation. The subtle structural differences lead to remarkable adsorption performances enhancement. Among four MOF analogs, by integrating appropriate pore size and specific binding sites, [Cu(dps)₂(SiF₆)] (SIFSIX-dps-Cu, SIFSIX = SiF₆^2-, dps = 4.4'-dipyridylsulfide, also termed as NCU-100) exhibits the highest C₂H₂ uptake capacity and C₂H₂/CO₂ selectivity. At room temperature, the pore space of SIFSIX-dps-Cu significantly inhibits CO₂ molecules but takes up a large amount of C₂H₂ (4.57 mmol g^-1), resulting in a high IAST selectivity of 1787 for C₂H₂/CO₂ separation. The multiple host-guest interactions for C₂H₂ in both inter- and intralayer cavities are further revealed by dispersion-corrected density functional theory and grand canonical Monte Carlo simulations. Dynamic breakthrough experiments show a clean C₂H₂/CO₂ separation with a high C₂H₂ working capacity of 2.48 mmol g^-1.

Luminescent organic porous crystals from non-cyclic molecules and their applications

Organic porous crystals from small and non-cyclic organic molecules can be constructed by various intermolecular weak interactions. Owing to their precise stacking types, intermolecular interaction and pore microstructure, the relationship...

Synthesis of palm sheath derived-porous carbon for selective CO2 adsorption

Biomass-derived porous carbons are regarded as the most preferential adsorbents for CO₂ capture due to their well-developed textural properties, tunable porosity and low cost. Herein, novel porous carbons were facilely prepared by activation of palm sheath for the highly selective separation of CO₂ from gas mixtures. The textural features of carbon materials were characterized by the analysis of surface morphology and N₂ isotherms for textural characterization. The as-prepared carbon adsorbents possess an excellent CO₂ adsorption capacity of 3.48 mmol g⁻¹ (298 K) and 5.28 mmol g⁻¹ (273 K) at 1 bar, and outstanding IAST selectivities of CO₂/N₂, CO₂/CH₄, and CH₄/N₂ up to 32.7, 7.1 and 4.6 at 298 K and 1 bar, respectively. Also, the adsorption evaluation criteria of the vacuum swing adsorption (VSA) process, the breakthrough experiments, and the cyclic experiments have comprehensively demonstrated the palm sheath derived porous carbons as efficient adsorbents for practical applications.

Novel porous carbons were facilely prepared by activation of palm sheath for the highly selective separation of CO₂ from gas mixtures.

Photoinduced Electron-Transfer (PIET) Strategy for Selective Adsorption of CO2 over C2 H2 in a MOF

Similarities in sizes, shapes, and physical properties between carbon dioxide (CO₂ ) and acetylene (C₂ H₂ ) make it a great challenge to separate the major impurity CO₂ from products in C₂ H₂ production. The use of porous materials is an appealing path to replace current very costly and energy-consuming technologies, such as solvent extraction and cryogenic distillation; however, high CO₂ /C₂ H₂ uptake ratio with minor adsorption of C₂ H₂ at standard pressure was only unexpectedly observed in scarce examples in recent years although the related research started early at 1950s, and general design strategies to realize this aim are still absent. This work has successfully developed an efficient PIET strategy and obtained the second highest CO₂ /C₂ H₂ adsorption ratio for porous materials in a proof-of-concept MOF with a photochromism-active bipyridinium zwitterion. An unprecedented photocontrollable gate effect, owing to change of interannular dihedral after photoinduced generation of radical species, was also observed for the first time. These findings will inspire design and synthesis of porous materials for high efficient gas adsorption and separation.

Electrostatically Driven Selective Adsorption of Carbon Dioxide over Acetylene in an Ultramicroporous Material

Separating acetylene from carbon dioxide is important but highly challenging owing to their similar physical properties and molecular dimensions. Herein, we report highly efficient electrostatically driven CO2 /C2 H2 separation in an ultramicroporous cadmium nitroprusside (Cd-NP) with compact pore space and complementary electrostatic potential well fitting for CO2 , thus enabling molecular quadrupole moment recognition of CO2 over C2 H2 . This material shows a high CO2 /C2 H2 uptake ratio of 6.0 as well as remarkable CO2 /C2 H2 selectivity of 85 under ambient conditions with modest CO2 heat of adsorption. Neutron powder diffraction experiments and molecular simulations revealed that the electrostatic potential compatibility between pore structure and CO2 allows it to be trapped in a head-on orientation towards the Cd center, whereas the diffusion of C2 H2 is electrostatically forbidden. Dynamic breakthrough experiments have validated the separation performance of this compound for CO2 /C2 H2 separation.

Efficient and Highly Selective CO2 Capture, Separation, and Chemical Conversion under Ambient Conditions by a Polar-Group-Appended Copper(II) Metal-Organic Framework

A polar sulfone-appended copper(II) metal-organic framework (MOF; 1) has been synthesized from the dual-ligand approach comprised of tetrakis(4-pyridyloxymethylene)methane and dibenzothiophene-5,5'-dioxide-3,7-dicarboxylic acid under solvothermal conditions. This has been studied by different techniques that included single-crystal X-ray diffractometry, based on which the presence of Lewis acidic open-metal sites as well as polar sulfone groups aligned on the pore walls is identified. MOF 1 displays a high uptake of CO₂ over N₂ and CH₄ with an excellent selectivity (S = 883) for CO₂/N₂ (15:85) at 298 K under flue gas combustion conditions. Additionally, the presence of Lewis acidic metal centers facilitates an efficient size-selective catalytic performance at ambient conditions for the conversion of CO₂ into industrially valuable cyclic carbonates. The experimental investigations for this functional solvent-free heterogeneous catalyst are also found to be in good correlation with the computational studies provided by configurational bias Monte Carlo simulation for both CO₂ capture and its conversion.

Mechanistic Studies on Photoinduced Catalytic Olefin Migration Reactions at the Pd(II) Centers of a Porous Crystal, Metal-Macrocycle Framework

Porous crystals with well-defined active metal centers on the pore surface have high potential as heterogeneous metal catalysts. We have recently demonstrated that a porous molecular crystal, metal-macrocycle framework (MMF), catalyzes olefin migration reactions by photoactivation of its Pd^II Cl₂ moieties exposed on the crystalline channel surface. Herein we report a mechanistic study of the photoinduced olefin migration reactions at the Pd^II active centers of MMF. Several experiments, including a deuterium scrambling study, revealed that olefin migration is catalyzed via an alkyl mechanism by in situ generated Pd-H species on the channel surface during photoirradiation. This proposed mechanism was further supported by DFT and ONIOM calculations.

Recent progress and perspectives on the structural design on metal-organic zeolite (MOZ) frameworks

As a typical group of coordination polymers, metal-organic zeolite (MOZs) frameworks inherit the topological and structural advantages of inorganic zeolites and display great application potential in many areas, including gas adsorption/separation, catalysis, luminescence and chemical sensing. In this review, we outline the recent progress in the synthesis, functionalization and application of metal-organic zeolite frameworks, mainly focusing on the basic structural design principle and synthesis strategy on 4-connect inorganic nodes and 2-connect organic linkers. Employing different valent metals, small inorganic TO₄^2- units and high-nuclear clusters as 4-connect nodes, we derived multi-types of MOZs with a modified framework charge, improved stability and enhanced photo-/eletrocatalytic activity. Besides, the selection, functionalization and defect-engineering on the 2-connect ligands generated different topological and functional MOZs. Finally, the future trends and some perspectives in this area are outlined.

The multifunctional design of metal–organic framework by applying linker desymmetrization strategy: synergistic catalysis for high CO2-epoxide conversion

A novel copper-organic framework was synthesized by a linker desymmetrization strategy. Synergistic catalysis with Lewis and Brønsted acid sites promoted a high catalytic efficiency towards the CO2-propylene oxide cycloaddition reaction.

Pore engineering of metal-organic frameworks for ethylene purification

Ethylene production is an important and direct indicator related to the development of the petrochemical industry in a country. However, the separation and purification of ethylene is an extremely energy-consuming process. In this review, the latest progress in the purification of ethylene using metal organic frameworks (MOFs), a new type of physical adsorbent, is summarized according to four classifications of pore engineering, including pore surface functionalization, molecular sieving, controlled framework softness and dynamic pore-dominated molecular diffusion. Finally, the current challenges and future prospects in this field are also discussed.

A Highly Connected Trinuclear Cluster Based Metal-Organic Framework for Efficient Separation of C2H2/C2H4 and C2H2/CO2

One of the barriers for efficient gas separation is the trade-off between the selectivity and adsorption capacity. To address this issue, we synthesized an anionic trinuclear Co^II based 3D MOF (NbU-8), which is characterized by an ultramicroporous building unit (UBU) and Lewis basic binding sites on the pore surfaces. Remarkably, the combination of the two strategies can synergistically enhance the C₂H₂ adsorption capacity (182.9 cm³/g at 298 K) and simultaneously achieve a high separation performance toward C₂H₂/C₂H₄ and C₂H₂/CO₂ mixtures. Besides theoretical calculations, the separation efficiencies of C₂H₂/C₂H₄ and C₂H₂/CO₂ are also demonstrated using breakthrough experiments. Density functional theory calculations have further confirmed the -OH groups and ultramicroporous building units play an important synergistic effect in efficiently capturing acetylene molecules.

Unprecedented High Temperature CO2 Selectivity and Effective Chemical Fixation by a Copper-Based Undulated Metal-Organic Framework

Post- and precombustion CO₂ capture and separation are the vital challenges from industrial viewpoint, as the accessible technologies are not cost-effective and cumbersome. Thus, the development of functional metal-organic frameworks (MOFs) that are found to be promising materials for selective CO₂ capture, separation, and conversion is gaining an importance in the scientific world. Based on the strategic design, a new functionalized triazine-based undulated paddle-wheel Cu-MOF (1), {[Cu(MTABA)(H₂O)]·4H₂O·2EtOH·DMF}_n (where, H₂MTABA = 4,4'-((6-methoxy-1,3,5-triazine-2,4-diyl)bis(azanediyl))dibenzoic acid), has been synthesized under solvothermal conditions and fully characterized. MOF 1 contains a one-dimensional channel along the a-axis with pore walls decorated with open metal sites, and multifunctional groups (amine, triazine, and methoxy). Unlike other porous materials, activated 1 (1') possesses exceptional increment in CO₂/N₂ and CO₂/CH₄ selectivity with increased temperature calculated by the ideal adsorbed solution theory. With an increase in temperature from 298 to 313 K, the selectivity of CO₂ rises from 350.3 to 909.5 at zero coverage, which is unprecedented till date. Moreover, 1' behaves as a bifunctional heterogeneous catalyst through Lewis acid (open metal) and Brönsted acid sites to facilitate the chemical fixation of CO₂ to cyclic carbonates under ambient conditions. The high selectivity for CO₂ by 1' even at higher temperature was further corroborated with configurational bias Monte Carlo molecular simulation that ascertains the multiple CO₂-philic sites and epoxide binding sites in 1' to further decipher the mechanistic pathway.

Removal of boron from water by GO/ZIF-67 hybrid material adsorption

With the development of the boron industry, boron pollution is getting more and more serious, and excessive boron will harm human health. In this paper, graphene oxide was used as a template to prepare ZIF-67, and GO/ZIF-67 was successfully prepared. GO/ZIF-67 was used for the first time to remove boron from water. SEM, XRD, and other characterization methods were used to confirm the structure. The adsorption kinetics, adsorption isotherm, adsorption thermodynamics, and adsorption mechanism of boron by GO/ZIF-67 were studied in this paper. The adsorption capacity of GO/ZIF-67 for boron is up to 66.65 mg·g^-1 at 25 °C, and adsorption process reaches equilibrium in 400 min. Adsorption kinetics indicates that the adsorption process conforms to the pseudo-first-order kinetic model, and adsorption thermodynamics indicates that the adsorption process is a spontaneous endothermic process controlled by entropy change. The adsorption capacity of boron by GO/ZIF-67 does not decrease significantly after four cycles. The adsorption of boron by GO/ZIF-67 has both chemical and physical adsorption. From Zeta potential and adsorption kinetics, it can be seen that there is physical adsorption during the adsorption process and boron mainly has positive charge on the surface of GO/ZIF-67 and graphene oxide hydroxyl bonding. Based on the adsorption thermodynamics and XPS, it is known that there is chemisorption during the adsorption process, and mainly the combination of boron and cobalt sites.

Shaping of gallate-based metal-organic frameworks for adsorption separation of ethylene from acetylene and ethane

Shaping metal-organic frameworks (MOFs) powders into formed bodies plays a crucial role in opening up the excellent properties of MOFs to a broad range of applications. Gallate-based MOFs, termed as M-gallate (M = Co, Mg, Ni), have shown excellent performance for adsorption separation of C₂ hydrocarbons. However, the industrial applications of MOF powders will inevitably confront problems of high pressure drop, pipe blockage, and dust pollution. Herein, we use hydroxypropyl cellulose (HPC) as a binder to produce gallate-based MOFs pellets. The crystal structure of the well-shaped materials after molding remained intact, and the surface area of the materials hardly decreases after shaping. Adsorption isotherms of C₂ hydrocarbons including ethylene, ethane and acetylene on the activated powders and pellets of M-gallate were recorded and compared with the outperformers. The shaped pellets were also examined by breakthrough experiments on the fixed-bed separation of C₂H₂/C₂H₄ (1:99, v/v) and C₂H₄/C₂H₆ (50:50, v/v) gas mixtures. These results proved that M-gallate pellets was promising candidates for the practical industrial realization of C₂ hydrocarbons separation.

Reduced Graphene Oxide/ZIF-67 Aerogel Composite Material for Uranium Adsorption in Aqueous Solutions

Safe and sustainable development of the nuclear industry has become the focus of attention, so it is important to manage byproducts of radioactive elements, such as uranium, which is inevitably discharged into water bodies. In this work, an adsorbent was fabricated by the in-site assembly of zeolitic imidazolate framework-67 (ZIF-67) on reduced graphene oxide (rGO) hydrogel. The adsorption property of the rGO/ZIF-67 aerogel toward U(VI) was studied via batch adsorption experiment. According to kinetic fitting tests, the adsorption property was in accord well with the pseudo-second-order model, revealing that the adsorption process was chemisorption; the results of the isothermal model conform to the Langmuir model, which exhibited an excellent adsorption capacity of 1888.55 mg/g. The thermodynamic parameter (ΔH° = 11.7 kJ/mol) obtained from the experimental data demonstrated that temperature rise is favorable for the adsorption. Based on the characterization of the material and results of the adsorption, the adsorption mechanism for U(VI) may be explained by surface complexation and electrostatic attraction. In general, all these results and characteristics of the adsorbent show that the rGO/ZIF-67 aerogel provides an alternative way to fabricate novel uranium adsorbent.