Enhanced water stability of MOFs via multiple hydrogen bonds and their application in water harvesting

A mechanism based on multiple hydrogen bonds was proposed to describe the great water stability of some hydrated Cu paddle-wheel-based MOFs, which was demonstrated through density functional theory (DFT) calculations and single-crystal X-ray diffraction (SCXRD) of water-loaded MOFs. This mechanism endowed Cu-TDPAT with exceptional water stability and outstanding atmospheric water harvesting capability.

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

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

A Scalable Ultramicroporous Coordination Network for Ethylene Separation from the Quaternary Mixture

Adsorptive ethylene separation from the C2H2/C2H4/C2H6/CO2 four-component gas mixture provides a low-energy input solution for industrial ethylene purification, yet it is still a great challenge. Herein, we report a facile scaled-up synthesis of a stable ultramicroporous coordination network of Zn-CO3-datz (Hdatz = 3,5-diamine-1,2,4-triazole), which enables selective adsorption of C2H2, C2H4 and CO2 over C2H4, thanks to its specific pore environment supported by GCMC simulation of gas adsorption sites. Dynamic breakthrough experiments exhibited efficient one-step production of polymer-grade (≥99.95%) C2H4 from the quaternary C2H4/C2H2/C2H6/CO2 (1/1/1/1) mixture, with excellent C2H4 productivity of 0.12 mol kg-1 at 298 K. Moreover, it can be easily synthesized in kilogram scale with an affordable and low-cost ligand, rendering its further potential industrial applications.

Pore Chemistry and Architecture Control in Anionic Functional Ultramicroporous Materials for Record Dense Packing of Xenon

Adsorptive separation of Xe and Kr is an industrially promising but challenging process because of their identical shape and similar physicochemical properties. Herein, we demonstrate a strategy through rationally designing the linkers of anionic functional ultramicroporous materials (FUMs) to finely regulate the pore chemistry and architecture, which creates unique stepped channels incorporating dense polar nanotraps to generate a larger effective pore space and enables dense packing of Xe. A new hydrolytically stable FUM (ZUL-530) was prepared, which for the first time achieves a Xe packing density exceeding the liquid Xe density at atmospheric conditions in metal-organic frameworks (MOFs) (based on experimental data), resulting in both excellent Xe uptake (2.55 mmol g-1 at 0.2 bar) and high IAST selectivity (20.5). GCMC and DFT-D calculations reveal the essential role of the stepped traps in the dense packing of Xe. Breakthrough experiments demonstrate remarkable productivities of both high-purity Kr (6.70 mmol g-1) and Xe (1.78 mmol g-1) for the Xe/Kr (20:80) mixture. In a model nuclear industry exhaust gas, ZUL-530 exhibits a top-class Xe dynamic capacity (28.8 mmol kg-1) for trace Xe, which proves it is one of the best candidates for Xe/Kr separation.

Recent Progress of Low-Dimensional Metal-Organic Frameworks for Aqueous Zinc-Based Batteries

Aqueous zinc-based batteries (AZBs) are promising energy storage solutions with remarkable safety, abundant Zn reserve, cost-effectiveness, and relatively high energy density. However, AZBs still face challenges such as anode dendrite formation that reduces cycling stability and limited cathode capacity. Recently, low-dimensional metal-organic frameworks (LD MOFs) and their derivatives have emerged as promising candidates for improving the electrochemical performance of AZBs owing to their unique morphologies, high structure tunability, high surface areas, and high porosity. However, clear guidelines for developing LD MOF-based materials for high-performance AZBs are scarce. In this review, the recent progress of LD MOF-based materials for AZBs is critically examined. The typical synthesis methods and structural design strategies for improving the electrochemical performance of LD MOF-based materials for AZBs are first introduced. The recent noteworthy research achievements are systematically discussed and categorized based on their applications in different AZB components, including cathodes, anodes, separators, and electrolytes. Finally, the limitations are addressed and the future perspectives are outlined for LD MOFs and their derivatives in AZB applications. This review provides clear guidance for designing high-performance LD MOF-based materials for advanced AZBs.

Cross-Linking CdSO4-Type Nets with Hexafluorosilicate Anions to Form an Ultramicroporous Material for Efficient C2H2/CO2 and C2H2/C2H4 Separation

A 44.610.8 topology hybrid ultramicroporous material (HUM), {[Cu1.5F(SiF6)(L)2.5]·G}n, (L = 4,4'-bisimidazolylbiphenyl, G = guest molecules), 1, formed by cross-linking interpenetrated 3D four-connected CdSO4-type nets with hexafluorosilicate anions is synthesized and evaluated in the context of gas sorption and separation herein. 1 is the first HUM functionalized with two different types of fluorinated sites (SiF6 2- and F- anions) lining along the pore surface. The optimal pore size (≈5 Å) combining mixed and high-density electronegative fluorinated sites enable 1 to preferentially adsorb C2H2 over CO2 and C2H4 by hydrogen bonding interactions with a high C2H2 isosteric heat of adsorption (Qst) of ≈42.3 kJ mol-1 at zero loading. The pronounced discriminatory sorption behaviors lead to excellent separation performance for C2H2/CO2 and C2H2/C2H4 that surpasses many well-known sorbents. Dynamic breakthrough experiments are conducted to confirm the practical separation capability of 1, which reveal an impressive separation factor of 6.1 for equimolar C2H2/CO2 mixture. Furthermore, molecular simulation and density functional theory (DFT) calculations validate the strong binding of C2H2 stems from the chelating fix of C2H2 between SiF6 2- anion and coordinated F- anion.

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

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

Non-cationic hyper-crosslinked ionic polymers with hierarchically ordered porous structures: facile synthesis and applications for highly efficient CO2 capture and conversion

Hyper-crosslinked porous ionic polymers (HCPIPs) have garnered significant attention due to their unique ionic properties and high specific surface areas. However, the limited variety of monomers, low ionic density, and difficulty in functionalization restrict their development. Herein, a series of functionalized non-cationic HCPIPs with high ionic density are designed and directly synthesized via an innovative and straightforward approach - anion (and cation) hyper-crosslinking of tetraphenylborate-based ionic liquids (ILs). These HCPIPs offer controllable hydroxyl group content (0-2.40 mmol g-1), high IL content (1.20-1.78 mmol g-1), and large specific surface area (636-729 m2 g-1) with hierarchically ordered porous structures. These HCPIPs demonstrate exceptional CO2 adsorption capacities and CO2/N2 adsorption selectivities, reaching up to 2.68-3.01 mmol g-1 and 166-237, respectively, at 273 K and 1 bar. Furthermore, these ionic porous materials serve as highly efficient heterogeneous catalysts for CO2 cycloaddition to epoxides under mild conditions (1 bar CO2, 60-80 °C, 12-24 h). Notably, the CO2 adsorption performances and catalytic activities of these HCPIPs are regulated by the hydroxyl groups within their structures, with enhancements observed as the number of hydroxyl groups increases. This work presents a facile and widely applicable method for constructing high-performance and task-specific HCPIPs.

Co/Cd-MOF-Derived Porous Carbon Materials for Moxifloxacin Adsorption from Aqueous Solutions

In this study, Co/Cd-MOFs were synthesized via a solvothermal method. The resulting material was subjected to calcination at 900 °C for 2 h and characterized using FT-IR, XRD, and SEM techniques to assess its efficacy in moxifloxacin removal. The experimental findings revealed that the maximum adsorption capacity of Co/Cd-MOFs for moxifloxacin was observed at 350.4 mg/g within a 5 h timeframe. Furthermore, the analysis based on the pseudo-second-order kinetic model demonstrated that the adsorption process adhered to this specific model. Additionally, the adsorption isotherm analysis indicated that Freundlich multilayer adsorption provided the best description of the interaction between moxifloxacin and the Co/Cd-MOF material. These experimental and theoretical results collectively suggest that employing Co/Cd-MOFs as adsorbents holds promise for wastewater treatment applications.

Precise Helium Sieving from Hydrogen Using Fluorine-Decorated Carbon Hollow Fiber Membranes

Separating helium (He) and hydrogen (H2), two gases that are extremely similar in molecular size and condensation properties, presents a formidable challenge in the helium industry. The development of membranes capable of precisely differentiating between these gases is crucial for achieving large-scale, energy-efficient He/H2 separation. However, the limited selectivity of current membranes has hindered their practical application. In this study, we propose a novel approach to overcome this challenge by engineering submicroporous membranes through the fluorination of partially carbonized hollow fibers. We demonstrate that the fluorine substitution on the inner rim of the micropore walls within the carbon hollow fibers enables tunability of the microporous architecture. Furthermore, it enhances interactions between H2 molecules and the micropore walls through the polarization and hydrogen bonding induced by C-F bonds, resulting in simultaneous improvements in both He/H2 diffusivity and solubility selectivities. The fluorinated HFM-550-F-1 min membrane exhibits exceptional mixed-gas separation performance, with a binary mixed-gas He/H2 selectivity of 10.5 and a ternary mixed-gas He/(H2+CO2) selectivity of 20.8, at 40 bar feed pressure and 35 °C, surpassing all previously reported polymer-based gas separation membranes, and remarkable plasticization resistance and long-term continuous stability over 30 days.

Ordered assembly of two different metal clusters with the same topological connectivity in one single coordination network

The introduction of heterogeneous components within one single coordination network leads to the multifunctionality of the final material. However, it is hard to precisely control the local distribution of these different components in such a coordination network, especially for different components with identical topological connectivity. In this study, we successfully achieved the ordered assembly of [Mn3(μ3-O)] nodes and [Mn6(μ3-O)2(CH3COO)3] nodes within one pacs coordination network. The resulting new structure (NPU-6) with heterogeneous metal nodes simultaneously inherits the advantages of both parent networks (good thermal stability and high pore volume). The significant effect of the reaction concentration of competing ligand CH3COO- on the mixed assembly of these two nodes in NPU-6 is revealed by a series of control experiments. This method is anticipated to offer a valuable reference for orderly assembling heterogeneous components in coordination networks.

Recent Advances of Multidentate Ligand-Based Anion-Pillared MOFs for Enhanced Separation and Purification Processes

As an important subclass of metal-organic frameworks (MOFs), anion-pillars MOFs (APMOFs) have recently exhibited exceptional performances in separation and purification processes. The adjustment of pore sizes and environments of APMOFs can be finely tuned through judicious combination of organic ligands, anion pillars, and metal ions. Compared to widely investigated anion pillars, organic ligands are more crucial as they allow for a broader range of pore sizes and environments at the nanometer scale. Furthermore, different from the bidentate ligand-based APMOFs that typically form three-dimensional (3D) frameworks with pcu topology, APMOFs constructed using multidentate nitrogen(N)-containing ligands (with a coordination number ≥ 3) offer opportunities to create APMOFs with diverse topologies. The larger dimensions and possible distortion of multidentate N-containing ligands prove advantageous for addressing multi-component hydrocarbon separations encompassing a broad spectrum of dynamic diameters. Therefore, this Review summarizes the structural characteristics of multidentate ligand-based APMOFs and their enhanced performances for gas separation and purification processes. Additionally, it discusses current challenges and prospects associated with constructing multidentate ligand-based APMOFs while providing prospects. This critical review will provide valuable insights and guides for designing and developing advanced multidentate ligand-based APMOF adsorbents.

Interpenetrated In(III)-MOF with Multiple Recognition Sites for Single-Step Ethylene Purification

An interpenetrated indium(III) metal-organic framework (MOF), NTUniv-73, with a rarely reported tetrameric indium cluster is developed for streamlining ethylene purification from C2 gases. At 298 K, the adsorption capacities exhibited a complete reversal sequence of C2H6 > C2H2 > C2H4. Grand canonical Monte Carlo simulation indicated that the corners in a octahedral cage facilitated the C2H2/C2H4 separation, while the pocket-like aperture situated between adjacent octahedral cages allows for full contact of C2H6. Breakthrough experiments illustrated that NTUniv-73 could yield pure C2H4 in a single step with a productivity of 0.42 mmol g-1.

Reverse Separation of Carbon Dioxide and Acetylene in Two Isostructural Copper Pyridine-Carboxylate Frameworks

Separating acetylene from carbon dioxide is important but highly challenging due to their similar molecular shapes and physical properties. Adsorptive separation of carbon dioxide from acetylene can directly produce pure acetylene but is hardly realized because of relatively polarizable acetylene binds more strongly. Here, we reverse the CO2 and C2H2 separation by adjusting the pore structures in two isoreticular ultramicroporous metal-organic frameworks (MOFs). Under ambient conditions, copper isonicotinate (Cu(ina)2), with relatively large pore channels shows C2H2-selective adsorption with a C2H2/CO2 selectivity of 3.4, whereas its smaller-pore analogue, copper quinoline-5-carboxylate (Cu(Qc)2) shows an inverse CO2/C2H2 selectivity of 5.6. Cu(Qc)2 shows compact pore space that well matches the optimal orientation of CO2 but is not compatible for C2H2. Neutron powder diffraction experiments confirmed that CO2 molecules adopt preferential orientation along the pore channels during adsorption binding, whereas C2H2 molecules bind in an opposite fashion with distorted configurations due to their opposite quadrupole moments. Dynamic breakthrough experiments have validated the separation performance of Cu(Qc)2 for CO2/C2H2 separation.

Avoiding the Kinetic Inertness of Chromium Ions Using a Coordination Substitution Strategy for the Rapid Synthesis of Chromium-Based Metal-Organic Frameworks

Chromium-based metal-organic frameworks (Cr-MOFs) are very attractive in a wide range of applications due to their robustness and high porosity. However, the kinetic inertness of chromium ions results in the synthesis of Cr-MOFs often taking prolonged reaction times, which limit their industrial applications. Herein, we report a novel synthesis strategy based on coordination substitution, which overcomes the kinetic inertness of chromium ions and can synthesize Cr-MOFs in a shorter time. The versatility of this strategy has been demonstrated by producing several known Cr-MOFs, such as TYUT-96Cr, MIL-100Cr, MIL-101Cr, and MIL-53Cr. PXRD, SEM, TEM, 77 K N2 adsorption, and TGA have proved that the Cr-MOFs synthesized using this new strategy have good crystallinity, high porosity, and excellent thermal stability. The synthesis mechanism was investigated using theoretical calculations.

Direct Ethylene Purification from a Four-Component Gas Mixture by a Microporous MOF with Aromatic Pore Surface and Carboxylates

The single-step purification of ethylene (C2H4) from a mixture of carbon dioxide (CO2), acetylene (C2H2), ethylene (C2H4), and ethane (C2H6) was achieved through MOF Compound-1, where the aromatic pore surface and carboxylates selectively recognized C2H6 and CO2, respectively, resulting in a reversal of the adsorption orders for both gases (C2H6 > C2H4 and CO2 > C2H4). Breakthrough testing verified that the C2H4 purification ability could be enhanced 2.6 times after adding impure CO2. Grand Canonical Monte Carlo (GCMC) simulations demonstrate that there are interactions between CO2 and C2H6 molecules as well as between CO2 molecules themselves. These interactions contribute to the enhancement of the C2H4 purification ability upon the addition of CO2 and the increased adsorption of CO2.

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.

Deciphering Mechanisms of CO2-Selective Recognition over Acetylene within Porous Materials

Reverse adsorption of carbon dioxide (CO2) from acetylene (C2H2) presents both significant importance and formidable challenges, particularly in the context of carbon capture, energy efficiency, and environmental sustainability. In this Review, we delve into the burgeoning field of reverse CO2/C2H2 adsorption and separation, underscoring the absence of a cohesive materials design strategy and a comprehensive understanding of the CO2-selective capture mechanisms from C2H2, in contrast to the quite mature methodologies available for C2H2-selective adsorption. Focusing on porous materials, the latest advancements in CO2-selective recognition mechanisms are highlighted. The review establishes that the efficacy of CO2 recognition from C2H2 relies intricately on a myriad of factors, including pore architecture, framework flexibility, functional group interactions, and dynamic responsive behaviors under operating conditions. It is noted that achieving selectivity extends beyond physical sieving, necessitating meticulous adjustments in pore chemistry to exploit the subtle differences between CO2 and C2H2. This comprehensive overview seeks to enhance the understanding of CO2-selective recognition mechanisms, integrating essential insights crucial for the advancement of future materials. It also lays the groundwork for innovative porous materials in CO2/C2H2 separation, addressing the pressing demand for more efficient molecular recognition within gas separation technologies.

Construction of a Ti-Based Bimetallic Metal-Organic Framework Using a One-Pot Method for Efficient C2H2/C2H4 and C2H2/CO2 Separation

Titanium (Ti)-based metal-organic frameworks (Ti-MOFs) have attracted intensive research attention due to their low toxicity and high abundance of titanium. However, limited by the high reactivity of titanium species in the reaction system, the construction of Ti-MOFs still faces great challenges. Herein, we successfully introduced Ti into MOF-74 using a one-pot method. Powder X-ray diffraction (PXRD) combined with X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) spectroscopy confirmed that the Ti(IV) ions were uniformly inserted into the MOF-74 structure. Our scanning electron microscopy (SEM)/energy-dispersive spectrometry (EDS) analysis showed that the Ti content was up to 44% with good sample homogeneity. The adsorption selectivity of Ti0.44/Ni0.56-MOF-74 at 1.0 bar and 298 K for C2H2/C2H4 and C2H2/CO2 (50/50, v/v) mixtures was 4.9 and 6.8, respectively, which are higher than that of pristine Ni-MOF-74. The results of our breakthrough simulation experiments revealed that the adsorption and separation performances of Ti0.44/Ni0.56-MOF-74 were greatly improved. This study provided insights for the construction of Ti-based bimetallic MOFs used for the separation of light hydrocarbons.

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

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

A Zeolitic Octahedral Metal Oxide with Ultrahigh Porosity for High-temperature and High-humidity Alkyne/Alkene Separation

Zeolitic octahedral metal oxide is a newly synthesized all-inorganic zeolitic material and has been used for adsorption, separation, and catalysis. Herein, a new zeolitic octahedral metal oxide was synthesized and characterized. The porous framework was established through the assembly of [P2Mo13O50] clusters with PO4 linkers. Guest molecules occupied the framework, which could be removed through heat treatment, thereby opening the micropores. The pore characteristics were controlled by the cations within the micropore, enabling the adjustment of the interactions with alkynes and alkenes. This resulted in good separation performance of ethylene/acetylene and propylene/propyne even under high temperature and humidity conditions. The high stability of the material enabled the efficient recovery and reuse without discernible loss in the separation performance. Due to the relatively weak interaction between the adsorbed alkyne and the framework, the adsorbent facilitated the recovery of a highly pure alkyne. This feature enhances the practical applicability of the material in various industrial processes.

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.

Water-Resistant, Scalable, and Inexpensive Chiral Metal-Organic Framework Featuring Global Negative Electrostatic Potentials for Efficient Acetylene Separation

Physical separation of acetylene (C2H2) from carbon dioxide (CO2) or ethylene (C2H4) on metal-organic frameworks (MOFs) is crucial for achieving high-purity feed gases with minimal energy penalty. However, such processes are exceptionally challenging due to their close physical properties and are also critically restricted by the high cost of large-scale MOF synthesis. Here, we demonstrate the readily scalable synthesis of a highly water-resistant chiral Cu-MOF (TAMOF-1) based on an inexpensive proteogenic amino acid derivative bearing rich N/O sites. Notably, the unique coordination in this ultramicroporous MOF has resulted in the generation of rare global negative electrostatic potentials, which greatly facilitate the electrostatic interactions with C2H2 molecules, thus leading to their efficient separation from C2H2/CO2 and C2H2/C2H4 mixtures under ambient conditions. The separation efficiency and mechanism are unequivocally validated by breakthrough experiments and computational simulations. This work not only highlights the pivotal role of creating a negative electro-environment in confined spaces for boosting C2H2 capture and separation but also opens up new ways of employing cheap amino acid derivatives bearing rich electro-negative N and O sites as organic linkers to constructing high-performing MOF materials for gas separation purposes.

Optimizing Trace Acetylene Removal from Acetylene/Ethylene Mixture in a Flexible Metal-Organic Framework by Crystal Downsizing

Improving the gas separation performance of metal-organic frameworks (MOFs) by crystal downsizing is an important but often overlooked issue. Here, we report three different-sized flexible ZUL-520 MOFs (according to the crystal size from large to small, the three samples are, respectively, named ZUL-520-0, ZUL-520-1, and ZUL-520-2) with the same chemical structure for optimizing trace acetylene (C2H2) removal from acetylene/ethylene (C2H2/C2H4) mixture. The three differently sized activated ZUL-520 (denoted as ZUL-520a) exhibited almost identical C2H2 uptake of 4.8 mmol/g at 100 kPa, while the C2H2 uptake at 1 kPa increased with a downsizing crystal. The C2H2 uptake of activated ZUL-520-2 (denoted as ZUL-520-2a) at 1 kPa was ∼55% higher than that of activated ZUL-520-0 (denoted as ZUL-520-0a). The adsorption isotherms and adsorption kinetics validated that gas adsorptive separation is governed not only by adsorption thermodynamics but also by adsorption kinetics. In addition, all three different-sized ZUL-520a MOFs showed high C2H2/C2H4 selectivity. Grand canonical Monte Carlo (GCMC) simulations and dispersion-corrected density functional theory (DFT-D) computations illustrated a plausible mechanism of C2H2 adsorption in MOFs. Importantly, breakthrough experiments demonstrated that ZUL-520a can effectively separate the C2H2/C2H4 (1/99, v/v) mixture and the C2H4 productivity obtained by ZUL-520-2a was much higher than that by ZUL-520-0a. Our work may provide an easy but powerful strategy for upgrading the performance of gas adsorptive separation in MOFs.

Fine-regulation of gradient gate-opening in nanoporous crystals for sieving separation of ternary C3 hydrocarbons

The adsorptive separation of ternary propyne (C3H4)/propylene (C3H6)/propane (C3H8) mixtures is of significant importance due to its energy efficiency. However, achieving this process using an adsorbent has not yet been accomplished. To tackle such a challenge, herein, we present a novel approach of fine-regulation of the gradient of gate-opening in soft nanoporous crystals. Through node substitution, an exclusive gate-opening to C3H4 (17.1 kPa) in NTU-65-FeZr has been tailored into a sequential response of C3H4 (1.6 kPa), C3H6 (19.4 kPa), and finally C3H8 (57.2 kPa) in NTU-65-CoTi, of which the gradient framework changes have been validated by in situ powder X-ray diffractions and modeling calculations. Such a significant breakthrough enables NTU-65-CoTi to sieve the ternary mixtures of C3H4/C3H6/C3H8 under ambient conditions, particularly, highly pure C3H8 (99.9%) and C3H6 (99.5%) can be obtained from the vacuum PSA scheme. In addition, the fully reversible structural change ensures no loss in performance during the cycling dynamic separations. Moving forward, regulating gradient gate-opening can be conveniently extended to other families of soft nanoporous crystals, making it a powerful tool to optimize these materials for more complex applications.

Flow Channel with Wrinkles and Calcium Sites in a Ca-MOF for Direct One-Step Ethylene Purification from C2 Gases and MTO Products Separation

The strategy of flow channel with wrinkles and calcium sites for single-step C2H4 purification from C2 gases and methanol-to-olefins (MTO) products separation was realized in FJI-Y9. The adsorption amounts showed a total reversal order of C3H6 > C2H6 > C2H2 > C2H4 at 298 K. Modeling indicated that the wrinkles and Ca2+ facilitated the full contact of C3H6 and C2H6. Breakthrough experiments illustrated that FJI-Y9 could yield pure C2H4 in a single step with a productivity of 0.78 mmol g-1. In a lone adsorption/desorption cycle for MTO product separation, the productivities of C3H6 and C2H4 were 1.96 and 1.29 mol g-1, standing as the highest recorded values.

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

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

Hydrophobic functionalization of a metal-organic framework as an ammonia visual sensing material under high humidity conditions

Since exhaled ammonia (NH3) is one of the metabolic markers of liver and kidney diseases, ammonia visual sensing materials in humid environments have received extensive attention and investigation. Herein, through a tailor-made pore environment provided by metal-organic framework (MOF) materials (CH3-Cu(BDC)), we achieved NH3 anti-interference sensing with apparent color changing under humid conditions. With methyl (CH3-) functionalization, CH3-Cu(BDC) demonstrated a strong response for trace ammonia and showed high selectivity under a humid environment. Grand canonical Monte Carlo (GCMC) simulations indicated that CH3-Cu(BDC) showed stronger attraction towards NH3 molecules than H2O. Benefiting from the target changing coordination environment, CH3-Cu(BDC) showed a rapid response and simple analysis properties for patients' exhaled air. The strategy used in this study not only provides a demonstration case for NH3 colorimetric sensing with high humidity and anti-interference but also introduces a new method for painless and quick exhaled breath analysis for diagnosis of patients with kidney and liver diseases.

Sulfonate Functional Ultramicroporous Materials with Suitable Pore Size and Layer-Stacked Structure for C4 Olefins Purification

Selective recognition of 1,3-butadiene from complex olefin isomers is vital for 1,3-butadiene purification, but the lack of porous materials with suitable pore structures results in poor selectivity and low capacity in C4 olefin separation. Herein, two sulfonate-functionalized organic frameworks, ZU-601 and ZU-602, are designed and show impressive separation performance toward C4 olefins. Benefiting from the suitable aperture size caused by the flexibility of coordinated organic ligand, ZU-601, ZU-602 that are pillared with different sulfonate anions could discriminate C4 olefin isomers with high uptake ratio: 1,3-butadiene/1-butene (207), 1,3-butadiene/trans-2-butene (10.1). Meanwhile, their layer-stacked structure enables the utilization of both intra- and interlayer space, enhancing the accommodation of guest molecules. ZU-601 exhibits record high 1,3-butadiene adsorption capacity of 2.90 mmol g-1 (0.5 bar, 298 K) among the reported flexible porous materials with high 1,3-butadiene/1-butene selectivity. The breakthrough experiments confirm their superior separation ability even for all five C4 olefin isomers, and the molecular-level structural change is well elucidated via powder, crystal analysis, and simulation studies. The work provides ideas toward advanced materials design with simultaneous high separation capacity and high separation selectivity for challenging separations.

Selective sorting of hexane isomers by anion-functionalized metal-organic frameworks with optimal energy regulation

Extensive efforts have been made to improve the separation selectivity of hydrocarbon isomers with nearly distinguishable boiling points; however, how to balance the high regeneration energy consumption remains a daunting challenge. Here we describe the efficient separation of hexane isomers by constructing and exploiting the rotational freedom of organic linkers and inorganic SnF62- anions within adaptive frameworks, and reveal the nature of flexible host-guest interactions to maximize the gas-framework interactions while achieving potential energy storage. This approach enables the discrimination of hexane isomers according to the degree of branching along with high capacity and record mono-/di-branched selectivity (6.97), di-branched isomers selectivity (22.16), and upgrades the gasoline to a maximum RON (Research Octane Number) of 105. Benefitting from the energy regulation of the flexible pore space, the material can be easily regenerated only through a simple vacuum treatment for 15 minutes at 25 °C with no temperature fluctuation, saving almost 45% energy compared to the commercialized zeolite 5 A. This approach could potentially revolutionize the whole scenario of alkane isomer separation processes.

Isoreticular Contraction of Cage-like Metal-Organic Frameworks with Optimized Pore Space for Enhanced C2H2/CO2 and C2H2/C2H4 Separations

The C2H2 separation from CO2 and C2H4 is of great importance yet highly challenging in the petrochemical industry, owing to their similar physical and chemical properties. Herein, the pore nanospace engineering of cage-like mixed-ligand MFOF-1 has been accomplished via contracting the size of the pyridine- and carboxylic acid-functionalized linkers and introducing a fluoride- and sulfate-bridging cobalt cluster, based on a reticular chemistry strategy. Compared with the prototypical MFOF-1, the constructed FJUT-1 with the same topology presents significantly improved C2H2 adsorption capacity, and selective C2H2 separation performance due to the reduced cage cavity size, functionalized pore surface, and appropriate pore volume. The introduction of fluoride- and sulfate-bridging cubane-type tetranuclear cobalt clusters bestows FJUT-1 with exceptional chemical stability under harsh conditions while providing multiple potential C2H2 binding sites, thus rendering the adequate ability for practical C2H2 separation application as confirmed by the dynamic breakthrough experiments under dry and humid conditions. Additionally, the distinct binding mechanism is suggested by theoretical calculations in which the multiple supramolecular interactions involving C-H···O, C-H···F, and other van der Waals forces play a critical role in the selective C2H2 separation.

Charge-Assisted Ionic Hydrogen-Bonded Organic Frameworks: Designable and Stabilized Multifunctional Materials

Hydrogen-bonded organic frameworks (HOFs) are a class of crystalline framework materials assembled by hydrogen bonds. HOFs have the advantages of high crystallinity, mild reaction conditions, good solution processability, and reproducibility. Coupled with the reversibility and flexibility of hydrogen bonds, HOFs can be assembled into a wide diversity of crystalline structures. Since the bonding energy of hydrogen bonds is lower than that of ligand and covalent bonds, the framework of HOFs is prone to collapse after desolventisation and the stability is not high, which limits the development and application of HOFs. In recent years, numerous stable and functional HOFs have been developed by π-π stacking, highly interpenetrated networks, charge-assisted, ligand-bond-assisted, molecular weaving, and covalent cross-linking. Charge-assisted ionic HOFs introduce electrostatic attraction into HOFs to improve stability while enriching structural diversity and functionality. In this paper, we review the development, the principles of rational design and assembly of charge-assisted ionic HOFs, and introduces the different building block construction modes of charge-assisted ionic HOFs. Highlight the applications of charge-assisted ionic HOFs in gas adsorption and separation, proton conduction, biological applications, etc., and prospects for the diverse design of charge-assisted ionic HOFs structures and multifunctional applications.

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.

Microporous Coordination Polymers for Efficient Recovery of Chloromethane from Organic Silicon Industrial Exhaust Gas

Removal and recovery of methyl chloride (CH3Cl) from exhaust gas of organic silicon industry is highly important from the perspective of environment and economy. For the first time, a tailor-made microporous coordination polymer (Mn-BDC-TPA) was synthesized and applied to the efficient capture and recovery of CH3Cl from related gas mixtures. The high adsorption capacity of CH3Cl (163.4 cm3/g) and high adsorption selectivity of CH3Cl over other impurity gases (1965 for N2, 65 for CH4, and 16 for C2H6) were achieved at 298 K and 100 kPa due to the dual-cage pore system and larger polarizability of CH3Cl. Dynamic breakthrough experiments demonstrate the excellent CH3Cl recovery performance (capacity of >98 cm3/g and purity of >95%) in one adsorption-desorption cycle from the CH3Cl-involved binary, ternary, or quaternary gas mixture.

Tuning Multiple Counter-Anions in Porous Coordination Polymers with Topology for Acetylene/Ethylene Separation

The efficient separation of acetylene (C2H2) and ethylene (C2H4) is an important and complex process in the industry. Herein, we report a new family of lcy-topologic coordination frameworks (termed NTU-90 to NTU-92) with Cu3MF6 (M = Si, Ti, and Zr) nodes. These charged frameworks are compensated by different counterbalanced ions (MF62-, BF4-, and Cl-), yielding changes in the size of the window apertures. Among these frameworks, NTU-92-a (activated NTU-92) shows good adsorption selectivity of C2H2/C2H4 and also significant ability in recovering both highly pure C2H4 (99.95%) and C2H2 (99.98%). Our work not only presents a potential alternative for energy-saving purification of C2 hydrocarbons but also provides a new approach for tuning the function of charged porous materials.

Three-Dimensional Polyoxometalate Organic Frameworks with One-Dimensional Channels Constructed by Multiple Helical Chains Based on 22-Core Ln/Mn/Mo Clusters for Proton Conduction

Two unique 22-core sandwich {[Mn6Mo6O37]Ln3[MnMo6O24]} (Ln = La or Pr) units have been assembled, featuring an undisclosed {Mn6Mo6} cluster. This assembly is subsequently integrated into two three-dimensional polyoxometalate organic frameworks, which exhibit one-dimensional hydrophilic hexagonal channels formed by six intertwined 63 helical chains, leading to effective proton conduction primarily facilitated by an abundance of water molecules within the channels.

Sulfate-Pillared Adsorbent for Efficient Acetylene Separation from Carbon Dioxide and Ethylene

The effective separation of acetylene (C2H2) from carbon dioxide (CO2) and ethylene (C2H4) presents considerable challenges in the petrochemical industry. In this work, we report a novel sulfate-pillared (SO4 2-) ultra-microporous material, denoted as SOFOUR-DPDS-Ni (SOFOUR = SO4 2-, 4-DPDS = 4,4'-dipyridyldisulfide), for efficient C2H2 capture from both CO2 and C2H4. The sulfate pillars play a crucial role in inducing robust negative electrostatic potentials within the intralayer cavities and interlayer channels, thereby facilitating the selective recognition of C2H2. As a result, SOFOUR-DPDS-Ni demonstrates a remarkable C2H2 adsorption capacity of 1.60 mmol g-1 at 0.01 bar, an exceptional selectivity of 174 for the 50/50 C2H2/CO2 mixture, and a high selectivity of 65 for the 1/99 C2H2/C2H4 mixture. These impressive metrics position SOFOUR-DPDS-Ni as a promising adsorbent for benchmark C2H2 separations. Dynamic breakthrough experiments validate its outstanding performance in separating C2H2 from both the CO2 and C2H4 mixtures. Computational simulations reveal the strong interactions between C2H2 and sulfate pillars, shedding light on the underlying mechanisms driving the adsorption process.

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.

Cis-Trans and Length-Selective Molecular Discrimination of Halogenated Organic Compounds by a Crystalline Hybrid Macrocyclic Arene

The development of adsorbents with robust molecular discrimination capabilities for halogenated organic compounds (HOCs) holds significant importance due to their potential in adsorptive separation and mitigation of associated health risks. In this study, we report a molecular discrimination behavior based on crystalline hybrid macrocyclic arene H, offering precise capture of cis-trans isomers and length-selective separation of HOCs. The activated H crystals (Hα) demonstrate exceptional discrimination and separation performance by selectively capturing trans-1,2-dichloroethylene (trans-DCE) from cis/trans-isomer mixtures with a high selectivity of 98.8%. Evidenced by single-crystal X-ray diffraction and density functional theory (DFT) calculations, this high adsorption selectivity arises from the formation of more stable complex crystals between H and the preferred guest trans-DCE. Moreover, Hα exhibits the ability to selectively trap size-matched 1,2-dibromoethane (DBE) from mixtures of alkylene dibromides with varying alkane-chain lengths, although their capture and separation are recognized to be difficult as a consequence of low-polarity bonds. The solid-state transformations between guest-free and guest-containing Hα crystals indicate their recyclability, showcasing promising prospects for potential applications.

Hydrogen bond unlocking-driven pore structure control for shifting multi-component gas separation function

Purification of ethylene (C2H4) as the most extensive and output chemical, from complex multi-components is of great significance but highly challenging. Herein we demonstrate that precise pore structure tuning by controlling the network hydrogen bonds in two highly-related porous coordination networks can shift the efficient C2H4 separation function from C2H2/C2H4/C2H6 ternary mixture to CO2/C2H2/C2H4/C2H6 quaternary mixture system. Single-crystal X-ray diffraction revealed that the different amino groups on the triazolate ligands resulted in the change of the hydrogen bonding in the host network, which led to changes in the pore shape and pore chemistry. Gas adsorption isotherms, adsorption kinetics and gas-loaded crystal structure analysis indicated that the coordination network Zn-fa-atz (2) weakened the affinity for three C2 hydrocarbons synchronously including C2H4 but enhanced the CO2 adsorption due to the optimized CO2-host interaction and the faster CO2 diffusion, leading to effective C2H4 production from the CO2/C2H2/C2H4/C2H6 mixture in one step based on the experimental and simulated breakthrough data. Moreover, it can be shaped into spherical pellets with maintained porosity and separation performance.

Enhancing CO2/N2 and CH4/N2 separation performance by salt-modified aluminum-based metal-organic frameworks

The energy-saving separation of CO2/N2 and CH4/N2 in the energy industry facilitates the reduction of greenhouse gas emissions and replenishes energy resources, but is a challenging separation process. The trade-off between adsorption capacity and selectivity of the adsorbents is one of the key bottlenecks in adsorption separation technologies' large-scale application in the above separation task. Herein, we introduced a series of fluoroborate or fluorosilicate salts (Cu(BF4)2, Zn(BF4)2 and ZnSiF6) into the open coordination nitrogen sites of aluminum-based metal-organic frameworks (MOF-253) to create multiple binding sites to simultaneously enhance the adsorption capacity and selectivity for the target gas. By the synergistic adsorption effect of metal ions (Cu2+ or Zn2+) and fluorinated anions (BF4- or (SiF6)2-), the single-component adsorption capacity and selectivity of salt-modified MOF-253 (MOF-253@Cu(BF4)2, MOF-253@Zn(BF4)2 and MOF-253@ZnSiF6) for CO2 and CH4 were effectively improved when compared to pristine MOF-253 at 298 K and 1 bar. In addition, the salt-modified MOF-253 has a moderate adsorption heat (<30 kJ mol-1) which could be rapidly regenerated at low energy by evacuation desorption. As confirmed by the ambient breakthrough experiments of MOF-253 and MOF-253@ZnSiF6, the real separation performance for both CO2/N2 (1/4) and CH4/N2 (1/4) was obviously improved. This work provides a feasible post-modification strategy on uncoordinated sites of the framework to improve adsorption separation performance and promote the development of ideal adsorbents with a view to realizing their application in the energy industry.

Flow Channel with Recognition Corners in a Stable La-MOF for One-Step Ethylene Production

Single-step ethylene (C2H4) production from acetylene (C2H2), ethylene (C2H4), and ethane (C2H6) mixtures was realized via the strategy of a flow channel with recognition corners in MOF NTUniv-64. Both the uptake amounts and the enthalpy of adsorption (Qst) showed the same order of C2H2 > C2H6 > C2H4. Breakthrough testing also verified the above data and the C2H4 purification ability. Grand Canonical Monte Carlo (GCMC) simulations indicated that uneven corners could precisely detain C2H2 and C2H6, in which the C-H···π interaction distance between C2H2 (2.84 Å) and C2H6 (3.03 Å) and the framework was shorter than that of C2H4 (3.85 Å).

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.

Collective Effects of Multiple Fluorine Atoms Causing π-philic Characteristic within a Caged Polyoxometalate Framework

Perfluorination brings about distinctive properties arising from the unusual nature of the F element, which have been extensively developed in materials science and chemistry. Herein we report that the construction of F-rich inner space within a hollowed Mo132 O372 cage ([Mo132 O372 (OCOR)30 (H2 O)72 ]42- ) leads to the emergence of unique guest binding activities in encapsulation. Prominently, the trifluoroacetate-modified cage (R=CF3 , 2) having as many as 90 F groups inside favors trapping cyclopentadiene (Cp), which is hardly trapped by the non-fluorinated counterpart (R=CH3 , 1). Systematic studies using related hydrocarbons show that the amount of the encapsulated guest is correlated with the unsaturation degree of the guests, implying the involvement of the attractive interaction of the CF3 -modified interior wall with the guest π-electron clouds. Control experiments using the semi-fluorinated analogues (R=CF2 H, CFH2 ) reveal that the perfluorination is a critical factor to facilitate the Cp encapsulation by 2, indicating that collective effects of polar C-F bonds spreading over the interior surface, rather than the polarity of the individual C-F bonds, are responsible. We also provide a successful example of the physical molecular confinement within the cage through the "ship-in-a-bottle" Diels-Alder reaction between trapped diene and dienophile.

A molecular sieve with ultrafast adsorption kinetics for propylene separation

The design of molecular sieves is vital for gas separation, but it suffers from a long-standing issue of slow adsorption kinetics due to the intrinsic contradiction between molecular sieving and diffusion within restricted nanopores. We report a molecular sieve ZU-609 with local sieving channels that feature molecular sieving gates and rapid diffusion channels. The precise cross-sectional cutoff of molecular sieving gates enables the exclusion of propane from propylene. The coexisting large channels constituted by sulfonic anions and helically arranged metal-organic architectures allow the fast adsorption kinetics of propylene, and the measured propylene diffusion coefficient in ZU-609 is one to two orders of magnitude higher than previous molecular sieves. Propylene with 99.9% purity is obtained through breakthrough experiments with a productivity of 32.2 L kg-1.

Anionic Ni-Based Metal-Organic Framework with Li(I) Cations in the Pores for Efficient C2H2/CO2 Separation

Acetylene (C2H2) is widely used as a raw material for producing various downstream commodities in the petrochemical and electronic industry. Therefore, the acquisition of high-purity C2H2 from a C2H2/CO2 mixture produced by partial methane combustion or thermal hydrocarbon cracking is of great significance yet highly challenging due to their similar physical and chemical properties. Herein, we report an anionic metal-organic framework (MOF) named LIFM-210, which has Li+ cations in the pores and shows a higher adsorption affinity for C2H2 than CO2. LIFM-210 is constructed by a unique tetranuclear Ni(II) cluster acting as a 10-connected node and an organic ligand acting as a 5-connected node. Single-component adsorption and transient breakthrough experiments demonstrate the good C2H2 selective separation performance of LIFM-210. Theoretical calculations revealed that Li+ ions strongly prefer C2H2 to CO2 and are primary adsorption sites, playing vital roles in the selective separation of C2H2/CO2.

Fine Tuning Metal-Organic Frameworks with Halogen Functional Groups for Ethylene Purification

One-step C2H4 purification from a mixture of C2H2/C2H4/C2H6 could be achieved by metal-organic framework (MOF) NTUniv-70 with an F-functional group. The selectivities of C2H4/C2H6 and C2H4/C2H2 of NTUnvi-70 based on ideal adsorbed solution theory were at least twice that of the original MOF platform, which was in line with the enthalpy of adsorption (Qst) and breakthrough testing. Grand canonical Monte Carlo simulations indicated that the C-H···F interactions played an important role in enhanced C2H4/C2H6 and C2H4/C2H2 adsorption selectivities.

Ultramicroporous Lonsdaleite Topology MOF with High Propane Uptake and Propane/Methane Selectivity for Propane Capture from Simulated Natural Gas

Propane (C3H8) is a widely used fuel gas. Metal-organic framework (MOF) physisorbents that are C3H8 selective offer the potential to significantly reduce the energy footprint for capturing C3H8 from natural gas, where C3H8 is typically present as a minor component. Here we report the C3H8 recovery performance of a previously unreported lonsdaleite, lon, topology MOF, a chiral metal-organic material, [Ni(S-IEDC)(bipy)(SCN)]n, CMOM-7. CMOM-7 was prepared from three low-cost precursors: Ni(SCN)2, S-indoline-2-carboxylic acid (S-IDECH), and 4,4'-bipyridine (bipy), and its structure was determined by single crystal X-ray crystallography. Pure gas adsorption isotherms revealed that CMOM-7 exhibited high C3H8 uptake (2.71 mmol g-1) at 0.05 bar, an indication of a higher affinity for C3H8 than both C2H6 and CH4. Dynamic column breakthrough experiments afforded high purity C3H8 capture from a gas mixture comprising C3H8/C2H6/CH4 (v/v/v = 5/10/85). Despite the dilute C3H8 stream, CMOM-7 registered a high dynamic uptake of C3H8 and a breakthrough time difference between C3H8 and C2H6 of 79.5 min g-1, superior to those of previous MOF physisorbents studied under the same flow rate. Analysis of crystallographic data and Grand Canonical Monte Carlo simulations provides insight into the two C3H8 binding sites in CMOM-7, both of which are driven by C-H···π and hydrogen bonding interactions.

Stepwise Synthesis of Cl-Decorated Trinuclear-Cu Cluster-Based Frameworks for C2H2/C2H4 and C2H2/CO2 Separation

A novel Cl-decorated trinuclear-Cu cluster-based MOF (NbU-7-Cl, NbU denotes Ningbo University) was synthesized by a stepwise synthesis strategy. Compared to one-step reactions, the strategy of combining cationic templates with single-crystal-to-single-crystal transformation provides more possibilities for the design and postsynthetic modification of multifunctional materials. Note that the chloride ions are attached to the copper ions of the planar trinuclear cluster nodes in a fully symmetric or partially asymmetric manner. The insertion of the chloride ion can alter the overall symmetry and adsorption energy in addition to occupying the appropriate asymmetric orbit and reducing the effective active sites of metal. The activated NbU-7-Cl displays improved C2H2 uptake capacity and C2H2/C2H4 and C2H2/CO2 separation performance, which is proved by breakthrough experiments.