Separation of Acetylene from Carbon Dioxide and Ethylene by a Water-Stable Microporous Metal-Organic Framework with Aligned Imidazolium Groups inside the Channels

Construction of magnetic MoS2/NiFe2O4/MIL-101(Fe) hybrid nanostructures for separation of dyes and antibiotics from aqueous media

In this study, MoS2/NiFe2O4/MIL-101(Fe) nanocomposite was synthesized by hydrothermal method and used as an adsorbent for the elimination of organic dyes and some antibiotic drugs in aqueous solutions. The synthesized nanocomposite underwent characterization through different techniques, including scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET) surface area analysis, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), zeta potential analysis, vibrating sample magnetometry (VSM), and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). These results demonstrated the successful insertion of MoS2within the cavities of MIL-101(Fe). The as-prepared magnetic nanocomposite was used as a new magnetic adsorbent for removing methylene blue (MB) and rhodamine B (RhB) organic dyes and tetracycline (TC) and ciprofloxacin (CIP) antibiotic drugs. For achieving the optimized conditions, the effects of initial pH, initial dye and drug concentration, temperature, and adsorbent dose on MB, TC, and CIP elimination were investigated. The results revealed that at a temperature of 25 °C, the highest adsorption capacities of MoS2/NiFe2O4/MIL-101(Fe) for MB, TC, and CIP were determined to be 999.1, 2991.3, and 1994.2 mg g-1, respectively. The pseudo-second-order model and Freundlich model are considered suitable for explaining the adsorption behavior of the MoS2/NiFe2O4/MIL-101(Fe) nanocomposite. The magnetic nanocomposite was very stable and had good recycling capability without any change in its structure.

Energy Application of Graphene Based Membrane: Hydrogen Separation

Hydrogen gas (H2 ) is a viable energy carrier that has the potential to replace the traditional fossil fuels and contribute to achieving zero net emissions, making it an attractive option for a hydrogen-based society. However, current H2 purification technologies are often limited by high energy consumption, and as a result, there is a growing demand for alternative techniques that offer higher H2 purity and energy efficiency. Membrane separation has emerged as a promising approach for obtaining high-purity H2 gas with low energy consumption. Nevertheless, despite years of development, commercial polymeric membranes have limited performance, prompting researchers to explore alternative materials. In this context, carbon-based membranes, specifically graphene-based nanomaterials, have gained significant attention as potential membrane materials due to their unique properties. In this review, we provide a comprehensive overview of carbon-based membranes for H2 gas separation, fabrication of the membrane, and its characterization, including their advantages and limitations. We also explore the current technological challenges and suggest insights into future research directions, highlighting potential ways to improve graphene-based membranes performance for H2 separations.

Cu2+@metal-organic framework-derived amphiphilic sandwich catalysts for enhanced hydrogenation selectivity of ketenes at the oil-water interface

Selective catalysis has always been an essential process for manufacturing various fine chemicals, such as food additives, pharmaceuticals and perfumes. Practically, pure target products are difficult to obtain even after complex purification procedures during industrial production. The development of a cost-effective, highly chemoselective and long-life catalyst may be an attractive solution, but such a catalyst is elusive. Herein, a novel class of amphiphilic N-doped carbon (NC), featuring graphitic carbon (GC) and highly dispersed Cu@Co NPs, was fabricated via simple calcination of a Cu2+-doped bimetallic metal-organic framework (MOF) precusor directly. Compared with monometallic Co@GC/NC, the side reaction of CO bond hydrogenation is obviously restrained, and thus, pure target product can be systematically obtained by Cu@Co@GC/NC, highlighting the high selectivity of Cu. More importantly, an amphiphilic characteristic in Cu@Co@GC/NC is a significant knob to integrate organic substrates with water very well. This amphiphilic material shows great potential as a field-deployable pathway for dispersible metal catalysts in organic systems.

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

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

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

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

Recent Advances in Mixed-Matrix Membranes for Light Hydrocarbon (C1–C3) Separation

Light hydrocarbons, obtained through the petroleum refining process, are used in numerous applications. The separation of the various light hydrocarbons is challenging and expensive due to their similar melting and boiling points. Alternative methods have been investigated to supplement cryogenic distillation, which is energy intensive. Membrane technology, on the other hand, can be an attractive alternative in light hydrocarbon separation as a phase change that is known to be energy-intensive is not required during the separation. In this regard, this study focuses on recent advances in mixed-matrix membranes (MMMs) for light hydrocarbon (C1–C3) separation based on gas permeability and selectivity. Moreover, the future research and development direction of MMMs in light hydrocarbon separation is discussed, considering the low intrinsic gas permeability of polymeric membranes.

Recent advances in the application of water-stable metal-organic frameworks: Adsorption and photocatalytic reduction of heavy metal in water

Heavy metals pollution in water is a global environmental issue, which has threatened the human health and environment. Thus, it is important to remove them under practical water environment. In recent years, metal-organic frameworks (MOFs) with water-stable properties have attracted wide interest with regard to the capture of hazardous heavy metal ions in water. In this review, the synthesis strategy and postsynthesis modification preparation methods are first summarized for water-stable MOFs (WMOFs), and then the recent advances on the adsorption and photocatalytic reduction of heavy metal ions in water by WMOFs are reviewed. In contrast to the conventional adsorption materials, WMOFs not only have excellent adsorption properties, but also lead to photocatalytic reduction of heavy metal ions. WMOFs have coupling and synergistic effects on the adsorption and photocatalysis of heavy metal ions in water, which make it more effective in treating single pollutants or different pollutants. In addition, by introducing appropriate functional groups into MOFs or synthesizing MOF-based composites, the stability and ability to remove heavy metal ions of MOFs can be effectively enhanced. Although WMOFs and WMOF-based composites have made great progress in removing heavy metal ions from water, they still face many problems and challenges, and their application potential needs to be further improved in future research. Finally, this review aims at promoting the development and practical application of heavy metal ions removal in water by WMOFs.

Dense Packing of Acetylene in a Stable and Low-Cost Metal-Organic Framework for Efficient C2 H2 /CO2 Separation

Porous materials for C₂ H₂ /CO₂ separation mostly suffer from high regeneration energy, poor stability, or high cost that largely dampen their industrial implementation. A desired adsorbent should have an optimal balance between excellent separation performance, high stability, and low cost. We herein report a stable, low-cost, and easily scaled-up aluminum MOF (CAU-10-H) for highly efficient C₂ H₂ /CO₂ separation. The suitable pore confinement in CAU-10-H can not only provide multipoint binding interactions with C₂ H₂ but also enable the dense packing of C₂ H₂ inside the pores. This material exhibits one of the highest C₂ H₂ storage densities of 392 g L^-1 and highly selective adsorption of C₂ H₂ over CO₂ at ambient conditions, achieved by a low C₂ H₂ adsorption enthalpy (27 kJ mol^-1 ). Breakthrough experiments confirm its exceptional separation performance for C₂ H₂ /CO₂ mixtures, affording both large C₂ H₂ uptake of 3.3 mmol g^-1 and high separation factor of 3.4. CAU-10-H achieves the benchmark balance between separation performance, stability, and cost for C₂ H₂ /CO₂ separation.

Interpenetration symmetry control within ultramicroporous robust boron cluster hybrid MOFs for benchmark purification of acetylene from carbon dioxide

The separation of C2H2/CO2 is an important process in industry but challenged by the trade-off of capacity and selectivity owning to their similar physical properties and identical kinetic molecular size. Herein, we report the first example of symmetrically interpenetrated dodecaborate pillared MOF, ZNU-1, for benchmark selective separation of C2H2 from CO2 with a high C2H2 capacity of 76.3 cm3 g-1 and record C2H2/CO2 selectivity of 56.6 (298 K, 1 bar) among all the robust porous materials without open metal sites. Single crystal structure analysis and modelling study indicated that the interpenetration shifting from asymmetric to symmetric mode provided optimal pore chemistry with ideal synergistic "2+2" dihydrogen bonding sites for tight C2H2 trapping. The exceptional separation performance was further evidenced by simulated and experimental breakthroughs with excellent recyclability and high productivity (2.4 mol/kg) of 99.5% purity C2H2 during stepped desorption process.

Optimal Pore Chemistry in an Ultramicroporous Metal-Organic Framework for Benchmark Inverse CO2 /C2 H2 Separation

Isolation of CO₂ from acetylene (C₂ H₂ ) via CO₂ -selective sorbents is an energy-efficient technology for C₂ H₂ purification, but a strategic challenge due to their similar physicochemical properties. There is still no specific methodology for constructing sorbents that preferentially trap CO₂ over C₂ H₂ . We report an effective strategy to construct optimal pore chemistry in a Ce^IV -based ultramicroporous metal-organic framework Ce^IV -MIL-140-4F, based on charge-transfer effects, for efficient inverse CO₂ /C₂ H₂ separation. The ligand-to-metal cluster charge transfer is facilitated by Ce^IV with low-lying unoccupied 4f orbitals and electron-withdrawing F atoms functionalized tetrafluoroterephthalate, affording a perfect pore environment to match CO₂ . The exceptional CO₂ uptake (151.7 cm³  cm^-3 ) along with remarkable separation selectivities (above 40) set a new benchmark for inverse CO₂ /C₂ H₂ separation, which is verified via simulated and experimental breakthrough experiments. The unique CO₂ recognition mechanism is further unveiled by in situ powder X-ray diffraction experiments, Fourier-transform infrared spectroscopy measurements, and molecular calculations.

Benchmark C2 H2 /CO2 Separation in an Ultra-Microporous Metal-Organic Framework via Copper(I)-Alkynyl Chemistry

Separation of acetylene from carbon dioxide remains a daunting challenge because of their very similar molecular sizes and physical properties. We herein report the first example of using copper(I)-alkynyl chemistry within an ultra-microporous MOF (Cu^I @UiO-66-(COOH)₂ ) to achieve ultrahigh C₂ H₂ /CO₂ separation selectivity. The anchored Cu^I ions on the pore surfaces can specifically and strongly interact with C₂ H₂ molecule through copper(I)-alkynyl π-complexation and thus rapidly adsorb large amount of C₂ H₂ at low-pressure region, while effectively reduce CO₂ uptake due to the small pore sizes. This material thus exhibits the record high C₂ H₂ /CO₂ selectivity of 185 at ambient conditions, significantly higher than the previous benchmark ZJU-74a (36.5) and ATC-Cu (53.6). Theoretical calculations reveal that the unique π-complexation between Cu^I and C₂ H₂ mainly contributes to the ultra-strong C₂ H₂ binding affinity and record selectivity. The exceptional separation performance was evidenced by breakthrough experiments for C₂ H₂ /CO₂ gas mixtures. This work suggests a new perspective to functionalizing MOFs with copper(I)-alkynyl chemistry for highly selective separation of C₂ H₂ over CO₂ .

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.

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

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

Precise Pore Space Partitions Combined with High-Density Hydrogen-Bonding Acceptors within Metal-Organic Frameworks for Highly Efficient Acetylene Storage and Separation

The high storage capacity versus high selectivity trade-off barrier presents a daunting challenge to practical application as an acetylene (C₂ H₂ ) adsorbent. A structure-performance relationship screening for sixty-two high-performance metal-organic framework adsorbents reveals that a moderate pore size distribution around 5.0-7.5 Å is critical to fulfill this task. A precise pore space partition approach was involved to partition 1D hexagonal channels of typical MIL-88 architecture into finite segments with pore sizes varying from 4.5 Å (SNNU-26) to 6.4 Å (SNNU-27), 7.1 Å (SNNU-28), and 8.1 Å (SNNU-29). Coupled with bare tetrazole N sites (6 or 12 bare N sites within one cage) as high-density H-bonding acceptors for C₂ H₂ , the target MOFs offer a good combination of high C₂ H₂ /CO₂ adsorption selectivity and high C₂ H₂ uptake capacity in addition to good stability. The optimized SNNU-27-Fe material demonstrates a C₂ H₂ uptake of 182.4 cm³  g^-1 and an extraordinary C₂ H₂ /CO₂ dynamic breakthrough time up to 91 min g^-1 under ambient conditions.

Graphene-based Membranes for H2 Separation: Recent Progress and Future Perspective

Hydrogen (H2) is an industrial gas that has showcased its importance in several well-known processes such as ammonia, methanol and steel productions, as well as in petrochemical industries. Besides, there is a growing interest in H2 production and purification owing to the global efforts to minimize the emission of greenhouse gases. Nevertheless, H2 which is produced synthetically is expected to contain other impurities and unreacted substituents (e.g., carbon dioxide, CO2; nitrogen, N2 and methane, CH4), such that subsequent purification steps are typically required for practical applications. In this context, membrane-based separation has attracted a vast amount of interest due to its desirable advantages over conventional separation processes, such as the ease of operation, low energy consumption and small plant footprint. Efforts have also been made for the development of high-performance membranes that can overcome the limitations of conventional polymer membranes. In particular, the studies on graphene-based membranes have been actively conducted most recently, showcasing outstanding H2-separation performances. This review focuses on the recent progress and potential challenges in graphene-based membranes for H2 purification.

Rational Design of Microporous MOFs with Anionic Boron Cluster Functionality and Cooperative Dihydrogen Binding Sites for Highly Selective Capture of Acetylene

Separation of acetylene (C₂ H₂ ) from carbon dioxide (CO₂ ) or ethylene (C₂ H₄ ) is important in industry but limited by the low capacity and selectivity owing to their similar molecular sizes and physical properties. Herein, we report two novel dodecaborate-hybrid metal-organic frameworks, MB₁₂ H₁₂ (dpb)₂ (termed as BSF-3 and BSF-3-Co for M=Cu and Co), for highly selective capture of C₂ H₂ . The high C₂ H₂ capacity and remarkable C₂ H₂ /CO₂ selectivity resulted from the unique anionic boron cluster functionality as well as the suitable pore size with cooperative proton-hydride dihydrogen bonding sites (B-H^δ- ⋅⋅⋅H^δ+ -C≡C-H^δ+ ⋅⋅⋅H^δ- -B). This new type of C₂ H₂ -specific functional sites represents a fresh paradigm distinct from those in previous leading materials based on open metal sites, strong electrostatics, or hydrogen bonding.

Metrics for Evaluation and Screening of Metal-Organic Frameworks for Applications in Mixture Separations

For mixture separations, metal-organic frameworks (MOFs) are of practical interest. Such separations are carried out in fixed bed adsorption devices that are commonly operated in a transient mode, utilizing the pressure swing adsorption (PSA) technology, consisting of adsorption and desorption cycles. The primary objective of this article is to provide an assessment of the variety of metrics that are appropriate for screening and ranking MOFs for use in fixed bed adsorbers. By detailed analysis of several mixture separations of industrial significance, it is demonstrated that besides the adsorption selectivity, the performance of a specific MOF in PSA separation technologies is also dictated by a number of factors that include uptake capacities, intracrystalline diffusion influences, and regenerability. Low uptake capacities often reduce the efficacy of separations of MOFs with high selectivities. A combined selectivity-capacity metric, Δq, termed as the separation potential and calculable from ideal adsorbed solution theory, quantifies the maximum productivity of a component that can be recovered in either the adsorption or desorption cycle of transient fixed bed operations. As a result of intracrystalline diffusion limitations, the transient breakthroughs have distended characteristics, leading to diminished productivities in a number of cases. This article also highlights the possibility of harnessing intracrystalline diffusion limitations to reverse the adsorption selectivity; this strategy is useful for selective capture of nitrogen from natural gas.

Mixed Metal-Organic Framework with Multiple Binding Sites for Efficient C2 H2 /CO2 Separation

The separation of C2 H2 /CO2 is particularly challenging owing to their similarities in physical properties and molecular sizes. Reported here is a mixed metal-organic framework (M'MOF), [Fe(pyz)Ni(CN)4 ] (FeNi-M'MOF, pyz=pyrazine), with multiple functional sites and compact one-dimensional channels of about 4.0 Å for C2 H2 /CO2 separation. This MOF shows not only a remarkable volumetric C2 H2 uptake of 133 cm3  cm-3 , but also an excellent C2 H2 /CO2 selectivity of 24 under ambient conditions, resulting in the second highest C2 H2 -capture amount of 4.54 mol L-1 , thus outperforming most previous benchmark materials. The separation performance of this material is driven by π-π stacking and multiple intermolecular interactions between C2 H2 molecules and the binding sites of FeNi-M'MOF. This material can be facilely synthesized at room temperature and is water stable, highlighting FeNi-M'MOF as a promising material for C2 H2 /CO2 separation.

Adsorptive Separation of Acetylene from Ethylene in Isostructural Gallate-Based Metal-Organic Frameworks

The separation of acetylene from ethylene is of paramount importance in the purification of chemical feedstocks for industrial manufacturing. Herein, an isostructural series of gallate-based metal-organic frameworks (MOFs), M-gallate (M=Ni, Mg, Co), featuring three-dimensionally interconnected zigzag channels, the aperture size of which can be finely tuned within 0.3 Å by metal replacement. Controlling the aperture size of M-gallate materials slightly from 3.69 down to 3.47 Å could result in a dramatic enhancement of C₂ H₂ /C₂ H₄ separation performance. As the smallest radius among the studied metal ions, Ni-gallate exhibits the best C₂ H₂ /C₂ H₄ adsorption separation performance owing to the strongest confinement effect, ranking after the state-of-the-art UTSA-200a with a C₂ H₄ productivity of 85.6 mol L^-1 from 1:99 C₂ H₂ /C₂ H₄ mixture. The isostructural gallate-based MOFs, readily synthesized from inexpensive gallic acid, are demonstrated to be a new top-performing porous material for highly efficient adsorption of C₂ H₂ from C₂ H₄ .

A Microporous Metal-Organic Framework Supramolecularly Assembled from a CuII Dodecaborate Cluster Complex for Selective Gas Separation

A novel 3D metal-organic framework BSF-1 based on the closo-dodecaborate cluster [B₁₂ H₁₂ ]^2- was readily prepared at room temperature by supramolecular assembly of CuB₁₂ H₁₂ and 1,2-bis(4-pyridyl)acetylene. The permanent microporous structure was studied by X-ray crystallography, powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and gas sorption. The experimental and theoretical study of the gas sorption behavior of BSF-1 for N₂ , C₂ H₂ , C₂ H₄ , CO₂ , C₃ H₈ , C₂ H₆ , and CH₄ indicated excellent separation selectivities for C₃ H₈ /CH₄ , C₂ H₆ /CH₄ , and C₂ H₂ /CH₄ as well as moderately high separation selectivities for C₂ H₂ /C₂ H₄ , C₂ H₂ /CO₂ , and CO₂ /CH₄ . Moreover, the practical separation performance of C₃ H₈ /CH₄ and C₂ H₆ /CH₄ was confirmed by dynamic breakthrough experiments. The good cyclability and high water/thermal stability render it suitable for real industrial applications.