Stable MOF Research Articles

A highly stable yttrium-based metal-organic framework with two-fold interpenetrated and cage-like pore structure for one-step purification of ethylene from ethylene/ethane mixture

One-step purification of ethylene (C2H4) from C2H6/C2H4 mixture is of paramount significance, but it is still challenging for C2H6-selective adsorbents to balance the trade-off between C2H6 adsorption capacity and C2H6/C2H4 uptake ratio or selectivity. Herein, we reported a stable yttrium-based MOF, Y-TATB, constructed with two distinct Y(III) clusters, Y3 and Y9, and ligand 4,4′,4″-(1,3,5-triazine-2,4,6-triyl)benzoic acid (H3TATB). Y-TATB featured a two-fold interpenetrated structure, of which a cage-like pore formed out for better C2H6 recognition and storage. Y-TATB exhibited both high C2H6 uptake and C2H6/C2H4 uptake ratio of 4.33 mmol/g and 1.45 at 298 K and 1 bar, exceeding most C2H6-selective MOFs. GCMC simulations demonstrated that the N-rich and nonpolar pore surfaces of Y-TATB generated multiple C-H···π interactions between the framework and C2H6, rendering the discrimination between C2H6 and C2H4. Dynamic breakthrough experiments further validated its feasibility in one-step production of high-purity C2H4 (>99.95%), endowing Y-TATB a promising candidate for practical implementation in industry.

Ultra-Microporous and Stable MOFs with Zero-Linker Ligands for Gas Capture and Separation.

Zero-linker ligands have maximized the size coordination efficiency of the metal ions in MOF framework which is important in constructing ultra-microporous MOFs with high stability and density, a bridge between zeolites and traditional MOFs. This article highlighted several recently developed ultra-microporous MOFs with zero-linker ligands for gas capture and separation.

High dye separation performance of novel Cu‐BTC/PES MMMs with water‐stabilized Cu‐BTC nanoparticles

AbstractMetal–organic frameworks (MOFs), as porous materials, have been extensively applied in a variety of realms, but little of these has been reported used in sewage disposal field owing to its precariousness toward water. Herein, a novel mixed matrix membrane of polyethersulfone (PES) was synthesized using Cu‐BTC‐IPA, a hydrolytic resistance MOF modified with isopropanol (IPA), which exhibits high permeability and water stability. A significant increase in hydrophilicity of the membrane was found in the modified membranes compared with the pure membrane. The porosity measurement confirmed the increased efficiency of mass transfer in the modified membranes. An enhancement in membrane performance was observed by introducing the Cu‐BTC‐IPA filler into the PES matrix, with a remarkable increase (207%) in pure water flux observed compared to that of the pristine PES membrane (264.2 L m−2 h−1 bar−1), reaching 546.4 L m−2 h−1 bar−1. Meanwhile, it exhibited superior rejection of dyestuffs (98.4% for Congo red and 98.9% for Coomassie brilliant blue). In addition, the Cu‐BTC‐IPA/PES mixed matrix membrane demonstrated remarkable anti‐biofouling properties, as evidenced by its high flux recovery rates of bovine serum albumin (BSA) solutions. The consequences indicate that introducing stable MOF into mixed matrix membranes (MMMs) is extremely effective in improving membrane performance for sewage treatment.

Homoelemental effect boosted stable ZIF-8 membrane with super high H2 permeance

Fabricating stable MOF membranes with high permeance for H2 separation and purification faces significant challenges primarily due to the heterogeneous nucleation of MOF on substrate. Herein, we propose a simple but effective homoelemental strategy by choosing the Zn-based ZIF-8 and Zn foam substrate. Without any chemical or physical modification, a serials of highly stable and compact ZIF-8 membranes are assembled on the Zn foam which exhibit high H2 permeance both for H2/CH4 and H2/CO2 separation. Especially, the 1-Zn-Foam/ZIF-8-24 membrane displays the high H2 permeance close to 104 GPU, surpassing most MOF membranes for H2/CH4 and H2/CO2 separation. Further, the excellent stability displays steady H2 permeance and selectivity, even after 96-hour test, high temperature of 100 °C, or high pressure. This is the first exploration by adopting Zn foam as a substrate for gas separation, not only demonstrating the Zn foam is an ideal carrier for assembling the Zn-based MOF membranes, but also implying the potential of the homoelemental strategy in fabricating other MOF membranes.

The Emergence of 2D Building Units in Metal‐Organic Frameworks for Photocatalytic Hydrogen Evolution: A Case Study with COK‐47

AbstractMetal‐organic frameworks (MOFs) are promising materials for photocatalytic water splitting reactions, but examples of visible light‐responsive, catalytically active, and stable MOFs are still rare. A detailed investigation is conducted for COK‐47 – a recently described MOF comprising 2D Ti‐O6 secondary building units (SBUs) – toward a photocatalytic hydrogen evolution reaction (HER), showing how overall particle morphology, surface area, and missing ligand defects are central parameters governing the material's ultimate performance. The newly synthesized COK‐47ISO is among the most active MOFs to date, yielding HER‐rates of 8.6 µmol h−1, and an apparent quantum yield (AQY) of 0.5% under visible light illumination. Optoelectronic and photoluminescence investigations, supported by theoretical calculations, enable the unraveling of its electronic structure along with charge transfer and recombination kinetics. A wavelength‐dependent reaction mechanism is proposed involving ligand to metal charge transfer (LMCT) and the main challenges for visible or UV photoexcitation are identified, demonstrating that the unique 2D layered structure aids charge separation and is key to the high performance. This work introduces COK‐47 as a promising alternative to the well‐known MIL‐125 family and offers directions for future studies

Hydrolytically Stable Luminescent Cationic MOF for Selective Detection of Toxic Organic Arsenic in Water

Drugs containing organic arsenic moiety are extensively utilized as food additives in the poultry industry, and release of these organic arsenics through poultry litter to natural water bodies can prove fatal and noxious to the ecosystem. Pertaining to this, sensitive detection of organic arsenic drugs in a selective manner from livestock waste water remains pivotal but indeed very challenging. In this work, we explored a cationic MOF, viz., iMOF-12C, as a fluorescence sensor toward precise recognition of organic arsenic molecules such as roxarsone (ROX) and nitarsone (NIT). Here we explore the potential of ionic MOFs for the first time toward recognition of organic arsenic drugs. iMOF-12C displayed excellent potency as a suitable sensory material toward selective detection of both ROX and NIT in water medium. The quenching efficiency of iMOF-12C toward ROX and NIT recognition was found to be 78 and 82%, respectively. The limit of detection (LOD) of iMOF-12C for ROX and NIT was calculated as 3.95 and 1.35 ppb, respectively, well below WHO’s safety limit. Further, for practical application, iMOF-12C-based mixed-matrix membranes (MMM) were casted, which showed excellent organic arsenic detection in water. The findings of this work highlight the potential of iMOF-12C toward real-time detection of organic arsenic molecules in water bodies.

Two anthracene-based zirconium metal–organic frameworks with fcu and hcp topologies as versatile fluorescent sensors for detection of inorganic ions and nitroaromatics

Two anthracene-based zirconium metal–organic frameworks (UiO-68-AN-fcu and UiO-68-AN-hcp) with blue emission were synthesized by the solvothermal reaction of ZrCl4 with anthracene-based ligand 4,4′-(9,10-anthracenediyl)dibenzoic acid. The two MOFs inherited the luminescence properties of anthracene-based ligand and exhibited different topologies due to the change of connection mode of Zr-O clusters. The two stable anthracene-based zirconium MOFs served as luminescent sensors for selectively detecting 2-nitrophenol, Fe3+ and Cr2O72−. UiO-68-AN-hcp with flower morphology exhibited stronger quenching effect for 2-nitrophenol, Fe3+ and Cr2O72− by comparing to UiO-68-AN-fcu. Adsorption tests, fluorescence lifetime and spectroscopy studies demonstrated that the fluorescence responses of MOFs for analytes can be primarily attributed to the dynamic quenching mechanism involving energy and electron transfer. These results revealed that the combination of luminescent anthracene-based ligand and Zr-O clusters is a feasible strategy to construst MOFs-based fluorescent sensors.

Binding of CsPbBr3 Nanocrystals to MOF-5 for the Detection of Cadmium Ions in Aqueous Media

CsPbBr3 perovskite nanocrystals (CNCs) have emerged as promising candidates for optoelectronics, although instability issues have retarded their progress toward commercialization. As a solution to this core issue, herein CNCs are bound to the metal–organic framework MOF-5 to form a stable composite MOF:CNC for sensing applications in aqueous media. The electrostatic interaction of Pb2+ and Br– ions of CNCs with the terephthalate and Zn2+ ions of MOF-5 do not disturb the structural integrity of the MOFs and the photoluminescence (PL) properties of the CNCs but renders more stability to both the MOFs and CNCs in a water medium. As a proof-of-concept experiment, this water-resistant MOF:CNC probe was successfully validated for the detection of Cd2+ in a water medium. The mechanism of fluorescence enhancement during the sensing of Cd2+ is elucidated using X-ray photoelectron spectroscopy, temperature-dependent, and time-resolved PL studies. The high stability and photoefficiency exhibited by this MOF:CNC composite proves that it is a viable system for applications in aqueous media.

Expanding nonpolar pore surfaces in stable ethane-selective MOF to boost ethane/ethylene separation performance

Ethylene is an important raw material in chemical production. Reducing energy consumption by one-step separation of ethylene from C2H6/C2H4 mixtures is a significant and challenging task. Designing a material with high C2H6 selectivity and adsorption capacity is very demanding. Here, we report a method to improve the performance of C2H6/C2H4 separation. By changing the carboxylic ligand in UiO-67, we synthesized a new material called UiO-67-BN. At room temperature, compared with the base material UiO-67, the optimized material UiO-67-BN has a significant increase in the adsorption capacity of C2H6 and the selectivity of C2H6/C2H4 due to its suitable pore size and numerous non-polar aromatic rings on the pore surface. Theoretical calculation results reveal that the optimized material can provide more C-H∙∙∙π interactions with C2H6. The breakthrough experiments demonstrate that UiO-67-BN can efficiently capture C2H6 from 50/50 and 1/99 C2H6/C2H4 mixtures at various conditions and realize one-step acquisition of C2H4.

MOF-derived crystalline carbon with graphite-like crystal: A high initial coulombic efficiency, low potential and large capacity anode for Na-ion batteries

Carbonaceous materials, such as hard carbon and porous carbon, have gained great attentions as the anode materials for Na-ion batteries (NIBs). However, their defects and disordered structure cause the low initial coulombic efficiency (ICE), high-potential slope region and small charge capacity below 0.5 V. Herein, a structurally stable MOF contained 1,3,5-triazine-2,4,6-triamine moieties, belonging to the tetragonal space group I 4/m, is synthesized. On this basis, MOF-derived crystalline carbon with graphite-like crystal, instead of amorphous porous carbon, can be obtained due to slow pyrolysis of MOF framework along with timely and sufficient reassembly of the pyrolyzed carbon atoms into graphite-like crystal under graphite-induced condition. The graphite-like crystal has a geometrically similar unit cell to graphite crystal but with a magnification ratio of 1.25, yielding proportionally expanded d-spacing of (002) plane (4.2 Å), which enables the reversible Na+ intercalation/de-intercalation. When applied in NIBs, it exhibits a very high ICE of 96.0% and reversible charge capacity of 356.2 mAh g−1, reaching the advanced level of graphite applied in LIBs. More importantly, its charge capacity below 0.5 V can account for 90% of the total charge capacity, which is also the key parameter to effectively increase the energy density of full batteries.

Rational Construction of Ultrahigh Thermal Stable MOF for Efficient Separation of MTO Products and Natural Gas

Considering the important application foundation of propylene (C3H6) and ethylene (C2H4) production, as well as methane (CH4), in petrochemical industries, this report comprehensively investigated an innovative MOF material (Zn-BPZ-SA) that was synthesized by 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (H2BPZ) and squaric acid (H2SA) for separating methanol-to-olefins (MTO) products (C3H6/C2H4 mixtures) and natural gas (C3H8/C2H6/CH4 mixtures). Zn-BPZ-SA with great resistance toward water and exceptional thermal stability (520 °C), can preferentially adsorb C3H8 and C3H6 rather than C2H6 and C2H4, and in particular, reveals high C3H6 and C3H8 uptakes of 46.6 and 48.0 cm3 g–1 under the crucial low pressure (10 kPa, 298 K). The experimental and simulated transient breakthroughs for C3H6/C2H4 binary mixtures and C3H8/C2H6/CH4 ternary mixtures demonstrated that the MOF can separate these mixtures with long breakthrough time differences, yielding high-purity (>99.95%) products with high productivities: C2H4 (21.9–142.8 L kg–1) and CH4 (34.9–73.0 L kg–1). The excellent separation abilities can be attributed to the rich accessbile O/N and methyl binding sites scattered at the pore surfaces in framework.

Zirconium Metal-Organic Framework bearing V-shape letrozole dicarboxylic acid for versatile fluorescence detection

Metal-Organic Frameworks with both organic and inorganic components are widely used as fluorescent sensors due to their high thermal stability, special optical properties, etc. Current studies have shown that azole groups have rich nitrogen sites and optical properties, which can significantly improve the host-guest interaction sites and fluorescence sensing properties if the azole groups could be introduced into the backbone of MOF. However, it is still a great challenge to effectively introduce nitrogen-containing azole groups into the backbone of MOF and to explore their fluorescence sensing properties. In this work, a readily available precursor, letrozole, was selected, which could be converted into the dicarboxylic acid ligand by virtue of its angular structure, azole units and easily modified cyano groups. The connection of Zr6 cluster and V-shape letrozole dicarboxylic acid can form a stable MOF in water. The structural advantages of the resulted Zr-MOF as the certain porosity and abundant nitrogen-containing azole sites generate strong interactions for the adsorption and accumulation of analytes, and ensure sensitive fluorescence detection. The carefully constructed Zr-MOF can be adopted as the high sensitive fluorescent sensor for inorganic metal ions, aromatic nitro compounds and nitrofuran antibiotics (NFAs). Especially for NFAs, the established fluorescence sensor has a low detection limit, giving a KSV value of 3.28×102 M−1 and a detection limit of 9.15×10–5 mol L–1. The related results exhibit the expected potential application for the luminescent determination of pollutants in water.

Two Dual-Function Zr/Hf-MOFs as High-Performance Proton Conductors and Amines Impedance Sensors.

In the field of sensing, finding high-performance amine molecular sensors has always been a challenging topic. Here, two highly stable 3D MOFs DUT-67(Hf) and DUT-67(Zr) with large specific surface areas and hierarchical pore structures were conveniently synthesized by solvothermal reaction of ZrCl4/HfCl4 with a simple organic ligand, 2,5-thiophene dicarboxylic acid (H2TDC) according to literature approach. By analyzing TGA data, it was found that the two MOFs have defects (unsaturated metal sites) that can interact with substrates (H2O and volatile amine gas), which is conducive to proton transfer and amine compound identification. Further experiments showed that at 100 °C and 98% relative humidity (RH), the optimized proton conductivities of DUT-67(Zr) and DUT-67(Hf) can reach the high values of 2.98 × 10-3 and 3.86 × 10-3 S cm-1, respectively. Moreover, the room temperature sensing characteristics of MOFs' to amine gases were evaluated at 68, 85 and 98% RHs, respectively. Impressively, the prepared MOFs-based sensors have the desired stability and higher sensitivity to amines. Under 68% RH, the detection limits of DUT-67(Zr) or DUT-67(Hf) for volatile amine gases were 0.5 (methylamine), 0.5 (dimethylamine) and 1 ppm (trimethylamine), and 0.5 (methylamine), 0.5 (dimethylamine) and 0.5 ppm (trimethylamine), respectively. As far as we know, this is the best performance of ammonia room temperature sensors in the past proton-conductive MOF sensors.

Boosting Xe/Kr separation by a Mixed-linker strategy in Radiation-Resistant Aluminum-Based Metal − Organic frameworks

Capturing and separating radioactive isotopes of Xenon (Xe) and Krypton (Kr) from off-gas streams in the reprocessing of used nuclear fuel (UNF) gaseous radioactive nuclides emerges as a major concern to meet the rapid growth and sustainable development of nuclear energy. Owing to the inert atomic gases (Xe and Kr) nature without dipole or quadruple moments and their existing extremely low concentrations in radioactive off-gas mixture, it is a grand challenge to design radiation-resistant porous adsorbents for efficient Xe capture and Xe/Kr separation at dilute conditions. Herein, we report a mixed-linker strategy to realize a confined aliphatic pore environment in high radioactive stable CAU-10 type Aluminum-based MOFs using isophthalate and 5-methylisophthalate as mixed linkers for Xe/Kr separation at low concentration. By systematically tune the ratio of the two linkers, the precise and appropriate amount of aliphatic methyl groups could be immobilized on the framework to achieve delicate regulation of pore structure (pore shape and pore size), which significantly increase Xe binding affinity. Mixed-linker CAU-10-H-CH3-0.21–0.79 shows significantly enhanced Xe capture and separation performance at dilute conditions compared to pristine CAU-10-H and fully methyl functionalized CAU-10-CH3, demonstrated by adsorption isotherms and breakthrough curves. The high radioactive stability of CAU-10 type Al-MOFs was also identified by gamma-ray irradiation experiments, suggesting a great potential for practical application.

2D porphyrin-based MOFs with highly dispersed Pt nanoparticles via in-situ partial reduction strategy from porphyrin embedded with single-atom Pt for enhancing photocatalytic hydrogen production

An efficient and stable 2D MOF TMF-Pt/Pt NPs photocatalyst was prepared by in-situ partial hydrogenation reduction of TMF-Pt with single-atom Pt embedded in porphyrin center to improve photocatalytic hydrogen production. It is important to note that TMF-Pt/Pt NPs has an extremely high photocatalytic hydrogen generation rate (33185.66 µmol·g−1·h−1) in comparison to the majority of previous MOFs photocatalysts, which could be due to the in-situ uniformly grown Pt NPs are very adjacent to the Ti-oxo clusters within the 2D MOFs so that the gradually accumulated electrons around the Ti-oxo clusters via LMCT pathway could instantaneously transfer to Pt NPs through the Schottky injection field effect. Through a series of experimental characterizations, especially atomic force microscopy (AFM) and transmission scanning electron microscope (TEM), confirmed the highly dispersed Pt NPs within the 2D MOFs. This work provided us with a novel idea to realize the uniform distribution of noble metals nanoparticles in the channel cavity of MOFs through an in-situ synthesis strategy, so as to facilitate the more efficient Schottky injection field effect between noble metals nanoparticles and metal clusters of the MOFs, thereby achieving more excellent charge carrier separation efficiency.

Pore size effects on high-efficiency proton conduction in three stable 3D Al-based MOFs modified with imidazole

Three stable porous aluminum-based MOFs 1–3 with different pore sizes were selected as an imidazole (Im) supporter and three proton conductive composites Im@1–3 were prepared. Due to the pore size effect, the σ value of Im@3 can be up to 2.55 × 10−1 S cm−1 at 80 °C and 100% RH.

Selective recognition of Hg2+ ions in aqueous solution by a CdII-based metal-organic framework with good stability and vacant coordination sites.

A novel water-stable CdII-based metal-organic framework, namely {[Cd(BIBT)(TDC)]·2H2O}n (JXUST-28, BIBT = 4,7-bi(1H-imidazol-1-yl)benzo-[2,1,3]thiadiazole and H2TDC = 2,5-thiophenedicarboxylic acid), was synthesized using a mixed-ligand strategy. Structural analysis demonstrates that JXUST-28 exhibits a two-dimensional layer structure with 4-connected sql topology. Intriguingly, JXUST-28 presents good stability in boiling water (at least 5 days), common organic solvents and aqueous solutions with different pH values of 2-12 (more than 24 hours). Furthermore, fluorescence experiments revealed that JXUST-28 could sense Hg2+ ions in aqueous solution via a quenching effect with a detection limit of 0.097 μM. Meanwhile, JXUST-28 can also be regenerated at least 5 times to detect Hg2+ ions. In addition, light-emitting diode lamps, luminescent films, and test papers of JXUST-28 have been successfully developed for practical applications.

Enhancing the sensitivity of a water stable MOF as a H2S gas sensor by the fabrication of a mixed-matrix membrane

For the real-time sensing application of MOF in a device, a mixed-matrix membrane has been synthesized using a water-stable 2D MOF. This is the first example of an essential metal-based composite membrane for the detection of H2S with the lowest LOD value of 5.3 μM.

Constructing multiple sites of metal-organic frameworks for efficient adsorption and selective separation of CO2

Efficient capture and selective separation of CO2 is of great significance for alleviating the greenhouse effect. However, it is still a challenge to achieve efficient, reversible and selective capture of CO2. Here, stable Al-based MOFs with multiple adsorption sites were constructed for capture and selective separation CO2. It was found that MOF-303(Al) with multiple active sites (μ-OH, N-H, N-N and H-C) demonstrated a high CO2 capacity of 5.1 mmol/g, and can be recycled for more than 50 times. Moreover, MOF-303(Al) shows excellent selective separation performance of CO2 from CO2/CH4 and CO2/N2 mixtures, which could be used as a potential material for natural gas purification. Mechanism results revealed that the excellent CO2 adsorption and selective separation performance is arose from the multiple adsorption sites (μ-OH, N-H, N-N and C-H) of MOF-303(Al), where the contribution of μ-OH and N-H adsorption sites are higher than that of N-N and H-C sites.

Construction of stable MOFs integrated with open metal sites and amine groups for CO2 capture and conversion

CO2 is deemed as the major greenhouse gas causing global warming over the past several decades. Developing porous solid materials to achieve the capture and utilization of CO2, in this work, two metal–organic frameworks, [Ni2(5H-Ade)(TCPE)(H2O)3]·3DMF·6H2O (Ni-Ade-TCPE), and [Co4.5(HCOO)3(4H-Ade)2(TCPE)(H2O)5]·5DMF·7H2O (Co-Ade-TCPE) have been synthesized by employing mixed adenine and tetrakis(4-carboxyphenyl)ethylene (H4TCPE). The structural analysis demonstrates they are 3D frameworks possessing 1D open channels with –NH2 groups and open metal sites modified surfaces. They display impressive chemical stability in acidic and basic water solutions and high adsorption capacity for CO2. At 70 ​°C and 1 ​bar, Ni-Ade-TCPE exhibits outstanding activity, selectivity, and recyclability in the cycloaddition reaction of epoxides with CO2 due to Lewis acid–base bifunctional sites. Moreover, a reasonable catalytic reaction mechanism has been proposed.