High Propene/Propane Selectivity in Isostructural Metal-Organic Frameworks with High Densities of Open Metal Sites

Tuning ethylene gas adsorption via metal node modulation: Cu-MOF-74 for a high ethylene deliverable capacity

Co and Cu-MOF-74s are promising candidates for efficient ethylene abatement or storage and delivery, respectively.

A comparative study of the effect of functional groups on C2H2 adsorption in NbO-type metal–organic frameworks

A comparative study of the effect of functional groups on C₂H₂ adsorption was performed in NbO-type metal–organic frameworks.

A comparative study of C2H2 adsorption properties in five isomeric copper-based MOFs based on naphthalene-derived diisophthalates

Five copper-based MOF isomers based on naphthalene-derived diisophthalates were constructed to reveal the ligand positional isomeric effect on C₂H₂ adsorption properties.

Efficient kinetic separation of propene and propane using two microporous metal organic frameworks

An excellent performance for the kinetic separation of propene and propane is realized in two microporous MOF analogues, namely Zn(ox)_0.5(trz) and Zn(ox)_0.5(atrz).

A rare Pb9 cluster-organic framework constructed from a flexible cyclotriphosphazene-functionalized hexacarboxylate exhibiting selective gas separation

A rare Pb₉ cluster-based organic framework constructed from a flexible cyclotriphosphazene-functionalized hexacarboxylate exhibits selective adsorption separation of C₂ hydrocarbons and CO₂ from CH₄ under ambient conditions.

Computational screening of functional groups for capture of toxic industrial chemicals in porous materials

Functional groups are screened computationally to understand how they bind and capture toxic industrial chemicals.

An in situ investigation of the water-induced phase transformation of UTSA-74 to MOF-74(Zn)

In water, UTSA-74 transforms through a dissolution–recrystallization process to its polymorph MOF-74(Zn).

Liquid-phase oxidation of alkylaromatics to aromatic ketones with molecular oxygen over a Mn-based metal–organic framework

A microporous Mn-based metal–organic framework (Mn-MOF-74) acts as a heterogeneous catalyst active for liquid-phase oxidation of alkylaromatics with molecular O₂.

MOF-74 as an Efficient Catalyst for the Low-Temperature Selective Catalytic Reduction of NOx with NH3

In this work, Mn-MOF-74 with hollow spherical structure and Co-MOF-74 with petal-like shape have been prepared successfully via the hydrothermal method. The catalysts were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry-mass spectrum analysis (TG-MS), N₂ adsorption/desorption, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). It is found that MOF-74(Mn, Co) exhibits the capability for selective catalytic reduction (SCR) of NO_x at low temperatures. Both experimental (temperature-programmed desorption, TPD) and computational methods have shown that Co-MOF-74 and Mn-MOF-74 owned high adsorption and activation abilities for NO and NH₃. The catalytic activities of Mn-MOF-74 and Co-MOF-74 for low-temperature denitrification (deNO_x) in the presence of NH₃ were 99% at 220 °C and 70% at 210 °C, respectively. It is found that the coordinatively unsaturated metal sites (CUSs) in M-MOF-74 (M = Mn and Co) played important roles in SCR reaction. M-MOF-74 (M = Mn and Co), especially Mn-MOF-74, showed excellent catalytic performance for low-temperature SCR. In addition, in the reaction process, NO conversion on Mn-MOF-74 decreased with the introduction of H₂O and SO₂ and almost recovered when gas was cut off. However, for Co-MOF-74, SO₂ almost has no effect on the catalytic activity. This work showed that MOF-74 could be used prospectively as deNO_x catalyst.

Enhanced ethylene separation and plasticization resistance in polymer membranes incorporating metal-organic framework nanocrystals

The implementation of membrane-based separations in the petrochemical industry has the potential to reduce energy consumption significantly relative to conventional separation processes. Achieving this goal, however, requires the development of new membrane materials with greater selectivity, permeability and stability than available at present. Here, we report composite materials consisting of nanocrystals of metal-organic frameworks dispersed within a high-performance polyimide, which can exhibit enhanced selectivity for ethylene over ethane, greater ethylene permeability and improved membrane stability. Our results suggest that framework-polymer interactions reduce chain mobility of the polymer while simultaneously boosting membrane separation performance. The increased stability, or plasticization resistance, is expected to improve membrane utility under real process conditions for petrochemical separations and natural gas purification. Furthermore, this approach can be broadly applied to numerous polymers that encounter aggressive environments, potentially making gas separations possible that were previously inaccessible to membranes.

Capturing Guest Dynamics in Metal-Organic Framework CPO-27-M (M = Mg, Zn) by (2)H Solid-State NMR Spectroscopy

Metal-organic frameworks (MOFs) are promising porous materials for gas separation and storage as well as sensing. In particular, a series of isostructural MOFs with coordinately unsaturated metal centers, namely, CPO-27-M or M-MOF-74 (M = Mg, Zn, Mn, Fe, Ni, Co, Cu), have shown exceptional adsorption capacity and selectivity compared to those of classical MOFs that contain only fully coordinated metal sites. Although it is widely accepted that the interaction between guest molecules and exposed metal centers is responsible for good selectivity and large maximum uptake, the investigation of such guest-metal interaction is very challenging because adsorbed molecules are usually disordered in the pores and undergo rapid thermal motions. (2)H solid-state NMR (SSNMR) spectroscopy is one of the most extensively used techniques for capturing guest dynamics in porous materials. In this work, variable-temperature (2)H wide-line SSNMR experiments were performed on CPO-27-M (M = Mg, Zn) loaded with four prototypical guest molecules: D2O, CD3CN, acetone-d6, and C6D6. The results indicate that different guest molecules possess distinct dynamic behaviors inside the channel of CPO-27-M. For a given guest molecule, its dynamic behavior also depends on the nature of the metal centers. The binding strength of guest molecules is discussed on the basis of the (2)H SSNMR data.

Selective Adsorption of n-Alkanes from n-Octane on Metal-Organic Frameworks: Length Selectivity

The liquid-phase adsorption of n-alkanes (from n-octane (C8) solvent) with different chain lengths was carried out over three metal-organic frameworks (MOFs), viz., metal-azolate framework-6 (MAF-6), copper-benzenetricarboxylate (Cu-BTC), and iron-benzenetricarboxylate (MIL-100(Fe)), and a conventional adsorbent activated carbon (AC). MAF-6 and Cu-BTC were found to have significant selectivity for the adsorption of n-dodecane (C12) and n-heptane (C7), respectively, from C8. Selectivity for C12 on MAF-6 was also observed in competitive adsorption from binary adsorbate systems. To understand the selective adsorption of C12 on MAF-6 more, the adsorption of C12 from C8 over MAF-6 was investigated in detail and compared with that over AC. The obtained selectivities over MAF-6 and Cu-BTC for C12 and C7, respectively, might be explained by the similarity between cavity size of adsorbents and molecular length of n-alkanes. In the case of AC and MIL-100(Fe), no specific adsorption selectivity was observed because the cavity sizes of the two adsorbents are larger than the size of the n-alkanes used in this study. The adsorption capacities (qt) of n-alkanes over AC and MIL-100(Fe) decreased and increased, respectively, as the polarity (or length) of the adsorbates increased, probably because of nonpolar and polar interactions between the adsorbents and n-alkanes. On the basis of the results obtained, it can be concluded that matching the cavity size (of adsorbents) with the molecular length (of n-alknaes) is more important parameter than the MOF's hydrophilicity/hydrophobicity for the selective adsorption/separation of alkanes.

Tunable integration of absorption-membrane-adsorption for efficiently separating low boiling gas mixtures near normal temperature

Separation of low boiling gas mixtures is widely concerned in process industries. Now their separations heavily rely upon energy-intensive cryogenic processes. Here, we report a pseudo-absorption process for separating low boiling gas mixtures near normal temperature. In this process, absorption-membrane-adsorption is integrated by suspending suitable porous ZIF material in suitable solvent and forming selectively permeable liquid membrane around ZIF particles. Green solvents like water and glycol were used to form ZIF-8 slurry and tune the permeability of liquid membrane surrounding ZIF-8 particles. We found glycol molecules form tighter membrane while water molecules form looser membrane because of the hydrophobicity of ZIF-8. When using mixing solvents composed of glycol and water, the permeability of liquid membrane becomes tunable. It is shown that ZIF-8/water slurry always manifests remarkable higher separation selectivity than solid ZIF-8 and it could be tuned to further enhance the capture of light hydrocarbons by adding suitable quantity of glycol to water. Because of its lower viscosity and higher sorption/desorption rate, tunable ZIF-8/water-glycol slurry could be readily used as liquid absorbent to separate different kinds of low boiling gas mixtures by applying a multistage separation process in one traditional absorption tower, especially for the capture of light hydrocarbons.

A metal-organic framework with immobilized Ag(i) for highly efficient desulfurization of liquid fuels

A metal-organic framework immobilized with Ag(i) sites, namely, (Cr)-MIL-101-SO3Ag, was successfully developed as a highly efficient desulfurization adsorbent because of the strong binding of these Ag(i) sites for thiophene derivatives.

Pentiptycene-Based Luminescent Cu (II) MOF Exhibiting Selective Gas Adsorption and Unprecedentedly High-Sensitivity Detection of Nitroaromatic Compounds (NACs)

The assembly of a fluorescent pentiptycene-based ligand with copper ion resulted in the formation of a 3D porous metal-organic framework (UPC-21) based on well-known paddlewheel SBUs. UPC-21 exhibits selective adsorption of CO2 over CH4 and N2 at 273 K and 295 K, C2H2 over CH4 at 273 K. The most significant performance of UPC-21 is its highly efficient detection of NACs such as 4-NP, 1,4-DNB, NB, and 1,3-DNB with the calculated quenching constants, Ksv, being 3.097 × 10(6), 1.406 × 10(6), 4.420 × 10(5), and 1.498 × 10(5 )M(-1) for 4-NP, 1,4-DNB, NB, 1,3-DNB, respectively, which keeps a record on the fluorescence detection of NACs. This is the first porous Cu(II) MOF that exhibits fluorescent detection of NACs with high sensitivities.

Computational Characterization of Defects in Metal-Organic Frameworks: Spontaneous and Water-Induced Point Defects in ZIF-8

Zeolitic imidazolate frameworks (ZIFs) are an important class of porous crystalline metal-organic framework (MOF) materials that have attracted widespread attention for applications ranging from gas adsorption and separation to catalysis. Although the bulk crystal structures of MOFs are typically well-characterized, comparatively little is known regarding MOF defect structures. Drawing on analogies with conventional silicon-based zeolites, we utilize computational methods to examine the structure and stability of putative point-defect structures (including vacancies, substitutions, and "dangling" linkers) within the prototypical ZIF-8 structure. Considering both postsynthetic (gas-phase) and synthetic (solution-phase) conditions, we find that several of the defect structures lie low in energy relative to the defect-free parent crystal, with barriers to defect formation that are large but surmountable under relevant temperatures. These results are consistent with prior experimental observations of ZIF stability and reactivity and suggest that defects may play an important role in influencing the long-term stability of MOFs under conditions that include exposure to water vapor and trace contaminants such as acid gases.

Nano iron pyrite (FeS2) exhibits bi-functional electrode character

Sustainable charge storage devices require materials that are environmentally benign, readily moldable, easily synthesizable, and profitable for applications in the electronics industry.

Central-metal exchange, improved catalytic activity, photoluminescence properties of a new family of d10 coordination polymers based on the 5,5′-(1H-2,3,5-triazole-1,4-diyl)diisophthalic acid ligand

Five d¹⁰ coordination polymers (CPs) have been successfully isolated. Central-metal exchange in CP 2 leads to a series of isostructural M(ii)–Cd CPs (M = Cu, Co, Ni) showing improved catalytic activity.

Diamine-appended metal–organic frameworks: enhanced formaldehyde-vapor adsorption capacity, superior recyclability and water resistibility

This study presents a convenient modification of the well-known MOF, MIL-101, with ethylenediamine (ED) on its open-metal sites to substantially improve the HCHO adsorption properties.

Constructing luminescent particle/MOF composites by employing polyvinylpyrrolidone-modified organic crystals as seeds

Two types of organic particle/MOF structures, i.e. Znq₂@ZIF-8 core–shell and multiple Znq₂ particles on each ZIF-8, can be constructed by modulating the Znq₂–ZIF-8 interfacial energy with PVP.

Liquid self-diffusion of H2O and DMF molecules in Co-MOF-74: molecular dynamics simulations and dielectric spectroscopy studies

Dielectric spectroscopy, supported by molecular dynamics simulations, is found to be a fast and non-destructive technique to study molecular transport within porous MOFs and related materials.

High acetylene/ethylene separation in a microporous zinc(ii) metal–organic framework with low binding energy

A novel MOF UTSA-67a with narrow one-dimensional pore channels and inner cages of moderate size has been developed for highly selective separation of C₂H₂/C₂H₄ mixtures at room temperature.

Adsorptive Separation of Methanol-Acetone on Isostructural Series of Metal-Organic Frameworks M-BTC (M = Ti, Fe, Cu, Co, Ru, Mo): A Computational Study of Adsorption Mechanisms and Metal-Substitution Impacts

The adsorptive separation properties of M-BTC isostructural series (M = Ti, Fe, Cu, Co, Ru, Mo) for methanol-acetone mixtures were investigated by using various computational procedures of grand canonical Monte Carlo simulations (GCMC), density functional theory (DFT), and ideal adsorbed solution theory (IAST), following with comprehensive understanding of adsorbate-metal interactions on the adsorptive separation behaviors. The obtained results showed that the single component adsorptions were driven by adsorbate-framework interactions at low pressures and by framework structures at high pressures, among which the mass effects, electrostatics, and geometric accessibility of the metal sites also played roles. In the case of methanol-acetone separation, the selectivity of methanol on M-BTCs decreased with rising pressures due to the pressure-dependent separation mechanisms: the cooperative effects between methanol and acetone hindered the separation at low pressures, whereas the competitive effects of acetone further resulted in the lower selectivity at high pressures. Among these M-BTCs, Ti and Fe analogues exhibited the highest thermodynamic methanol/acetone selectivity, making them promising for adsorptive methanol/acetone separation processes. The investigation provides mechanistic insights on how the nature of metal centers affects the adsorption properties of MOFs, and will further promote the rational design of new MOF materials for effective gas mixture separation.

Adsorptive Separation of Olefin/Paraffin Mixtures with ZIF-4

The microporous zeolitic imidazolate framework ZIF-4 has been synthesized, and its ethylene/ethane and propylene/propane separation potentials have been evaluated by single-component adsorption isotherms and breakthrough experiments of the respective binary mixtures. In all experiments, a higher selectivity for the paraffin is observed that is manifested by a steeper equilibrium isotherm as well as a later breakthrough in the fixed-bed adsorber experiments. Microporous adsorbents with paraffin selectivity are rare but highly interesting for cyclic adsorption processes such as pressure-swing adsorption (PSA).

Direct structural evidence of commensurate-to-incommensurate transition of hydrocarbon adsorption in a microporous metal organic framework

The efficiency of physisorption-based separation of gas-mixtures depends on the selectivity of adsorbent which is directly linked to size, shape, polarizability and other physical properties of adsorbed molecules. Commensurate adsorption is an interesting and important adsorption phenomenon, where the adsorbed amount, location, and orientation of an adsorbate are commensurate with the crystal symmetry of the adsorbent. Understanding this phenomenon is important and beneficial as it can provide vital information about adsorbate-adsorbent interaction and adsorption-desorption mechanism. So far, only sporadic examples of commensurate adsorption have been reported in porous materials such as zeolites and metal organic frameworks (MOFs). In this work we show for the first time direct structural evidence of commensurate-to-incommensurate transition of linear hydrocarbon molecules (C₂-C₇) in a microporous MOF, by employing a number of analytical techniques including single crystal X-ray diffraction (SCXRD), in situ powder X-ray diffraction coupled with differential scanning calorimetry (PXRD-DSC), gas adsorption and molecular simulations.

Understanding Small-Molecule Interactions in Metal-Organic Frameworks: Coupling Experiment with Theory

Metal-organic frameworks (MOFs) have gained much attention as next-generation porous media for various applications, especially gas separation/storage, and catalysis. New MOFs are regularly reported; however, to develop better materials in a timely manner for specific applications, the interactions between guest molecules and the internal surface of the framework must first be understood. A combined experimental and theoretical approach is presented, which proves essential for the elucidation of small-molecule interactions in a model MOF system known as M2 (dobdc) (dobdc(4-) = 2,5-dioxido-1,4-benzenedicarboxylate; M = Mg, Mn, Fe, Co, Ni, Cu, or Zn), a material whose adsorption properties can be readily tuned via chemical substitution. It is additionally shown that the study of extensive families like this one can provide a platform to test the efficacy and accuracy of developing computational methodologies in slightly varying chemical environments, a task that is necessary for their evolution into viable, robust tools for screening large numbers of materials.

Isolation of a structural intermediate during switching of degree of interpenetration in a metal-organic framework

A known pillared layered metal-organic framework [Co2(ndc)2(bpy)] is shown to undergo a change in degree of interpenetration from a highly porous doubly-interpenetrated framework (2fa) to a less porous triply-interpenetrated framework (3fa). The transformation involves an intermediate empty doubly-interpenetrated phase (2fa') which has been isolated for the first time for this kind of phenomenon by altering the conditions of activation of the as-synthesized material. Interestingly, all the transformations occur in single-crystal to single-crystal fashion. Changes in degree of interpenetration have not been explored much to date and their implications with regard to the porosity of MOFs still remain largely unknown. The present study not only provides a better understanding of such dramatic structural changes in MOF materials, but also describes an original way of controlling interpenetration by carefully optimizing the temperature of activation. In addition to studying the structural mechanism of conversion from 2fa to 3fa, sorption analysis has been carried out on both the intermediate (2fa') and the triply-interpenetrated (3fa) forms to further explain the effect that switching of interpenetration mode has on the porosity of the MOF material.

A microporous metal-organic framework with rare lvt topology for highly selective C2H2/C2H4 separation at room temperature

A new lvt-type metal-organic framework UTSA-60a with suitable pore channels and open metal sites has been developed for highly selective separation of C2H2/C2H4 at room temperature.

Enhanced performance of mixed-matrix membranes through a graft copolymer-directed interface and interaction tuning approach

Herein, a high performance mixed-matrix membrane (MMM) is reported with simultaneously large improvements in the CO2 permeability by 880 % from 70.2 to 687.7 Barrer (1 Barrer=1×10(-10)  cm(3)  cm cm(-2)  s(-1)  cmHg(-1) ) and CO2 /N2 selectivity by 14.4 % from 30.5 to 34.9. These findings represent one of the most dramatic improvements ever reported for MMMs. These improvements are obtained through an interface and interaction tuning approach based on an amphiphilic grafted copolymer. Poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g-POEM) graft copolymer plays a key role as a soft organic matrix to provide good permeation properties, uniform distribution of zeolite imidazole frameworks-8 (ZIF-8), and better interfacial contact with inorganic compounds. In particular, the CO2 /C3 H8 and CO2 /C3 H6 selectivities reached 10.5 and 42.7, respectively, for PVC-g-POEM/ZIF (40 %) MMMs; this indicates that it could be a promising membrane material for the purification of C3 hydrocarbons.