Room Temperature Reduction of Nitrogen Oxide on Iron Metal-Organic Frameworks.

Nitrogen oxides represent one of the main threats for the environment. Despite decades of intensive research efforts, a sustainable solution for NOx removal under environmental conditions is still undefined. Using theoretical modelling, material design, state-of-the-art investigation methods and mimicking enzymes, it is found that selected porous hybrid iron(II/III) based MOF material are able to decompose NOx, at room temperature, in the presence of water and oxygen, into N2 and O2 and without reducing agents. This paves the way to the development of new highly sustainable heterogeneous catalysts to improve air quality.

Tuning Hydrophilicity of Aluminum MOFs by a Mixed-Linker Strategy for Enhanced Performance in Water Adsorption-Driven Heat Allocation Application.

Water adsorption-driven heat transfer (AHT) technology has emerged as a promising solution to address crisis of the global energy consumption and environmental pollution of current heating and cooling processes. Hydrophilicity of water adsorbents plays a decisive role in these applications. This work reports an easy, green, and inexpensive approach to tuning the hydrophilicity of metal-organic frameworks (MOFs) by incorporating mixed linkers, isophthalic acid (IPA), and 3,5-pyridinedicarboxylic acid (PYDC), with various ratios in a series of Al-xIPA-(100-x)PYDC (x: feeding ratio of IPA) MOFs. The designed mixed-linkers MOFs show a variation of hydrophilicity along the fraction of the linkers. Representative compounds with a proportional mixed linker ratio denoted as KMF-2, exhibit an S-shaped isotherm, an excellent coefficient of performance of 0.75 (cooling) and 1.66 (heating) achieved with low driving temperature below 70 °C which offers capability to employ solar or industrial waste heat, remarkable volumetric specific energy capacity (235 kWh m-3 ) and heat-storage capacity (330 kWh m-3 ). The superiority of KMF-2 to IPA or PYDC-containing single-linker MOFs (CAU-10-H and CAU-10pydc, respectively) and most of benchmark adsorbents illustrate the effectiveness of the mixed-linker strategy to design AHT adsorbents with promising performance.

Low-Valent Metal Ions as MOF Pillars: A New Route Toward Stable and Multifunctional MOFs.

PCM-102 is a new organophosphine metal-organic framework (MOF) featuring diphosphine pockets that consist of pairs of offset trans-oriented P(III) donors. Postsynthetic addition of M(I) salts (M = Cu, Ag, Au) to PCM-102 induces single-crystal to single-crystal transformations and the formation of trans-[P2M]+ solid-state complexes (where P = framework-based triarylphosphines). While the unmetalated PCM-102 has low porosity, the addition of secondary Lewis acids to install rigid P-M-P pillars is shown to dramatically increase both stability and selective gas uptake properties, with N2 Brunauer-Emmett-Teller surface areas >1500 m2 g-1. The Ag(I) analogue can also be obtained via a simple, one-pot peri-synthetic route and is an ideal sacrificial precursor for materials with mixed bimetallic MA/MB pillars via postsynthetic, solvent-assisted metal exchange. Notably, the M-PCM-102 family of MOFs contain periodic trans-[P2M]+ sites that are free of counter anions, unlike traditional analogous molecular complexes, since the precursor PCM-102 MOF is monoanionic, enabling access to charge-neutral metal-pillared materials. Four M-PCM-102 materials were evaluated for the separation of C2 hydrocarbons. The separation performance was found to be tunable based on the metal(s) incorporated, and density functional theory was employed to elucidate the nature of the unusual observed sorption preference, C2H2 > C2H6 > C2H4.

Crystals springing into action: metal-organic framework CUK-1 as a pressure-driven molecular spring.

Mercury porosimetry and in situ high pressure single crystal X-ray diffraction revealed the wine-rack CUK-1 MOF as a unique crystalline material capable of a fully reversible mechanical pressure-triggered structural contraction. The near-absence of hysteresis upon cycling exhibited by this robust MOF, akin to an ideal molecular spring, is associated with a constant work energy storage capacity of 40 J g-1. Molecular simulations were further deployed to uncover the free-energy landscape behind this unprecedented pressure-responsive phenomenon in the area of compliant hybrid porous materials. This discovery is of utmost importance from the perspective of instant energy storage and delivery.

Catalytic Performance of Zr-Based Metal-Organic Frameworks Zr-abtc and MIP-200 in Selective Oxidations with H2 O2.

The catalytic performance of Zr-abtc and MIP-200 metal-organic frameworks consisting of 8-connected Zr6 clusters and tetratopic linkers was investigated in H2 O2 -based selective oxidations and compared with that of 12-coordinated UiO-66 and UiO-67. Zr-abtc demonstrated advantages in both substrate conversion and product selectivity for epoxidation of electron-deficient C=C bonds in α,ß-unsaturated ketones. The significant predominance of 1,2-epoxide in carvone epoxidation, coupled with high sulfone selectivity in thioether oxidation, points to a nucleophilic oxidation mechanism over Zr-abtc. The superior catalytic performance in the epoxidation of unsaturated ketones correlates with a larger amount of weak basic sites in Zr-abtc. Electrophilic activation of H2 O2 can also be realized, as evidenced by the high activity of Zr-abtc in epoxidation of the electron-rich C=C bond in caryophyllene. XRD and FTIR studies confirmed the retention of the Zr-abtc structure after the catalysis. The low activity of MIP-200 in H2 O2 -based oxidations is most likely related to its specific hydrophilicity, which disfavors adsorption of organic substrates and H2 O2 .

Water adsorption fingerprinting of structural defects/capping functions in Zr-fumarate MOFs: a hybrid computational-experimental approach.

Engineering structural defects in MOFs has been intensively applied to modulate their adsorption-related properties. Zr-fumarate MOF (also known as MOF-801) is a prototypical defective MOF with proven versatile adsorption/separation performances depending on the synthetic conditions, however the relationship between the nature/concentration of both structure defects/capping functions and its adsorption features is still far from being fully understood. In this work, we first present a systematic theoretical exploration of the individual contributions of linker and cluster defects as well as of the capping functions to the overall water adsorption profile of the MOF-801 framework. This computational effort based on the construction of defective structure models and the use of Grand Canonical Monte Carlo simulations further enabled the identification of the overarching defective structure for two MOF-801 samples based on their experimental adsorption isotherms reported previously. An experimental effort was then deployed to synthesize two Zr-fumarate MOF samples with controlled nature and concentration of structural defects as well as capping functions. This computational-experimental hybrid strategy revealed the water adsorption isotherm as a fingerprint of the nature and concentration of structural defect/capping groups exhibited by the MOF adsorbent. We expect this study to deliver meaningful insights to further design MOFs with target adsorption features through a rational engineering of structural defects.

Defective Zr-Fumarate MOFs Enable High-Efficiency Adsorption Heat Allocations.

Adsorption-driven heat transfer devices incorporating an efficient "adsorbent-water" working pair are attracting great attention as a green and sustainable technology to address the huge global energy demands for cooling and heating. Herein, we report the improved heat transfer performance of a defective Zr fumarate metal-organic framework (MOF) prepared in a water solvent (Zr-Fum HT). This material exhibits an S-shaped water sorption isotherm (P/P0 = 0.05-0.2), excellent working capacity (0.497 mLH2O mL-1MOF) under adsorption-driven cooling/chiller working conditions (Tadsorption(ads) = 30 °C, Tcondensation (con) = 30 °C, and Tdesorption(des) = 80 °C), very high coefficient of performances for both cooling (0.83) and heating (1.76) together with a relatively low driving temperature at 80 °C, a remarkable heat storage capacity (423.6 kW h m-3MOF), and an outstanding evaporation heat (343.8 kW h m-3MOF). The level of performance of the resultant Zr-Fum HT MOF is above those of all existing benchmark water adsorbents including MOF-801 previously synthesized in the N,N-dimethylformamide solvent under regeneration at 80 °C which is accessible from the solar source. This is coupled with many other decisive advantages including green synthesis and high proven chemical and mechanical robustness. The microscopic water adsorption mechanism of Zr-Fum HT at the origin of its excellent water adsorption performance was further explored computationally based on the construction of an atomistic defective model online with the experimental data gained from a subtle combination of characterization techniques.

Rational design of a robust aluminum metal-organic framework for multi-purpose water-sorption-driven heat allocations.

Adsorption-driven heat transfer technology using water as working fluid is a promising eco-friendly strategy to address the exponential increase of global energy demands for cooling and heating purposes. Here we present the water sorption properties of a porous aluminum carboxylate metal-organic framework, [Al(OH)(C6H3NO4)]·nH2O, KMF-1, discovered by a joint computational predictive and experimental approaches, which exhibits step-like sorption isotherms, record volumetric working capacity (0.36 mL mL-1) and specific energy capacity (263 kWh m-3) under cooling working conditions, very high coefficient of performances of 0.75 (cooling) and 1.74 (heating) together with low driving temperature below 70 °C which allows the exploitation of solar heat, high cycling stability and remarkable heat storage capacity (348 kWh m-3). This level of performances makes this porous material as a unique and ideal multi-purpose water adsorbent to tackle the challenges of thermal energy storage and its further efficient exploitation for both cooling and heating applications.

Microporous 3D Graphene-like Zeolite-Templated Carbons for Preferential Adsorption of Ethane.

Microporous 3D graphene-like carbons were synthesized in Faujasite (FAU)-, EMT-, and beta-zeolite templates using the recently developed Ca2+ ion-catalyzed synthesis method. The microporous carbons liberated from these large-pore zeolites (0.7-0.9 nm) retain the structural regularity of zeolite. FAU-, EMT-, and beta zeolite-templated carbons (ZTCs) with faithfully constructed pore diameters of 1.2, 1.1, and 0.9 nm, respectively, and very large Brunauer-Emmet-Teller areas (2700-3200 m2 g-1) were obtained. We have discovered that these schwarzite-like carbons exhibit preferential adsorption of ethane over ethylene at pressures in the range of 1-10 bar. The curved graphene structure, consisting of a diverse range of carbon polygons with a narrow pore size of ∼1 nm, provides abundant adsorption sites in micropores and retains its ethane selectivity at pressures up to 10 bar. After varying the oxygen content in the beta ZTC, the ethane and ethylene adsorption isotherms show that the separation ability is not significantly affected by surface oxygen groups. Based on these adsorption results, a breakthrough separation procedure using a C2H4/C2H6 gas mixture (9:1 molar ratio) is demonstrated to produce ethylene with a purity of 99.9%.

Unique design of superior metal-organic framework for removal of toxic chemicals in humid environment via direct functionalization of the metal nodes.

Unique chemical and thermal stabilities of a zirconium-based metal-organic framework (MOF) and its functionalized analogues play a key role to efficiently remove chemical warfare agents (ex., cyanogen chloride, CNCl) and simulant (dimethyl methylphosphonate, DMMP) as well as industrial toxic gas, ammonia (NH3). Herein, we for the first time demonstrate outstanding performance of MOF-808 for removal of toxic chemicals in humid environment via special design of functionalization of hydroxo species bridging Zr-nodes using a triethylenediamine (TEDA) to form ionic frameworks by gas phase acid-base reactions. In situ experimental analyses and first-principles density functional theory calculations unveil underlying mechanism on the selective deposition of TEDA on the Zr-bridging hydroxo sites (µ3-OH) in Zr-MOFs. The crystal structure of TEDA-grafted MOF-808 was confirmed using synchrotron X-ray powder diffraction (SXRPD). Furthermore, operando FT-IR spectra elucidate why the TEDA-grafted MOF-808 shows by far superior sorption efficiency to other MOF varieties. This work provides design principles and applications how to optimize MOFs for the preparation for versatile adsorbents using diamine grafting chemistry, which is also potentially applicable to various catalysis.

Porous Metal-Organic Framework CUK-1 for Adsorption Heat Allocation toward Green Applications of Natural Refrigerant Water.

The development of new water adsorbents that are hydrothermally stable and can operate more efficiently than existing materials is essential for the advancement of water adsorption-driven chillers. Most of the existing benchmark materials and related systems in this field suffer from clear limitations that must be overcome to meet global requirements for sustainable and green energy production and utilization. Here, we report the energy-efficient water sorption properties of three isostructural metal-organic frameworks (MOFs) based on the simple ligand pyridine-2,4-dicarboxylate, named M-CUK-1 [M3(µ3-OH)2(2,4-pdc)2] (where M = Co2+, Ni2+, or Mg2+). The highly hydrothermally stable CUK-1 series feature step-like water adsorption isotherms, relatively high H2O sorption capacities between P/P0 = 0.10-0.25, stable cycling, facile regeneration, and, most importantly, benchmark coefficient of performance values for cooling and heating at a low driving temperature. Furthermore, these MOFs are prepared under green hydrothermal conditions in aqueous solutions. Our joint experimental-computational approach revealed that M-CUK-1 integrates several optimal features, resulting in promising materials as advanced water adsorbents for adsorption-driven cooling and heating applications.

Molecular Encapsulation of Trimeric Chromium Carboxylate Clusters in Metal-Organic Frameworks and Propylene Sorption.

Oxo-bridged trimeric chromium acetate clusters [Cr3 O(OOCCH3 )6 (H2 O)3 ]NO3 have been encapsulated for the first time in the mesoporous cages of the chromium terephthalate MIL-101(Cr). The isolated clusters in MIL-101(Cr) have increased affinity towards propylene compared to propane, due to generation of a new kind of pocket-based propylene-binding site, as supported by DFT calculations.

Formation of Polyaniline-MOF Nanocomposites Using Nano-Sized Fe(III)-MOF for Humidity Sensing Application.

Polyaniline (PA)-MOF nanocomposites have been successfully synthesized through an in-situ chemical oxidative polymerization of aniline in the presence of nano-sized iron trimestate (named as MIL-100(Fe)) particles, which was prepared by a microwave-irradiation method. Water sorption and humidity sensing results clearly showed that water sorption rate and humidity sensitivity are dramatically enhanced by the composites using nano-sized MIL-100(Fe) as compared with that using micrometer-sized MIL-100(Fe) particles.

Guest-Assisted Proton Conduction in the Sulfonic Mesoporous MIL-101 MOF.

Post-synthesis modification of MIL-101(Cr)-NO2 was explored in order to decorate the organic backbone by propyl-sulfonic groups, with the aim to incorporate mobile and acidic protons for solid-state proton electrolyte applications. The resulting solid switched from insulating towards proton superconductive behavior under humidity, while the conductivity recorded at 363 K and 95 % relative humidity reached 4.8×10-3  S cm-1 . Propitiously, the impregnation of the material by strong acidic molecules (H2 SO4 ) further boosted the proton conductivity performances up to the remarkable σ value of 1.3×10-1  S cm-1 at 363 K/95 % RH, which reaches the performances of the best proton conductive MOF reported so far.

Investigating the effect of alumina shaping on the sorption properties of promising metal-organic frameworks.

Three promising MOF candidates, UiO-66(Zr), MIL-100(Fe) and MIL-127(Fe) are shaped through granulation with a ρ-alumina binder. Subsequently, changes in the surface characteristics and adsorption performance are evaluated through adsorption microcalorimetry at 303 K with several common probes (N2, CO2, CO, CH4, C2H6, C3H8, C3H6 and C4H10), generating a detailed picture of adsorbate-adsorbent interactions. Vapour adsorption experiments with water and methanol were further used to gauge changes in hydrophobicity caused by the addition of the alumina binder. Upon shaping, a decrease in gravimetric capacity and specific surface area is observed, accompanied by an increased capacity on a volumetric basis, attributed to densification induced by the shaping process, as well as a surprising lack of pore environment changes. However, the magnitude of these effects depends on the MOF, suggesting a high dependence on material structure. Out of the three materials, MIL-127(Fe) shows the least changes in adsorption performance and is highlighted as a promising candidate for further study.

Organoarsine Metal-Organic Framework with cis-Diarsine Pockets for the Installation of Uniquely Confined Metal Complexes.

ACM-1 is the first example of an organoarsine metal-organic framework (MOF), prepared using a new pyridyl-functionalized triarylarsine ligand coordinated to Ni(II) nodes. ACM-1 has micropores that are decorated with cis-diarsine coordination pockets. Postsynthetic metalation of ACM-1 with AuCl under facile conditions studied by single-crystal X-ray diffraction reveals the installation of dimeric Au2Cl2 complexes via the formation of As-Au bonds. The Au(I) dimers display exceptionally short aurophilic bonds (2.76 Å) induced by the rigidity of the MOF, which acts as a unique solid-state ligand.

A Metal-Organic Framework with Cooperative Phosphines That Permit Post-Synthetic Installation of Open Metal Sites.

PCM-101 is a phosphine coordination material comprised of tris(p-carboxylato)triphenylphosphine and secondary pillaring groups coordinated to [M3 (OH)]5+ nodes (M=Co, Ni). PCM-101 has a unique topology in which R3 P: sites are arranged directly trans to one another, with a P⋅⋅⋅P separation distance dictated by the pillars. Post-synthetic coordination of soft metals to the P: sites proceeds at room temperature to provide X-ray quality crystals that permit full structural resolution. Addition of AuCl groups forces a large distortion of the parent framework. In contrast, CuBr undergoes insertion directly between the trans-P sites to form dimers that mimic solution-phase complexes, but that are geometrically strained due to steric pressure exerted by the MOF scaffold. The metalated materials are active in heterogeneous hydroaddition catalysis under mild conditions, yielding different major products compared to their molecular counterparts.

Bifunctional Pyridinium-Based Ionic-Liquid-Immobilized Diindium Tris(diphenic acid) Bis(1,10-phenanthroline) for CO2 Fixation.

A pyridinium-based ionic-liquid-decorated 1 D metal-organic framework (MOF; IL-[In2 (dpa)3 (1,10-phen)2 ]; IL=ionic liquid; dpa=diphenic acid; 1,10-phen=1,10-phenanthroline) was developed as a bifunctional heterogeneous catalyst system for CO2 -oxirane coupling reactions. An aqueous-microwave route was employed to perform the hydrothermal reaction for the synthesis of the [In2 (dpa)3 (1,10-phen)2 ] MOF, and the IL-[In2 (dpa)3 (1,10-phen)2 ] catalyst was synthesized by covalent postfunctionalization. As a result of the synergetic effect of the dual-functional sites, which include Lewis acid sites (coordinatively unsaturated In sites) and the I- ion in the IL functional sites, IL-[In2 (dpa)3 (1,10-phen)2 ] displayed a high catalytic activity for CO2 -epoxide cycloaddition reactions under mild and solvent-free conditions. Microwave pulses were employed for the first time in MOF-catalyzed CO2 -epoxide cycloaddition reactions to result in a high turnover frequency of 2000-3100 h-1 . The catalyst had an excellent reusability and maintained a continuous high selectivity. Furthermore, only a small amount of leaching was observed from the spent catalyst. A plausible reaction mechanism based on the synergistic effect of the dual-functional sites that catalyze the CO2 -epoxide cycloaddition reaction effectively is proposed.

Novel amine-functionalized iron trimesates with enhanced peroxidase-like activity and their applications for the fluorescent assay of choline and acetylcholine.

We herein describe novel amine-grafted metal-organic frameworks (MOFs) as a promising alternative to natural peroxidase enzyme and their applications for a fluorescent assay of choline (Cho) and acetylcholine (ACh). Among diverse amine-functionalized MOFs, N,N,N',N'-tetramethyl-1,4-butanediamine (TMBDA)-functionalized MIL-100(Fe) (TMBDA-MIL-100(Fe)) exhibited the highest peroxidase activity by developing intense fluorescence from Amplex UltraRed (AUR) in the presence of H2O2, which was presumably due to the synergetic effect of the enhanced negative potential and precisely controlled molecular size of the grafted diamine. Based on the excellent peroxidase-like activity of TMBDA-MIL-100(Fe), choline and ACh were reliably determined down to 0.027 and 0.036µM, respectively. Furthermore, practical applicability of this strategy was successfully demonstrated by detecting choline and ACh in spiked samples of milk and serum, respectively. This work highlights the advantages of amine-grafted MOFs for the preparation of biomimetic catalysts, extending their scope to biosensor applications.

Highly selective adsorption of p-xylene over other C8 aromatic hydrocarbons by Co-CUK-1: a combined experimental and theoretical assessment.

High quality crystalline Co-CUK-1 can be synthesized rapidly and efficiently by a microwave-assisted method. The resulting microporous coordination material is a highly effective adsorbent for the separation of xylene isomers and ethylbenzene, as demonstrated here through sorption isotherm analysis, Ideal Adsorbed Solution Theory (IAST) calculations, and grand canonical Monte Carlo (GCMC) simulations. Co-CUK-1 showed high sorption capacity and high adsorption selectivity for p-xylene over the corresponding m- and o-isomers, and ethylbenzenes. According to the data obtained from IAST and GCMC simulations, the Co-CUK-1 is found to strongly favour p-xylene adsorption because p-xylene molecules undergo well-defined molecular packing in the 1-D channels; by comparison, the packing efficiencies of o-xylene, m-xylene and ethylbenzene are significantly lower, as is evidenced by lower saturation capacities.