Crystalline MOF Research Articles

Unraveling the timescale of the structural photo-response within oriented metal-organic framework films.

Fundamental knowledge on the intrinsic timescale of structural transformations in photo-switchable metal-organic framework films is crucial to tune their switching performance and to facilitate their applicability as stimuli-responsive materials. In this work, for the first time, an integrated approach to study and quantify the temporal evolution of structural transformations is demonstrated on an epitaxially oriented DMOF-1-on-MOF film system comprising azobenzene in the DMOF-1 pores (DMOF-1/AB). We employed time-resolved Grazing Incidence Wide-Angle X-Ray Scattering measurements to track the structural response of the DMOF-1/AB film upon altering the length of the azobenzene molecule by photo-isomerization (trans-to-cis, 343 nm; cis-to-trans, 450 nm). Within seconds, the DMOF-1/AB response occurred fully reversible and over several switching cycles by cooperative photo-switching of the oriented DMOF-1/AB crystallites as confirmed further by infrared measurements. Our work thereby suggests a new avenue to elucidate the timescales and photo-switching characteristics in structurally responsive MOF film systems.

Syntheses of two copper metal-organic frameworks with tri(1,2,4-triazole) and biscarboxylate and graphene oxide composites for decomposition of dye by visible-light driven and ultrasonic assisted

Two crystalline and nano-sized new Cu(II) MOFs {[Cu(ttpa)(1,3-bdc)(H2O)]·CH3OH}n (Cu(ttpa)-1) and {[Cu(ttpa)(mip)(H2O)]•2H2O} (Cu(ttpa)-2) were prepared and characterized (ttpa ​= ​tris(4-(1,2,4-triazol-1-yl)phenyl)amine, 1,3-bdc ​= ​1,3-benzenedicarboxylate, mip ​= ​5-methyl-isophthalate) by hydrothermal method and sonochemical method. Cu(ttpa)-1 and Cu(ttpa)-2 exhibited the 2D network with point symbol {44⋅62}{44⋅62}. The effect of sonicated time, power, frequency and temperature on the morphology of nano-sized Cu(ttpa)-1 and Cu(ttpa)-2 were studied. The MOFs@10%GO composites (GO ​= ​graphite oxide) exhibited the highest activities. The catalytic decomposition of methylene blue (MB) using Cu(ttpa)-1, Cu(ttpa)-2, Cu(ttpa)-1@GO and Cu(ttpa)-2@GO composites were examined under visible light and ultrasound. Cu(ttpa)-1, Cu(ttpa)-2, Cu(ttpa)-1@GO and Cu(ttpa)-2@GO exhibited high degradation efficiency. The degradation efficiency of MB for Cu(ttpa)-1@GO was 91.2% at pH ​= ​8 after 15 ​min visible light irradiation and the photocatalytic rate constant (k) was 0.1165 ​min−1. The •OH hydroxyl radicals and •O2- superoxide were the main active matters for catalyst Cu(ttpa)-1@GO and Cu(ttpa)-2@GO in the degradation of MB. Cu(ttpa)-1@GO has the higher catalytic efficiency of degradation of MB than most of MOFs, MOFs composites and inorganic photocatalysts. Cu(ttpa)-1@GO is the good photocatalytic material.

(Invited) Electro- and Photoelectro- Catalysts Obtained by Pyrolysis of Bimetallic Amorphous Metal-Organic Frameworks

The rising world population and industrialization are predicted to provoke a global power demand of 28 TW and a CO2 emission of 45 Gt by 2040.[1] Proton exchange membranes fuel cells (PEMFCs) and electrochemical water splitting have attracted wide attention to face with the demand of energy, the dwindling of fossil fuels and the deterioration of the environment. In PEMFCs, hydrogen is oxidized at the anode (hydrogen oxidation reaction = HOR) and oxygen is reduced at the cathode (oxygen reduction reaction = ORR), with water as the major product. In the opposite process, the hydrolysis of water produces hydrogen and oxygen at the cathode (hydrogen evolution reaction = HER) and anode (oxygen evolution reaction = OER), respectively.[2] Under operating conditions, both efficiency and conversion rate are hindered by activation barriers, which result in overpotentials. Platinum group metals (PGM) and their derivatives have shown high catalytic capacity. However, the industrial applications of these catalysts are restricted by their scarcity and cost. Consequently, efforts have been made to design alternative, cheap and active catalysts to make the hydrogen economy closer to reality.[3] The present study describes an approach toward the general synthesis of bimetallic amorphous metal-organic frameworks (aMOFs) to subsequently prepare mono- or multimetallic electro- and photoelectro- catalysts. It is worth mentioning that aMOFs are starting to emerge as alternative materials, beyond the dictatorial domain of crystalline MOFs. The aforementioned approach is based on merging our liquid-liquid interface synthesis method,[4] together with the metalloligand approach.[5] As prove of concept, we have synthesized and characterized a family of bimetallic aMOFs: NEU-5 (= [Zn(FeTpyCOOH)(PF6)2]n), NEU-6 (= [Zn(Ru(terpy*)2)(PF6)2]n), NEU-7 (= [Fe(Ru(terpy*)2)(PF6)2]n) and NEU-8 (= [Ti(Ru(terpy*)2)(PF6)2]n). Electro- and photoelectro- catalysts based on the controlled pyrolysis of these frameworks have been subsequently developed for efficient catalysis toward HER, OER and ORR in both acidic and alkaline media. Thus, functional Fe2P@PNDCN, RuP@PNDCN, Fe3O4/RuO2@NEU-7 and Ru2O/TiN/TiO2@NEU-8 have been fabricated by controlled pyrolysis of NEU-5, NEU-6, NEU-7 and NEU-8, respectively. As a catalyst electrode for ORR, the half-wave potentials of Fe2P@PNDCN have been 0.78, 0.78 and 0.91 V in 0.5 M H2SO4, 0.1 M HClO4 and 1 M KOH, respectively. The as-obtained RuP@PNDCN has exhibited excellent HER activity. RuP@PNDCN has shown a very low overpotential of 65 mV at a current density of 10 mA cm-2 in 0.5 M H2SO4. RuP@PNDCN have been also active toward the HER in 1 M KOH, displaying a low overpotential of 74 mV at a catalytic current density of 10 mA cm-2. Fe3O4/RuO2@NEU-7 has exhibited outstanding electrocatalytic activity upon the OER with overpotentials of only 250 and 450 mV to reach 10 mA cm-2 current density in 1 M KOH and 0.5 M H2SO4, respectively. In acid conditions at a catalytic current density of 10 mA cm-2, while as-synthesized Ru2O/TiN/TiO2@NEU-8 has exhibited an overpotential of 67 mV, Ru2O/TiN/TiO2@NEU-8 excited under blue light irradiation has promoted HER and displayed an ultralow overpotential of 33 mV.[2] Therefore, this work presents a synthesis strategy to develop bimetallic aMOFs, which can be subsequently pyrolyzed to fabricate electro- and photoelectro- catalysts. We anticipate that great improvements in the field of catalysis will be achieved by the rational synthesis of new bimetallic aMOFs.

Hierarchically Porous Biocatalytic MOF Microreactor as a Versatile Platform towards Enhanced Multienzyme and Cofactor‐Dependent Biocatalysis

AbstractMetal‐organic frameworks (MOFs) have recently emerged as excellent hosting matrices for enzyme immobilization, offering superior physical and chemical protection for biocatalytic reactions. However, for multienzyme and cofactor‐dependent biocatalysis, the subtle orchestration of enzymes and cofactors is largely disrupted upon immobilizing in the rigid crystalline MOF network, which leads to a much reduced biocatalytic efficiency. Herein, we constructed hierarchically porous MOFs by controlled structural etching to enhance multienzyme and cofactor‐dependent enzyme biocatalysis. The expanded size of the pores can provide sufficient space for accommodated enzymes to reorientate and spread within MOFs in their lower surface energy state as well as to decrease the inherent barriers to accelerate the diffusion rate of reactants and intermediates. Moreover, the developed hierarchically porous MOFs demonstrated outstanding tolerance to inhospitable surroundings and recyclability.

Guest size limitation in metal–organic framework crystal–glass composites

MOF crystal-glass composites (MOF CGCs) are materials with crystalline MOFs embedded within a MOF glass. Here we develop two novel MOF CGCs, and explore the gas uptake and guest-size limitations within these materials.

A donor–acceptor liganded metal–organic framework showcases the hydrogen-bond-enhanced sensing of N-heterocyclic explosives

Zn(ii)-based MOF for detecting FOX-7 like explosives is designed via hydrogen-bond-intensified host–guest interactions. The crystalline MOF achieves 0.14 ppm detection limit and a highest fluorescence quenching constant of 3.22 × 104 M−1.

The reactivity of an inorganic glass melt with ZIF-8.

The thermal behaviour of ZIF-8, Zn(meIm)2 in the presence of a sodium fluoroaluminophosphate glass melt was probed through differential scanning calorimetry and thermogravimetric analysis. The structural integrity of ZIF-8 was then determined by a combination of powder X-ray diffraction, Fourier transform infra-red and 1H nuclear magnetic resonance spectroscopy.

Crystalline Cu(ii) metal–organic frameworks based on a carboxamide pincer ligand and an NCONCON–Pd(ii) pincer complex

Two copper MOFs based on carboxamide linkers are presented. This work shows how organometallic complexes with carboxylate functionalities can be repurposed to produce crystalline MOFs which can be used in carbon dioxide conversion.

Efficient air epoxidation of cycloalkenes over bimetal-organic framework ZnCo-MOF materials

To date, it was difficult to develop catalytic systems for activating O2 in the absence of initiator and sacrificial co-reductant for high-efficiency epoxidation of olefins under mild conditions. Herein, different compositions of ZnCo-MOF have been prepared via a dry-gel crystallization method, which were used to catalyze the epoxidation of α-pinene with air at 90 °C. Zn0.1Co1-MOF-D2-24 performed the best catalysis activity to give 95.5 % α-pinene conversion and 96.7 % epoxide selectivity. The epoxidation results showed that Zn and Co could effectively activate air to epoxidize α-pinene in high efficiency. This bimetal catalytic effect was assigned to the contribution of interacted lattice Zn and Co ions embedded into crystalline MOF framework with similar electronic structure and ion radius, which avoided the use of organic peroxide initiators and other co-reducing agents. Under anhydrous conditions, Zn0.1Co1-MOF-D2-24 showed stable catalytic activity in the epoxidation of α-pinene with air by at least six recycles.

Extension of Surface Organometallic Chemistry to Metal-Organic Frameworks: Development of a Well-Defined Single Site [(≡Zr-O-)W(═O)(CH2tBu)3] Olefin Metathesis Catalyst.

We report here the first step by step anchoring of a W(≡CtBu)(CH2tBu)3 complex on a highly crystalline and mesoporous MOF, namely Zr-NU-1000, using a Surface Organometallic Chemistry (SOMC) concept and methodology. SOMC allowed us to selectively graft the complex on the Zr6 clusters and characterize the obtained single site material using state of the art experimental methods including extensive solid-state NMR techniques and HAADF-STEM imaging. Further FT-IR spectroscopy revealed the presence of a W═O moiety arising from the in situ reaction of the W≡CtBu functionality with the coordinated water coming from the 8-connected hexanuclear Zr6 clusters. All the steps leading to the final grafted molecular complex have been identified by DFT. The obtained material was tested for gas phase and liquid phase olefin metathesis and exhibited higher catalytic activity than the corresponding catalysts synthesized by different grafting methods. This contribution establishes the importance of applying SOMC to MOF chemistry to get well-defined single site catalyst on MOF inorganic secondary building units, in particular the in situ synthesis of W═O alkyl complexes from their W carbyne analogues.

Ordered Large-Pore MesoMOFs Based on Synergistic Effects of TriBlock Polymer and Hofmeister Ion.

Ordered mesoporous metal-organic frameworks (mesoMOFs) were constructed with a uniform pore size up to about 10 nm and thick microporous walls, opening up the possibility for the mass diffusion of large-size molecules through crystalline MOFs. The synergistic effects based on triblock copolymer templates and the Hofmeister salting-in anions promote the nucleation of stable MOFs in aqueous phase and the in situ crystallization of MOFs around templates, rendering the generation of a microcrystal with periodically arranged large mesopores. The improved mass transfer benefiting from large-pore channels, together with robust microporous crystalline structure, endows them as an ideal nanoreactor for the highly efficient digestion of various biogenic proteins. This strategy could set a guideline for the rational design of new ordered large-pore mesoMOFs with a variety of compositions and functionalities and pave a way for their potential applications with biomacromolecules.

Ordered Large‐Pore MesoMOFs Based on Synergistic Effects of TriBlock Polymer and Hofmeister Ion

AbstractOrdered mesoporous metal–organic frameworks (mesoMOFs) were constructed with a uniform pore size up to about 10 nm and thick microporous walls, opening up the possibility for the mass diffusion of large‐size molecules through crystalline MOFs. The synergistic effects based on triblock copolymer templates and the Hofmeister salting‐in anions promote the nucleation of stable MOFs in aqueous phase and the in situ crystallization of MOFs around templates, rendering the generation of a microcrystal with periodically arranged large mesopores. The improved mass transfer benefiting from large‐pore channels, together with robust microporous crystalline structure, endows them as an ideal nanoreactor for the highly efficient digestion of various biogenic proteins. This strategy could set a guideline for the rational design of new ordered large‐pore mesoMOFs with a variety of compositions and functionalities and pave a way for their potential applications with biomacromolecules.

Isostructural MOFs with Higher Proton Conductivity for Improved Oxygen Evolution Reaction Performance.

Here we synthesized two new isostructural MOFs (FJU-82-Co/FJU-82-Zn) and first observed that tuning of the proton conductivity may provide an effective strategy to improve the electrocatalytic OER perfomances of isostructural crystalline MOF materials. The conductivity value for FJU-82-Co is 7.40 × 10-5 S cm-1, which is 127-fold that for FJU-82-Zn with 5.80 × 10-7 S cm-1 at 60 °C and 98% RH, while the overpotential of FJU-82-Co is 0.57 V at 1 mA cm-2, which is better than that of FJU-82-Zn with 1.17 V.

A new route to porous metal–organic framework crystal–glass composites

A lower temperature route to metal–organic framework crystal–glass composites is presented. Specifically, the annealing pre-formed ZIF-62 glass with a crystalline MOF aboveTgwill enable formation of a greatly expanded range of materials.

Directional Engraving within Single Crystalline Metal-Organic Framework Particles via Oxidative Linker Cleaving.

An oxidative linker cleaving (OLC) process was developed for surgical manipulation of the engraving process within single crystalline MOFs particles. The strategy relies on selective degradation of 2,5-dihydroxyterephthalic acid linker into small molecular fragments by oxidative ring-opening reactions, resulting in controllable scissoring of framework. By regulation of the generation and diffusion of oxidative species, the core MOFs will undergo divergent etching routes, producing a series of single crystalline hollow and yolk-shell MOF structures. In addition, the OLC process can be initiated and localized around the pre-embedded Pd NPs through on-site catalytic generation of oxidative species, leading to solitary confinement of multiple NPs within one single crystalline MOF particle, namely, a multi-yolk-shell structure. This unique architecture can effectively protect NPs from agglomeration while realizing size selective catalysis at the same time.

Synthesis and Properties of a Compositional Series of MIL-53(Al) Metal-Organic Framework Crystal-Glass Composites.

Metal–organic framework crystal-glass composites (MOF-CGCs) are materials in which a crystalline MOF is dispersed within a MOF glass. In this work, we explore the room-temperature stabilization of the open-pore form of MIL-53(Al), usually observed at high temperature, which occurs upon encapsulation within a ZIF-62(Zn) MOF glass matrix. A series of MOF-CGCs containing different loadings of MIL-53(Al) were synthesized and characterized using X-ray diffraction and nuclear magnetic resonance spectroscopy. An upper limit of MIL-53(Al) that can be stabilized in the composite was determined for the first time. The nanostructure of the composites was probed using pair distribution function analysis and scanning transmission electron microscopy. Notably, the distribution and integrity of the crystalline component in a sample series were determined, and these findings were related to the MOF-CGC gas adsorption capacity in order to identify the optimal loading necessary for maximum CO2 sorption capacity.

A Metal-Organic Framework as Selectivity Regulator for Fe3+ and Ascorbic Acid Detection.

Ferric ion (Fe3+) plays a vital role in cellular homeostasis. However, the detection of Fe3+ with rhodamine B (RhB) has potential problems, such as poor selectivity and low photostability. To address these problems, we rationally designed an RhB@MOF nanocomposite-based "on-off-on" fluorescent switching nanoprobe for highly sensitive and selective detection of Fe3+ and ascorbic acid. This RhB@MOF nanoprobe was prepared through a facile one-pot synthesis. Here MOF served as a selectivity regulator for the detection of Fe3+. By embedding RhB into the porous crystalline MOF, enhanced photostability and fluorescence lifetime of RhB to Fe3+ were achieved. The as-prepared RhB@MOF was demonstrated to be an ultrasensitive and selective nanoprobe for the detection of Fe3+ in human serum and ascorbic acid in rat brain microdialysate. Furthermore, inner filter effect (IFE) and photoinduced electron transfer (PET) were proposed and discussed to explain the selectivity and sensitivity of RhB to Fe3+ against other interfering substances. Our novel "on-off-on" nanoprobe provides insight into the rational design of MOF-based biosensors for selective and sensitive detection of analytes.

Sulfur Chemistry for Stable and Electroactive Metal-Organic Frameworks: The Crosslinking Story.

The versatile sulfur chemistry, as exemplified by the reactive yet tractable thiol group (-SH), offers unique opportunities for bypassing the obstacles in accessing stable and electroactive metal-organic frameworks. Of particular interest are recent advances in assembling MOF materials equipped with free-standing thiol functions: metal guests can be conveniently inserted to install electroactive metal-sulfur bonds, which, as crosslinks, also stabilize the host coordination net. Here the historical development of the bifunctional, two-step design embodied by the thiol-tagged MOF solids is traced, in order to highlight the underlying spirit that has driven research efforts in the past two decades. Going forward, broad new horizons are foreseen in solid-state materials synthesis, for example, arising from various sulfur-based hard-and-soft combinations, in synergy with the crystalline and modular MOF structural platform.

Fabrication of a Spherical Superstructure of Carbon Nanorods.

Hierarchical superstructures in nano/microsize have attracted great attention owing to their wide potential applications. Herein, a self-templated strategy is presented for the synthesis of a spherical superstructure of carbon nanorods (SS-CNR) in micrometers through the morphology-preserved thermal transformation of a spherical superstructure of metal-organic framework nanorods (SS-MOFNR). The self-ordered SS-MOFNR with a chestnut-shell-like superstructure composed of 1D MOF nanorods on the shell is synthesized by a hydrothermal transformation process from crystalline MOF nanoparticles. After carbonization in argon, the hierarchical SS-MOFNR transforms into SS-CNR, which preserves the original chestnut-shell-like superstructure with 1D porous carbon nanorods on the shell. Taking the advantage of this functional superstructure, SS-CNR immobilized with ultrafine palladium (Pd) nanoparticles (Pd@SS-CNR) exhibits excellent catalytic activity for formic acid dehydrogenation. This synthetic strategy provides a facile method to synthesize uniform spherical superstructures constructed from 1D MOF nanorods or carbon nanorods for applications in catalysis and energy storage.

Metal-dependent photocatalytic activity and magnetic behaviour of a series of 3D Co-Ni metal organic frameworks.

Crystalline MOF materials with adjustable properties are of great interest for multiple potential applications. In this study, a series of 3D isostructural mixed metal MOFs {[M3(L)2(4,4'-bpy)2(H2O)2]·14H2O}n (M = Co (1), Co0.7Ni0.3 (2), Ni0.5Co0.5 (3), Co0.3Ni0.7 (4), Co0.1Ni0.9 (5), and Ni (6); H3L = 1-aminobenzene-3,4,5-tricarboxylic acid) have been synthesized. The crystal color changed regularly with the increase in the Ni ion content from red to green, and a new ultraviolet absorption spectrophotometry method has been developed for the accurate determination of the metal content of Co in MOF materials. In the detection of magnetic behaviour, 1 shows antiferromagnetism. As the Ni ion component gradually increases in 2-6, the magnetic behaviour of the complexes appears to transition from antiferromagnetic to ferromagnetic. Moreover, complex 1 exhibits preeminent photocatalysis activity in the degradation of organic dyes under visible light irradiation. As the ratio of Ni ions increases gradually in the complexes, the photocatalytic activities of 1-6 decrease. This work offers controllable regulation of the photocatalytic properties and magnetic behaviour of MOFs by changing the metal ions.