Metal-organic Frameworks Growth Research Articles

Designing a MOF-functionalized Nanofibrous Aerogel via Vapor-Phase Synthesis.

Designing 3D mechanically robust and high-surface-area substrates for uniform and high-density deposition of metal-organic frameworks (MOFs) provide a promising strategy to enhance surface accessibility and application of these highly functional materials. Nanofibrous aerogel (NFA) with its highly porous self-supported structure composed of interconnected nanofibrous network offers an ideal platform in this regard. Herein, a facile one-pot strategy is introduced, which utilizes direct deposition of MOF on the nanofibrous surface of the NFAs. NFAs are synthesized using electrospun polyacrylonitrile/polyvinylpyrrolidone (PAN/PVP) polymer nanofibers containing zinc acetate (Zn(Ac)2), which are subjected to freeze drying and thermal treatment. The latter converts Zn(Ac)2 to zinc oxide (ZnO), providing the sites for MOF growth while also adding mechanical integrity to the NFAs through cyclization of the PAN. Exposure of the NFA to the vapor-phase of organic ligand, 2-methylimidazole (2-MeIm) enables in situ growth of zeolitic imidazolate framework-8 (ZIF-8) MOF on the NFA. ZIF-8 loading on the NFAs is further improved by more than tenfold by synthesizing ZnO nanorods/protrusions on the nanofibers, which enables more sites for MOF growth. These findings underscore a significant advancement in designing MOF-based hybrid aerogels, offering a streamlined approach for their use in diverse applications, from catalysis to sensing and water purification.

Locally controlled MOF growth on functionalized carbon nanotubes

Metal-organic frameworks (MOFs) are highly versatile materials because of their tunable properties. However, the typically poor electrical conductivity of MOFs presents challenges for their integration into electrical devices. By adding carbon nanotubes to MOF synthesis, a highly intergrown material with increased conductivity and chemiresistive sensing properties can be obtained. Here, we present a patterning technique to control MOF growth on predefined areas of one particular carbon nanotube. We found that electron beam pretreatment of -COOH functionalized multi-walled carbon nanotubes inhibits the growth of UiO-66 MOF on these multi-walled carbon nanotubes. By irradiating individual multi-walled carbon nanotubes, we show that MOF growth can be inhibited in predefined tube areas, creating MOF-free spaces on the nanotube. In this way, our method shows a possibility to pattern MOF growth on individual nanotubes.

Metal‐Organic Frameworks: Direct Synthesis by Organic Acid‐Etching and Reconstruction Disclosure as Oxygen Evolution Electrocatalysts

AbstractMetal‐organic frameworks (MOFs) have emerged as promising oxygen evolution reaction (OER) electrocatalysts. Chemically bonded MOFs on supports are desirable yet lacking in routine synthesis, as they may allow variable structural evolution and the underlying structure‐activity relationship to be disclosed. Herein, direct MOF synthesis is achieved by an organic acid‐etching strategy (AES). Using π‐conjugated ferrocene (Fc) dicarboxylic acid as the etching agent and organic ligand, a series of MFc‐MOF (M=Ni, Co, Fe, Zn) nanosheets are synthesized on the metal supports. The crystal structure is studied using X‐ray diffraction and low‐dose transmission electron microscopy, which is quasi‐lattice‐matched with that of the metal, enabling in situ MOF growth. Operando Raman and attenuated total reflectance Fourier transform infrared spectroscopy disclose that the NiFc‐MOF features dynamic structural rebuilding during OER. The reconstructed one showing optimized electronic structures with an upshifted total d‐band center, high M−O bonding state occupancy, and localized electrons on adsorbates indicated by density functional theory calculations, exhibits outstanding OER performance with a fairly low overpotential (130 mV at 10 mA cm−2) and good stability (144 h). The newly established approach for direct MOF synthesis and structural reconstruction disclosure stimulate the development of more prudent catalysts for advancing OER.

Metal-Organic Frameworks: Direct Synthesis by Organic Acid-Etching and Reconstruction Disclosure as Oxygen Evolution Electrocatalysts.

Metal-organic frameworks (MOFs) have emerged as promising oxygen evolution reaction (OER) electrocatalysts. Chemically bonded MOFs on supports are desirable yet lacking in routine synthesis, as they may allow variable structural evolution and the underlying structure-activity relationship to be disclosed. Herein, direct MOF synthesis is achieved by an organic acid-etching strategy (AES). Using π-conjugated ferrocene (Fc) dicarboxylic acid as the etching agent and organic ligand, a series of MFc-MOF (M=Ni, Co, Fe, Zn) nanosheets are synthesized on the metal supports. The crystal structure is studied using X-ray diffraction and low-dose transmission electron microscopy, which is quasi-lattice-matched with that of the metal, enabling in situ MOF growth. Operando Raman and attenuated total reflectance Fourier transform infrared spectroscopy disclose that the NiFc-MOF features dynamic structural rebuilding during OER. The reconstructed one showing optimized electronic structures with an upshifted total d-band center, high M-O bonding state occupancy, and localized electrons on adsorbates indicated by density functional theory calculations, exhibits outstanding OER performance with a fairly low overpotential (130 mV at 10 mA cm-2 ) and good stability (144 h). The newly established approach for direct MOF synthesis and structural reconstruction disclosure stimulate the development of more prudent catalysts for advancing OER.

Encrusting MOF nanoparticles onto nanofibers via spray-initiated synthesis to boost the filtration performances of nanofiber membranes

Metal-organic frameworks (MOFs) are currently one of the most attractive porous materials. Integrating MOFs into an organic polymer matrix is considered a promising approach for controlling air pollutants. Especially, the nanoscale miniaturization of MOFs is promising to serve as membranes for efficient air quality control. Here, we proposed the use of spray-initiation as a facile and rapid methodology to assemble homogeneous growth of nanoMOFs on the electrospun fibers, yielding the composite fiber with diameters smaller than 300 nm. The developed ZIF-8-encrusted nanofiber membrane achieved superior filtration performance. Compared with the filter without MOF growth, the MOF-encrusted nanofiber filter achieved enhanced filtration efficiency and almost no change in pressure drop. For the most penetrating particles, the ZIF-8-encrusted nanofiber filter can even reach a 10% increment. This work shows that introducing the MOF nanoparticles onto the nanofibers with homogenous distribution can significantly improve the capacity of the filters in controlling submicron particles, and provide an important reference for the rational design of structures of composite materials.

Porphyrin-Based MOF Thin Film on Transparent Conducting Oxide: Investigation of Growth, Porosity and Photoelectrochemical Properties.

Synthesizing metal-organic frameworks (MOFs) composites with a controlled morphology is an important requirement to access materials of desired patterning and composition. Since the last decade, MOF growth from sacrificial metal oxide layer is increasingly developed as it represents an efficient pathway to functionalize a large number of substrates. In this study, porphyrin-based Al-PMOF thin films were grown on conductive transparent oxide substrates from sacrificial layers of ALD-deposited alumina oxide. The control of the solvent composition and the number of atomic layer deposition (ALD) cycles allow us to tune the crystallinity, morphology and thickness of the produced thin films. Photophysical studies evidence that Al-PMOF thin films present light absorption and emission properties governed by the porphyrinic linker, without any quenching upon increasing the film thickness. Al-PMOF thin films obtained through this methodology present a remarkably high optical quality both in terms of transparency and coverage. The porosity of the samples is demonstrated by ellipsometry and used for Zn(II) insertion inside the MOF thin film. The multifunctional transparent, porous and luminescent thin film grown on fluorine-doped tin oxide (FTO) is used as an electrode capable of photoinduced charge separation upon simulated sunlight irradiation.

In Situ Synchrotron X-ray Scattering Investigation of Cathodic ZIF-8 Deposition on Graphite Using 3D-Printed Cells

Electrochemical approaches provide unique means to fabricate thin films of metal-organic frameworks (MOFs). However, the kinetics of electrochemical MOF deposition has not been quantitatively investigated so far. In this study, we report the first in situ measurements of electrochemical MOF growth using transmission synchrotron X-ray scattering. Electrochemical cells based on poly(lactic acid) with two windows were fabricated using fused-deposition modeling. The resulting three-dimensional (3D)-printed cells, the surface of which was coated with paraffin wax to prevent solvent percolation through the polymer material, were used to monitor the cathodic growth of zeolitic imidazolate framework-8 (ZIF-8) on graphite in a methanol solution containing ZnCl2 and 2-methylimidazole (Hmim) at different cathodic potentials. The resulting time-resolved X-ray diffraction data showed a gradual increase in crystal size with negligible changes in crystal orientation during the cathodic ZIF-8 deposition. More importantly, the time-resolved data provided a means to quantitatively assess the kinetics of the cathodic ZIF-8 growth using the Gualtieri model, revealing that the cathodic potential and Hmim concentration affected crystal growth kinetics but not nucleation kinetics. These ZIF-8 samples exhibited changes in X-ray diffraction patterns after being washed with methanol and dried in air, indicating that in situ measurements are essential to investigate mechanisms behind MOF electrodeposition.

Stress-Dispersed Superstructure of Sn3 (PO4 )2 @PC Derived from Programmable Assembly of Metal-Organic Framework as Long-Life Potassium/Sodium-Ion Batteries Anodes.

The structures of anode materials significantly affect their properties in rechargeable batteries. Material nanosizing and electrode integrity are both beneficial for performance enhancement of batteries, but it is challenging to guarantee optimized nanosizing particles and high structural integrity simultaneously. Herein, a programmable assembly strategy of metal-organic frameworks (MOFs) is used to construct a Sn-based MOF superstructure precursor. After calcination under inert atmosphere, the as-fabricated Sn3 (PO4 )2 @phosphorus doped carbon (Sn3 (PO4 )2 @PC-48) well inherited the morphology of Sn-MOF superstructure precursor. The resultant new material exhibits appreciable reversible capacity and low capacity degradation for K+ storage (144.0mAhg-1 at 5Ag-1 with 90.1% capacity retained after 10000 cycles) and Na+ storage (202.5mAhg-1 at 5Ag-1 with 96.0% capacity retained after 8000 cycles). Detailed characterizations, density functional theory calculations, and finite element analysis simulations reveal that the optimized electronic structure and the stress-dispersed superstructure morphology of Sn3 (PO4 )2 @PC promote the electronic conductivity, enhance K+ / Na+ binding ability and improve the structure stabilization efficiently. This strategy to optimize the structure of anode materials by controlling the MOF growth process offer new dimension to regulate the materials precisely in the energy field.

Mesoporous Silica‐Guided Synthesis of Metal–Organic Framework with Enhanced Water Adsorption Capacity for Smart Indoor Humidity Regulation

Metal–organic frameworks (MOFs) are promising for indoor humidity regulation due to steep stepwise water uptake and moderate regeneration temperature. Current approaches for performance improvement of MOFs such as impregnating hygroscopic salts and grafting functional groups face the challenge of corrosion and instability. Herein, a template‐guided tuning strategy is proposed to synthesize binary nanocomposite. Highly ordered mesoporous channels of MCM‐41 provide uniform nucleation sites for MOF growth, enabling a 21.5% promotion of specific surface area (3188.14 m2 g−1) and 23.4% improvement of water uptake (1.53 g g−1 at 20°C/90% relative humidity) for the nanocomposite compared with parent MIL‐101(Cr). The fast kinetics and superior stability together guarantee its practical application. Further, a paradigm of continuous indoor humidity regulation driven by sunlight is demonstrated, which realizes smart regulation of the indoor humidity to the human comfort zone (40–60%) with near‐zero energy input.

Fabrication of PA-PEI-MOF303(Al) by Stepwise Impregnation Layer-by-Layer Growth for Highly Efficient Removal of Ammonia.

NH3 is a typical alkaline gaseous pollutant widely derived from industrial production and poses great risks to humans and other biota. Metal-organic frameworks (MOFs) have excellent adsorption capacities relative to materials traditionally used to adsorb NH3. However, in practice, applications of MOFs as adsorbents are restricted because of its powder form. We prepared a polyamide (PA) macroporous polyester substrate using an emulsion template method and modified the surface with polyethylenimine (PEI) to improve the MOF growth efficiency on the substrate. The difficulty of loading the MOF because of the fast nucleation rate inside the PA macroporous polyester substrate was solved using a stepwise impregnation layer-by-layer (LBL) growth method, and a PA-PEI-MOF303(Al) hierarchical pore composite that very efficiently adsorbed NH3 was successfully prepared. The PA-PEI-MOF303(Al) adsorption capacity for NH3 was 16.07 mmol·g-1 at 298 K and 100 kPa, and the PA-PEI-MOF303(Al) could be regenerated repeatedly under vacuum at 423 K. The NH3 adsorption mechanism was investigated by in situ Fourier transform infrared spectroscopy and by performing two-dimensional correlation analysis. Unlike for the MOF303(Al) powder, the formation of multi-site hydrogen bonds between Al-O-Al/C-OH, N-H, -OH, C=O, and NH3 in PA-PEI-MOF303(Al) was found to be an important reason for efficient NH3 adsorption. This study will provide a reference for the preparation of other MOF-polymer composites.

Metal Organic Framework Cubosomes

AbstractWe demonstrate a general strategy for the synthesis of ordered bicontinuous‐structured metal organic frameworks (MOFs) by using polymer cubosomes (PCs) with a double primitive structure (Im m symmetry) as the template. The filling of MOF precursors in the open channel of PCs, followed by their coordination and removal of the template, generates MOF cubosomes with a single primitive topology (Pm m) and average mesopore diameters of 60–65 nm. Mechanism study reveals that the formation of ZIF‐8 cubosomes undergoes a new MOF growth process, which involves the formation of individual MOF seeds in the template, their growth and eventual fusion into the cubosomes. Their growth kinetics follows the Avrami equation with an Avrami exponent of n=3 and a growth rate of k=1.33×10−4, indicating their fast 3D heterogeneous growth mode. Serving as a bioreactor, the ZIF‐8 cubosomes show high loading of trypsin enzyme, leading to a high catalytic activity in the proteolysis of bovine serum albumin.

Metal Organic Framework Cubosomes.

We demonstrate a general strategy for the synthesis of ordered bicontinuous-structured metal organic frameworks (MOFs) by using polymer cubosomes (PCs) with a double primitive structure (Im m symmetry) as the template. The filling of MOF precursors in the open channel of PCs, followed by their coordination and removal of the template, generates MOF cubosomes with a single primitive topology (Pm m) and average mesopore diameters of 60-65 nm. Mechanism study reveals that the formation of ZIF-8 cubosomes undergoes a new MOF growth process, which involves the formation of individual MOF seeds in the template, their growth and eventual fusion into the cubosomes. Their growth kinetics follows the Avrami equation with an Avrami exponent of n=3 and a growth rate of k=1.33×10-4 , indicating their fast 3D heterogeneous growth mode. Serving as a bioreactor, the ZIF-8 cubosomes show high loading of trypsin enzyme, leading to a high catalytic activity in the proteolysis of bovine serum albumin.

Metal-Organic Framework-Based Composites for the Detection and Monitoring of Pharmaceutical Compounds in Biological and Environmental Matrices.

The production of synthetic drugs is considered a huge milestone in the healthcare sector, transforming the overall health, aging, and lifestyle of the general population. Due to the surge in production and consumption, pharmaceutical drugs have emerged as potential environmental pollutants that are toxic with low biodegradability. Traditional chromatographic techniques in practice are time-consuming and expensive, despite good precision. Alternatively, electroanalytical techniques are recently identified to be selective, rapid, sensitive, and easier for drug detection. Metal-organic frameworks (MOFs) are known for their intrinsic porous nature, high surface area, and diversity in structural design that provides credible drug-sensing capacities. Long-term reusability and maintaining chemo-structural integrity are major challenges that are countered by ligand-metal combinations, optimization of synthetic conditions, functionalization, and direct MOFs growth over the electrode surface. Moreover, chemical instability and lower conductivities limited the mass commercialization of MOF-based materials in the fields of biosensing, imaging, drug release, therapeutics, and clinical diagnostics. This review is dedicated to analyzing the various combinations of MOFs used for electrochemical detection of pharmaceutical drugs, comprising antibiotics, analgesics, anticancer, antituberculosis, and veterinary drugs. Furthermore, the relationship between the composition, morphology and structural properties of MOFs with their detection capabilities for each drug species is elucidated.

Switchable Ion Current Saturation Regimes Enabled via Heterostructured Nanofluidic Devices Based on Metal-Organic Frameworks.

The use of track-etched membranes allows further fine-tuning of transport regimes and thus enables their use in (bio)sensing and energy-harvesting applications, among others. Recently, metal-organic frameworks (MOFs) have been combined with such membranes to further increase their potential. Herein, the creation of a single track-etched nanochannel modified with the UiO-66 MOF is proposed. By the interfacial growth method, UiO-66-confined synthesis fills the nanochannel completely and smoothly, yet its constructional porosity renders a heterostructure along the axial coordinate of the channel. The MOF heterostructure confers notorious changes in the transport regime of the nanofluidic device. In particular, the tortuosity provided by the micro- and mesostructure of UiO-66 added to its charged state leads to iontronic outputs characterized by an asymmetric ion current saturation for transmembrane voltages exceeding 0.3V. Remarkably, this behavior can be easily and reversibly modulated by changing the pH of the media and it can also be maintained for a wide range of KCl concentrations. In addition, it is found that the modified-nanochannel functionality cannot be explained by considering just the intrinsic microporosity of UiO-66, but rather the constructional porosity that arises during the MOF growth process plays a central and dominant role.

A binder-free, well-integrated metal–organic frameworks@polypyrrole nanofilm electrocatalyst for highly efficient and selective reduction of carbon dioxide

Metal–organic frameworks (MOFs) are promising electrocatalysts for carbon dioxide reduction reaction (CO2RR) due to their designable crystalline structures, large surface area, and atomically dispersed active sites. However, the poor electric conductivity of MOFs, leading to the low utilization of large amounts of active sites, greatly inhibits their practical applications in electrocatalysis. Herein, a binder-free, MOF-based nanofilm electrocatalyst for highly efficient and selective CO2RR is achieved by well-grafting conductive polypyrrole (PPy) chains into surface-mounted MOF (ZIF-8) nanofilm electrocatalyst based on a combination of the layer-by-layer assembly MOF growth technique and the in-situ electrochemical polymerization method. Experimental and theoretical results confirm that the grafting of PPy not only significantly accelerates the electron transfer for high utilization of active sites but also optimizes the electronic structure of the electrocatalysts for high electrocatalytic activity. As a result, the optimized ZIF-8@PPy nanofilm electrocatalyst exhibits the excellent electrocatalytic CO2RR performance with a selectivity of 96% and a current density of up to 18 mA/cm2 at −1.1 V. The strategy in this work has also demonstrated the broad potential application to a variety of other electrochemical purposes.

Boosting Protein Encapsulation through Lewis-Acid-Mediated Metal-Organic Framework Mineralization: Toward Effective Intracellular Delivery.

Encapsulation of biomolecules using metal–organic frameworks (MOFs) to form stable biocomposites has been demonstrated to be a valuable strategy for their preservation and controlled release, which has been however restricted to specific electrostatic surface conditions. We present a Lewis-acid-mediated general in situ strategy that promotes the spontaneous MOF growth on a broad variety of proteins, for the first time, regardless of their surface nature. We demonstrate that MOFs based on cations exhibiting considerable inherent acidity such as MIL-100(Fe) enable efficient biomolecule encapsulation, including elusive alkaline proteins previously inaccessible by the well-developed in situ azolate-based MOF encapsulation. Specifically, we prove the MIL-100(Fe) scaffold for the encapsulation of a group of proteins exhibiting very different isoelectric points (5 < pI < 11), allowing triggered release under biocompatible conditions and retaining their activity after exposure to denaturing environments. Finally, we demonstrate the potential of the myoglobin-carrying biocomposite to facilitate the delivery of O2 into hypoxic human lung carcinoma A549 cells, overcoming hypoxia-associated chemoresistance.

Creating hierarchically porous banana paper-metal organic framework (MOF) composites with multifunctionality

We report a robust approach to integrate metal-organic frameworks (MOF) via vapor phase synthesis on a cost-effective and mechanically durable fibrous banana paper (BP) substrate developed from lignocellulosic biomass. The unique hollow fibrous structure of BP combined with the methodology used produces MOF-fiber composites with uniform MOF distribution and enhanced functionalities, with minimal use of organic solvents. The BP-MOF composites demonstrate a high surface area of 552 m2/g and uniform surface growth of MOF on them. Mechanical strength and bending flexibility of the substrate is well retained after the MOF growth, while the hollow tubular nature and hierarchical porosity of the BP facilitate gas diffusion. The BP-MOF composites demonstrate strong antibacterial activity with 99.2% of E.coli destroyed within the first hour of incubation. Preliminary studies with smartphone-based volatile organic compound (VOC) sensor show enhanced 1-octen-3-ol vapor absorption on BP-MOF, indicating its potential for VOC capture and sensing. We believe that the sustainable nature and flexibility of the lignocellulosic BP substrate taken together with uniform growth of MOF on the hierarchically porous BP impart impressive attributes to these composites, which can be explored in diverse applications.

Simultaneous electrical and defect engineering of nickel iron metal-organic-framework via co-doping of metalloid and non-metal elements for a highly efficient oxygen evolution reaction

Metal-organic frameworks (MOFs) are promising electrocatalysts for oxygen evolution reaction (OER) due to their large amounts of active sites reacting with water molecules and desired adsorption/desorption characteristics with oxygen intermediate. However, the intrinsically low electrical conductivity of MOFs hinders their commercialization for the highly efficient OER catalyst. Here, we report 2D morphological NiFe MOF electrocatalyst co-doped with metalloid and non-metal elements for the enhanced OER performances. Te metalloid incorporation on MOFs facilitates electron transfer from transition metals of MOFs to embedded metalloids, which improves OER kinetics enabling favorable adsorption of oxygen intermediate on the surface of the electrocatalyst. Incorporated halogen Cl element could effectively induce defects on MOF as leach out from the surface of electrocatalyst during OER, allowing more active sites exposed to reactants. With the synergistic effect of metalloid (Te) and halogen (Cl) doping on NiFe MOF, the Te and Cl co-doped NiFe MOF growth on Ni foam (NF) present an excellent OER property requiring low overpotential for 224 mV at 30 mA cm−2 in alkaline condition and long-term stability over 120 h.

Autocatalysis and Oriented Attachment Direct the Synthesis of a Metal-Organic Framework.

Synthesis of porous, covalent crystals such as zeolites and metal–organic frameworks (MOFs) cannot be described adequately using existing crystallization theories. Even with the development of state-of-the-art experimental and computational tools, the identification of primary mechanisms of nucleation and growth of MOFs remains elusive. Here, using time-resolved in-situ X-ray scattering coupled with a six-parameter microkinetic model consisting of ∼1 billion reactions and up to ∼100 000 metal nodes, we identify autocatalysis and oriented attachment as previously unrecognized mechanisms of nucleation and growth of the MOF UiO-66. The secondary building unit (SBU) formation follows an autocatalytic initiation reaction driven by a self-templating mechanism. The induction time of MOF nucleation is determined by the relative rate of SBU attachment (chain extension) and the initiation reaction, whereas the MOF growth is primarily driven by the oriented attachment of reactive MOF crystals. The average size and polydispersity of MOFs are controlled by surface stabilization. Finally, the microkinetic model developed here is generalizable to different MOFs and other multicomponent systems.

Lattice-Guided Construction and Harvest of a Naturally Nonpreferred Metal-Organic Framework.

Constructing metal-organic frameworks (MOFs) to have a desired structure from the given components is critical to achieve ideal MOFs with optimal properties. However, thermodynamics and/or kinetics typically impose a restriction on MOF structures. Here, we report the MOF farming concept to produce a naturally nonpreferred structure from the given components. The HKUST-1 template offers ideal places for the efficient seeding and epitaxial growth of Ga-MIL-88B that is a naturally nonpreferred structure however intentionally produced instead of the preferred Ga-MIL-68. The MOF growth on the differently shaped HKUST-1 templates (octahedral, cuboctahedral, and cubic), containing different exposed lattices, proves that a hexagonal lattice with an exposed {111} plane of HKUST-1 selectively directs the perpendicular growth of Ga-MIL-88B, owing to the lattice matching with the {001} plane of Ga-MIL-88B. The grown Ga-MIL-88B is isolated in a pure form, and the refreshed template is reused to grow additional Ga-MIL-88B.