Bulk Metal-organic Frameworks Research Articles

Metal‐organic Frameworks in Semiconductor Devices

AbstractMetal‐organic frameworks (MOFs) are a specific class of hybrid, crystalline, nano‐porous materials made of metal‐ion‐based ‘nodes’ and organic linkers. Most of the studies on MOFs largely focused on porosity, chemical and structural diversity, gas sorption, sensing, drug delivery, catalysis, and separation applications. In contrast, much less reports paid attention to understanding and tuning the electrical properties of MOFs. Poor electrical conductivity of MOFs (~10−7–10−10 S cm−1), reported in earlier studies, impeded their applications in electronics, optoelectronics, and renewable energy storage. To overcome this drawback, the MOF community has adopted several intriguing strategies for electronic applications. The present review focuses on creatively designed bulk MOFs and surface‐anchored MOFs (SURMOFs) with different metal nodes (from transition metals to lanthanides), ligand functionalities, and doping entities, allowing tuning and enhancement of electrical conductivity. Diverse platforms for MOFs‐based electronic device fabrications, conductivity measurements, and underlying charge transport mechanisms are also addressed. Overall, the review highlights the pros and cons of MOFs‐based electronics (MOFtronics), followed by an analysis of the future directions of research, including optimization of the MOF compositions, heterostructures, electrical contacts, device stacking, and further relevant options which can be of interest for MOF researchers and result in improved devices performance.

Catalysis with Two-Dimensional Metal-Organic Frameworks: Synthesis, Characterization, and Modulation.

The demand for the exploration of highly active and durable electro/photocatalysts for renewable energy conversion has experienced a significant surge in recent years. Metal-organic frameworks (MOFs), by virtue of their high porosity, large surface area, and modifiable metal centers and ligands, have gained tremendous attention and demonstrated promising prospects in electro/photocatalytic energy conversion. However, the small pore sizes and limited active sites of 3D bulk MOFs hinder their wide applications. Developing 2D MOFs with tailored thickness and large aspect ratio has emerged as an effective approach to meet these challenges, offering a high density of exposed active sites, better mechanical stability, better assembly flexibility, and shorter charge and photoexcited state transfer distances compared to 3D bulk MOFs. In this review, synthesis methods for the most up-to-date 2D MOFs are first overviewed, highlighting their respective advantages and disadvantages. Subsequently, a systematic analysis is conducted on the identification and electronic structure modulation of catalytic active sites in 2D MOFs and their applications in renewable energy conversion, including electrocatalysis and photocatalysis (electro/photocatalysis). Lastly, the current challenges and future development of 2D MOFs toward highly efficient and practical electro/photocatalysis are proposed.

Vapor-phase methods for synthesizing metal-organic framework thin films

<p>Due to their unique structures and exceptional physical and chemical properties, metal-organic framework (MOF) materials have garnered extensive attention in various fields, including catalysis, separations, sensing, and optics. Compared with powders or bulk MOF materials, MOF thin films exhibit large vertical and horizontal dimensions, higher specific surface areas, and abundant active sites and undergo facile combination with other functional centers for adsorption/separation, catalysis, and photoelectronic device applications. Among the methods used in preparing MOF thin films, the vapor phase approach enables more effective growth of MOF films with controllable thicknesses, uniformity, and compatibility; thus, it has attracted significant interest. This extensive review presents four vapor-phase approaches for preparing MOF thin films: the steam-assisted conversion method, vapor-phase transformations of metal oxide templates, vapor-phase linker exchange, and the atomic layer deposition/molecular layer deposition method. We summarize the advantages and disadvantages of these different vapor-phase-based methods for thin-film preparation, aiming to promote their use in precise and controllable surface syntheses.</p>

One-pot growth of metal-organic frameworks on polymers for catalytic performance enhancement in the CO2 cycloaddition to epoxides

A novel approach is reported to prepare 3D-printed polymers that incorporate metal-organic frameworks (MOFs) through a one-pot growth process, involving covalent grafting and growth onto 3D polymeric surfaces. The resulting hybrid materials were subjected to comprehensive characterization using techniques such as SEM, XRD, FTIR, Raman, and XPS. The findings demonstrated an excellent dispersion of the inorganic units on the polymer matrix while preserving their metal-organic structure. The hybrid materials exhibited the presence of Lewis acid and basic groups within the MOF. The catalytic performance of these hybrid materials was evaluated in the mild cycloaddition reaction of carbon dioxide (CO2) to epoxides. Notably, the polymers incorporating UiO-67 MOFs displayed remarkable activity, even at low CO2 pressures and in the absence of auxiliary co-catalysts or additives. The catalytic activity of these hybrid materials exhibited a significant improvement, up to two orders of magnitude higher than analogous bulk MOFs. This observation highlights the superior performance of the 3D-printed polymer/MOF hybrids in this catalytic transformation.

Ultrathin Metal-Organic Framework Nanosheets for Selective Photocatalytic C2 H2 Semihydrogenation in Aqueous Solution.

The selective semihydrogenation of C2 H2 to C2 H4 in crude C2 H4 (with ~1 vol % C2 H2 contamination) is a crucial process in the manufacture of polyethylene. Comparing to conventional thermalcatalytic route with Pd as catalyst under high temperature with H2 as hydrogen source, photocatalytic C2 H2 reduction reaction with H2 O as hydrogen source can achieve high selectivity under milder conditions, but has rarely been reported. Here, we present a kind of ultrathin metal-organic framework nanosheets (Cu-Co-MNSs) that demonstrate excellent catalytic activities in the semihydrogenation of C2 H2 . Employing Ru(bpy)3 2+ as the photosensitizer, this catalyst attains a noteworthy turnover number (TON) of 2124 for C2 H4 , coupled with an impressive selectivity of 99.5 % after 12 h visible light irradiation. This performance is comparable to molecular catalysts and notably surpasses the efficiency of bulk metal-organic framework materials. Furthermore, Cu-Co-MNSs achieve a 99.95 % conversion of C2 H2 under industrial relevant conditions (1.10 % C2 H2 in C2 H4 ) with 90.3 % selectivity for C2 H4 over C2 H6 , demonstrating a great potential for polymer-grade C2 H4 production.

New trends in metal-organic framework membranes for biomedical applications

Metal-organic framework (MOF) membranes are constructed with various organic ligands and metal ions or clusters. Due to their high porosity, tunable chemical composition, and potential for subsequent synthetic modifications, they are widely used in biomedicine, especially in biosensing, bioimaging, and drug delivery. Although MOF membranes have found many applications in various fields, including biomedicine, there are still fundamental gaps in studies on various aspects of such membranes. This lack of interest in the study of MOF membranes is because most researchers prefer to use bulk or powder MOFs because of the problematic aspects of fabricating perfect and defect-free MOF-based membranes. Therefore, in this review, applications of MOF membranes in nanomedicine are presented, focusing on their functions ranging from drug delivery, therapeutic agents for various diseases, and imaging contrast agents. Applications of MOF membrane derivatives in nanomedicine will also be presented. Finally, the challenges and prospects for MOF membranes in future applications will be highlighted.

Pyridine-Regulated Lamellar Nickel-Based Metal-Organic Framework (Ni-MOF) for Nonenzymatic Electrochemical Glucose Sensor.

2D metal-organic frameworks (MOFs) are considered as promising electrochemical sensing materials and have attracted a lot of attention in recent years. Compared with bulk MOFs, the construction of 2D MOFs can increase the exposure of active sites by obtaining a larger surface area ratio. Herein, a facile one-pot hydrothermal synthesis of pyridine-regulated lamellar Ni-MOFs with ultrathin and well-defined 2D morphology is described. Compared with the bulk structure, the 2D lamellar Ni-MOF has higher surface area and active site density, showing better electrochemical glucose sensing performance. The 2D lamellar Ni-MOF exhibits a fast amperometric response of less than 3 s and a high sensitivity of 907.54µA mm-1 cm-2 toward glucose with a wide linear range of 0.5-2665.5 µm. Furthermore, the 2D lamellar Ni-MOF also possesses excellent stability and reproducibility, and can be used to detect glucose with high accuracy and reliability in different environments.

Assembling Triphenylene-Based Metal-Organic Framework Nanosheets at the Air/Liquid Interface: Modification by Tuning the Spread Solution Concentration.

Metal-organic frameworks (MOFs)─crystalline coordination polymers─with unique characteristics such as structural designability accompanied by tunable electronic properties and intrinsic uniform nanopores have become the platform for applications in diverse scientific areas ranging from nanotechnology to energy/environmental sciences. To utilize the superior features of MOF in potential applications, the fabrication and integration of thin films are of importance and have been actively sought. Especially, downsized MOFs into nanosheets can act as ultimately thin functional components in nanodevices and potentially display unique chemical/physical properties rarely seen in bulk MOFs. Assembling nanosheets by aligning amphiphilic molecules at the air/liquid interface has been known as the Langmuir technique. By utilizing the air/liquid interface as a reaction field between metal ions and organic ligands, MOFs are readily formed into the nanosheet state. The expected features in MOF nanosheets including electrical conduction largely depend on the nanosheet characteristics such as lateral size, thickness, morphology, crystallinity, and orientation. However, their control has not been achieved as yet. Here, we demonstrate how changing the concentration of a ligand spread solution can modify the assembly of MOF nanosheets, composed of 2,3,6,7,10,11-hexaiminotriphenylene (HITP) and Ni2+ ions (HITP-Ni-NS), at the air/liquid interface. A systematic increase in the concentration of the ligand spread solution leads to the enlargement of both the lateral size and the thickness of the nanosheets while retaining their perfect alignment and preferred orientation. On the other hand, at much higher concentrations, we find that unreacted ligand molecules are included in HITP-Ni-NS, introducing disorder in HITP-Ni-NS. These findings can develop further sophisticated control of MOF nanosheet features, accelerating fundamental and applied studies on MOFs.

Metal-Organic Framework-Based Colloidal Particle Synthesis, Assembly, and Application.

Metal-organic frameworks (MOFs) assembled from metal nodes and organic ligands have received significant attention over the past two decades for their fascinating porous properties and broad applications. Colloidal MOFs (CMOFs) not only inherit the intrinsic properties of MOFs, but can also serve as building blocks for self-assembly to make functional materials. Compared to bulk MOFs, the colloidal size of CMOFs facilitates further manipulation of CMOF particles in a single or collective state in a liquid medium. The resulting crystalline order obtained by self-assembly in position and orientation can effectively improve performance. In this review, we summarize the latest developments of CMOFs in synthesis strategies, self-assembly methods, and related applications. Finally, we discuss future challenges and opportunities of CMOFs in synthesis and assembly, by which we hope that CMOFs can be further developed into new areas for a wider range of applications.

Hierarchical copper-based metal-organic frameworks nanosheet assemblies for electrochemical ascorbic acid sensing

Noninvasive human health monitoring requires the development of efficient electrochemical sensors for the quantitative analysis of infinitesimal biomolecules. In this work, we reported a novel hierarchical nanosheet assemblies (HSA) of copper-based metal-organic frameworks (MOFs) as an electrochemical sensor for ascorbic acid (AA) detection. Copper 1,4-benzenedicarboxylate (CuBDC) HSA was constructed by three steps of in situ growth on stone paper, including hydrolysis, anion exchange, and heteroepitaxy growth. The monodispersed two-dimensional MOFs nanosheet units were aligned in an orderly manner and arranged into three-dimensional hierarchical assemblies. The CuBDC HSA-based AA sensor displayed a high sensitivity of 396.8 μA mM-1 cm-2 and a low detection limit of 0.1 μM. Excellent selectivity, stability and reproducibility were also obtained. Benefiting from the advantages of ultrathin nanosheets and nature-inspired hierarchy, this unique architecture facilitated reactant dispersion and maximized the accessible active sites and charge-transport capability and thus had superior catalytic ability for the electro-oxidation of ascorbic acid compared to bulk MOFs. Moreover, the CuBDC HSA sensor performed AA level detection in juice samples with acceptable accuracy and verified the feasibility for sweat AA sensing. This novel MOFs architecture holds great potential as an electrochemical sensor to detect AA for noninvasive human health monitoring in the future.

Nanoporous Metal-Organic Framework Thin Films Prepared Directly from Gaseous Precursors by Atomic and Molecular Layer Deposition: Implications for Microelectronics.

Atomic/molecular layer deposition (ALD/MLD) allows for the direct gas-phase synthesis of crystalline metal-organic framework (MOF) thin films. Here, we show for the first time using krypton and methanol physisorption measurements that ALD/MLD-fabricated copper 1,4-benzenedicarboxylate (Cu-BDC) ultrathin films possess accessible porosity matching that of the corresponding bulk MOF.

Fabrication and Characterization of Nanoscale Metal-Organic Frameworks (MOFs) for Gas Storage and Separation

In recent years, Metal-Organic Frameworks (MOFs) have emerged as a promising class of materials for gas storage and separation applications due to their high surface area, tunable pore size, and chemical functionality. In this study, we report the successful fabrication and characterization of nanoscale MOFs for enhanced gas storage and separation performance. We synthesized a series of MOFs with varying metal nodes and organic linkers, and systematically investigated their structural, thermal, and chemical stability. Advanced characterization techniques, including X-ray diffraction, scanning electron microscopy, and gas adsorption isotherms, were employed to elucidate the structural and morphological features of the synthesized MOFs. The gas storage capacities of the MOFs were evaluated for hydrogen, methane, and carbon dioxide, revealing a significant enhancement in storage capacity compared to bulk MOFs. Furthermore, we investigated the gas separation performance of the MOFs for CO2/CH4 and CO2/N2 mixtures, demonstrating high selectivity and separation efficiency. The results of this study provide valuable insights into the design and fabrication of nanoscale MOFs for gas storage and separation applications, and pave the way for the development of next-generation materials for clean energy and environmental applications.

Cu-THQ-EFG Composite for Highly Selective Electrochemical CO2 Reduction to Formate at Low Overpotentials

Metal organic framework (MOFs) are promising materials for electrocatalysis. However, the active sites of bulk MOFs crystal normally cannot be fully utilized because of the slow reagent penetration of pores and blockage of active sites. Herein, we report a facile way to deposit copper-benzoquinoid (Cu-THQ) on the edge-functionalized graphene (EFG) which prevented material's aggregation. EFG used as a substrate provides higher electrical conductivity and stability in water than previously utilized graphene oxide (GO). Besides, the plate-like morphology of EFG proved to be more beneficial to support the MOF, because of the functional groups on its edge regions and much lower resistance compared to the sheet GO. Therefore, EFG can boost the resultant material's catalytic activity for CO2 electroreduction (CO2RR). Furthermore, Cu-THQ exhibits high selectivity for formate formation in CO2RR. Representing as the only CO2 reduced liquid product, formate can be separated from gaseous products and further extracted from the electrolyte for practical use. The electrocatalytic results of Cu-THQ-EFG indicate the composite exhibits a higher current density of -3 mA/cm2 and faradaic efficiency of -0.25 V vs. RHE, corresponding to 50 mV of overpotential. Moreover, it features a less negative on-set potential of -0.22 V vs. RHE, which is close to the equilibrium potential of CO2RR (-0.2 V vs. RHE) and is 0.16 V more positive than the on-set potential of Cu-THQ-GO (-0.38 V vs. RHE).

Deconvolution of metal apportionment in bulk metal-organic frameworks.

We report a general route to decipher the apportionment of metal ions in bulk metal-organic frameworks (MOFs) by solid-state nuclear magnetic resonance spectroscopy. We demonstrate this route in Mg1-xNix-MOF-74, where we uncover all eight possible atomic-scale Mg/Ni arrangements through identification and quantification of the distinct chemical environments of 13C-labeled carboxylates as a function of the Ni content. Here, we use magnetic susceptibility, bond pathway, and density functional theory calculations to identify local metal bonding configurations. The results refute the notion of random apportionment from solution synthesis; rather, we reveal that only two of eight Mg/Ni arrangements are preferred in the Ni-incorporated MOFs. These preferred structural arrangements manifest themselves in macroscopic adsorption phenomena as illustrated by CO/CO2 breakthrough curves. We envision that this nondestructive methodology can be further applied to analyze bulk assembly of other mixed-metal MOFs, greatly extending the knowledge on structure-property relationships of MOFs and their derived materials.

H2O2 activation by two-dimensional metal-organic frameworks with different metal nodes for micropollutants degradation: Metal dependence of boosting reactive oxygen species generation

The existence of organic micropollutants (OPMs) in water poses a considerable threat to the environment. A centralized approach towards pollutants abatement has dominated over the recent decades wherein heterogeneous Fenton-like based advanced oxidation processes can be a promising technology. The application of engineered nanomaterials offers more opportunities to enhance their catalyst properties. This study synthesizes a series of ultrathin two-dimensional (2D) Metal-organic frameworks (MOFs) nanosheets with tunable metal clusters. The formation of reactive oxygen species (•OH and 1O2) can be significantly boosted via transferring the adsorbed H2O2 onto the solid-liquid interface by systematically tuning the metal species. The Co-MOF nanosheets exhibited an ultrafast degradation kinetic for BPA with a rate of 2.23 min−1 (4.98 times higher than that of the bulk MOF) and TOF (turnover frequency) value of 9.99 min−1, which are observably greater than that of the existing materials reported to date. Density functional theory simulation and experimental results unravel the mechanism for ROS formation, which is strongly metal-depend. We further loaded the powder onto a flow-through poly (vinylidene fluoride) (PVDF) microfiltration membrane and observed that the representative OPMs could be rapidly degraded, indicating promising properties for practical application.

Charge. transport, conductivity and Seebeck coefficient in pristine and TCNQ loaded preferentially grown metal-organic framework films

This investigation on metal-organic framework (MOF) HUKUST-1 films focuses on comparing the undoped pristine state and with the case of doping by TCNQ infiltration of the MOF pore structure. We have determined the temperature dependent charge transport and p-type conductivity for HKUST-1 films. Furthermore, the electrical conductivity and the current–voltage characteristics have been characterized in detail. Because the most common forms of MOFs, bulk MOF powders, do not lend themselves easily to electrical characterization investigations, here in this study the electrical measurements were performed on dense, compact surface-anchored metal-organic framework (SURMOF) films. These monolithic, well-defined, and (001) preferentially oriented MOF thin films are grown using quasi-liquid phase epitaxy (LPE) on specially functionalized silicon or borosilicate glass substrates. In addition to the pristine SURMOF films also the effect of loading these porous thin films with TCNQ has been investigated. Positive charge carrier conduction and a strong anisotropy in electrical conduction was observed for highly oriented SURMOF films and corroborated with Seebeck coefficient measurements. Van der Pauw four-point Hall sample measurements provide important insight into the electrical behavior of such porous and hybrid organic–inorganic crystalline materials, which renders them attractive for potential use in microelectronic and optoelectronic devices and thermoelectric applications.

Advances in Nano-Sized Metal-Organic Frameworks and Biomedical Applications: A Review

Metal-organic frameworks (MOFs) have attracted much attention since their discovery and have potential applications in many fields, including gas storage, separation, catalysis, and thermal energy conversion, due to their unique high porosity structure, tunable pore size, and functionalizability. Nano-sized MOFs (NMOFs) possessed both the properties of conventional bulk MOFs and additional physical/chemical properties because of their nanometer size, and thus can exhibit even better performance than related conventional bulk MOFs. In this paper, we introduced the development of NMOFs and presented several classical NMOFs structures and their applications. It also focused on the preparation methods and applications of some important NMOFs in recent years, and provided an outlook on the applications of NMOFs in novel material fields and their development perspective.

Iron-containing metal-organic framework thin film as a drug delivery system

Selective bulk metal-organic frameworks (MOFs) have exhibited great potential in biomedical applications. However, topical treatments and drug elution coatings will require uniform films as drug delivery systems. This work studies the use of surface supportive MOF thin films for drug loading and releasing. More specifically, we focus on an iron-containing MOF, MIL-88B(Fe), on a COOH-terminated self-assembled monolayer (SAM) modified Au surface for encapsulating ibuprofen as a model drug. A combined experimental and computational approach was employed to study the fabrication of MIL-88B(Fe) film on functionalized Au surfaces. We used several surface characterization techniques, including infrared spectroscopy and scanning electron microscopy, to confirm the chemical composition and morphological changes of the surface after each modification step. The resulting MIL-88B(Fe) thin film was found capable of loading 8.7 wt% of ibuprofen using quartz crystal microbalance analysis. Moreover, we applied cluster simulations to study the binding mechanisms of MIL-88B(Fe) and its interactions with ibuprofen based on the density functional theory (DFT). The unsaturated Fe site was confirmed kinetically more favorable to bind to the COOH-end group on the SAM. Hydrogen bonding and π-CH interactions between ibuprofen and MIL-88B(Fe) promote ibuprofen being retained inside of the cages of MIL-88B(Fe).

Metalloporphyrin-anchored 2D MOF nanosheets as highly accessible heterogeneous photocatalysts towards cytocompatible living radical polymerization

Two-dimensional (2D) metal–organic framework (MOF) nanosheets have emerged as a promising hybrid material due to the highly exposed active sites and high aspect ratio originating from their large lateral dimension and ultrathin thickness. Herein, PCN-134(Zn)-2D (PCN = porous coordination network) nanosheets were investigated as a versatile and effective platform supporting metalloporphyrins to boost their photocatalytic performance for single oxygen generation and living radical polymerization. This method enabled the radical polymerizations of various monomers using low catalyst dosages under a wide range of wavelengths, affording well-defined polymers with high monomer conversions, low polydispersities and tunable functionalities. Compared to three-dimensional (3D) bulk MOF crystals, PCN-134(Zn)-2D exhibited fast polymerization kinetics due to the larger surface area and more accessible catalytic sites within the 2D planar architecture. Most significantly, the polymerization kinetics could be orthogonally regulated by solution pH and light stimuli. Exploiting the oxygen tolerance and fast kinetics, we demonstrated PET-RAFT polymerization at high monomer dilutions and in a human cell culture medium. Illustrations of chain extension and catalyst-recycling test further substantiated the photocatalytic performance of these 2D MOF catalysts outperforming most reported metalloporphyrin-based heterogeneous catalysts towards living radical polymerization.

Acetate promotes the formation of NiRu/NiO towards efficient hydrogen evolution.

The introduction of acetate in the precursor of metal-organic frameworks (MOFs) turns the final product from MOFs to NiRu/Ni(OH)2. Followed by annealing treatment, the obtained NiRu/NiO catalyst exhibits high hydrogen evolution reaction (HER) activity with a low overpotential (18 mV at 10 mA cm-2), and a small Tafel slope of 43.3 mV dec-1 in alkaline electrolyte.