Layered Metal-organic Frameworks Research Articles

Research progress on the substrate for metal–organic framework (MOF) membrane growth for separation

During the last decade, metal–organic frameworks (MOFs) have been applied in various fields due to their unique chemical and functional advantages. One of the widespread research hotspots is MOF-based membranes for separations, specifically continuous defect-free MOF membranes, which are usually grown on porous substrates. The substrate not only serves as the MOF layer support but also has a great influence on the membrane fabrication process and the final separation performance of the resultant membrane. In this review, we mainly introduce the progress focused on the substrates for MOF membranes fabrication. The substrate modifications and seeding methods aimed at synthesizing high-quality MOF membranes are also summarized systematically.

Layered 2D MOF nanosheets grown on CNTs substrates for efficient nitrite sensing

In this work, we report a ligand-deficient layered cerium-based metal-organic framework (MOF) nanosheets grown on carbon nanotube (CNT) substrates and its application in electrochemical sensors. The construction of layered MOF nanosheet materials is based on CNTs as the backbone and relies on the low ligand-metal ratios which is controlled by the loaded organic ligands on the surface of CNTs, providing a new approach for the application of 2D MOFs in the field of electrochemical sensing. The obtained 2D MOFs possess unique layered structure and hierarchical connectivity channels, providing highly efficient and stable pathways for electron, ion, and mass transport. The synthesized layered 2D CNTs@Ce-MOF nanosheet hybrid material uses Ce as the center ion and electrocatalytic active material for nitrite sensing. This material exhibits excellent nitrite detection performance within two wider linear ranges of 0.65–3.25 μM and 3.25–7000 μM with the sensitivity of 87.65 ± 0.6 μA·μM−1·cm2 and 0.35 ± 0.03 μA·μM−1·cm−2, respectively. The detection limit is estimated to be 0.12 μM according to signal to noise ratio (S/N) = 3. As the result, the prepared sensors possess advantages in aspects of reproducibility, stability, selectivity and responsiveness in comparison to the reported ones.

Rational Design and Assembly of Two-Dimensional Layered Metal–Organic Frameworks: Structure, Morphology, Fluorescence Regulation, and High Iodine Adsorption

Two-dimensional (2D) layered metal–organic frameworks (LMOFs), an emerging type of 2D materials, have aroused significant attention recently. Although a great number of LMOFs with diverse topologies have been reported, their predictable preparation remains challenging. Inspired by the transformation of three-dimensional pillared-layer MOFs (PLMOFs) to 2D layers via solvent-assisted link exchanging, we developed herein a novel de novo synthesis strategy, i.e., in situ capping, for the rational fabrication of 2D LMOFs. During PLMOF construction, the pillars are in situ substituted by terminal ligands to seal both sides of the instantaneously generated layers, forming the targeted 2D LMOFs. Employing such a strategy, 2D LMOFs {[Zn(hsb-2)(benzoate)2]·0.5H2O}n (HSB-W11), [Zn(hsb-2)(2-benzoylbenzoate)2]n (HSB-W12), [Zn(hsb-2)(2-acetylbenzoate)2]n (HSB-W13), and {[Zn(hsb-2)(2-naphthoate)2]·DMF·H2O}n (HSB-W14) were obtained predictably by exchanging the terephthalate pillar (bdc) of HSB-W1 (a 3D PLMOF composed of bdc and 1,2-bis(4′-pyridylmethylamino)-ethane) with the capping ligand benzoate or its analogues. The strategy is also valid for other PLMOF systems with bipyridine-type ligands as pillars, X-pcu-1-Zn, for example. Furthermore, the undersized materials of HSB-W11–W14 have been prepared by the instant in situ exfoliation method. The structure, morphology, and fluorescence were tuned by changing the anchoring terminal ligands. In addition, LMOFs HSB-W11–W14 were utilized as I2 adsorbents; remarkably, HSB-W13 displayed a record-high volatile iodine uptake at room temperature. The in situ capping strategy has many merits including high designability and efficiency, facile green synthesis, and atom economy, which may be widely adapted to fabricate diverse 2D LMOFs.

Erasable Photopatterning of Stilbene-Based Metal-Organic Framework Films.

The development of photosensitive materials for erasable photopatterning is of significant interest in anti-counterfeiting and information storage applications. Herein two kinds of stilbene-based metal-organic framework (MOF) films with layer by layer method for studying photopatterning is reported. The resulting 2D Zn2 (sdc)2 MOF film (sdc = 4,4'-stilbenedicarboxylate) exhibits excellent photosensitive features with a very short photoconversion time (<35s) while the 3D MOF Zn4 O(sdc)6 film does not have the property due to the fact that only parallel and short distance arrangement of olefin groups in the adjacent MOF layers can trigger [2+2] photocycloaddition. Furthermore, the Zn2 (sdc)2 film indicates obvious reversible fluorescent photoswitch behavior between yellow and blue fluorescence emission, which can achieve high-efficient, erasable photopatterning with various sizes (ca. 20 microns to decimeter). This study not only develops a new kind of photosensitive crystalline network film but also provides erasable photopatterning from macroscopic to microscopic in optical applications.

Rewritable Paper Based on Layered Metal–Organic Frameworks with NIR‐Triggered Reversible Color Switching

AbstractPhotoreversible color‐switching materials, which can reversibly change color in response to external light stimuli, have attracted increasing attention for their applications in time‐sensitive information storage and optical data storage fields. But most of the related materials are dyes or redox compounds with ultraviolet as the light source, dramatically limiting the cycling stability during discoloration processes. To address this problem, a near‐infrared (NIR)‐responsive rewritable paper via doping layered Co‐metal–organic frameworks (MOFs) into the stable polyvinylidene fluoride matrix is reported for the first time. Layered Co‐MOF shows a rapid color‐switching characteristic between orange and black blue upon NIR illumination on/off because of the interlayer spacing changes. Benefiting from the soft network structures of the matrix, Co‐MOF can be homogeneously distributed to deliver an outstanding reversibility performance, including rapid response, coloration in a short period, and decoloration within about 3 min in ambient air. The fabrication of new photoreversible color switching system holds great potential in communication security, which offers a viable pathway to achieve ink‐free photoreversible printing.

Triple Threshold Transitions and Strong Polariton Interaction in 2D Layered Metal-Organic Framework Microplates.

Room-temperature interaction between light-matter hybrid particles such as exciton-polaritons under extremely low-pump plays a crucial role in future coherent quantum light sources. However, the practical and scalable realization of coherent quantum light sources operating under low-pump remains a challenge because of the insufficient polariton interaction strength. Here, at room temperature, a very large polariton interaction strength is demonstrated, g≈ 128 ± 21 µeV µm2 realized in a 2D nanolayered metal-organic framework (MOF). As a result, a polariton lasing at an extremelylow pump fluence of P1 ≈ 0.01 ± 0.0015 µJ cm-2 (first threshold) is observed. Interestingly, as pump fluence increases to P2 ≈ 0.031 ± 0.003 µJ cm-2 (second threshold), a spontaneous transition to a polariton breakdown region occurs, whichhas notbeen reported before. Finally, an ordinary photon lasing occurs at P3 ≈ 0.11 ± 0.077 µJ cm-2 (third threshold), or above. These experiments and the theoretical model reveal new insights into the transition mechanisms characterized by three distinct optical regions. This work introduces MOF as a new type of quantum material, with naturally formed polariton cavities, thatis a cost-effective and scalable solution to build microscale coherent quantum light sources and polaritonic devices.

Role of Counterions in the Structural Stabilisation of Redox-Active Metal-Organic Frameworks.

The crystal structures of metal-organic frameworks (MOFs) are typically determined by the strong chemical bonds formed between the organic and inorganic building units. However, the latest generation of redox-active frameworks often rely on counterions in the pores to access specific charge states of the components. Here, we model the crystal structures of three layered MOFs based on the redox-active ligand 2,5-dihydroxybenzoquinone (dhbq): Ti2 (Cl2 dhbq)3 , V2 (Cl2 dhbq)3 and Fe2 (Cl2 dhbq)3 with implicit and explicit counterions. Our full-potential first-principles calculations indicate that while the reported hexagonal structure is readily obtained for Ti and V, the Fe framework is stabilised only by the presence of explicit counterions. For high counterion concentrations, we observe the formation of an electride-like pocket in the pore center. An outlook is provided on the implications of solvent and counterion control for engineering the structures and properties of porous solids.

In Silico High-Throughput Design and Prediction of Structural and Electronic Properties of Low-Dimensional Metal-Organic Frameworks.

The advent of π-stacked layered metal-organic frameworks (MOFs), which offer electrical conductivity on top of permanent porosity and high surface area, opened up new horizons for designing compact MOF-based devices such as battery electrodes, supercapacitors, and spintronics. Permutation of structural building blocks, including metal nodes and organic linkers, in these electrically conductive (EC) materials, results in new systems with unprecedented and unexplored physical and chemical properties. With the ultimate goal of providing a platform for accelerated material design and discovery, here we lay the foundations for the creation of the first comprehensive database of EC-MOFs with an experimentally guided approach. The first phase of this database, coined EC-MOF/Phase-I, is composed of 1,057 bulk and monolayer structures built by all possible combinations of experimentally reported organic linkers, functional groups, and metal nodes. A high-throughput screening (HTS) workflow is constructed to implement density functional theory calculations with periodic boundary conditions to optimize the structures and calculate some of their most relevant properties. Because research and development in the area of EC-MOFs has long been suffering from the lack of appropriate initial crystal structures, all of the geometries and property data have been made available for the use of the community through an online platform that was developed during the course of this work. This database provides comprehensive physical and chemical data of EC-MOFs as well as the convenience of selecting appropriate materials for specific applications, thus accelerating the design and discovery of EC-MOF-based compact devices.

Dual-Modal Apoptosis Assay Enabling Dynamic Visualization of ATP and Reactive Oxygen Species in Living Cells.

ATP and reactive oxygen species (ROS) are considered significant indicators of cell apoptosis. However, visualizing the interplay between apoptosis-related ATP and ROS is challenging. Herein, we developed a metal-organic framework (MOF)-based nanoprobe for an apoptosis assay using duplex imaging of cellular ATP and ROS. The nanoprobe was fabricated through controlled encapsulation of gold nanorods with a thin zirconium-based MOF layer, followed by modification of the ROS-responsive molecules 2-mercaptohydroquinone and 6-carboxyfluorescein-labeled ATP aptamer. The nanoprobe enables ATP and ROS visualization via fluorescence and surface-enhanced Raman spectroscopy, respectively, avoiding the mutual interference that often occurs in single-mode methods. Moreover, the dual-modal assay effectively showed dynamic imaging of ATP and ROS in cancer cells treated with various drugs, revealing their apoptosis-related pathways and interactions that differ from those under normal conditions. This study provides a method for studying the relationship between energy metabolism and redox homeostasis in cell apoptosis processes.

Conductive Metal-Organic Framework Microelectrodes Regulated by Conjugated Molecular Wires for Monitoring of Dopamine in the Mouse Brain.

Herein, we demonstrated a strategy to regulate the conductive metal-organic framework (MOF) surface, by the conjugated molecule wires for selective and sensitive determination of dopamine (DA) in the live brain. The MOFs were decorated at the carbon fiber electrode deposited by Au nanoleaves as the upper electric transducer to provide rich electrocatalytic sites for electron transfer of neurochemicals at the electrode surface, leading to greatly enhanced sensitivity for detection of neurochemicals. On the other hand, the conjugated molecular wire, 4-(thiophen-3-ylethynyl)-benzaldehyde (RP1), was synthesized and assembled as an underlying bridge to regulate the electrochemical processes at the MOF-based electrode, specifically decreasing the reaction Gibbs free energy of DA oxidation, thus selectively promoting the heterogeneous electron transfer of DA from the MOF layer to the electrode surface. Owing to the electrocatalytic activity for DA oxidation, the present microsensor exhibited high selectivity for real-time tracking of DA in a good linear relationship in the range of 0.004-0.4 μM with a detection limit of 1 nM. Eventually, this functionalized electrode was successfully applied for in vivo monitoring of DA in mouse brains with Parkinson's disease (PD) model. The results indicated that the levels of DA were obviously decreased in both acute and subacute PD models. Moreover, the level of DA strongly depended on the amount of uric acid (UA), a physiological antioxidant, which rose as the UA amount was lower than 200 mg kg-1 but was downregulated again after treatment by a higher amount of UA.

Fe(iii)-carboxythiolate layered metal–organic frameworks with interest as active materials for rechargeable alkali-ion batteries

A series of Fe(iii)-thiolate layered MOFs was prepared. These solids present a strong absorption in the visible range, a good chemical stability and an interesting electrochemical activity.

Novel DNA-based polysulfide sieves incorporated with MOF providing excellent 3D Li+ pathway for high-performance lithium-sulfur batteries

For enhancing the performance of lithium-sulfur batteries (LSBs), deoxyribonucleic acid (DNA) as a bio-macromolecular adsorbing agent was incorporated into metal–organic frameworks (MOFs) to fabricate a MOF/carbon nanotube (CNT)@DNA double interlayer (MCDDI). Simulation calculations show that the adsorption energy (Ea) increased in the order of CNT-Li2S8 (–0.051 eV) < DNA(=N)-Li2S8 (–1.095 eV) < DNA(–PO)-Li2S8 (–1.137 eV), confirming that DNA-functionalized conductive CNT (CNT@DNA) layer facing the cathode with abundant anchoring sites can block and inhibit the shuttle effect of lithium polysulfides. The MOF layer on the surface of the CNT@DNA layer provides 3D pathways to realize fast Li-ion transport and homogeneous Li deposition for inhibition of voltage polarization and dendritic Li growth. LSBs using the MCDDI exhibited a high specific capacity of 1126 mAh/g and stable cycling performance with a small capacity decay (851 mAh/g after 100 cycles) at 0.5C. A small polarization effect (ΔE = 0.33 V at 2C) is observed from the excellent rate performance. In addition, owing to the homogenous Li-ion fluxes, a high Li+ transference number (tLi+ = 0.62) and stable Li plating/stripping for a long cycle life (500 h, 1000 cycles) were achieved without Li dendrites.

Coupling tandem MOFs in metal-insulator-metal resonator advanced chemo-sieving sensing

Metal-insulator-metal (MIM) resonator allows concentrating light into deep-subwavelength volumes for filtering by accessing surface plasmon polariton mode, which is typically constructed by using inorganic materials and polymers as an insulator. Although MIM filters can manipulate light, dynamic color change upon environmental stimuli is still challenging. Here, we report a metal-organic frameworks (MOFs) based MIM resonator with tunable bandwidth that can realize visualized sensing of chemicals. Different bandwidths of the resonator show distinct color reflection that can be tailored by different types of MOFs and thickness of the MOFs layers. Chemical sensing on the MOFs-based MIM resonators shows breakthrough enhancement of sensitivity. Moreover, we configure tandem MOFs thin films in the MIM to form a metal-insulator-insulator-metal (MIIM) resonator for promoting selective sensing of chemicals. Also, molecular dynamics simulations demonstrated that the MIIM resonator achieved selective adsorption of xylenes in a mixture of xylene and methanol due to the chemo-sieving effect. The MIIM resonators show not only host-guest chemistry and sieving performance of tandem MOFs with high durability, but also anti-interference selective sensing of analyte in the mixture.

Fabrication of Multifunctional Electronic Textiles Using Oxidative Restructuring of Copper into a Cu-Based Metal-Organic Framework.

This paper describes a novel synthetic approach for the conversion of zero-valent copper metal into a conductive two-dimensional layered metal-organic framework (MOF) based on 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) to form Cu3(HHTP)2. This process enables patterning of Cu3(HHTP)2 onto a variety of flexible and porous woven (cotton, silk, nylon, nylon/cotton blend, and polyester) and non-woven (weighing paper and filter paper) substrates with microscale spatial resolution. The method produces conductive textiles with sheet resistances of 0.1-10.1 MΩ/cm2, depending on the substrate, and uniform conformal coatings of MOFs on textile swatches with strong interfacial contact capable of withstanding chemical and physical stresses, such as detergent washes and abrasion. These conductive textiles enable simultaneous detection and detoxification of nitric oxide and hydrogen sulfide, achieving part per million limits of detection in dry and humid conditions. The Cu3(HHTP)2 MOF also demonstrated filtration capabilities of H2S, with uptake capacity up to 4.6 mol/kgMOF. X-ray photoelectron spectroscopy and diffuse reflectance infrared spectroscopy show that the detection of NO and H2S with Cu3(HHTP)2 is accompanied by the transformation of these species to less toxic forms, such as nitrite and/or nitrate and copper sulfide and Sx species, respectively. These results pave the way for using conductive MOFs to construct extremely robust electronic textiles with multifunctional performance characteristics.

MOF-Derived Robust and Synergetic Acid Sites Inducing C-N Bond Disruption for Energy-Efficient CO2 Desorption.

Amine-based scrubbing technique is recognized as a promising method of capturing CO2 to alleviate climate change. However, the less stability and poor acidity of solid acid catalysts (SACs) limit their potential to further improve amine regeneration activity and reduce the energy penalty. To address these challenges, here, we introduce two-dimensional (2D) cobalt-nitrogen-doped carbon nanoflakes (Co-N-C NSs) driven by a layered metal-organic framework that work as SACs. The designed 2D Co-N-C SACs can exhibit promising stability, superhydrophilic surface, and acidity. Such 2D structure also contains well-confined Co-N4 Lewis acid sites and -OH Brønsted acid sites to have a synergetic effect on C-N bond disruption and significantly increase CO2 desorption rate by 281% and reduce the reaction temperatures to 88 °C, minimizing water evaporation by 20.3% and subsequent regeneration energy penalty by 71.7% compared to the noncatalysis.

Suppressing the Dark Current through Interfacial Modification Using Metal–Organic Framework Thin Film Grown with Layer-By-Layer Method

Dye-sensitized solar cells (DSSCs) are promising photovoltaic devices and research was done in enhancing their efficiency so that they could be the potential alternatives to the p-n junction devices. Metal–organic frameworks (MOF) with porphyrin linkers as the photosensitizer have demonstrated their potential in preventing the aggregation of the dye over the transparent electrode surface. We aim to achieve the suppression of dark current by modifying the interface between the electrode and the photosensitizing film so that the efficiency can be further enhanced. To achieve this, we utilized the layer-by-layer growth method aiming for the control of the very layer(s) in between the indium tin oxide(ITO) electrode and the MOF layers. A change in the dark current produced by ITO/Insulation-layer/MOF system can be observed.

Dual-conductive metal-organic framework@MXene heterogeneity stabilizes lithium-ion storage

Although a few pristine metal-organic frameworks (MOFs) of graphene analogue topology exhibit high intrinsic electrical conductivity, their use in lithium-ion batteries (LIBs) is still hampered by unfavorable Li+ adsorption energy (ΔEa). In this paper, an electroconductive ferrocene-based MOF@MXene heterostructure is built to provide stable anodes for Li+ storage. Charge density difference and planar average potential charge density show substantial redistribution of charges at the interfaces, transferring from MXene to MOF layers. Moreover, density functional theory (DFT) calculations reveal that the interaction between MXene and MOF significantly increases the ΔEa. As a result, the heterostructure anode exhibits high capacities and outstanding cycling stability with a capacity retention of 80% after 5000 cycles at 5 A g−1, outperforming mono-component MXene and MOF. Furthermore, the heterostructure anode is built into a full cell with a commercial NCM 532 cathode, delivering a high energy density of 611 Wh kg−1 and power density of 7600 W kg−1. The developed conductive MOF@MXene heterogeneity for improved LIB offers valuable insights into the design of advanced electrode materials for energy storage.

Engineered subnanochannel ionic diode membranes based on metal–organic frameworks for boosted lithium ion transport and osmotic energy conversion in organic solution

Harvesting Gibbs energy from a salinity gradient of waste organic solutions can not only alleviate the environmental pollution but also provide new energy resources to mitigate the energy shortage. However, the membranes with high ion selectivity, excellent ionic flux, and high-performance power output in organic solutions remain considerably unexplored. Here, we report on the metal–organic framework (MOF) based subnanochannel ionic diode membrane (IDM), comprising a large-area and continuous zeolitic imidazolate framework-8/polystyrene sulfonate membrane and a highly ordered alumina nanochannel membrane, for highly efficient osmotic energy conversion in organic solution. We show that a distinctly asymmetric design of pore sizes, charges, and wettabilities and the numerous highly negatively charged and angstrom-scale window-cavity pore structures in the MOF layer endow the subnanochannel IDM with directional and amplified Li+ ion transport and enhanced selectivity in methanol. Thus, an unprecedented power density of ∼23.4 W/m2 is achieved when a 2 M LiCl-methanol solution is mixed with the pure methanol, 5-times more than the existing value. This work provides significant insights into the use of rectified ion channel-mimetic membranes for achieving ultrafast Li+ ion transport at the confinement and high-performance energy harvesting from organic solutions.

Two-Dimensional Metal-Organic Framework Superstructures from Ice-Templated Self-Assembly.

Here, we report the synthesis of two-dimensional (2D) layered metal-organic framework (MOF) nanoparticle (NP) superstructures via an ice-templating strategy. MOF NP monolayers and bilayers can be obtained by regulating the concentration of colloidal MOF NPs without any external fields during self-assembly. Adjacent polyhedral MOF NPs are packed and aligned through crystalline facets, resulting in the formation of a quasi-ordered array superstructure. The morphology of the MOF layers is well preserved when subjected to pyrolysis, and the obtained carbon NPs have hollow interiors driven by the outward contraction of MOF precursors during pyrolysis. With the advantages of large surface areas, hierarchical porosity, high exposure of active sites, and fast electron transport of the 2D layered structure, the mono- and bilayered carbon NP superstructures show better oxygen reduction activity than isolated carbon particles in alkaline media. Our work demonstrates that ice-templating is a powerful strategy to fabricate superstructures of various MOFs and their derivatives.

Deciphering the Structure Activity Relationship of Nickel Containing Materials towards Electrocatalytic Oxidation of Urea

Nickel based materials have been extensively reported to be highly effective for the electrochemical oxidation of urea in the wastewater, which are critical for the energy utilization as well as contamination elimination. In this study, two Ni containing materials of nickel-aluminum layered double hydroxides (NiAl-LDH) and metal organic framework (Ni-MOF) were synthesized and compared with Ni disk towards urea oxidation reaction (UOR). Physical characterization proved the existence of Ni with the same valence of +2 in the as-prepared catalysts. Moreover, the electrochemical analysis showed that more active Ni centers with surface concentrations of 1.01 × 10−6 and 1.17 × 10−6 mol cm−2 existed in both NiAl-LDH and Ni-MOF, which was significant higher than Ni disk of 3.74 × 10−7 mol cm−2. Moreover, Ni-MOF was found to be a better catalyst due to its lower activated energy, tafel slope & overpotential as well as higher stable current density and turnover frequency (TOF) value than NiAl-LDH. This phenomenon might be explained by the protection of Ni2+ by the lattice of layered double hydroxides, which led to an obstacle for its transformation to Ni3+ and thus obviously hindered UOR.