Layered Metal-organic Frameworks Research Articles

Enhancement of Synaptic Behavior in Organic Electrochemical Transistors via the Introduction of Layer‐by‐Layer Grown Metal‐Organic Framework

AbstractOrganic electrochemical transistors (OECTs) are promising for neuromorphic architectures as they can generate multiple electrical states through the control of ion transport. However, conventional OECTs face limitations in mimicking a fully functional biological synapse due to their inability to achieve long‐term plasticity. In this study, a metal‐organic framework (MOF)‐enhanced OECT (MOECT) is fabricated by introducing MOF into the ion‐organic semiconductor (OSC) layer. MOFs are synthesized using the layer‐by‐layer (LBL) method, and additional cross‐linked OSC is introduced to prevent damage to the semiconductor layers during synthesis. The synthesized MOF layers hinder the rediffusion of ions in OECT, allowing ions to remain in the OSC for an extended period. In this study, the MOECT showed a change in current depending on the doping level, recording a current state 4.4 × 107 times higher than that of pristine OECT. Ultimately, the developed MOECTs are applied as synaptic transistors. MOECTs show 14% higher excitatory postsynaptic current (EPSC) after 130 s compared to pristine OECT, thereby strengthening the long‐term plasticity characteristics of neuromorphic devices. This method enhances the performance of synaptic transistors by introducing MOF, offering various possibilities through the selection of different MOF structures and ions, indicating it is a methodological approach with high potential.

A Stable Layered Microporous MOF Assembled with Y-O Chains for Separation of MTO Products.

Benefiting from highly tunable pore environments, some metal-organic frameworks (MOFs) have recently shown promising prospects in the separation of methanol-to-olefin (MTO) products (mainly C3H6 and C2H4). However, the "trade-off" between gas storage capacity and selectivity always results in inefficient separation. In addition, poor stability of MOFs also limits practical separation applications. Herein, we have successfully assembled a layered Y-MOF (FJI-W9) with bent diisophthalate ligands (H4L), Y-O chains, and 2-fluorobenzoic acids. As expected, FJI-W9 not only exhibits good chemical stability but also shows significant potential for C3H6/C2H4 separation. For FJI-W9, the C3H6 uptake at 298 K and 10 kPa is 63 cm3/g, and the IAST selectivity of FJI-W9 for C3H6/C2H4 (V/V = 50/50) is calculated to be 20.5. To the best of our knowledge, both C3H6 uptake and selectivity of FJI-W9 surpass most porous materials. GCMC simulation indicates that the special supramolecular binding sites in FJI-W9 have much stronger interactions with C3H6 than C2H4 molecules. More importantly, practical breakthrough experiments demonstrate that FJI-W9 can effectively separate C3H6/C2H4 (50/50) mixtures, thus obtaining high-purity C2H4 and C3H6, respectively.

Self-exfoliating Bimetallic Metal–Organic Framework Layer with Intralayer π–π Interactions for Efficient Electrical Transport and CO2 Electroreduction

Self-exfoliating Bimetallic Metal–Organic Framework Layer with Intralayer π–π Interactions for Efficient Electrical Transport and CO₂ Electroreduction

Pillar-Supported 2D Layered MOFs with Abundant Active-Site Distributions for High-Performance Alkaline Supercapacitors.

The development of two-dimensional (2D) layered metal-organic frameworks (MOFs) through precise molecular-level design and synthesis has emerged as a prominent research endeavor. However, the utilization of MOFs in their pristine form as electrodes for supercapacitors poses a significant challenge due to their limited tolerance in alkaline environments. To address these issues, we have developed Co- and Cu-based pillar-layered MOFs by regulating the structure of their inner layers through introducing an alkaline N-containing "pillar" to enhance the performance of alkaline supercapacitor electrodes. From the microstructure study and theoretical calculation, the high-density redox centers and efficient chemical bonding modes of Co-MOF determine a unique electron conduction pathway, resulting in excellent energy storage performance. This study underscores the significance of chemical bonding modes and active-site distribution in enhancing the energy storage capabilities of pillar-layered MOFs in alkaline environments, presenting a promising approach for the development of high-performance MOF-based materials for supercapacitor applications.

Fabrication of a ZIF-8/PVA Membrane on PVDF Fiber by Spray for the Highly Efficient Separation of Oil-in-Water Emulsions.

In human life and production, excessive oily wastewaters containing detergents are produced and discharged, causing severe environmental pollution and water resource problems. A metal-organic framework (MOF)-based membrane is an economical and environmentally friendly tool for emulsion separation but is limited by a complex preparation process and poor flexibility. Herein, we developed a simple method to synthesize a MOF-based mixed-matrix membrane (MMM) by spray and fabricated the membrane on poly(vinylidene fluoride) (PVDF) fibers via postdeposition and in situ growth manners. The prepared ZIF-8/PVA MMMs have uniform distribution of ZIF-8 particles and poly(vinyl alcohol) (PVA) on the PVDF fibers. PVA improved the adhesion between the ZIF-8 particles and between the MOF layer and PVDF fiber, endowing the separation membrane with high flexibility and bendability. The prepared ZIF-8/PVA membrane exhibited hydrophilicity and underwater superoleophobicity, which showed high separation efficiency and considerable water flux for emulsions, emulsion containing dye, and surfactant-stabilized emulsion. In addition, the fabricated ZIF-8/PVA/PVDF fibers exhibited good antifouling property and flexibility and can maintain stable separation efficiency after working several times and even under bending, demonstrating the stability and potentiality of the ZIF-8/PVA/PVDF fibers in practical applications. This work paves a new avenue for the synthesis and application of MOF-based MMMs.

Facile Synthesis of a Layered Bismuth-Based MOF With Superhydrophobic-Oleophilic Property and High Oil-Water Separation Performance.

Metal organic frameworks (MOFs) are a class of potential superhydrophobic-oleophilic materials. The organic ligands in superhydrophobic MOFs usually contain long alkyl chains, fluorine groups or aromatic rings with large π conjugation, the preparation of which suffers from high cost, complex operation and so on. In addition, the topological structure of MOFs plays an important role in the hydrophobicity, which may be ignored previously. Here we report a superhydrophobic-oleophilic MOF (BiPPA2) obtained by a facile and fast method, which not only displays a large water contact angle of up to 163° and a small sliding angle of nearly equal to 0°, but also exhibits high sorption capacity for multiple oils and organic solvents, well reusability and high oil retention. In addition, BiPPA2 is stable in a wide pH range (0.5-11.0). Finally, the single crystal structure of BiPPA2 is resolved to reveal the intrinsic reason for the super-hydrophobicity. This work may inspire the further design of pristine superhydrophobic MOFs based on a simple method, which enriches the family of superhydrophobic MOFs and has great significance for practical applications.

Superhydrophobic metal-organic framework layers as multifunctional ion-conducting interfaces for ultra-stable Zn anodes

Aqueous zinc batteries (AZBs) show great promise for cost-effective, high-safety, and large-scale energy storage. Yet, corrosion and dendrite formation at the Zn anode interface undermine its stability, shortening the cycle life. In this work, a fluorosilane-modified metal-organic framework layer (F-MOF) is successfully prepared as a multifunctional ion-conductive interface to stabilize the Zn anode. The designed MOF-based artificial layer provides a uniform pathway for Zn deposition, while its hydrophobic nature prevents negative effects such as hydrogen evolution and corrosion. According to density functional theory (DFT) calculations, the hydration energy of Zn2+ in F-MOF@Zn(002) is reduced while the adsorption energy for Zn2+ is increased. This facilitates the desolvation process on the Zn anode surface, promoting uniform Zn deposition. Consequently, the lifespan of the F-MOF-coated Zn anode extends beyond 2000 h at a current density of 1 mA cm−2 (areal capacity: 0.5 mAh cm−2), significantly outlasting both bare Zn (225 h) and MOF-coated Zn (751 h) anodes. Additionally, the assembled coin cells and pouch-type full cells prove the practical availability of F-MOF@Zn anodes for AZBs. The F-MOF@Zn//MnO2 full cell maintains a high-capacity retention exceeding 91.9 % even after 1000 cycles. This work highlights the practical application potential of hydrophobic MOF coatings for AZBs.

Revealing Ion Adsorption and Charging Mechanisms in Layered Metal-Organic Framework Supercapacitors with Solid-State Nuclear Magnetic Resonance.

Conductive layered metal-organic frameworks (MOFs) have demonstrated promising electrochemical performances as supercapacitor electrode materials. The well-defined chemical structures of these crystalline porous electrodes facilitate structure-performance studies; however, there is a fundamental lack in the molecular-level understanding of charge storage mechanisms in conductive layered MOFs. To address this, we employ solid-state nuclear magnetic resonance (NMR) spectroscopy to study ion adsorption in nickel 2,3,6,7,10,11-hexaiminotriphenylene, Ni3(HITP)2. In this system, we find that separate resonances can be observed for the MOF's in-pore and ex-pore ions. The chemical shift of in-pore electrolyte is found to be dominated by specific chemical interactions with the MOF functional groups, with this result supported by quantum mechanics/molecular mechanics (QM/MM) and density functional theory (DFT) calculations. Quantification of the electrolyte environments by NMR was also found to provide a proxy for electrochemical performance, which could facilitate the rapid screening of synthesized MOF samples. Finally, the charge storage mechanism was explored using a combination of ex-situ NMR and operando electrochemical quartz crystal microbalance (EQCM) experiments. These measurements revealed that cations are the dominant contributors to charge storage in Ni3(HITP)2, with anions contributing only a minor contribution to the charge storage. Overall, this work establishes the methods for studying MOF-electrolyte interactions via NMR spectroscopy. Understanding how these interactions influence the charging storage mechanism will aid the design of MOF-electrolyte combinations to optimize the performance of supercapacitors, as well as other electrochemical devices including electrocatalysts and sensors.

Two-Dimensional (2D) Layered Metal–Organic Framework (MOF) Composites as an Electrochemical Sensor for Nitrofurans

A two dimensional layer iron metal–organic framework (MOF), [Fe (bipy)(C4O4)(H2O)2]×3H2O (where bipy = 4,4’-bipyridine、 C4O4 2- (squarate) = dianion of squric acid) has been successfully synthesized. Hydrothermal synthesis was employed to incorporate these Fe-MOFs into reduced graphene oxide (rGO) nanosheets, forming Fe-MOF/rGO composites. SEM, TEM, XRD, XPS, and contact angle measurements were employed to analyze the composites. TEM studies revealed that the rod-shaped Fe-MOFs were uniformly dispersed on the rGO sheets. Incorporating Fe-MOF into rGO resulted in enhanced performance, which can be attributed to the composites' large surface area, chemical stability, and high electrical conductivity. The Fe-MOF/rGO modified electrodes exhibited significantly improved response signals for the electrochemical sensing of nitrofurazone, showcasing a lower detection limit. The sensor also demonstrated reproducible and stable anti-interference properties. To elucidate the mechanism behind the enhanced sensing performance, grand canonical Monte Carlo (GCMC) calculations were conducted. These calculations indicated that the interface between Fe-MOF and rGO effectively absorbed an increased number of NFZ molecules. These findings underscore the substantial improvement in the electrochemical performance of Fe-MOF/rGO composites, positioning them as promising materials for practical applications in nitrofurazone sensing.

Reverse-Selective Anion Separation Relies on Charged "Hourglass" Gate.

According to the hydration size and charge property of separated ions, the transport channel can be constructed to achieve precision ion separation, but the ion geometry as a separation parameter to design the channel structure is rarely reported. Herein, a reverse-selective anion separation membrane composed of a metal-organic frameworks (MOFs) layer with a charged "hourglass" channel as an ion-selective switch to manipulate oxoanion transport is developed. The gate in "hourglass" with tetrahedral geometry similar to the oxoanion (such as SO2- 4, Cr 2O2- 7, and MnO- 4) boosts the transmission effect oxoanion much larger than Cl- through geometric matching and Coulomb interaction. Specific channel structure exhibits an abnormal selectivity for SO2- 4/Cl- of 20, Cr 2O2- 7/Cl- of 6.6, and MnO- 4/Cl- of 4.0 in a binary-ion system. The transfer behavior of SO2- 4 in the channel revealed by molecular dynamics simulation and density functional theory calculation further indicates the mechanism of the abnormal separation performance. The universality of the membrane structure is validated by the formation of different nitrogen-containing modified layers, which also achieves in situ growth of the MOFs layer, and exhibits similar reversal separation performance. The geometric configuration control of ion transport channels presents a novel effective strategy to realize the precise separation of target ions.

Effective heat transfer associated with CO2 and CH4 adsorption on HKUST-1 metal-organic framework deposited in situ on heat exchanger

The aim of this study was to analyze the heat transfer properties a copper heat exchanger with the in situ synthesized HKUST-1 metal-organic framework (MOF). For this purpose, a dedicated reactor was constructed to enable the direct measurements of heat of adsorption of CO2 and CH4, that accompanies the dynamic course of these processes. In parallel, CO2 and CH4 adsorption isotherms were determined at various temperatures and the heat of adsorption was calculated by an indirect method. Temperature changes on the heat exchanger as a result of cyclic adsorption/desorption processes of CO2 and CH4 on the HKUST-1 layer were registered, and the results of adsorption heat by direct and indirect methods were compared. Comparing the results of indirect and direct measurements of temperature changes accompanying CO2 adsorption, a difference of 19 % was obtained. In the case of CH4 adsorption, the results obtained by the two methods differed by 22 %. Based on the experimental results, it was proven that HKUST-1 synthesized in situ on a copper heat exchanger has improved heat transfer properties. The proposed concept of MOF layer on heat exchanger allows for efficient thermal stimulation of sorption processes and simultaneous MOF regeneration while minimizing the thermal energy supplied to the system.

Boosting tough metal Zn anode by MOF layer for high-performance zinc-ion batteries

Metal-organic frameworks (MOFs) have been used to stabilize the metal zinc anode, yet the developed coating materials ignore the influence of intergranular space on deteriorating Zn electrode. Herein, we propose the channel sizes of MOFs as the key control factor to balance the zinc ion flux and Zn2+ desolvation behavior within the channels and between the intergranular spaces. Among three coating layers made by MOFs, the MOF-5W layer with confined spaces and channels is capable to promote the spontaneous desolvation process. The activated surface sites on MOF-5W endow the intergranular channels with accelerated ion transportation and spontaneous Zn2+ desolvation. Two kinds of migration paths are well-matched, as the MOF-5W@Zn anode shows Zn stripping/plating over 5000 cycles at 40 mA cm‒2, as well as cycling stability of 1050 h with high areal capacity of 10 mAh cm‒2. The findings enlighten the innovative research for tough Zn anode.

A Three-Blade-Paddlewheel Unit-Based Layered Metal–Organic Framework with Synergistic Intermolecular Interactions for Efficient Iodine Adsorption

A Three-Blade-Paddlewheel Unit-Based Layered Metal–Organic Framework with Synergistic Intermolecular Interactions for Efficient Iodine Adsorption

In situ coordinated ultrathin MOF-polymer electrolyte membrane with vertically aligned transfer channels for solid lithium metal batteries

Metal organic framework (MOF)-polymer composite solid electrolyte membrane with novel microstructure is expected to show attractive prospect for solid state lithium metal batteries. But the reported MOF were usually regarded as an entirety in composite solid electrolyte resulting in tradeoff between ionic conductivity and lithium dendrite inhibition ability. Herein, MOF-polymer composite membrane with vertically aligned channels and ultrathin MOF layer is proposed to decrease lithium ion transportation resistance obtained by simple phase inversion and in situ coordinated growth methods. The vertically aligned highways can decrease tortuous pathways and intensify ion conduction. The embedded ultrathin MOF layer on membrane surface leads to homogeneous plating/stripping of lithium. This novel structured MOF-polymer composite solid electrolyte exhibits improved ionic conductivity of 0.55 mS cm−1 at 22 ° C and lithium ion transference number of 0.87. Furthermore, the Li/Li symmetrical cell shows stable lithium plating/stripping performance for 1100 h at 0.1 mA cm−2 and 0.1 mA h cm−2. LiFePO4/MOF-polymer/Li coin battery demonstrates good rate capability and cycling performance with capacity retention of 82 % after 100 cycles at 0.2C and the pouch cell can light up the “DLUT” blue light lamp under folding and cutting states. This work encourages a new avenue to develop composite solid electrolytes with ion transportation highways and uniform distribution plane for solid lithium metal batteries.

Hollow ZIF-8 nanomaterial prepared via core-shell etching exhibits exceptional adsorption performance for malachite green

Metal-organic frameworks (MOFs) have attracted widespread attention due to their distinctive structural attributes, such as expansive surface areas and the ease of chemical modification. These characteristics endow MOFs with a high degree of versatility, making them suitable for a broad array of applications. Core-shell MOF@MOF structures have emerged as a notable research area, offering a strategy to enhance MOF functionality by depositing one MOF layer over another. In this study, hollow ZIF-8 nanocomposites were successfully synthesized via the etching process of ZIF-67@ZIF-8 structures. It is noteworthy that the nanomaterial exhibits exceptional adsorption capacity, with a maximum adsorption capacity of 7746 mg/g for malachite green (MG), surpassing that of many previously reported adsorbents. Moreover, the recyclability of these nanocomposites is also excellent, demonstrating sustained effectiveness over five adsorption-desorption cycles. The study systematically investigated key factors that influence MG adsorption, such as the amount of adsorbent used and the initial concentration of MG. Additionally, a comprehensive analysis of adsorption kinetics was conducted to gain insights into the adsorption behavior of the nanocomposites. In conclusion, the hollow ZIF-8 nanomaterial prepared via core-shell etching offers a promising platform for the efficient removal of MG, meeting the urgent demand for high adsorption capacity of MG in water treatment.

Cycling Stability of a 2D Pristine MOF Supercapacitors

AbstractTwo‐dimensional (2D) metal–organic frameworks (MOFs) have been a worldwide research interest due to their potential application in supercapacitors. Herein, a cobalt‐based layered MOF ([Co2(μ‐SO4)(Hppza)2(H2O)3]n, namely, SEU‐1; H2ppza=3‐(pyridin‐4‐yl)‐1H‐pyrazole‐5‐carboxylic acid) has been synthesized via a one‐step solvothermal method. Single X‐ray diffraction analysis shows that the SEU‐1 exhibits a (3,3,4)‐connected 2D structure with a Schläfli symbol of (62 ⋅ 8)(63)(64 ⋅ 8 ⋅ 10). Variable‐temperature magnetic susceptibility data display that antiferromagnetic interactions between two CoII ions exist in SEU‐1. The supercapacitive performance has been evaluated in the three‐electrode system. Its maximum specific capacitance is 145.5 F g−1 at 1 A g−1, along with the specific capacitance retention of 92.7 % at the current density of 5 A g−1 after 6000 cycles in 3 M KOH solution. These results demonstrate that SEU‐1 is a good candidate for electrode material for electrochemical energy storage.

Understanding Electrolyte Ion Size Effects on the Performance of Conducting Metal-Organic Framework Supercapacitors.

Layered metal-organic frameworks (MOFs) have emerged as promising materials for next-generation supercapacitors. Understanding how and why electrolyte ion size impacts electrochemical performance is crucial for developing improved MOF-based devices. To address this, we investigate the energy storage performance of Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with a series of 1 M tetraalkylammonium tetrafluoroborate (TAABF4) electrolytes with different cation sizes. Three-electrode experiments show that Cu3(HHTP)2 exhibits an asymmetric charging response with all ion sizes, with higher energy storage upon positive charging and a greater charging asymmetry with larger TAA+ cations. The results further show that smaller TAA+ cations demonstrate superior capacitive performances upon both positive and negative charging compared to larger TAA+ cations. To gain further insights, electrochemical quartz crystal microbalance measurements were performed to probe ion electrosorption during charging and discharging. These reveal that Cu3(HHTP)2 has a cation-dominated charging mechanism, but interestingly indicate that the solvent also participates in the charging process with larger cations. Overall, the results of this study suggest that larger TAA+ cations saturate the pores of the Cu3(HHTP)2-based electrodes. This leads to more asymmetric charging behavior and forces solvent molecules to play a role in the charge storage mechanism. These findings significantly enhance our understanding of ion electrosorption in layered MOFs, and they will guide the design of improved MOF-based supercapacitors.

Exploiting Co-C interface and graphitic carbon belts for enhanced structural stability of a porous layered Co-C catalyst for CO2 hydrogenation

Addressing the urgent need for efficient CO2 reduction, a novel Co@C catalyst was synthesized through the pyrolysis of a unique layered metal–organic framework (MOF), featuring tunable thickness, pore sizes. The CO2 hydrogenation performance demonstrates an enhancement by an optimized structure that significantly improves stability, maintaining a 25% CO2 conversion rate over an extended 80-hour period. The catalyst's composite structure exhibits a dual-confinement effect, where the Co-C interface and graphitic carbon belt stabilize Co nanoparticles, preventing sintering during reaction cycles. This study delves into the structural modifications necessary for catalytic optimization in CO2 hydrogenation, offering valuable insights for designing efficient catalysts for CO2 reduction and advancing sustainable energy solutions.

K2[(VOHPO4)2(C2O4)]·2H2O as a high‐potential cathode material for potassium‐ion batteries

AbstractPotassium‐ion batteries (KIBs) represent a promising energy storage solution owing to the abundance of potassium resources. The efficacy of KIBs relies significantly on the electrochemical attributes of both their electrode materials and electrolytes. In the current investigation, we synthesized a layered compound K2[(VOHPO4)2(C2O4)]·2H2O via a heterogeneous nucleation approach and assessed its viability as a cathode material for KIBs. When integrated with a salt‐concentrated electrolyte with oxidation stability over 6 V, the compounds exhibit a high discharge potential of 4.1 V (vs. K+/K) alongside a reversible capacity of 106.2 mAh g−1. Furthermore, there is no capacity decay after 500 cycles at 100 mA g−1. This study shows the promise of layered metal organic frameworks as high‐potential materials for KIBs.

Asymmetric ionogel electrolyte with an ultrathin metal–organic framework layer for lithium dendrite inhibition in solid-state lithium-metal batteries

Solid-state electrolytes (SSEs) are used to prevent internal short circuits caused by the growth of lithium dendrites in solid-state lithium-metal batteries (SSLMBs). Ionogel electrolytes are new polymeric SSEs with outstanding processability, excellent flexibility, and superior ionic conductivity. Lithium-ion transport in ionogel electrolytes depends on ionic liquid (IL) content; however, increasing the IL content improves ionic conductivity but sharply decreases mechanical properties, thus limiting the ability to resist lithium dendrites. Thus, ionogel electrolytes must strike a balance between ionic conductivity and mechanical properties. Herein, we adopt a new strategy to suppress the growth of lithium dendrites by in situ polymerizing an ultrathin metal–organic framework (MOF) layer (9.8 μm) onto a highly ionic conductive ionogel electrolyte. The ionogel electrolyte provides an asymmetric SSE (ASSE) with a remarkable ionic conductivity of 4.8 × 10−4 S cm−1 (30 °C), whereas the ultrathin MOF layer regulates uniform dissolution/deposition of lithium and inhibits lithium dendrite growth, thereby increasing critical current density of the ASSE to 0.65 mA cm−2. An SSLMB assembled with the ASSE and LiFePO4 exhibits excellent performance and cycling stability, maintaining a specific capacity of 125.4 mAh g−1 after 500 cycles at 0.3C.