Charge Transport in Zirconium-Based Metal-Organic Frameworks

Preparation of gold nanoparticles decorated UiO-66-NH2 incorporated epichlorohydrin and cyclodextrin as novel efficient catalyst in cross coupling and carbonylative reactions

This study presents a new, highly effective, and reusable catalyst: UiO-66-NH2@Epichlorohydrin@Cyclodextrin@Au-NPs. This innovative catalyst starts with the Zr-based UiO-66 material, which is functionalized with amino groups (-NH2). We enhanced its surface compatibility by modifying it with epichlorohydrin and cyclodextrin via a post-synthesis modification method. Gold nanoparticles were then stabilized on this modified composite, resulting in the UiO-66-NH2@Epichlorohydrin@Cyclodextrin@Au-NPs complex. We used this catalyst for C-C coupling and Carbonylative Sonogashira reactions in mild conditions. Its effectiveness was underscored by various analytical techniques, including XRD, EDS, SEM, FT-IR, TEM, BET, ICP, TGA, and elemental mapping. The catalyst exhibited exceptional performance in Sonogashira, Heck, Suzuki coupling, and Carbonylative reactions, achieving good to excellent yields. It proved to be highly recyclable, maintaining its catalytic activity for up to nine cycles with minimal loss.

Post-Modification of MOF with Electron Donor for Efficient Photocatalytic Oxidative Organic Transformations

Construction of donor-accepter systems via self-assembling electron donor and acceptor chromophores within one single metal-organic framework (MOF) for advanced artificial photosynthesis is of great intertest yet a major challenge. Herein, an electron donor porphyrin 5-(4-carboxyphenyl)-10,15,20-triphenylporphyrin (PCOOH) was successfully integrated into a highly stable and porous electron acceptor naphthalene diimide (NDI)-based MOF (Zr-NDI) through the postmodified approach of solvent-assisted ligand incorporation (SALI). Benefiting from the efficient photoinduced electron transfer (PET) from the donor PCOOH anchored on the Zr-nodes to the acceptor NDI ligand, which contributes to the abundant generation of reactive oxygen species (ROS) of superoxide radical (O2 •-), the resulting MOF Zr-NDI-PCOOH exhibited superior photocatalytic activities that among the highest levels of MOF-based photocatalysts to aerobic oxidation reactions, including hydroxylation of arylboronic acids and homocoupling of amines. This work exemplifies an avenue to develop high-efficiency MOF-based donor-acceptor systems for advanced artificial photosynthesis through facile post-modified approach.

Design and engineering of microenvironments of supported catalysts toward more efficient chemical synthesis

Catalytic species such as molecular catalysts and metal catalysts are commonly attached to varieties of supports to simplify their separation and recovery and accommodate various reaction conditions. The physicochemical microenvironments surrounding catalytic species play an important role in catalytic performance, and the rational design and engineering of microenvironments can achieve more efficient chemical synthesis, leading to greener and more sustainable catalysis. In this review, we highlight recent works addressing the topic of the design and engineering of microenvironments of supported catalysts, including supported molecular catalysts and supported metal catalysts. Six types of materials, including oxide nano/microparticle, mesoporous silica nanoparticle (MSN), polymer nanomaterial, reticular material, zeolite, and carbon-based nanomaterial, are widely used as supports for the immobilization of catalytic species. We summarize and discuss the synthesis and modification of supports and the positive effects of microenvironments on catalytic properties such as metal-support interaction, molecular recognition, pseudo-solvent effect, regulating mass transfer, steric effect, etc. These design principles and engineering strategies allow access to a better understanding of structure-property relationships and advance the development of more efficient catalytic processes.

Peptide-Induced Hydrogelation with Ordered Metal-Organic Framework Nanoparticles Generating Reactive Oxygen Species for Integrated Wound Repair

Hydrogels, with their high water content and flexible nature, are a promising class of medical dressings for combating bacterial wound infections. However, their development has been hindered by low sterilization efficiency. Here, this issue is addressed by designing a peptide hydrogel that assembles ordered metal-organic framework (MOF) nanoparticles with photocatalytic bactericidal activity. Specifically, a short peptide, Nap-Gly-Phe-Phe-His (Nap-GFFH), is used to induce the assembly of zinc-imidazolate MOF (ZIF-8) into a hydrogel (NHZ gel). This innovative structure integrates three key features: 1) ZIF-8 nanoparticles are encapsulated within the hydrogel, overcoming their inherent brittleness, insolubility, and limited moldability; 2) the ordered ZIF-8 structure enhances charge transfer, enabling efficient generation of reactive oxygen species (ROS); and 3) ZIF-8 simultaneously improves the photocatalytic bactericidal efficiency and mechanical properties of the hydrogel. The NHZ gel demonstrates remarkable antibacterial performance, achieving >99.9% and 99.99% inactivation of Escherichia coli and Staphylococcus aureus, respectively, within 15 min of simulated solar radiation. Additionally, the NHZ gel exhibits excellent biocompatibility, water retention, and exudate absorption, highlighting its broad potential for wound healing.

Reductive Photocatalytic Proton-Coupled Electron Transfer by a Zirconium-Based Molecular Platform

Reductive proton-coupled electron transfer (PCET) has important energetic implications in numerous synthetic and natural redox processes. The development of catalytic systems that can mediate such transformations has become an attractive target, especially when light is used to generate the reactive species towards solar-to-chemicals conversion. However, such approach becomes challenged by kinetic competition with H2 evolution. Here we describe the excited state reactivity of a molecular Zr-based platform under visible light irradiation for the efficient reduction of multiple bonds. Mechanistic investigations shine light on a charge separation process that colocalizes an excited electron and an acidic proton to promote selective PCET. We further leveraged this reactivity for the photocatalytic reduction of a variety of organic substrates. Our results demonstrate the promise of this molecular platform to design strong photocatalytic PCET mediators for reductive transformations. More broadly, we also show the potential relevance of PCET mechanisms in the (photo)redox chemistry of Zr-based molecular materials.

Electrochemically Determined and Structurally Justified Thermochemistry of H atom Transfer on Ti-Oxo Nodes of the Colloidal Metal-Organic Framework Ti-MIL-125

Titanium dioxide (TiO2) has long been employed as a (photo)electrode for reactions relevant to energy storage and renewable energy synthesis. Proton-coupled electron transfer (PCET) reactions with equimolar amounts of protons and electrons at the TiO2 surface or within the bulk structure lie at the center of these reactions. Because a proton and an electron are thermochemically equivalent to an H atom, these reactions are essentially H atom transfer reactions. Thermodynamics of H atom transfer has a complex dependence on the synthetic protocol and chemical history of the electrode, the reaction medium, and many others; together, these complications preclude the understanding of the H atom transfer thermochemistry with atomic-level structural knowledge. Herein, we report our success in employing open-circuit potential (EOCP) measurements to quantitatively determine the H atom transfer thermochemistry at structurally well-defined Ti-oxo clusters within a colloidally stabilized metal-organic framework (MOF), Ti-MIL-125. The free energy to transfer H atom, Ti3+O-H bond dissociation free energy (BDFE), was measured to be 68(2) kcal mol-1. To the best of our understanding, this is the first report on using EOCP measurements to quantify thermochemistry on any MOFs. The proton topology, the structural change upon the redox reaction, and BDFE values were further quantitatively corroborated using computational simulations. Furthermore, comparisons of the EOCP-derived BDFEs of Ti-MIL-125 to similar parameters in the literature suggest that EOCP should be the preferred method for quantitatively accurate BDFE calculations. The reported success in employing EOCP for nanosized Ti-MIL-125 should lay the ground for thermochemical measurements of other colloidal systems, which are otherwise challenging. Implications of these measurements on Ti-MIL-125 as an H atom acceptor in chemical reactions and comparisons with other MOFs/metal oxides are discussed.

Sulfonate-Functionalized Metal-Organic Framework as a Porous "Proton Reservoir" for Boosting Electrochemical Reduction of Nitrate to Ammonia

The electrochemical reduction reaction of nitrate (NO3RR) is an attractive route to produce ammonia at ambient conditions, but the conversion from nitrate to ammonia, which requires nine protons, has to compete with both the two-proton process of nitrite formation and the hydrogen evolution reaction. Extensive research efforts have thus been made in recent studies to develop electrocatalysts for the NO3RR facilitating the production of ammonia. Rather than designing another better electrocatalyst, herein, we synthesize an electrochemically inactive, porous, and chemically robust zirconium-based metal-organic framework (MOF) with enriched intraframework sulfonate groups, SO3-MOF-808, as a coating deposited on top of the catalytically active copper-based electrode. Although both the overall reaction rate and electrochemically active surface area of the electrode are barely affected by the MOF coating, with negatively charged sulfonate groups capable of enriching more protons near the electrode surface, the MOF coating significantly promotes the selectivity of the NO3RR toward the production of ammonia. In contrast, the use of MOF coating with positively charged trimethylammonium groups to repulse protons strongly facilitates the conversion of nitrate to nitrite, with selectivity of more than 90% at all potentials. Under the optimal operating conditions, the copper electrocatalyst with SO3-MOF-808 coating can achieve a Faradaic efficiency of 87.5% for ammonia production, a nitrate-to-ammonia selectivity of 95.6%, and an ammonia production rate of 97 μmol/cm2 h, outperforming all of those achieved by both the pristine copper (75.0%; 93.9%; 87 μmol/cm2 h) and copper with optimized Nafion coating (83.3%; 86.9%; 64 μmol/cm2 h). Findings here suggest the function of MOF as an advanced alternative to the commercially available Nafion to enrich protons near the surface of electrocatalyst for NO3RR, and shed light on the potential of utilizing such electrochemically inactive MOF coatings in a range of proton-coupled electrocatalytic reactions.

Electronic, optical and charge transport properties of Zn-porphyrin-C60 MOFs: a combined periodic and cluster modeling

Density functional theory (DFT) calculations were performed on the 5,15 meso-positions of nine porphyrin-containing MOFs; Zn2(TCPB)-(NMe2-ZnP); (H4TCPB = 1,2,4,5-tetrakis(4-carboxyphenyl)benzene), (NMe2-ZnP = [5,15-bis[(4-pyridyl)-ethynyl]-10,20-bis-(dimethylamine) porphinato]zinc(II)) functionalized with nitrogen-, oxygen-, and sulfur-containing groups to study their effects on the electronic, optical and transport properties of the materials. The properties of these materials have also been investigated by encapsulating fullerene (C60) in their pores (C60@MOFs). The results indicate that the guest C60 in the MOF generates high photoconductivity through efficient porphyrin/fullerene donor-acceptor (D-A) interactions, which are facilitated by oxygen and sulfur functionalities. DFT calculations show that C60 interacts favorably in MOFs due to negative Eint values. Encapsulated C60 molecules modify the electronic band structure, affecting the conduction band and unoccupied states of MOFs corresponding to C60 p orbitals. TD-DFT calculations show that incorporating C60 promotes D-A interactions in MOFs, leading to charge transfer in the near-infrared and visible photoinduced electron transfer (PET) from porphyrins to C60. Nonequilibrium Green's function-based calculations for MOFs with sulfur group, with and without C60, performed using molecular junctions with Au(111)-based electrodes show increased charge transport for the doped MOF. These insights into tuning electronic/optical properties and controlling charge transfer can aid in the design of new visible/near-infrared MOF-based optoelectronic devices.

The Molecular Nature of Redox-Conductive Metal-Organic Frameworks

ConspectusRedox-conductive metal-organic frameworks (RC-MOFs) are a class of porous materials that exhibit electrical conductivity through a chain of self-exchange reactions between molecularly defined, neighboring redox-active units of differing oxidation states. To maintain electroneutrality, this electron hopping transport is coupled to the translocation of charge balancing counterions. Owing to the molecular nature of the redox active components, RC-MOFs have received increasing attention for potential applications in energy storage, electrocatalysis, reconfigurable electronics, etc. While our understanding of fundamental aspects that govern electron hopping transport in RC-MOFs has improved during the past decade, certain fundamental aspects such as questions that arise from the coupling between electron hopping and diffusion migration of charge balancing counterions are still not fully understood.In this Account, we summarize and discuss our group's efforts to answer some of these fundamental questions while also demonstrating the applicability of RC-MOFs in energy-related applications. First, we introduce general design strategies for RC-MOFs, fundamentals that govern their charge transport properties, and experimental diagnostics that allow for their identification. Selected examples with redox-active organic linkers or metallo-linkers are discussed to demonstrate how the molecular characteristics of the redox-active units inside RC-MOFs are retained. Second, we summarize experimental techniques that can be used to characterize charge transport properties in a RC-MOF. The apparent electron diffusion coefficient, Deapp, that is frequently determined in the field and obtained in large perturbation, transient experiments will be discussed and related to redox conductivity, σ, that is obtained in a steady state setup. It will be shown that both MOF-intrinsic (topology, pore size, and apertures) and experimental (nature of electrolyte, solvent) factors can have noticeable impact on electrical conductivity through RC-MOFs. Lastly, we summarize our progress in utilizing RC-MOFs as electrochromic materials, materials for harvesting minority carriers from illuminated semiconductors and within electrocatalysis. In the latter case, recent work on multivariate RC-MOFs in which redox active linkers are used to "wire" redox catalysts in the crystal interiors will be presented, offering opportunities to independently optimize charge transport and catalytic function.The ambition of this Account is to inspire the design of new RC-MOF systems, to aid their identification, to provide mechanistic insights into the governing ion-coupled electron hopping transport mode of conductivity, and ultimately to promote their applications in existing and emerging areas. With basically unlimited possibilities of molecular engineering tools, together with research in both fundamental and applied fields, we believe that RC-MOFs will attract even more attention in the future to unlock their full potential.

Linker Conformation Controls Oxidation Potentials and Electrochromism in Highly Stable Zr-Based Metal-Organic Frameworks

The development of tailor-made electrochromic (EC) materials requires a large variety of available substances with properties that precisely match the task. Since the inception of electrochromic metal-organic frameworks (MOFs), the field relies only on a limited set of building blocks, providing the desired electrochromic effect. Herein, we demonstrate for the first time the implementation of a Piccard-type system (N,N,N',N'-benzidinetetrabenzoate) into Zr-MOFs to obtain electrochromic materials. With fast switching rates, high contrast ratio, long-life stability, and exceptional chemical and physical stability, the novel material is on par with inorganic EC material. The new EC system exhibits an ultrahigh contrast from the bleaching state, with transmittance in the visible region >53%, to the colored state with a transmittance of ca. 3%. The 5 μm thick film attained up to 90% of the coloring in 12.5 s and exhibited high electrochemical reversibility. Moreover, the conformational lability of the electrochromic ligand chosen is locked via the topology design of the framework, which is not attainable in the solution. Locked conformations of the redox active linker in distinct polymorphous frameworks (DUT-65 and DUT-66) feature different redox characteristics and opens the door to the overarching control of the oxidation pathway in the Piccard-type systems.

Palladium(II) Modulation Enhances the Water Stability and Aqueous 99TcO4-/ReO4- Removal Performance of Metal-Organic Frameworks

Improving the water stability of metal-organic frameworks (MOFs) is essential for their use in water pollution treatment and environmental remediation, though it remains technically challenging. Herein, we report a novel cationic MOF constructed with [Th6O4(OH)4(COO)12] units and [CoN4·Cl2] units possessing a ftw-type topology (denoted as 1-Th-Co). 1-Th-Co itself exhibited poor water stability but excellent stability following a palladium(II) modulation strategy. Experimental studies reveal that Co(II) ions in 1-Th-Co were replaced by Pd(II) ions through cation exchange in N,N-diethylformamide (yielding 1-Th-Pd). The planar PdN4 units in 1-Th-Pd were responsible for improving the water stability of the framework. As a result, 1-Th-Pd offered excellent stability, fast adsorption kinetics, and high removal ratios for 99TcO4- and ReO4- (as a 99TcO4- surrogate) in contaminated water. When used in packed columns, 1-Th-Pd can dynamically capture ReO4- from groundwater. This work provides a new avenue for improving the water stability of MOFs, offering new vistas for the decontamination of aqueous solutions containing 99TcO4- and ReO4-.

Reticular Chemistry Directed "One-Pot" Strategy to in situ Construct Organic Linkers and Zirconium-Organic Frameworks

Zirconium-based metal-organic frameworks (Zr-MOFs) have emerged as one of the most studied MOFs due to the unlimited numbers of organic linkers and the varying Zr-oxo clusters. However, the synthesis of carboxylic acids, especially multitopic carboxylic acids, is always a great challenge for the discovery of new Zr-MOFs. As an alternative approach, the in situ "one-pot" strategy can address this limitation, where the generation of organic linkers from the corresponding precursors and the sequential construction of MOFs are integrated into one solvothermal condition. Herein, inspired by benzimidazole-contained compounds synthesized via reaction of aldehyde and o-phenylenediamine, tri-, tetra-, penta- and hexa-topic carboxylic acids and a series of corresponding Zr-MOFs can be prepared via the in situ "one-pot" method under the same solvothermal conditions. This strategy can be utilized not only to prepare reported Zr-MOFs constructed using benzimidazole-contained linkers, but also to rationally design, construct and realize functionalities of zirconium-pentacarboxylate frameworks guided by reticular chemistry. More importantly, in situ "one-pot" method can facilitate the discovery of new Zr-MOFs, such as zirconium-hexacarboxylate frameworks. The present study demonstrates the promising potential of benzimidazole-inspired in situ "one-pot" approach in the crystal engineering of structure- and property-specific Zr-MOFs, especially with the guidance of reticular chemistry.

Kinetic and stability studies of amino acid metal-organic frameworks for encapsulating of amino acid dehydrogenase

Zr-MOFs was applied for the immobilization of hyperthermophilic and halophilic amino acid dehydrogenase (Zr-MOFs-NTAaDH) by physical adsorption for the biosynthesis of L-homophenylalanine. Activity of Zr-MOFs-NTAaDH was enhanced by 3.3-fold of the free enzyme at 70°C. And the enzyme activity of Zr-MOFs-NTAaDH was maintained at 4.16 U/mg at pH 11, which was 7.8 folds of that of NTAaDH. Kinetic parameters indicated catalytic efficiency of Zr-MOFs-NTAaDH was increased compared to the free enzyme as kcat of Zr-MOFs-NTAaDH was 12.3-fold of that of free enzyme. After 7 recycles, the activity of Zr-MOFs-NTAaDH remained 68 %. And Zr-MOFs-NTAaDH exhibited high ionic liquid tolerance which indicated the great potential for industrial application.

Zirconium-based metal-organic frameworks and their roles in electrocatalysis

Due to their exceptional chemical stability in water and high structural tunability, zirconium(IV)-based MOFs (Zr-MOFs) have been considered attractive materials in the broad fields of electrocatalysis. Numerous studies published since 2015 have attempted to utilise Zr-MOFs in electrocatalysis, with the porous framework serving as either the active electrocatalyst or the scaffold or surface coating to further enhance the performance of the actual electrocatalyst. Herein, the roles of Zr-MOFs in electrocatalytic processes are discussed, and some selected examples reporting the applications of Zr-MOFs in various electrocatalytic reactions, including several studies from our group, are overviewed. Challenges, limitations and opportunities in using Zr-MOFs in electrocatalysis in future studies are discussed.

An Appraisal for Providing Charge Transfer (CT) Through Synthetic Porous Frameworks for their Semiconductor Applications

In recent years, there has been considerable focus on the development of charge transfer (CT) complex formation as a means to modify the band gaps of organic materials. In particular, CT complexes alternate layers of aromatic molecules with donor (D) and acceptor (A) properties to provide inherent electrical conductivity. In particular, the synthetic porous frameworks as attractive D-A components have been extensively studied in recent years in comparison to existing D-A materials. Therefore, in this work, the synthetic porous frameworks are classified into conjugated microporous polymers (CMPs), covalent organic frameworks (COFs), and metal-organic frameworks (MOFs) and compare high-quality materials for CT in semiconductors. This work updates the overview of the above porous frameworks for CT, starting with their early history regarding their semiconductor applications, and lists CT concepts and selected key developments in their CT complexes and CT composites. In addition, the network formation methods and their functionalization are discussed to provide access to a variety of potential applications. Furthermore, several theoretical investigations, efficiency improvement techniques, and a discussion of the electrical conductivity of the porous frameworks are also highlighted. Finally, a perspective of synthetic porous framework studies on CT performance is provided along with some comparisons.

Defect-enabling zirconium-based metal-organic frameworks for energy and environmental remediation applications

This comprehensive review explores the diverse applications of defective zirconium-based metal-organic frameworks (Zr-MOFs) in energy and environmental remediation. Zr-MOFs have gained significant attention due to their unique properties, and deliberate introduction of defects further enhances their functionality. The review encompasses several areas where defective Zr-MOFs exhibit promise, including environmental remediation, detoxification of chemical warfare agents, photocatalytic energy conversions, and electrochemical applications. Defects play a pivotal role by creating open sites within the framework, facilitating effective adsorption and remediation of pollutants. They also contribute to the catalytic activity of Zr-MOFs, enabling efficient energy conversion processes such as hydrogen production and CO2 reduction. The review underscores the importance of defect manipulation, including control over their distribution and type, to optimize the performance of Zr-MOFs. Through tailored defect engineering and precise selection of functional groups, researchers can enhance the selectivity and efficiency of Zr-MOFs for specific applications. Additionally, pore size manipulation influences the adsorption capacity and transport properties of Zr-MOFs, further expanding their potential in environmental remediation and energy conversion. Defective Zr-MOFs exhibit remarkable stability and synthetic versatility, making them suitable for diverse environmental conditions and allowing for the introduction of missing linkers, cluster defects, or post-synthetic modifications to precisely tailor their properties. Overall, this review highlights the promising prospects of defective Zr-MOFs in addressing energy and environmental challenges, positioning them as versatile tools for sustainable solutions and paving the way for advancements in various sectors toward a cleaner and more sustainable future.

Diffusional Electron Transport Coupled to Thermodynamically Driven Electron Transfers in Redox-Conductive Multivariate Metal-Organic Frameworks

The development of redox-conductive metal-organic frameworks (MOFs) and the fundamental understanding of charge propagation through these materials are central to their applications in energy storage, electronics, and catalysis. To answer some unresolved questions about diffusional electron hopping transport and redox conductivity, mixed-linker MOFs were constructed from two statistically distributed redox-active linkers, pyromellitic diimide bis-pyrazolate (PMDI) and naphthalene diimide bis-pyrazolate (NDI), and grown as crystalline thin films on conductive fluorine-doped tin oxide (FTO). Owing to the distinct redox properties of the linkers, four well-separated and reversible redox events are resolved by cyclic voltammetry, and the mixed-linker MOFs can exist in five discrete redox states. Each state is characterized by a unique spectroscopic signature, and the interconversions between the states can be followed spectroscopically under operando conditions. With the help of pulsed step-potential spectrochronoamperometry, two modes of electron propagation through the mixed-linker MOF are identified: diffusional electron hopping transport between linkers of the same type and a second channel that arises from thermodynamically driven electron transfers between linkers of different types. Corresponding to the four redox events of the mixed-linker MOFs, four distinct bell-shaped redox conductivity profiles are observed at a steady state. The magnitude of the maximum redox conductivity is evidenced to be dependent on the distance between redox hopping sites, analogous to the situation for apparent electron diffusion coefficients, Deapp, that are obtained in transient experiments. The design of mixed-linker redox-conductive MOFs and detailed studies of their charge transport properties present new opportunities for future applications of MOFs, in particular, within electrocatalysis.

Boosting Enzyme Activity in Enzyme Metal-Organic Framework Composites

Enzymes, as highly efficient biocatalysts, excel in catalyzing diverse reactions with exceptional activity and selective properties under mild conditions. Nonetheless, their broad applications are hindered by their inherent fragility, including low thermal stability, limited pH tolerance, and sensitivity to organic solvents and denaturants. Encapsulating enzymes within metal-organic frameworks (MOFs) can protect them from denaturation in these harsh environments. However, this often leads to a compromised enzyme activity. In recent years, extensive research efforts have been dedicated to enhancing enzymatic activity within MOFs, leading to the development of new enzyme-MOF composites that not only preserve their catalytic potential but also outperform their free counterparts. This Review provides a comprehensive review on recent developments in enzyme-MOF composites with a specific emphasis on their enhanced enzymatic activity compared to free enzymes.

Time-Resolved Spectroscopy for Dynamic Investigation of Photoresponsive Metal-Organic Frameworks

Photoresponsive MOFs with precise and adjustable reticular structures are attractive for light conversion applications. Uncovering the photoinduced carrier dynamics lays the essential foundation for the further development and optimization of the MOF material. With the application of time-resolved spectroscopy, photophysical processes including excimer formation, energy transfer/migration, and charge transfer/separation have been widely investigated. However, the identification of distinct photophysical processes in real experimental MOF spectra still remains difficult due to the spectral and dynamic complexity of MOFs. In this Perspective, we summarize the typical spectral features of these photophysical processes and the related analysis methods for dynamic studies performed by time-resolved photoluminescence (TR-PL) and transient absorption (TA) spectroscopy. Based on the recent understanding of excited-state properties of photoresponsive MOFs and the discussion of challenges and future outlooks, this Perspective aims to provide convenience for MOF kinetic analysis and contribute to the further development of photoresponsive MOF material.

Reticular chemistry guided precise construction of zirconium-pentacarboxylate frameworks with 5-connected Zr6 clusters

Zirconium-based metal-organic frameworks (Zr-MOFs) have been extensively studied due to their very rich structural chemistry. The combination of nearly unlimited carboxylic acid-based linkers and Zr6 clusters with multiple connectivities has led to diverse structures and specific properties of resultant Zr-MOFs. Herein, we demonstrate the successful use of reticular chemistry to construct two novel Zr-MOFs, HIAM-4040 and HIAM-4040-OH, with zfu topology. Based on a thorough structural analysis of (4,4)-connected lvt-type Zr-tetracarboxylate frameworks and a judicious linker design, we have obtained the first example of a Zr-pentacarboxylate framework featuring unprecedented 5-connected organic linkers and 5-connected Zr6 clusters. Compared with HIAM-4040, a larger Stokes shift is achieved in HIAM-4040-OH via hydroxyl group induced excited-state intramolecular proton transfer (ESIPT). HIAM-4040-OH exhibits high chemical and thermal stability and is used for HClO detection in aqueous solution with excellent sensitivity and selectivity.

On-off conduction photoswitching in modelled spiropyran-based metal-organic frameworks

Materials with photoswitchable electronic properties and conductance values that can be reversibly changed over many orders of magnitude are highly desirable. Metal-organic framework (MOF) films functionalized with photoresponsive spiropyran molecules demonstrated the general possibility to switch the conduction by light with potentially large on-off-ratios. However, the fabrication of MOF materials in a trial-and-error approach is cumbersome and would benefit significantly from in silico molecular design. Based on the previous proof-of-principle investigation, here, we design photoswitchable MOFs which incorporate spiropyran photoswitches at controlled positions with defined intermolecular distances and orientations. Using multiscale modelling and automated workflow protocols, four MOF candidates are characterized and their potential for photoswitching the conductivity is explored. Using ab initio calculations of the electronic coupling between the molecules in the MOF, we show that lattice distances and vibrational flexibility tremendously modulate the possible conduction photoswitching between spiropyran- and merocyanine-based MOFs upon light absorption, resulting in average on-off ratios higher than 530 and 4200 for p- and n-conduction switching, respectively. Further functionalization of the photoswitches with electron-donating/-withdrawing groups is demonstrated to shift the energy levels of the frontier orbitals, permitting a guided design of new spiropyran-based photoswitches towards controlled modification between electron and hole conduction in a MOF.

Membrane-catalysis integrated system for contaminants degradation and membrane fouling mitigation: A review

The integration of catalytic degradation and membrane separation processes not only enables continuous degradation of contaminants but also effectively alleviates inevitable membrane fouling, demonstrating fascinating practical value for efficient water purification. Such membrane-catalysis integrated system (MCIS) has attracted tremendous research interest from scientists in chemical engineering and environmental science recently. In this review, the advantages of MCIS are discussed, including the membrane structure regulation, stable catalyst loading, nano-confinement effect, and efficient natural organic matter (NOM) exclusion, highlighting the synergistic effect between membrane separation and catalytic process. Subsequently, the design considerations for the fabrication of catalytic membranes, including substrate membrane, catalytic material, and fabrication method, are comprehensively summarized. Afterward, the mechanisms and performance of MCIS based on different catalytic types, including liquid-phase oxidants/reductants involved MCIS, gas involved MCIS, photocatalysis involved MCIS, and electrocatalysis involved MCIS are reviewed in detail. Finally, the research direction and future perspectives of catalytic membranes for water purification are proposed. The current review provides an in-depth understanding of the design of catalytic membranes and facilitates their further development for practical applications in efficient water purification.

Growth mechanisms and anisotropic softness-dependent conductivity of orientation-controllable metal-organic framework nanofilms

Conductive metal-organic frameworks (cMOFs) manifest great potential in modern electrical devices due to their porous nature and the ability to conduct charges in a regular network. cMOFs applied in electrical devices normally hybridize with other materials, especially a substrate. Therefore, the precise control of the interface between cMOF and a substrate is particularly crucial. However, the unexplored interface chemistry of cMOFs makes the controlled synthesis and advanced characterization of high-quality thin films, particularly challenging. Herein, we report the development of a simplified synthesis method to grow "face-on" and "edge-on" cMOF nanofilms on substrates, and the establishment of operando characterization methodology using atomic force microscopy and X-ray, thereby demonstrating the relationship between the soft structure of surface-mounted oriented networks and their characteristic conductive functions. As a result, crystallinity of cMOF nanofilms with a thickness down to a few nanometers is obtained, the possible growth mechanisms are proposed, and the interesting anisotropic softness-dependent conducting properties (over 2 orders of magnitude change) of the cMOF are also illustrated.

Aggregation behaviour of pyrene-based luminescent materials, from molecular design and optical properties to application

Molecular aggregates are self-assembled from multiple molecules via weak intermolecular interactions, and new chemical and physical properties can emerge compared to their individual molecule. With the development of aggregate science, much research has focused on the study of the luminescence behaviour of aggregates rather than single molecules. Pyrene as a classical fluorophore has attracted great attention due to its diverse luminescence behavior depending on the solution state, molecular packing pattern as well as morphology, resulting in wide potential applications. For example, pyrene prefers to emit monomer emission in dilute solution but tends to form a dimer via π-π stacking in the aggregation state, resulting in red-shifted emission with quenched fluorescence and quantum yield. Over the past two decades, much effort has been devoted to developing novel pyrene-based fluorescent molecules and determining the luminescence mechanism for potential applications. Since the concept of "aggregation-induced emission (AIE)" was proposed by Tang et al. in 2001, aggregate science has been established, and the aggregated luminescence behaviour of pyrene-based materials has been extensively investigated. New pyrene-based emitters have been designed and synthesized not only to investigate the relationships between the molecular structure and properties and advanced applications but also to examine the effect of the aggregate morphology on their optical and electronic properties. Indeed, new aggregated pyrene-based molecules have emerged with unique properties, such as circularly polarized luminescence, excellent fluorescence and phosphorescence and electroluminescence, ultra-high mobility, etc. These properties are independent of their molecular constituents and allow for a number of cutting-edge technological applications, such as chemosensors, organic light-emitting diodes, organic field effect transistors, organic solar cells, Li-batteries, etc. Reviews published to-date have mainly concentrated on summarizing the molecular design and multi-functional applications of pyrene-based fluorophores, whereas the aggregation behaviour of pyrene-based luminescent materials has received very little attention. The majority of the multi-functional applications of pyrene molecules are not only closely related to their molecular structures, but also to the packing model they adopt in the aggregated state. In this review, we will summarize the intriguing optoelectronic properties of pyrene-based luminescent materials boosted by aggregation behaviour, and systematically establish the relationship between the molecular structure, aggregation states, and optoelectronic properties. This review will provide a new perspective for understanding the luminescence and electronic transition mechanism of pyrene-based materials and will facilitate further development of pyrene chemistry.

Cu2+@metal-organic framework-derived amphiphilic sandwich catalysts for enhanced hydrogenation selectivity of ketenes at the oil-water interface

Selective catalysis has always been an essential process for manufacturing various fine chemicals, such as food additives, pharmaceuticals and perfumes. Practically, pure target products are difficult to obtain even after complex purification procedures during industrial production. The development of a cost-effective, highly chemoselective and long-life catalyst may be an attractive solution, but such a catalyst is elusive. Herein, a novel class of amphiphilic N-doped carbon (NC), featuring graphitic carbon (GC) and highly dispersed Cu@Co NPs, was fabricated via simple calcination of a Cu2+-doped bimetallic metal-organic framework (MOF) precusor directly. Compared with monometallic Co@GC/NC, the side reaction of CO bond hydrogenation is obviously restrained, and thus, pure target product can be systematically obtained by Cu@Co@GC/NC, highlighting the high selectivity of Cu. More importantly, an amphiphilic characteristic in Cu@Co@GC/NC is a significant knob to integrate organic substrates with water very well. This amphiphilic material shows great potential as a field-deployable pathway for dispersible metal catalysts in organic systems.

Room Temperature Synthesis Mediated Porphyrinic NanoMOF Enables Benchmark Electrochemical Biosensing

Leveraging size effects, nanoparticles of metal-organic frameworks, nanoMOFs, have recently gained traction, amplifying their scopes in electrochemical sensing. However, their synthesis, especially under eco-friendly ambient conditions remains an unmet challenge. Herein, an ambient and fast secondary building unit (SBU)-assisted synthesis (SAS) route to afford a prototypal porphyrinic MOF, Fe-MOF-525 is introduced. Albeit the benign room temperature conditions, Fe-MOF-525(SAS) nanocrystallites obtained are of ≈30 nm size, relatively smaller than the ones conventional solvothermal methods elicit. Integrating Fe-MOF-525(SAS) as a thin film on a conductive indium tin oxide (ITO) surface affords Fe-MOF-525(SAS)/ITO, an electrochemical biosensor. Synergistic confluence of modular MOF composition, analyte-specific redox metalloporphyrin sites, and crystal downsizing contribute to its benchmark voltammetric uric acid (UA) sensing. Showcasing a wide linear range of UA detection with high sensitivity and low detection limit, this SAS strategy coalesces ambient condition synthesis and nanoparticle size control, paving a green way to advanced sensors.

Experimental manifestation of redox-conductivity in metal-organic frameworks and its implication for semiconductor/insulator switching

Electric conductivity in metal-organic frameworks (MOFs) follows either a band-like or a redox-hopping charge transport mechanism. While conductivity by the band-like mechanism is theoretically and experimentally well established, the field has struggled to experimentally demonstrate redox conductivity that is promoted by the electron hopping mechanism. Such redox conductivity is predicted to maximize at the mid-point potential of the redox-active units in the MOF, and decline rapidly when deviating from this situation. Herein, we present direct experimental evidence for redox conductivity in fluorine-doped tin oxide surface-grown thin films of Zn(pyrazol-NDI) (pyrazol-NDI = 1,4-bis[(3,5-dimethyl)-pyrazol-4-yl]naphthalenediimide). Following Nernstian behavior, the proportion of reduced and oxidized NDI linkers can be adjusted by the applied potential. Through a series of conductivity measurements, it is demonstrated that the MOF exhibits minimal electric resistance at the mid-point potentials of the NDI linker, and conductivity is enhanced by more than 10000-fold compared to that of either the neutral or completely reduced films. The generality of redox conductivity is demonstrated in MOFs with different linkers and secondary building units, and its implication for applications that require switching between insulating and semiconducting regimes is discussed.

Bioinspired Framework Catalysts: From Enzyme Immobilization to Biomimetic Catalysis

Enzymatic catalysis has fueled considerable interest from chemists due to its high efficiency and selectivity. However, the structural complexity and vulnerability hamper the application potentials of enzymes. Driven by the practical demand for chemical conversion, there is a long-sought quest for bioinspired catalysts reproducing and even surpassing the functions of natural enzymes. As nanoporous materials with high surface areas and crystallinity, metal-organic frameworks (MOFs) represent an exquisite case of how natural enzymes and their active sites are integrated into porous solids, affording bioinspired heterogeneous catalysts with superior stability and customizable structures. In this review, we comprehensively summarize the advances of bioinspired MOFs for catalysis, discuss the design principle of various MOF-based catalysts, such as MOF-enzyme composites and MOFs embedded with active sites, and explore the utility of these catalysts in different reactions. The advantages of MOFs as enzyme mimetics are also highlighted, including confinement, templating effects, and functionality, in comparison with homogeneous supramolecular catalysts. A perspective is provided to discuss potential solutions addressing current challenges in MOF catalysis.

Crystalline Unipolymer Monolayer with High Modulus and Conductivity

The synthesis of crystalline polymer with a well-defined orientated state and a two-dimensional crystalline size beyond a micrometer will be essential to achieve the highest physical feature of polymer material but remain challenging. Herein, we show the synthesis of the crystalline unipolymer monolayer with an unusual ultrahigh modulus that is higher than the ITO substrate and high conductance by simultaneous electrosynthesis and manipulation. We find that the polymer monolayer has fully extended in the vertical and unidirectional orientation, which is proposed to approach their theoretically highest density, modulus, and conductivity among all aggregation formations of the current polymer. The modulus and current density can reach 40 and 1000 times higher than their amorphous counterpart. It is also found that these monolayers exhibit the bias- and length-dependent multiple charge states and asymmetrically negative differential resistance (NDR) effect, indicating that this unique molecular tailoring and ordering design is promising for multilevel resistive memory devices. Our work demonstrates the creation of a crystalline polymer monolayer for approaching the physical limit of polymer electronic materials and also provides an opportunity to challenge the synthetically iterative limit of an isolated ultra-long polymer.

Photodynamic Inactivation of Bacteria and Biofilms with Benzoselenadiazole-Doped Metal-Organic Frameworks

Bacterial biofilms are difficult to treat due to their resistance to traditional antibiotics. Although photodynamic therapy (PDT) has made significant progress in biomedical applications, most photosensitizers have poor water solubility and can thus aggregate in hydrophilic environments, leading to the quenching of photosensitizing activity in PDT. Herein, a benzoselenadiazole-containing ligand was designed and synthesized to construct the zirconium (IV)-based benzoselenadiazole-doped metal-organic framework (Se-MOF). Characterizations revealed that Se-MOF is a type of UiO-68 topological framework with regular crystallinity and high porosity. Compared to the MOF without benzoselenadiazole, Se-MOF exhibited a higher ¹O₂ generation efficacy and could effectively kill Staphylococcus aureus bacteria under visible-light irradiation. Importantly, in vitro biofilm experiments confirmed that Se-MOF could efficiently inhibit the formation of bacteria biofilms upon visible-light exposure. This study provides a promising strategy for developing MOF-based PDT agents, facilitating their transformation into clinical photodynamic antibacterial applications.

Ionic metal-organic frameworks (iMOFs): progress and prospects as ionic functional materials

Metal-organic frameworks (MOFs) have been a research hotspot for the last two decades, witnessing an extraordinary upsurge across various domains in materials chemistry. Ionic MOFs (both anionic and cationic MOFs) have emerged as next-generation ionic functional materials and are an important subclass of MOFs owing to their ability to generate strong electrostatic interactions between their charged framework and guest molecules. Furthermore, the presence of extra-framework counter-ions in their confined nanospaces can serve as additional functionality in these materials, which endows them a significant advantage in specific host-guest interactions and ion-exchange-based applications. In the present review, we summarize the progress and future prospects of iMOFs both in terms of fundamental developments and potential applications. Furthermore, the design principles of ionic MOFs and their state-of-the-art ion exchange performances are discussed in detail and the future perspectives of these promising ionic materials are proposed.

Synthesis and shaping of metal-organic frameworks: a review

Metal-organic frameworks (MOFs) possess excellent advantages, such as high porosity, large specific surface area, and an adjustable structure, showing good potential for applications in gas adsorption and separation, catalysis, conductivity, sensing, magnetism, etc. However, they still suffer from significant limitations in terms of the scale-up synthesis and shaping, hindering the realization of large-scale commercial applications. Despite some attempts having been devoted to addressing this, challenges remain. In this paper, we outline the advantages and drawbacks of existing synthetic routes such as electrochemistry, microwave, ultrasonic radiation, green solvent reflux, room temperature stirring, steam-assisted transformation, mechanochemistry, and fluid chemistry in terms of scale-up production. Then, the shaping methods of MOFs such as extrusion, mechanical compaction, rolling granulation, spray drying, gel technology, embedded granulation, phase inversion, 3D printing and other shaping methods for the preparation of membranes, coatings and nanoparticles are discussed. Finally, perspectives on the large-scale synthesis and shaping of MOFs are also proposed. This work helps provide in-depth insight into the scale-up production and shaping process of MOFs and boost commercial applications of MOFs.

Ultrafine Silver Nanoparticle Encapsulated Porous Molecular Traps for Discriminative Photoelectrochemical Detection of Mustard Gas Simulants by Synergistic Size-Exclusion and Site-Specific Recognition

The rapid, discriminative, and portable detection of highly toxic chemical warfare agents is extremely important for response to public security emergencies but remains a challenge. One plausible solution involves the integration of porous molecular traps onto a photoelectrochemical (PEC) sensor. Here, a fast and facile protocol is developed to fabricate sub-1 nm AgNPs encapsulated hydrogen-bonded organic framework (HOF) nanocomposite materials through an in situ photoreduction and subsequent encapsulation process. Compared to traditional semiconductors and selected metal-organic frameworks (MOF) materials, these AgNPs@HOFs show significantly enhanced photocurrent. Most importantly, the portable PEC device based on AgNPs@HOF-101 can selectively recognize 13 different mustard gas simulants, including 2-chloroethyl ethyl sulfide (CEES), based on synergistic size-exclusion and specific recognition. The extremely low detection limit for CEES (15.8 nmol L^-1 ), reusability (at least 30 cycles), and long-term working stability (at least 30 d) of the portable PEC device warrant its use as a chemical warfare agents (CWAs) sensor in practical field settings. More broadly, this work indicates that integrating porous molecular traps onto PEC sensors offers a promising strategy to further develop portable devices for CWAs detection with both ultrahigh sensitivity and selectivity.

Photoelectrochemical Water Oxidation over Novel Semiconducting Zinc-Based Metal-Thiolate Framework

Designing an efficient catalyst for a sustainable photoelectrochemical water oxidation reaction is very challenging in the context of renewable energy research. Here, we have introduced a new semiconducting porous zinc-thiolate framework via successful stitching of an "N" donor linker with a triazine-based tristhiolate secondary building unit in the overall architecture. The introduction of both linker and tristhiolate ligand synergistically modifies the architecture by making it a rigid, crystalline, three-dimensional, thermally stable, and porous framework. Our novel zinc-thiolate framework is used as an n-type semiconductor as revealed from the solid-state UV-vis DRS spectroscopic analysis, ac and dc conductivity analysis, and Mott-Schottky plot. This n-type semiconductor-based zinc-thiolate framework is utilized in the photoelectrochemical water oxidation reaction. It displayed a very high efficiency for a visible-light-driven oxygen evolution reaction (OER) in a KOH medium using standard Ag/AgCl as the reference electrode. The superiority of this material was further revealed from the low onset potential (0.822 mV vs RHE), high photocurrent density (0.204 mA cm^-2), good stability, and high O₂ evolution rate (77 μmol g^-1 of oxygen evolution within 2 h), and a good efficiency (ABPE 0.42%, IPCE 29.6% and APCE 34.5%). Furthermore, the porosity in the overall framework seems to be a blessing to the photoelectrochemical performance due to better mass diffusion of the electrolyte. A detailed mechanism for the OER reaction was analyzed through density functional theory analysis suggesting the potential future of this Zn-thiolate framework for achieving a high efficiency in the sustainable water oxidation reaction.

Versatilely Manipulating the Mechanical Properties of Polymer Nanocomposites by Incorporating Porous Fillers: A Molecular Dynamics Simulation Study

Polymer nanocomposites (PNCs) have been attracting myriad scientific and technological attention due to their promising mechanical and functional properties. However, there remains a need for an efficient method that can further strengthen the mechanical performance of PNCs. Here, we propose a strategy to design and fabricate novel PNCs by incorporating porous fillers (PFs) such as metal-organic frameworks with ultrahigh specific surface areas and tunable nanospaces to polymer matrices via coarse-grained molecular dynamics simulations. Three important parameters─the polymer chain stiffness (k), the interaction strength between the PF center and the end functional groups of polymer chains (ε_center end), and the PF weight fraction (w)─are systematically examined. First, attributed to the penetration of polymer chains into PFs at a strong ε_center end, the dimension of polymer chains such as the radius of gyration and the end-to-end distance increases greatly as a function of k compared to the case of the neat polymer system. The penetration of polymer chains is validated by characterizing the radial distribution function between end functional groups and filler centers, as well as the visualization of the snapshots. Also, the dispersion state of PFs tends to be good because of the chain penetration. Then, the glass transition temperature ratio of PNCs to that of the neat systems exhibits a maximum in the case of k = 5ε, indicating that the strongest interlocking between polymer chains and PFs occurs at intermediate chain stiffness. The polymer chain dynamics of PNCs decreases to a plateau at k = 5ε and then becomes stable, and the relative mobility to that of the neat system as well presents the same variation trend. Furthermore, the mechanical property under uniaxial deformation is thoroughly studied, and intermediates k, ε_center end, and w can bring about the best mechanical property. This is because of the robust penetration and interaction, which is confirmed by calculating the stress of every component of PNCs with and without end functional groups and PF centers as well as the nonbonded interaction energy change between different components. Finally, the optimal condition (k = 5.36ε, ε_center end = 5.29ε, and w = 6.54%) to design the PNC with superior mechanical behavior is predicted by Gaussian process regression, an active machine learning (ML) method. Overall, incorporating PFs greatly enhances the entanglements and interactions between polymer chains and nanofillers and brings effective mechanical reinforcements with lower filler weight fractions. We anticipate that this will provide new routes to the design of mechanically reinforced PNCs.

A comparative study of the toxic effect of ZIF-8 and ZIF-L on the colonization and decomposition of shaded outdoor mice carrions by arthropods

Metal–organic frameworks (MOFs) are promising materials for several applications. Thus, they have been intensively reported and commercialized by several international companies. However, little is known about the fate and risk of MOFs to living organisms. Here, the toxic effect of two Zinc (Zn)-based MOFs; zeolitic imidazolate frameworks (ZIF-8) and leaf-like ZIF (ZIF-L), was tested to investigate the impact of the postmortem period of mice carrions and arthropods which found in decomposing carrions. The data analysis revealed an increase in zinc content over time. Toxicology in forensics studies biological materials for the presence of poisons, such as pharmaceuticals. The toxicology report can provide important details about the types of chemicals present in a person and whether the amount of those substances is in line with a therapeutic dose or exceeds a dangerous level. These findings conclude the possible fate and impact after mortality. This study presents the first study of the toxic effect of ZIFs materials using mice carrions and arthropods (Sarcophaga sp. Larvae) via morphological and microscopic studies compared with control, providing important biological information could aid in the environmental impact of the toxic level of MOF materials.

Metal-Organic Framework-Derived Electrocatalysts Competent for the Conversion of Acrylonitrile to Adiponitrile

Electrochemical conversion of acrylonitrile (AN) to produce adiponitrile (ADN), the raw material for the production of Nylon 66, has become a crucial process owing to the increasing market demand of Nylon 66. Although the metallic Pb or Cd electrodes are commonly used for this reaction, the use of electrocatalysts or electrodes modified with catalysts has been barely investigated. In this study, nanoporous and electrically conductive metal-organic framework (MOF)-derived materials composed of Pb, PbO, and carbon are synthesized by carbonizing a Pb-based MOF through thermal treatments, and these MOF-derived materials are served as electrocatalysts for the electrosynthesis of ADN. The crystallinity, morphology, elemental composition, porosity, electrical conductivity, and electrochemically active surface area of each MOF-derived material are investigated. Mass-transport-corrected Tafel analysis is used to probe the enhanced kinetics for the electrochemical reduction of AN occurring at the electrode modified with the MOF-derived material. Electrolytic experiments at various applied potentials are conducted to quantify the production rate and Faradaic efficiency toward ADN, and the result shows that the MOF-derived materials can act as electrocatalysts to initiate the electrochemical reduction of AN to produce ADN at a reduced overpotential. The optimal MOF-derived electrocatalyst can achieve a Faradaic efficiency of 67% toward ADN at an applied potential of -0.85 V versus reversible hydrogen electrode─a much lower overpotential compared to that typically required for this reaction without the use of catalysts. Findings here shed light on the design and development of advanced electrocatalysts to boost the performances for the electrosynthesis of ADN.

Visible-Light-Driven Zr-MOF/BiOBr Heterojunction for the Efficient Synchronous Removal of Hexavalent Chromium and Rhodamine B from Wastewater

With the rapid industrial development, the coexistence of multiple pollutants in wastewater has become a common phenomenon. Thus, developing highly efficient decontamination methods is imperative. In this work, a string of UiO-66-NH₂/BiOBr heterojunctions with varying ratios of BiOBr were prepared and applied to remove hexavalent chromium Cr(VI) and rhodamine B (RhB). The possible growth process of BiOBr nanosheets on UiO-66-NH₂, removal activity of contaminants, and photocatalysis mechanism were investigated. When the mass ratio of UiO-66-NH₂ to BiOBr reaches 1:0.75, the heterojunction (NB-75) shows optimal photocatalytic activity. After 30 min of adsorption, the total removal rates of Cr(VI) (50 mg/L) and RhB (10 mg/L) over NB-75 (0.25 g/L) reaches 96.7% within 120 min of illumination and 98.9% within 80 min of illumination, respectively. For the removal process, there are two factors. The first is the high adsorption capacity for RhB and Cr(VI) owing to the high porosity of UiO-66-NH₂ and interlayer surface positive charge of BiOBr. The second is the improved visible-light photocatalytic performance of the UiO-66-NH₂/BiOBr heterojunction via rapid separation of photoinduced carriers. In addition, the active species capture study reveals that the electrons (e^-) and the superoxide radicals (^•O₂ ^-) play key roles in Cr(VI) reduction, while the holes (h⁺) are major reactive groups participating in the degradation of RhB. This work demonstrated a kind of promising MOF-based photocatalysis material for eliminating Cr(VI) and RhB simultaneously.

Metal-organic framework functionalized poly-cyclodextrin membranes confining polyaniline for charge storage

Crystals of a metal-organic framework, UiO-66, are grown on electrospun crosslinked poly-cyclodextrin (poly-CD) fibrous membranes with an ultrahigh coverage, and polyaniline (PANI) is further confined within the MOF pores. The obtained PANI@UiO-66/poly-CD membranes are used as free-standing electrodes towards use in wearable energy-storage devices.

Two-Dimensional Metal-Organic Framework Nanosheets: Synthesis and Applications in Electrocatalysis and Photocatalysis

Two-dimensional metal-organic nanosheets (2D MONs) are an emerging class of ultrathin, porous, and crystalline materials. The organic/inorganic hybrid nature offers MONs distinct advantages over other inorganic nanosheets in terms of diversity of organic ligands and metal notes. Compared to bulk three-dimensional metal-organic frameworks, 2D MONs possess merits of high density and readily accessible catalytic sites, reduced diffusion pathways for reactants/products, and fast electron transport. These features endow MONs with enhanced physical/chemical properties and are ideal for heterogeneous catalysis. In this Review, state-of-the-art synthetic methods for the fabrication of 2D MONs were summarized. The advances of 2D MONs-based materials for electrocatalysis and photocatalysis, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO₂ RR), and electro-/photocatalytic organic transformations were systematically discussed. Finally, the challenges and perspectives regarding future design and synthesis of 2D MONs for high-performance electrocatalysis and photocatalysis were provided.

A Ni(II) Metal-Organic Framework with Mixed Carboxylate and Bipyridine Ligands for Ultrafast and Selective Sensing of Explosives and Photoelectrochemical Hydrogen Evolution

We report a Ni-MOF (nickel metal-organic framework), Ni-SIP-BPY, synthesized by using two linkers 5-sulfoisophthalic acid (SIP) and 4,4'-bipyridine (BPY) simultaneously. It displays an orthorhombic crystal system with the Ama2 space group: a = 31.425 Å, b = 19.524 Å, c = 11.2074 Å, α = 90°, β = 90°, γ = 90°, and two different types of nickel(II) centers. Interestingly, Ni-SIP-BPY exhibits excellent sensitivity (limit of detection, 87 ppb) and selectivity toward the 2,4,6-trinitrophenol (TNP)-like mutagenic environmental toxin in the pool of its other congeners via "turn-off" fluorescence response by the synergism of resonance energy transfer, photoinduced electron transfer, intermolecular charge transfer, π-π interactions, and competitive absorption processes. Experimental studies along with corroborated theoretical experimentation, vide density functional theory studies, shed light on determining the plausible mechanistic pathway in selective TNP detection, which is highly beneficial in the context of homeland security perspective. Along with the sensing of nitroaromatic explosives, the moderately low band gap and the p-type semiconducting behavior of Ni-SIP-BPY make it suitable as a photoanode material for visible-light-driven water splitting. Highly active surface functionalities and sufficient conduction band minima effectively reduce the water and result in a seven times higher photocurrent density under visible-light illumination.

Probing the electronic and ionic transport in topologically distinct redox-active metal-organic frameworks in aqueous electrolytes

Three topologically distinct zirconium-based metal-organic frameworks (Zr-MOFs) constructed from redox-innocent linkers, MOF-808, defective UiO-66, and CAU-24, are synthesized, and the spatially dispersed redox-active manganese sites are post-synthetically immobilized on the hexa-zirconium nodes of these Zr-MOFs. The crystallinity, morphology, porosity, manganese loading, and bulk electrical conductivity of each material are studied. The redox-hopping-based electrochemical reaction between the installed Mn(III) and Mn(IV) occurring within the thin films of these MOFs in aqueous electrolytes is investigated, in the presence of various concentrations of Na₂SO₄ in the electrolytes. Cyclic voltammetry is used to qualitatively study the redox-hopping process, and chronoamperometry is used to quantify the electrochemically active fractions of manganese sites within the MOF thin film as well as the values of apparent diffusivity for the redox-hopping process. By adjusting the concentration of Na₂SO₄ in the electrolyte, the rate-determining step for the redox-hopping process can be tuned from ionic transport to electronic transport, and the Mn-decorated MOF-808, which possesses the largest pore size, can achieve the highest value of apparent diffusivity. Findings here shed light on the selection of Zr-MOF as well as the choice of electrolyte concentration for the applications of MOFs in supercapacitors and electrocatalysis relying on such redox-hopping processes in aqueous electrolytes.

Redox-Hopping-Based Charge Transport Mediated by Ru(II)-Polypyridyl Species Immobilized in a Mesoporous Metal-Organic Framework

Electronic charge transport through crystalline metal-organic frameworks (MOFs) can be accomplished by site-to-site electron (or hole) hopping, provided that redox-active sites, such as easily reducible or oxidizable MOF linkers, are present. If the framework itself is redox-inert, solvent-assisted ligand incorporation of redox-active moieties can serve to enable hopping-based charge transport. Here we have studied the redox hopping process within Ru-bpy@NU-1008, where Ru-bpy is a carboxylate-functionalized derivative, i.e., a node-ligating derivative, of the well-known chromophore Ru(2,2′-bipyridine)32+, and NU-1008 is a redox-inert MOF featuring hierarchical porosity and csq topology. Chronoamperometry experiments with electrode-supported thin films of Ru-bpy@NU-1008 show that charge transport is feasible through portions of the MOF, with other portions being inaccessible. Possible confounding features are the undersized c-pores that cross-connect 1D mesoporous channels, as ingress and egress of charge-compensating anions is believed to accompany the net oxidation of Ru(II) to Ru(III) and the reduction of Ru(III) to Ru(II). Phenomenologically, transport through the electroactive portion of the films is diffusion-like, with the magnitude of the apparent diffusion coefficient being 6 × 10−12 cm2/s.