Metal-organic framework membranes: From synthesis to electrocatalytic applications

Metal-organic frameworks (MOFs), as an emerging family of porous inorganic-organic crystal materials, exhibit widely applications in gas storage and separation, drug release, sensing, and catalysis, owing to easily adjustable pore sizes, uniformly distributed metal centers, high surface areas, and tunable functionalities. However, MOF crystal powders are usually difficult to be directly applied into specific devices because of their brittleness, insolubility and low compatibility. Therefore, to expand versatile MOF membranes with robustness and operational flexibility is urgent to satisfy practical applications. Although numerous reports have reviewed the synthesis and applications of MOF membranes, relatively few reports the electrocatalytic properties based on MOF membranes. Herein, this mini-review provides an overview of preparation of MOF membranes, including directed synthesis, secondary growth and electrochemical deposition method. Meanwhile, fabrication of ultrathin 2D MOF nanosheets those can be also defined as a kind of nanoscale MOF membranes is also mentioned. Electrocatalytic performance of oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and CO₂ reduction reaction (CO₂RR) for diverse MOF membranes/nanosheets and their derivatives are introduced.     

金属-有机框架衍生中空超级结构的研究进展:合成与应用（英文）

金属-有机框架(MOF)衍生功能材料的合理设计对于其应用具有重要意义.以简单MOF衍生物为基本单元组装成中空超级结构(HSSs)是提升材料性能的有效策略.目前关于MOF衍生物的综合评述已有诸多报道,然而鲜少针对HSSs的构筑和应用.本文系统总结了MOF衍生HSSs相关研究的最新进展.首先,根据结构差异将MOF衍生HSSs分为5种类型;其次,总结了由MOF衍生物构建HSSs的策略,着重阐述如何设计MOF前驱体和选择转化条件;随后,展示了MOF衍生HSSs在能源和催化相关领域的一些应用;最后,提出了MOF衍生HSSs研究领域所面临的挑战和机遇,旨在为MOF衍生材料的结构设计和性能强化提供一些思路.     

碳量子点-金属有机骨架复合材料的合成和应用

金属-有机骨架材料(MOF)与碳量子点(CD)的复合材料CD@MOF是一种应用范围很广的新型材料。本文介绍了MOF和CD@MOF复合材料的合成方法和复合材料在各领域中的应用,并对其未来发展作出了展望。     

Direct Fabrication of Free‐Standing MOF Superstructures with Desired Shapes by Micro‐Confined Interfacial Synthesis

Recently, metal–organic frameworks (MOFs) with multifunctional pore chemistry have been intensively investigated for positioning the desired morphology at specific locations onto substrates for manufacturing devices. Herein, we develop a micro‐confined interfacial synthesis (MIS) approach for fabrication of a variety of free‐standing MOF superstructures with desired shapes. This approach for engineering MOFs provides three key features: 1) in situ synthesis of various free‐standing MOF superstructures with controlled compositions, shape, and thickness using a mold membrane; 2) adding magnetic functionality into MOF superstructures by loading with Fe₃O₄ nanoparticles; 3) transferring the synthesized MOF superstructural array on to flat or curved surface of various substrates. The MIS route with versatile potential opens the door for a number of new perspectives in various applications.     

An updated review of metal–organic framework materials in photo(electro)catalytic applications: From CO2 reduction to wastewater treatments

This review summarizes recent advances in the development of metal–organic framework (MOF) materials, focusing on their photocatalytic and photoelectrocatalytic activities for different applications, such as CO₂ reduction, water splitting, elimination of inorganic contaminants, and degradation of organic pollutants. In each section, the first applications described focus on the photocatalysts developed using MOF materials. Meanwhile, the latest are centered on photoelectrode applications using these materials. The last advances in the synthesis process are discussed in terms of improvement in electron transfer and charge separation, which enhance the activity of the photo (electro)catalysts. Finally, some insights about the upcoming applications of MOF materials are provided.     

MOF thin films: existing and future applications

The applications and potentials of thin film coatings of metal-organic frameworks (MOFs) supported on various substrates are discussed in this critical review. Because the demand for fabricating such porous coatings is rather obvious, in the past years several synthesis schemes have been developed for the preparation of thin porous MOF films. Interestingly, although this is an emerging field seeing a rapid development a number of different applications on MOF films were either already demonstrated or have been proposed. This review focuses on the fabrication of continuous, thin porous films, either supported on solid substrates or as free-standing membranes. The availability of such two-dimensional types of porous coatings opened the door for a number of new perspectives for functionalizing surfaces. Also for the porous materials themselves, the availability of a solid support to which the MOF-films are rigidly (in a mechanical sense) anchored provides access to applications not available for the typical MOF powders with particle sizes of a few μm. We will also address some of the potential and applications of thin films in different fields like luminescence, QCM-based sensors, optoelectronics, gas separation and catalysis. A separate chapter has been devoted to the delamination of MOF thin films and discusses the potential to use them as free-standing membranes or as nano-containers. The review also demonstrates the possibility of using MOF thin films as model systems for detailed studies on MOF-related phenomena, e.g. adsorption and diffusion of small molecules into MOFs as well as the formation mechanism of MOFs (101 references).     

A Surfactant‐Free and Scalable General Strategy for Synthesizing Ultrathin Two‐Dimensional Metal–Organic Framework Nanosheets for the Oxygen Evolution Reaction

Metal–organic framework (MOFs) two‐dimensional (2D) nanosheets have many coordinatively unsaturated metal sites that act as active centres for catalysis. To date, limited numbers of 2D MOFs nanosheets can be obtained through top‐down or bottom‐up synthesis strategies. Herein, we report a 2D oxide sacrifice approach (2dOSA) to facilely synthesize ultrathin MOF‐74 and BTC MOF nanosheets with a flexible combination of metal sites, which cannot be obtained through the delamination of their bulk counterparts (top‐down) or the conventional solvothermal method (bottom‐up). The ultrathin iron–cobalt MOF‐74 nanosheets prepared are only 2.6 nm thick. The sample enriched with surface coordinatively unsaturated metal sites, exhibits a significantly higher oxygen evolution reaction reactivity than bulk FeCo MOF‐74 particles and the state‐of‐the‐art MOF catalyst. It is believed that this 2dOSA could provide a new and simple way to synthesize various ultrathin MOF nanosheets for wide applications.     

Two-dimensional MOFs: Design & Synthesis and Applications

For the past few years, two-dimensional materials have attracted widespread attention owing to their special properties and potential applications. It is well-known that graphene, transition metal disulfide compounds (TMDC), carbon nitride, transition metal carbonitrides (Mxenes), silene and hexagonal boron nitride are typical two-dimensional materials. Compared with these traditional two-dimensional materials, two-dimensional MOF is favored by numerous researchers because of its unique structure. Based on the unique metal ion and organic ligand coordination of MOF and two-dimensional layered structure, the applications of two-dimensional MOF were getting serious, including catalysis, supercapacitor, gas adsorption/separation, sensors and so on. This review presents a relatively comprehensive summary of the design & synthesis and applications of two-dimensional MOF over the past few years. Furthermore, the opportunities and challenges have been discussed to supply a promising prospect to this field.     

Novel route to size-controlled Fe-MIL-88B-NH2 metal-organic framework nanocrystals

A new approach for the synthesis of uniform metal-organic framework (MOF) nanocrystals with controlled sizes and aspect ratios has been developed using simultaneously the non-ionic triblock co-polymer F127 and acetic acid as stabilizing and deprotonating agents, respectively. The alkylene oxide segments of the triblock co-polymer can coordinate with metal ions and stabilize MOF nuclei in the early stage of the formation of MOF nanocrystals. Acetic acid can control the deprotonation of carboxylic linkers during the synthesis and, thus, enables the control of the rate of nucleation, leading to the tailoring of the size and aspect ratio (length/width) of nanocrystals. Fe-MIL-88B-NH(2), as an iron-based MOF crystal, was selected as a typical example to illustrate our approach. The results reveal that this approach is used for not only the synthesis of uniform nanocrystals but also the control of the size and aspect ratio of the materials. The size and aspect ratio of nanocrystals increase with an increase in the concentration of acetic acid in the synthetic mixture. The non-ionic triblock co-polymer F127 and acetic acid can be easily removed from the Fe-MIL-88B-NH(2) nanocrystal products by washing with ethanol, and thus, their amine groups are available for practical applications. The approach is expected to synthesize various nanosized carboxylate-based MOF members, such as MIL-53, MIL-89, MIL-100, and MIL-101.     

Well‐Defined Metal–Organic Framework Hollow Nanocages

Metal–organic frameworks (MOFs) have demonstrated great potentials in a variety of important applications. To enhance the inherent properties and endow materials with multifunctionality, the rational design and synthesis of MOFs with nanoscale porosity and hollow feature is highly desired and remains a great challenge. In this work, the formation of a series of well‐defined MOF (MOF‐5, Fe^II‐MOF‐5, Fe^III‐MOF‐5) hollow nanocages by a facile solvothermal method, without any additional supporting template is reported. A surface‐energy‐driven mechanism may be responsible for the formation of hollow nanocages. The addition of pre‐synthesized poly(vinylpyrrolidone)‐ (PVP) capped noble‐metal nanoparticles into the synthetic system of MOF hollow nanocages yields the yolk–shell noble metal@MOF nanostructures. The present strategy to fabricate hollow and yolk–shell nanostructures is expected to open up exciting opportunities for developing a novel class of inorganic–organic hybrid functional nanomaterials.     

PolyMOF Nanoparticles: Dual Roles of a Multivalent polyMOF Ligand in Size Control and Surface Functionalization

Metal–organic framework nanoparticles (MOF NPs) have emerged as an important class of materials that display significantly enhanced performance in many applications compared to bulk MOF materials; their synthesis, however, commonly involves a tedious sequence that controls particle size and surface properties in separate steps. Now, a simple strategy to access functional MOF NPs in one pot is reported that uses a polyMOF ligand possessing a polymer block for surface functionalization and a coordination block with tunable multivalency for size control. This strategy produces uniform polyMOF‐5 NPs with sizes down to 20 nm, displaying exceptional structural and colloidal stability upon exposure to ambient conditions. A detailed time‐dependent study revealed that the polyMOF NPs were formed following an aggregation‐confined crystallization mechanism. Generality was demonstrated through the synthesis of well‐defined polyUiO‐66 NPs.     

Pore‐Environment Engineering in Multifunctional Metal‐Organic Frameworks

As a new type of highly ordered porous crystalline material, metal‐organic frameworks (MOFs) have been extensively studied in many fields due to their high specific surface area and porosity, flexible modifiability and tailorability. After nearly 20 years of development, the synthesis of MOF materials has gradually evolved from exploration and trial to precise design. The synthesis method has also evolved from an early one‐step synthesis to the coexistence of various synthesis strategies, including functional‐oriented microstructural design optimization, pore size adjustment, and secondary structural unit modification, enabling MOF materials to expand their potential applications in many fields. In this review, we mainly discuss the pore regulation of function‐oriented MOF through different synthesis strategies, including (1) direct synthesis, (2) post‐synthesis modification (PSM), (3) building block replacement (BBR), (4) pore space partition (PSP), (5) construction of multi‐mesoporous MOF, (6) dynamic septal ligand insertion, and discuss the relationship between related performance optimization through framework structure and pore environment/size optimization.     

Anodized Aluminum Oxide Templated Synthesis of Metal–Organic Frameworks Used as Membrane Reactors

The incorporation of metal–organic frameworks (MOFs) into membrane‐shaped architectures is of great importance for practical applications. The currently synthesized MOF‐based membranes show many disadvantages, such as poor compatibility, low dispersity, and instability, which severely limit their utility. Herein, we present a general, facile, and robust approach for the synthesis of MOF‐based composite membranes through the in situ growth of MOF plates in the channels of anodized aluminum oxide (AAO) membranes. After being used as catalysis reactors, they exhibit high catalytic performance and stability in the Knoevenagel condensation reaction. The high catalytic performance might be attributed to the intrinsic structure of MOF‐based composite membranes, which can remove the products from the reaction zone quickly, and prevent the aggregation and loss of catalysts during reaction and recycling process.     

Electric Field-Controlled Synthesis and Characterisation of Single Metal–Organic-Framework (MOF) Nanoparticles

Achieving control over the size distribution of metal–organic-framework (MOF) nanoparticles is key to biomedical applications and seeding techniques. Electrochemical control over the nanoparticle synthesis of the MOF, HKUST-1, is achieved using a nanopipette injection method to locally mix Cu²⁺ salt precursor and benzene-1,3,5-tricarboxylate (BTC³⁻) ligand reagents, to form MOF nanocrystals, and collect and characterise them on a TEM grid. In situ analysis of the size and translocation frequency of HKUST-1 nanoparticles is demonstrated, using the nanopipette to detect resistive pulses as nanoparticles form. Complementary modelling of mass transport in the electric field, enables particle size to be estimated and explains the feasibility of particular reaction conditions, including inhibitory effects of excess BTC³⁻. These new methods should be applicable to a variety of MOFs, and scaling up synthesis possible via arrays of nanoscale reaction centres, for example using nanopore membranes.     

Self-assembly of 3p-Block Metal-based Metal-Organic Frameworks from Structural Perspective

Metal-organic frameworks(MOFs) are a class of porous inorganic-organic hybrid materials, which are constructed from diverse inorganic building units and multi-functional organic ligands. Highly ordered pore structures and tailored functionalization have made MOF materials potential for applications in many fields. Among various MOF materials, 3p-block metal(Al, Ga, and In)-based MOFs exhibit higher chemical stability than divalent transition metal-based MOFs due to their higher valence. In this review, Al-MOFs and In-MOFs were mainly discussed from the perspective of categories of inorganic building blocks, coordination types, and numbers of organic ligands. This review will give intuitive guidance to the design and synthesis of novel 3p-block metal-based MOFs with potential applications.     

Solvent‐Assisted Linker Exchange: An Alternative to the De Novo Synthesis of Unattainable Metal–Organic Frameworks

Metal‐organic frameworks (MOFs) have gained considerable attention as hybrid materials—in part because of a multitude of potential useful applications, ranging from gas separation to catalysis and light harvesting. Unfortunately, de novo synthesis of MOFs with desirable function–property combinations is not always reliable and may suffer from vagaries such as formation of undesirable topologies, low solubility of precursors, and loss of functionality of the sensitive network components. The recently discovered synthetic approach coined solvent‐assisted linker exchange (SALE) constitutes a simple to implement strategy for circumventing these setbacks; its use has already led to the generation of a variety of MOF materials previously unobtainable by direct synthesis methods. This Review provides a perspective of the achievements in MOF research that have been made possible with SALE and examines the studies that have facilitated the understanding and broadened the scope of use of this invaluable synthetic tool.     

Advances of Metal‐Organic Frameworks in Energy and Environmental Applications

Nowadays, energy shortage and environmental pollution issues are increasingly severe and urgent to be solved. The effective storage and use of environmentally friendly fuels and removal of harmful gases from the environment are great challenges and of great importance both for the environment protection and for human health. Porous metal‐organic frameworks (MOFs) are highly ordered crystalline materials formed by the self‐assembly process of metal ions and organic ligands. Their good features such as ultrahigh porosity, large surface area, structural diversity and functionalities make them promising candidates for applications in energy and environmental fields. MOF thin films and MOF composites have also been investigated to further enhance the properties and introduce new functionalities. This review provides an overview of the synthesis methods of pristine MOFs, MOF thin films and MOF composites, and significant advances of MOFs in energy and environment applications such as energy storage (H₂, CH₄), CO₂ capture and separation, adsorption removal and sensing of harmful gases in the environment.     

金属-有机骨架材料及其在催化反应中的应用

金属-有机骨架(metal-organic frameworks, MOFs)材料是由金属离子和有机配体通过自组装而成的具有多孔结构的特殊晶体材料。由于其种类的多样性、孔道的可调性和结构的易功能化,已在气体的吸附和分离、催化、磁学、生物医学等领域表现出了诱人的应用前景。本文介绍了MOFs材料的类型和常用的合成方法,综述了近年来MOFs材料在催化领域的应用,特别是以MOFs材料中骨架金属作为活性中心、骨架有机配体作为活性中心和负载催化活性组分的催化反应,并对MOFs材料的催化应用趋势做了展望,以期对MOFs材料的催化性能有比较全面的认识。     

A roadmap to implementing metal-organic frameworks in electronic devices: challenges and critical directions

Metal-organic frameworks (MOFs) and related material classes are attracting considerable attention for applications such as gas storage, separations, and catalysis. In contrast, research focused on potential uses in electronic devices is in its infancy. Several sensing concepts in which the tailorable chemistry of MOFs is used to enhance sensitivity or provide chemical specificity have been demonstrated, but in only a few cases are MOFs an integral part of an actual device. The synthesis of a few electrically conducting MOFs and their known structural flexibility suggest that MOF-based electronic devices exploiting these properties could be constructed. It is clear, however, that new fabrication methods are required to take advantage of the unique properties of MOFs and extend their use to the realms of electronic circuitry. In this Concepts article, we describe the basic functional elements needed to fabricate electronic devices and summarize the current state of relevant MOF research, and then review recent work in which MOFs serve as active components in electronic devices. Finally, we propose a high-level roadmap for device-related MOF research, the objective of which is to stimulate thinking within the MOF community concerning the development these materials for applications including sensing, photonics, and microelectronics.     

金属有机框架膜的制备及应用

金属有机框架化合物是一类新颖的纳米孔结晶材料,其由金属离子或簇以强的配位键形式连接多种多样的有机配体构成．金属有机框架化合物的均一孔径、高比表面积和吸附亲和力等独特的结构特点使其在组装成具有优异性能的膜方面具有很强的吸引力．金属有机框架膜在基础理论和实际应用方面显示了巨大的潜力．本文主要介绍近年来关于金属有机框架膜的制备及其在分离、化学传感、催化和电化学中的应用等研究,同时指出了目前需要克服的问题．