Fabrication Methods of Continuous Pure Metal-Organic Framework Membranes and Films: A Review

Metal-organic frameworks (MOFs) have drawn intensive attention as a class of highly porous, crystalline materials with significant potential in various applications due to their tunable porosity, large internal surface areas, and high crystallinity. This paper comprehensively reviews the fabrication methods of pure MOF membranes and films, including in situ solvothermal synthesis, secondary growth, electrochemical deposition, counter diffusion growth, liquid phase epitaxy and solvent-free synthesis in the category of different MOF families with specific metal species, including Zn-based, Cu-based, Zr-based, Al-based, Ni-based, and Ti-based MOFs.

Interfacial Engineering of Heterogeneous Reactions for MOF-on-MOF Heterostructures

Metal-organic frameworks (MOFs), as a subclass of porous crystalline materials with unique structures and multifunctional properties, play a pivotal role in various research domains. In recent years, significant attention has been directed toward composite materials based on MOFs, particularly MOF-on-MOF heterostructures. Compared to individual MOF materials, MOF-on-MOF structures harness the distinctive attributes of two or more different MOFs, enabling synergistic effects and allowing for the tailored design of diverse multilayered architectures to expand their application scope. However, the rational design and facile synthesis of MOF-on-MOF composite materials are in principle challenging due to the structural diversity and the intricate interfaces. Hence, this review primarily focuses on elucidating the factors that influence their interfacial growth, with a specific emphasis on the interfacial engineering of heterogeneous reactions, in which MOF-on-MOF hybrids can be conveniently obtained by using pre-fabricated MOF precursors. These factors are categorized as internal and external elements, encompassing inorganic metals, organic ligands, lattice matching, nucleation kinetics, thermodynamics, etc. Meanwhile, these intriguing MOF-on-MOF materials offer a wide range of advantages in various application fields, such as adsorption, separation, catalysis, and energy-related applications. Finally, this review highlights current complexities and challenges while providing a forward-looking perspective on future research directions.

Emerging Pristine MOF-Based Heterostructured Nanoarchitectures: Advances in Structure Evolution, Controlled Synthesis, and Future Perspectives

Metal-organic frameworks (MOFs) can be customized through modular assembly to achieve a wide range of potential applications, based on their desired functionality. However, most of the initially reported MOFs are limited to microporous systems and are not sufficiently stable, which restricts their popularization. Heterogeneity is introduced into a simple MOF framework to create MOF-based heterostructures with fascinating properties and interesting functions. Heterogeneity can be introduced into the MOFs via postsynthetic/ligand exchange. Although the ligand exchange has shown potential, it is difficult to precisely control the degree of exchange or position. Among the various synthesis strategies, hierarchical assembly is particularly attractive for constructing MOF-based heterostructures, as it can achieve precise regulation of MOF-based heterostructured nanostructures. The hierarchical assembly significantly expands the compositional diversity of MOF-based heterostructures, which has high elasticity for lattice matching during the epitaxial growth of MOFs. This review focuses on the synthetic evolution mechanism of hierarchical assemblies of MOF-based nanoarchitectures. Subsequently, the precise control of pore structure, pore size, and morphology of MOF-based nanoarchitectures by hierarchical assembly is emphasized. Finally, possible solutions to address the challenges associated with heterogeneous interfaces are presented, and potential opportunities for innovative applications are proposed.

Effect of steric hindrance on the interfacial connection of MOF-on-MOF architectures

MOF-on-MOF is attracting great attention due to its improved and/or synergistic properties not exhibited in a single MOF. In particular, the non-isostructural pairs of MOF-on-MOFs can have great potential induced by large heterogeneity, which enables diverse applications in a wide range of fields. HKUST-1@IRMOF is a fascinating platform because the alteration of the IRMOF pores with bulkier substituent groups on the ligands can provide a more microporous environment. However, the sterically hindered linker can affect the seamless growth at the interface, an important issue in practical research fields. Despite many efforts to reveal the growth of a MOF-on-MOF, there is still a lack of studies on a MOF-on-MOF consisting of a sterically hindered interface. Indeed, the effect of a bulky linker at an interface of HKUST-1@IRMOF, a non-isostructural MOF-on-MOF system, has not yet been reported, and thus, how the interfacial strain affects the interfacial growth remains unknown. In this study, we investigate the effect of an interfacial strain on a chemical connection point in an MOF-on-MOF system through a series of theoretical and synthetic experiments using a HKUST-1@IRMOF system. Our results reveal the importance of the proximity of each coordinating site at a MOF-on-MOF interface as well as lattice parameter matching for an effective secondary growth to achieve a well-connected MOF-on-MOF.

Fast Dynamic Synthesis of MIL-68(In) Thin Films in High Optical Quality for Optical Cavity Sensing

Fabrication of metal-organic framework (MOF) thin films rigidly anchored on suitable substrates is a crucial prerequisite for the integration of these porous hybrid materials into electronic and optical devices. Thus, far, the structural variety for MOF thin films available through layer-by-layer deposition was limited, as the preparation of those surface-anchored metal-organic frameworks (SURMOFs) has several requirements: mild conditions, low temperatures, day-long reaction times, and nonaggressive solvents. We herein present a fast method for the preparation of the MIL SURMOF on Au-surfaces under rather harsh conditions: Using a dynamic layer-by-layer synthesis for MIL-68(In), thin films of adjustable thickness between 50 and 2000 nm could be deposited within only 60 min. The MIL-68(In) thin film growth was monitored in situ using a quartz crystal microbalance. In-plane X-ray diffraction revealed oriented MIL-68(In) growth with the pore-channels of this interesting MOF aligned parallel to the support. Scanning electron microscopy data demonstrated an extraordinarily low roughness of the MIL-68(In) thin films. Mechanical properties and lateral homogeneity of the layer were probed through nanoindentation. These thin films showed extremely high optical quality. By applying a poly(methyl methacrylate) layer and further depositing an Au-mirror to the top, a MOF optical cavity was fabricated that can be used as a Fabry-Perot interferometer. The MIL-68(In)-based cavity showed a series of sharp resonances in the ultraviolet-visible regime. Changes in the refractive index of MIL-68(In) caused by exposure to volatile compounds led to pronounced position shifts of the resonances. Thus, these cavities are well suited to be used as optical read-out sensors.

Advances in metal-organic framework-based membranes

Membrane-based separations have garnered considerable attention owing to their high energy efficiency, low capital cost, small carbon footprint, and continuous operation mode. As a class of highly porous crystalline materials with well-defined pore systems and rich chemical functionalities, metal-organic frameworks (MOFs) have demonstrated great potential as promising membrane materials over the past few years. Different types of MOF-based membranes, including polycrystalline membranes, mixed matrix membranes (MMMs), and nanosheet-based membranes, have been developed for diversified applications with remarkable separation performances. In this comprehensive review, we first discuss the general classification of membranes and outline the historical development of MOF-based membranes. Subsequently, particular attention is devoted to design strategies for MOF-based membranes, along with detailed discussions on the latest advances on these membranes for various gas and liquid separation processes. Finally, challenges and future opportunities for the industrial implementation of these membranes are identified and outlined with the intent of providing insightful guidance on the design and fabrication of high-performance membranes in the future.

The electro-oxidation of primary alcohols via a coral-shaped cobalt metal-organic framework modified graphite electrode in neutral media

The electro-oxidation of alcohols into corresponding aldehydes achieved enormous attention. However, numerous challenges remain in exploring catalytic systems with high conversion efficiency and selectivity. Considering the worldwide attention toward metal–organic frameworks (MOFs) as outstanding crystalline porous materials, many chemists have been encouraged to use them in organic transformations. In this study, a novel coral-shaped cobalt organic framework was grown onto the surface of a functionalized graphite electrode (Co-MOF/C) to fabricate an efficient modified electrode in the electro-oxidation alcohols. The modified Co-MOF/C electrode showed high stability, large surface area, rich pores, and good conductivity as a desirable water-stable working electrode for selective oxidation of alcohols into aldehydes in good to excellent yields under a diffusion-controlled process.

Diels-Alder Cycloaddition with CO, CO2, SO2, or N2 Extrusion: A Powerful Tool for Material Chemistry

Phenyl, naphthyl, polyarylphenyl, coronene, and other aromatic and polyaromatic moieties primarily influence the final materials' properties. One of the synthetic tools used to implement (hetero)aromatic moieties into final structures is Diels-Alder cycloaddition (DAC), typically combined with Scholl dehydrocondensation. Substituted 2-pyranones, 1,1-dioxothiophenes, and, especially, 1,3-cyclopentadienones are valuable substrates for [4 + 2] cycloaddition, leading to multisubstituted derivatives of benzene, naphthalene, and other aromatics. Cycloadditions of dienes can be carried out with extrusion of carbon dioxide, carbon oxide, or sulphur dioxide. When pyranones, dioxothiophenes, or cyclopentadienones and DA cycloaddition are aided with acetylenes including masked ones, conjugated or isolated diynes, or polyynes and arynes, aromatic systems are obtained. This review covers the development and the current state of knowledge regarding thermal DA cycloaddition of dienes mentioned above and dienophiles leading to (hetero)aromatics via CO, CO2, or SO2 extrusion. Particular attention was paid to the role that introduced aromatic moieties play in designing molecular structures with expected properties. Undoubtedly, the DAC variants described in this review, combined with other modern synthetic tools, constitute a convenient and efficient way of obtaining functionalized nanomaterials, continually showing the potential to impact materials sciences and new technologies in the nearest future.

Concluding remarks: current and next generation MOFs

This paper describes the content of my "Concluding remarks" talk at the Faraday Discussion meeting on "MOFs for energy and the environment" (online, 23-25 June 2021). The panel consisted of sessions on the design of MOFs and MOF hybrids (synthetic chemistry), their applications (e.g., capture, storage, separation, electrical devices, photocatalysis), advanced characterization (e.g., transmission electron microscopy, solid-state nuclear magnetic resonance), theory and modeling, and commercialization. MOF chemistry is undergoing a significant evolution from simply network chemistry to the chemistry of synergistic integration with heterogeneous materials involving other disciplines (we call this the fourth generation type). As reflected in the papers of the invited speakers and discussions with the participants, the present and future of this field will be described in detail.

The Importance of Highly Connected Building Units in Reticular Chemistry: Thoughtful Design of Metal-Organic Frameworks

The prediction of crystal structures assembled in three dimensions has been considered for a long time, simultaneously as a chemical wasteland and a certain growth point of the chemistry of the future. Less than 30 years after Roald Hoffmann's statement, we can categorically affirm that the elevation of reticular chemistry and the introduction of metal-organic frameworks (MOFs) significantly tackled this tridimensional assembly issue. MOFs result from the assembly of organic polytopic organic ligands bridging metal nodes, clusters, chains, or layers together into mostly three-periodic open frameworks. They can exhibit extremely high porosity and offer great potential as revolutionary catalysts, drug carrier systems, sensors, smart materials, and, of course, separation agents. Overall, the progressive development of reticular chemistry has been a game changer in materials chemistry during the last 25 years.Such diverse properties often result not only from the selected organic and inorganic molecular building blocks (MBBs) but also from their distribution within the framework. Indeed, the size and shape of the porous system, as well as the location of active sites influence the overall properties. Therefore, in the continuity of achieving the crystallization of three-periodic structures, chemists and crystal engineers faced the next challenge, as summarized by John Maddox: "it remains in general impossible to predict the structure of even the simplest crystallographic solids from knowledge of their chemical composition". This is where rational design takes place.In this Account, we detail three specific approaches developed by our group to facilitate the design and assembly of finely tuned MOFs. All are based on careful geometrical consideration and a deep study and understanding of the existing nets and topologies. We recognized that highly connected nets, if possible, edge-transitive, are ideal blueprints because their number is limited in contrast to nets with lower connectivity. Therefore, we embarked on taking advantage of existing highly connected MBBs, or, in parallel, promoting their formation to meet our requirements. This is achieved by utilizing externally decorated metal-organic polyhedra as supermolecular building blocks (SBBs), serving as a net-coding building unit, comprising the requisite connectivity and directional information coding for the chosen nets. The SBB approach allowed the synthesis of several families of SBB-based MOFs, including fcu, rht, and gea-MOFs, that are detailed here.The second strategy is directly inherited from the success of the SBB approach. In seeking highly connected building units, our group naturally expanded its research focus to nets that can be deconstructed into layers, pillared in various ways. In the supermolecular building layer (SBL) approach, the layers have an almost infinite connectivity, and the framework backbone is fixed in two dimensions while the third is free for pillar expansion and functionalization. The cases of trigonal pillaring leading to rtl, eea, and apo MOFs as well as the quadrangular pillaring leading to a family of tbo-MOFs are discussed here, along with recent cases of highly connected pillars in pek and aea-MOFs.Finally, our experience with highly coordinated MBBs led us to develop a novel way to use them as secondary building units of lower connectivity and unlock the possibility of assembling a novel class of zeolite-like MOFs (ZMOFs). The case of the Zr-sod-ZMOFs designed through a cantellation strategy is described as a future leading direction of MOF design.

Rational Design and Growth of MOF-on-MOF Heterostructures

Multiporous metal-organic frameworks (MOFs) have emerged as a subclass of highly crystalline inorganic-organic materials, which are endowed with high surface areas, tunable pores, and fascinating nanostructures. Heterostructured MOF-on-MOF composites are recently becoming a research hotspot in the field of chemistry and materials science, which focus on the assembly of two or more different homogeneous or heterogeneous MOFs with various structures and morphologies. Compared with one single MOF, the dual MOF-on-MOF composites exhibit unprecedented tunability, hierarchical nanostructure, synergistic effect, and enhanced performance. Due to the difference of inorganic metals and organic ligands, the lattice parameters in a, b, and c directions in the single crystal cells could bring about subtle or large structural difference. It will result in the composite material with distinct growth methods to obtain secondary MOF grown from the initial MOF. In this review, the authors wish to mainly outline the latest synthetic strategies of heterostructured MOF-on-MOFs and their derivatives, including ordered epitaxial growth, random epitaxial growth, etc., which show the tutorial guidelines for the further development of various MOF-on-MOFs.

Synthesis of MOF-on-MOF architectures in the context of interfacial lattice matching

This highlight summarises the previously reported MOF-on-MOF systems, with a focus on the presented crystallographic information and classification of the systems according to lattice parameter matching.

MOF-on-MOF Membrane with Cascading Functionality for Capturing Dichromate Ions and p-Arsanilic Acid Turn-On Sensing

It is very significant that functional porous metal-organic frameworks are used to manufacture hierarchical components to achieve cascading functions that cannot be achieved by a single-layer metal-organic framework (MOF). Here, we report two cases of novel MOFs constructed by the same ligand, Cu(I)-tpt and Cu(II)-tpt (Htpt = 5-[4(1H-1,2,4-triazol-1-yl)]phenyl-2H-tetrazole), and prepared a Cu(II)-tpt-on-Cu(I)-tpt membrane by a layer-by-layer approach ignoring the lattice mismatch problem. The first Cu(I)-tpt layer is grown on an oriented Cu₂O nanostructured array by a "one-pot" approach. The aligned second Cu(II)-tpt layer can be deposited using liquid-phase epitaxy. Notably, the prepared Cu(II)-tpt-on-Cu(I)-tpt membrane combines adsorption and fluorescence sensing, which exhibited significant adsorption for Cr₂O₇^2- (203.25 mg g^-1) as typical highly poisonous ions with a fluorescence quenching response. Hence, based on the oxidation-reduction between Cr₂O₇^2- and p-arsanilic acid (p-ASA), the Cu(II)-tpt-on-Cu(I)-tpt membrane's ability to adsorb Cr₂O₇^2- could be used to design "on-off-on" mode fluorescence probes to detect p-ASA with high sensitivity (limit of detection (LOD) = 0.0556 μg L^-1). p-ASA can be degraded into highly toxic inorganic arsenic compounds in the natural environment and has received widespread attention. Therefore, the integration of adsorption and fluorescence properties makes the Cu(II)-tpt-on-Cu(I)-tpt membrane a feasible multifunctional material for pollution control and detection.

Emergent Interface in Heterostructured Thin Films of Cu(II) and Cu(I) Coordination Polymers

In this work we report fabrication of high-quality AB- and BA-type heterostructured thin films of cubic Cu(II) (A-type) and tetragonal Cu(I) (B-type) coordination polymers (CPs) on the functionalized Au substrate by the layer-by-layer method. Successful growth of Cu(I)-CP on top of Cu(II)-CP was assigned to be due to the interfacial reduction reaction (IRR). Notably, electrical transport measurements across AB- and BA-type heterostructured thin films revealed rectification of current in opposite directions. We have attributed such an interestingly new observation to the formation of a well-defined interface of Cu(II)-CP and Cu(I)-CP resembling a p-n junction-a hitherto unreported phenomenon that is anticipated to open enormous opportunities for the heterostructured thin films of CPs, likewise celebrated interfaces of oxide heterostructures.

Concentration-Dependent Seeding as a Strategy for Fabrication of Densely Packed Surface-Mounted Metal-Organic Frameworks (SURMOF) Layers

The layer‐by‐layer (LbL) method is a well‐established method for the growth of surface‐attached metal–organic frameworks (SURMOFs). Various experimental parameters, such as surface functionalization or temperature, have been identified as essential in the past. In this study, inspired by these recent insights regarding the LbL SURMOF growth mechanism, the impact of reactant solutions concentration on LbL growth of the Cu₂(F₄bdc)₂(dabco) SURMOF (F₄bdc²⁻=tetrafluorobenzene‐1,4‐dicarboxylate and dabco=1,4‐diazabicyclo‐[2.2.2]octane) in situ by using quartz‐crystal microbalance and ex situ with a combination of spectroscopic, diffraction and microscopy techniques was investigated. It was found that number, size, and morphology of MOF crystallites are strongly influenced by the reagent concentration. By adjusting the interplay of nucleation and growth, we were able to produce densely packed, yet thin films, which are highly desired for a variety of SURMOF applications.

Continuous ultrathin UiO-66-NH2 coatings on a polymeric substrate synthesized by a layer-by-layer method: a kind of promising membrane for oil-water separation

In this paper, we successfully controllably synthesize continuous nanothickness MOF coatings (NTMCs) by a layer-by-layer method on a polymeric substrate. The polymeric substrate was pretreated with high energy γ-irradiation to induce a high surface density of living reactive groups, which ensure the formation of continuous surface-integrated NTMCs. SEM, FT-IR spectroscopy and XPS were used to characterize NTMCs. The thickness and morphology were tuned by the LBL cycles, and NTMCs with a thickness of ∼44 nm were obtained. The chemical bonds between the NTMCs and polymeric substrate were confirmed by XPS and EDS. Moreover, the NTMCs exhibit good performance for oil-water separation. We believe that our work will promote the design and precise synthesis of high-performance MOF based membranes for multiple practical applications in future.

Metal–Organic Framework Thin Films: Fabrication, Modification, and Patterning

Metal–organic frameworks (MOFs) have been of great interest for their outstanding properties, such as large surface area, low density, tunable pore size and functionality, excellent structural flexibility, and good chemical stability. A significant advancement in the preparation of MOF thin films according to the needs of a variety of applications has been achieved in the past decades. Yet there is still high demand in advancing the understanding of the processes to realize more scalable, controllable, and greener synthesis. This review provides a summary of the current progress on the manufacturing of MOF thin films, including the various thin-film deposition processes, the approaches to modify the MOF structure and pore functionality, and the means to prepare patterned MOF thin films. The suitability of different synthesis techniques under various processing environments is analyzed. Finally, we discuss opportunities for future development in the manufacturing of MOF thin films.

Luminescent lanthanide metal-organic framework test strip for immediate detection of tetracycline antibiotics in water

Tetracycline antibiotics (TCs) are a kind of commonly used antibiotics for treating infections, however, the overuse of TCs has adversely affected human health and the ecosystem. Thus, detection of TCs in water is important but challenging. In this work, a luminescent lanthanide metal-organic framework (LnMOF) sensor (1) for immediate detection of oxytetracycline (OTC) and tetracycline (TC) is developed. The sensor has high acid-base and water stability. Investigation reveals that among the 27 species of antibiotics, anions and cations under investigation, 1 shows highly selective sensing towards OTC and TC, and the detection is not disturbed by the presence of other species. The limit of detection (LOD) for OTC and TC are ultra-sensitive value of 1.95 and 2.77 nM, respectively. Investigation reveals the sensing mechanism is due to the inner filter effect. Further studies reveal that the sensor can be used in real sample monitoring. More importantly, test strips based on 1 are manufactured. They are an easy-to-use, low-cost, highly selective and sensitive sensing device for detecting OTC and TC. The sensing can be distinguished immediately and easily by the naked eyes, making it an excellent candidate to monitor OTC and TC in real use.

Core–shell metal–macrocycle framework (MMF): spatially selective dye inclusion through core-to-shell anisotropic transport along crystalline 1D-channels connected by epitaxial growth

Core–shell porous metal–macrocycle frameworks were fabricated via an epitaxial growth procedure to observe core-to-shell anisotropic transport of a dye.

Rising Up: Hierarchical Metal-Organic Frameworks in Experiments and Simulations

Controlled synthesis across several length scales, ranging from discrete molecular building blocks to size- and morphology-controlled nanoparticles to 2D sheets and thin films and finally to 3D architectures, is an advanced and highly active research field within both the metal-organic framework (MOF) domain and the overall material science community. Along with synthetic progress, theoretical simulations of MOF structures and properties have shown tremendous progress in both accuracy and system size. Further advancements in the field of hierarchically structured MOF materials will allow the optimization of their performance; however, this optimization requires a deep understanding of the different synthesis and processing techniques and an enhanced implementation of material modeling. Such modeling approaches will allow us to select and synthesize the highest-performing structures in a targeted rational manner. Here, recent progress in the synthesis of hierarchically structured MOFs and multiscale modeling and associated simulation techniques is presented, along with a brief overview of the challenges and future perspectives associated with a simulation-based approach toward the development of advanced hierarchically structured MOF materials.

Unbalanced MOF-on-MOF growth for the production of a lopsided core–shell of MIL-88B@MIL-88A with mismatched cell parameters

Atypical unbalanced MOF-on-MOF growth is demonstrated for the production of a lopsided core–shell of MIL-88B@MIL-88A with mismatched cell parameters.

Metal–Organic Framework Membranes: From Fabrication to Gas Separation

Gas membrane-based separation is considered one of the most effective technologies to address energy efficiency and large footprint challenges. Various classes of advanced materials, including polymers, zeolites, porous carbons, and metal–organic frameworks (MOFs) have been investigated as potential suitable candidates for gas membrane-based separations. MOFs possess a uniquely tunable nature in which the pore size and environment can be controlled by connecting metal ions (or metal ion clusters) with organic linkers of various functionalities. This unique characteristic makes them attractive for the fabrication of thin membranes, as both the diffusion and solubility components of permeability can be altered. Numerous studies have been published on the synthesis and applications of MOFs, as well as the fabrication of MOF-based thin films. However, few studies have addressed their gas separation properties for potential applications in membrane-based separation technologies. Here, we present a synopsis of the different types of MOF-based membranes that have been fabricated over the past decade. In this review, we start with a short introduction touching on the gas separation membrane technology. We also shed light on the various techniques developed for the fabrication of MOF as membranes, and the key challenges that still need to be tackled before MOF-based membranes can successfully be used in gas separation and implemented in an industrial setting.

Boosting Transport Distances for Molecular Excitons within Photoexcited Metal-Organic Framework Films

Herein, we describe the fabrication of porphyrin-containing metal-organic framework thin films with 1,4-diazabicyclo[2.2.2]octane (DABCO) pillaring linkers and investigate exciton transport within the films. Steady-state emission spectroscopy indicates that the exciton can traverse up to 26 porphyrin layers when DABCO is used as a pillaring linker, whereas on average only 9-11 layers can be traversed when either 4,4'-bipyridine (a pillaring linker) or pyridine (a nonpillaring, layer-interdigitating ligand) is used. These results can be understood by taking into account the decreased separation distances between transition dipoles associated with chromophores (porphyrins) sited in adjacent layers. Shorter distances translate into faster Förster-type exciton hopping and, therefore, more hops within the few nanosecond lifetime of the porphyrin's singlet excited-state. The findings have favorable implications for the development of MOF-based photoelectrodes and photoelectrochemical energy-conversion devices.

Mesoporous Metal-Organic Frameworks: Synthetic Strategies and Emerging Applications

Metal-organic frameworks (MOFs) have attracted much attention over the past two decades due to their highly promising applications not only in the fields of gas storage, separation, catalysis, drug delivery, and sensors, but also in relatively new fields such as electric, magnetic, and optical materials resulting from their extremely high surface areas, open channels and large pore cavities compared with traditional porous materials like carbon and inorganic zeolites. Particularly, MOFs involving pores within the mesoscopic scale possess unique textural properties, leading to a series of research in the design and applications of mesoporous MOFs. Unlike previous Reviews, apart from focusing on recent advances in the synthetic routes, unique characteristics and applications of mesoporous MOFs, this Review also mentions the derivatives, composites, and hierarchical MOF-based systems that contain mesoporosity, and technical boundaries and challenges brought by the drawbacks of mesoporosity. Moreover, this Review subsequently reveals promising perspectives of how recently discovered approaches to different morphologies of MOFs (not necessarily entirely mesoporous) and their corresponding performances can be extended to minimize the shortcomings of mesoporosity, thus providing a wider and brighter scope of future research into mesoporous MOFs, but not just limited to the finite progress in the target substances alone.