Metal–organic frameworks (MOFs) are a unique class of crystalline solids comprised of metal cations (or metal clusters) and organic ligands that have shown promise for a wide variety of applications Over the past 15 years, research and development of these materials have become one of the most intensely and extensively pursued areas A very interesting and well-investigated topic is their optical emission properties and related applications Several reviews have provided a comprehensive overview covering many aspects of the subject up to 2011 This review intends to provide an update of work published since then and focuses on the photoluminescence (PL) properties of MOFs and their possible utility in chemical and biological sensing and detection The spectrum of this review includes the origin of luminescence in MOFs, the advantages of luminescent MOF (LMOF) based sensors, general strategies in designing sensory materials, and examples of various applications in sensing and detection

Luminescent metal–organic frameworks for chemical sensing and explosive detection

Metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) are open, crystalline supramolecular coordination architectures with porous facets. These chemically tailorable framework materials are the subject of intense and expansive research, and are particularly relevant in the fields of sensory materials and device engineering. As the subfield of MOF-based sensing has developed, many diverse chemical functionalities have been carefully and rationally implanted into the coordination nanospace of MOF materials. MOFs with widely varied fluorometric sensing properties have been developed using the design principles of crystal engineering and structure–property correlations, resulting in a large and rapidly growing body of literature. This work has led to advancements in a number of crucial sensing domains, including biomolecules, environmental toxins, explosives, ionic species, and many others. Furthermore, new classes of MOF sensory materials utilizing advanced signal transduction by devices based on MOF photonic crystals and thin films have been developed. This comprehensive review summarizes the topical developments in the field of luminescent MOF and MOF-based photonic crystals/thin film sensory materials.

Metal-organic frameworks: functional luminescent and photonic materials for sensing applications.

Highly efficient removal of metal ion pollutants, such as toxic and nuclear waste-related metal ions, remains a serious task from the biological and environmental standpoint because of their harmful effects on human health and the environment. Recently, highly porous metal–organic frameworks (MOFs), with excellent chemical stability and abundant functional groups, have represented a new addition to the area of capturing various types of hazardous metal ion pollutants. This review focuses on recent progress in reported MOFs and MOF-based composites as superior adsorbents for the efficient removal of toxic and nuclear waste-related metal ions. Aspects related to the interaction mechanisms between metal ions and MOF-based materials are systematically summarized, including macroscopic batch experiments, microscopic spectroscopy analysis, and theoretical calculations. The adsorption properties of various MOF-based materials are assessed and compared with those of other widely used adsorbents. Finally, we propose our personal insights into future research opportunities and challenges in the hope of stimulating more researchers to engage in this new field of MOF-based materials for environmental pollution management.

Metal–organic framework-based materials: superior adsorbents for the capture of toxic and radioactive metal ions

Metal-organic frameworks (MOFs) are typically highlighted for their potential application in gas storage, separations and catalysis. In contrast, the unique prospects these porous and crystalline materials offer for application in electronic devices, although actively developed, are often underexposed. This review highlights the research aimed at the implementation of MOFs as an integral part of solid-state microelectronics. Manufacturing these devices will critically depend on the compatibility of MOFs with existing fabrication protocols and predominant standards. Therefore, it is important to focus in parallel on a fundamental understanding of the distinguishing properties of MOFs and eliminating fabrication-related obstacles for integration. The latter implies a shift from the microcrystalline powder synthesis in chemistry labs, towards film deposition and processing in a cleanroom environment. Both the fundamental and applied aspects of this two-pronged approach are discussed. Critical directions for future research are proposed in an updated high-level roadmap to stimulate the next steps towards MOF-based microelectronics within the community.

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An updated roadmap for the integration of metal–organic frameworks with electronic devices and chemical sensors

Metal-organic frameworks (MOFs) have been recognized as one of the most important classes of porous materials due to their unique attributes and chemical versatility. Unfortunately, some MOFs suffer from the drawback of relatively poor stability, which would limit their practical applications. In the recent past, great efforts have been invested in developing strategies to improve the stability of MOFs. In general, stable MOFs possess potential toward a broader range of applications. In this review, we summarize recent advances in the design and synthesis of stable MOFs and MOF-based materials via de novo synthesis and/or post-synthetic structural processing. Also, the relationships between the stability and functional applications of MOFs are highlighted, and finally, the subsisting challenges and the directions that future research in this field may take have been indicated.

https://pubs.rsc.org/en/content/articlepdf/2019/SC/C9SC03916C

Improving MOF stability: approaches and applications

A three-dimensional water-stable cationic metal-organic framework (MOF) pillared by a neutral ligand and with Ni(II)  metal nodes has been synthesized employing a rational design approach. Owing to the ordered arrangement of the uncoordinated tetrahedral sulfate (SO4 (2-) ) ions in the channels, the compound has been employed for aqueous-phase ion-exchange applications. The compound exhibits rapid and colorimetric aqueous-phase capture of environmentally toxic oxoanions (with similar geometries) in a selective manner. This system is the first example of a MOF-based system which absorbs both dichromate (Cr2 O7 (2-) ) and permanganate (MnO4 (-) ) ions, with the latter acting as a model for the radioactive contaminant pertechnetate (TcO4 (-) ).

A Water-Stable Cationic Metal-Organic Framework as a Dual Adsorbent of Oxoanion Pollutants.

Two porous hydrogen-bonded organic frameworks (HOFs) based on arene sulfonates and guanidinium ions are reported. As a result of the presence of ionic backbones appended with protonic source, the compounds exhibit ultra-high proton conduction values (σ) 0.75× 10−2 S cm−1 and 1.8×10−2 S cm−1 under humidified conditions. Also, they have very low activation energy values and the highest proton conductivity at ambient conditions (low humidity and at moderate temperature) among porous crystalline materials, such as metal–organic frameworks (MOFs) and covalent organic frameworks (COFs). These values are not only comparable to the conventionally used proton exchange membranes, such as Nafion used in fuel cell technologies, but is also the highest value reported in organic-based porous architectures. Notably, this report inaugurates the usage of crystalline hydrogen-bonded porous organic frameworks as solid-state proton conducting materials.

Hydrogen-Bonded Organic Frameworks (HOFs): A New Class of Porous Crystalline Proton-Conducting Materials.

Ionic metal-organic frameworks (iMOFs): Design principles and applications

ConspectusMetal–organic frameworks (MOFs) have evolved to be next-generation utility materials because of their serviceability in a wide variety of applications. Built from organic ligands with multiple binding sites in conjunction with metal ions/clusters, these materials have found profound advantages over their other congeners in the domain of porous materials. The plethora of applications that these materials encompass has motivated material chemists to develop such novel materials, and the catalogue of MOFs is thus ever-escalating. One key feature that MOFs possess is their responsiveness toward incoming guest molecules, resulting in changes in their physical and chemical properties. Such uniqueness generally arises owing to the influenceable ligands and/or metal units that govern the formation of these ordered architectures. The suitable host–guest interactions play an important role in determining the specific responses of these materials and thus find important applications in sensing, catalysis, ...

Avishek Karmakar

Papers

A Water-Stable Cationic Metal-Organic Framework as a Dual Adsorbent of Oxoanion Pollutants.

Hydrogen-Bonded Organic Frameworks (HOFs): A New Class of Porous Crystalline Proton-Conducting Materials.

Ionic metal-organic frameworks (iMOFs): Design principles and applications

Guest-Responsive Metal-Organic Frameworks as Scaffolds for Separation and Sensing Applications.

Dynamic Structural Behavior and Anion‐Responsive Tunable Luminescence of a Flexible Cationic Metal–Organic Framework