Chapter 6 - Platinum group-based metal-organic frameworks (MOFs) nanocomposites

Abstract

A new class of porous materials called metal-organic frameworks (MOFs, also called porous coordination networks, porous coordination polymers, or PCPs) is made up of organic linkers and metal-containing nodes (also known as secondary building units, or SBUs). Porous materials are excellent for storing gases, separating gases and vapors via adsorption, catalyzing reactions based on shape or size, delivering drugs, and serving as templates for low-dimensional materials. In the past, porous materials have either been organic or inorganic. Activated carbon is possibly the most widely used organic porous material. They are often created by the pyrolysis of carbon-rich materials. They lack organized structures but have huge surface areas and excellent adsorption capabilities. Despite this disarray, porous carbon materials are useful for a variety of processes, such as solvent removal and recovery, water purification, gas separation, and storage. Structures in inorganic porous frameworks are extremely well-ordered (e.g., zeolites). Inorganic or organic templates are frequently used for syntheses, and strong interactions between the inorganic framework and the template develop during the synthesis. As a result, removing the template may cause the framework to crumble. MOFs, which are stable, organized, and have high surface areas, are porous hybrids that can be produced to benefit from the features of both organic and inorganic porous materials. MOFs are simply coordination polymers that are created in the most basic sense by joining metal ions with polytopic organic linkers, frequently producing intriguing structural topologies. These materials have garnered a lot of interest in recent years, and it is impressive how many more papers have been published in this field. Ultrahigh porosity (up to 90% free volume) and extremely high internal surface areas, exceeding a Langmuir surface area of 10,000m2 g−1, are important structural characteristics of MOFs and are essential in functional applications, most commonly in storage and separation, sensing, proton conduction, and drug delivery. By generally regulating the length of the bi- or multipodal rigid organic linkers, the pore diameters of porous MOFs can be controlled from several angstroms to several nanometers, as opposed to the normal microporous characteristics of porous MOFs (2nm). Moreover, diverse framework functions that go beyond its porosity can be produced by the metal components (such as magnetism or catalysis) or the organic linkers (such as luminescence, nonlinear optics, and chirality), or a combination of the two. A significant amount of research over the past two decades has focused on creating new MOF structures and investigating their different applications; several MOFs are now commercially available. However, MOFs have a few flaws that prevent their full potential from being utilized, such as low chemical stability. It is desirable to add new functions and further improve the qualities of MOFs in order to fulfill their realistic applications. To combine the benefits and lessen the drawbacks of both components, it has recently been suggested to combine MOFs with a range of functional materials. The development of high-performance composites with complex topologies is made possible by research on MOF composites. One MOF and one or more separate constituent materials, including other MOFs, are combined to form MOF composites or hybrids, which have properties that are noticeably different from those of the individual parts. The benefits of both MOFs (structural adaptability and flexibility, high porosity with ordered crystalline pores) as well as different types of functional materials (unique optical, electrical, magnetic, and catalytic properties) can be effectively combined in composite materials, which opens the door to new physical and chemical properties as well as improved performance that are not possible with the constituent parts alone. As a result, a variety of applications can benefit from the exceptional qualities of composites that come from the synergistic interaction of MOF and other active components. By utilizing the library of porous crystals already in existence, the right MOF can be selected; alternatively, simulation techniques can be effectively used as a screening strategy. Active species have been successfully incorporated into MOF composites, such as metal nanoparticles/nanorods, oxides, quantum dots, polyoxometalates, polymers, graphene, carbon nanotubes, biomolecules, and others, leading to a performance that is unmatched by the individual constituents. Platinum has a wide range of features and applications, and when combined with the MOFs’ porous structure, these two factors provide one-of-a-kind building blocks for the creation of sophisticated porous materials.