The synthesis, characterization and applications of metal-organic frameworks

Over the past three decades, porous materials have attracted great attention in many research fields, including physics, chemistry and materials science. Metal-organic frameworks (MOFs), as a class of crystalline porous materials, constructed by metal ions/clusters and organic ligands via coordination self-assembly, featuring atomically precise and highly tailorable structures, which have broad applications in various fields of natural science. MOFs demonstrate compatibility with a diverse range of materials, including metal nanoparticles, polymers, metal oxides, metal complexes, organic molecules and even biological macromolecules such as enzymes and DNA. This versatility facilitates the construction of composites using MOFs and various guest species. By employing approaches such as direct or post-synthetic modification of ligands and metal secondary building units within the MOF framework, as well as introducing guest species, researchers can achieve meticulous modulation of the structural and functional properties of MOFs. From a fundamental science perspective, the interactions between MOFs and guest species are varied, encompassing van der Waals forces, hydrogen bonds, electrostatic interactions, π-π interactions, coordination interactions and more. These interactions are influenced by multiple factors, including the structural characteristics of MOFs, such as pore size, properties of metal nodes and organic ligands and framework flexibility; the properties of guest molecules, including size, shape, functional groups and chemical properties, as well as external environmental factors like temperature, pressure and solvent effects. In consideration of the large number of MOF-related reviews reported in recent years, this article provides a comprehensive overview of the green synthesis and structures of MOFs, advanced in-situ characterization techniques and their applications and prospects in various fields, including gas adsorption and separation, fluorescence sensing, proton conduction, catalysis and industry. Traditional synthesis methods have significantly limited the large-scale production and industrialization of MOFs. In this review, we first introduced the green synthesis of MOFs and their distinctive structural advantages, such as stability and pore characteristics, in detail. Subsequently, we systematically summarise advanced characterization techniques employed to investigate the relationship between the microstructure and properties of MOFs. The properties of MOFs are intricately influenced by their intrinsic structural characteristics, the physico-chemical properties of guest molecules, and various external environmental conditions. Given this complex interplay, the structural characterization of MOFs is of paramount importance. Hence, it is essential to characterize the structures of MOFs to understand their functions and enhance their properties Utilising advanced characterization techniques to analyze MOF structures and properties is critical for comprehending their functions and optimizing their performance. The scientific facilities, such as advanced light sources, spallation neutron sources, nuclear magnetic resonance spectrometers and electron microscopes, provide sophisticated experimental techniques and methodologies. Via the employment of advanced characterization methodologies to investigate the structure-activity correlation toward important applications of MOFs, theoretical foundations can be established for the rational design and controllable fabrication of function-oriented MOFs. Furthermore, we systematically introduce the exploration of MOFs in various functional applications, such as gas adsorption and separation, fluorescence sensing, proton conduction, catalysis and industry, with particular emphasis on the structure-performance relationship. Finally, the future development prospects of MOFs are discussed. Although significant progress has been achieved, challenges such as precisely modulating structures and interactions, as well as enhancing stability for practical applications remain unaddressed. Future research endeavors will be centered on the development of novel MOFs, in-depth exploration of interaction mechanisms, expansion of application fields and enhancement of transdisciplinary research. This will promote the further advancement of MOFs, thereby creating more opportunities to address scientific and practical challenges.