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Water is the most abundant and cleanest natural resource on earth, and it is the driving force of all nature. It not only affects food security, human health, and ecosystem integrity and maintenance, but is also an important driver of energy in industrial production and life. Importantly, water adsorption applications are considered to be highly energy-efficient and environmentally friendly technologies,1 including atmospheric water harvesting,2-4 desiccation of clean gases,5 indoor humidity control,6,7 and adsorptive heat transformation.8,9 However, current water adsorption-related applications are still constrained by properties of adsorbents, such as their low water uptake capacities, poor cyclic stabilities, limited feasibilities over a range of humidity conditions, and minimal commercial availabilities. Conventional nanoporous materials (e.g., silica gels, zeolites, and clays) were the first adsorbents used in water capture applications due to their low cost, commercial availability, and favorable water adsorption kinetics. However, these materials generally suffer from either low water uptake capacities or high regeneration temperature, limiting their use in practical water absorption applications.1,10 Metal-organic frameworks (MOFs), a class of crystalline porous materials, are assembled from inorganic nodes and organic linkers through coordination bonds.11,12 Benefiting from their exceptional porosity and surface area, tunable pore size and geometry, and highly tailorable and designable structures and functionalities, MOFs show considerable potential for gas storage and separation, heterogeneous catalysis, and other energy and environmental sustainability applications.13-17 In recent years, MOFs have also shown great potential for water vapor adsorption because of a growing understanding of the relationship between MOFs and water, as well as an increasing number of reports detailing MOFs that exhibit high water stability.1,4,9 Moreover, judicious design of the MOF structures enables control over their water adsorption properties and the water uptake capacities, which make MOFs ideal candidates for water adsorption-related applications. This review aims to provide an overview of recent advances in the development of MOFs for water adsorption, as well as to offer proposed guidelines to develop even better water adsorption materials. First, we briefly introduce the fundamentals of water adsorption, including how to ascertain key insights based on the shapes of water adsorption isotherms, descriptions of various water adsorption mechanisms, and a discussion on the stability of MOFs in water systems. Next, we discuss several recent reports have detailed how to improve water uptake capacity through the design and synthesis of MOFs. In particular, we highlight the importance of reticular chemistry in the designed synthesis of MOF-based water adsorbent materials. We then shift our focus to discussing the enormous potential of MOFs for use in selective water vapor adsorption applications with both theoretical and practical considerations considered. Finally, we offer our thoughts on the future development of this field in three aspects: chemistry and materials design, process engineering, and commercialization of MOFs for water adsorption. We hope that this review will provide fundamental insights for chemists and inspire them to synthesize MOFs with better water adsorption performance; and provide assistance to engineers researching MOF-based water adsorption devices and working towards the development of highly energy-efficient and environmentally friendly technologies with reduced carbon footprints. 

Ferrimagnets have received renewed attention as a promising platform for spintronic applications. Of particular interest is the Mn4N from the ε-phase of the manganese nitride as an emergent rare-earth-free spintronic material due to its perpendicular magnetic anisotropy, small saturation magnetization, high thermal stability, and large domain wall velocity. We have achieved high-quality (001)-ordered Mn4N thin film by sputtering Mn onto η-phase Mn3N2 seed layers on Si substrates. As the deposited Mn thickness varies, nitrogen ion migration across the Mn3N2/Mn layers leads to a continuous evolution of the layers to Mn3N2/Mn2N/Mn4N, Mn2N/Mn4N, and eventually Mn4N alone. The ferrimagnetic Mn4N, indeed, exhibits perpendicular magnetic anisotropy and forms via a nucleation-and-growth mechanism. The nitrogen ion migration is also manifested in a significant exchange bias, up to 0.3 T at 5 K, due to the interactions between ferrimagnetic Mn4N and antiferromagnetic Mn3N2 and Mn2N. These results demonstrate a promising all-nitride magneto-ionic platform with remarkable tunability for device applications. 

Functional porous metal–organic frameworks (MOFs) have been explored for a number of potential applications in catalysis, chemical sensing, water capture, gas storage, and separation. MOFs are among the most promising candidates to address challenges facing our society related to energy and environment, but the successful implementation of functional porous MOF materials are contingent on their stability; therefore, the rational design of stable MOFs plays an important role towards the development of functional porous MOFs. In this Focus article, we summarize progress in the rational design and synthesis of stable MOFs with controllable pores and functionalities. The implementation of reticular chemistry allows for the rational top-down design of stable porous MOFs with targeted topological networks and pore structures from the pre-selected building blocks. We highlight the reticular synthesis and applications of stable MOFs: (1) MOFs based on high valent metal ions ( e.g. , Al 3+ , Cr 3+ , Fe 3+ , Ti 4+ and Zr 4+ ) and carboxylate ligands; (2) MOFs based on low valent metal ions ( e.g. , Ni 2+ , Cu 2+ , and Zn 2+ ) and azolate linkers. We envision that the synthetic strategies, including modulated synthesis and post-synthetic modification, can potentially be extended to other more complex systems like metal-phosphonate framework materials.