The capture of water vapor at low relative humidity is desirable for producing potable water in desert regions and for heat transfer and storage. Here, we report a mesoporous metal–organic framework that captures 82% water by weight below 30% relative humidity. Under simulated desert conditions, the sorbent would deliver 0.82 gH2O gMOF–1, nearly double the quantity of fresh water compared to the previous best material. The material further demonstrates a cooling capacity of 400 kWh m–3 per cycle, also a record value for a sorbent capable of creating a 20 °C difference between ambient and output temperature. The water uptake in this sorbent is optimized: the pore diameter of our material is above the critical diameter for water capillary action, enabling water uptake at the limit of reversibility.

Metal–organic frameworks (MOFs) allow compositional and structural diversity beyond conventional solid-state materials. Continued interest in the field is justified by potential applications of exceptional breadth, ranging from gas storage and separation, which takes advantage of the inherent pores and their volume, to electronic applications, which requires precise control of electronic structure. In this Outlook we present some of the pertinent challenges that MOFs face in their conventional implementations, as well as opportunities in less traditional areas. Here the aim is to discuss select design concepts and future research goals that emphasize nuances relevant to this class of materials as a whole. Particular emphasis is placed on synthetic aspects, as they influence the potential for MOFs in gas separation, electrical conductivity, and catalytic applications.

Ammonia is a vital commodity in our food supply chain, but its toxicity and corrosiveness require advanced protection and mitigation. These needs are not met efficiently by current materials, which suffer from either low capacity or low affinity for NH. Here, we report that a series of microporous triazolate metal-organic frameworks containing open metal sites exhibit record static and dynamic ammonia capacities. Under equilibrium conditions at 1 bar, the materials adsorb up to 19.79 mmol NH g, more than twice the capacity of activated carbon, the industry standard. Under conditions relevant to personal protection equipment, capacities reach 8.56 mmol g, 27% greater than the previous best material. Structure-function relationships and kinetic analyses of NH uptake in isostructural micro- and mesoporous materials made from Co, Ni, and Cu reveal stability trends that are in line with the water substitution rates in simple metal-aquo complexes. Altogether, these results provide clear, intuitive descriptors that govern the static and dynamic uptake, kinetics, and stability of MOF sorbents for strongly interacting gases.

A series of new mesoporous metal-organic frameworks (MOFs) made from extended bisbenzenetriazolate linkers exhibit coordinatively unsaturated metal sites that are responsible for high and reversible uptake of ammonia. Isostructural Mn, Co, and Ni materials adsorb 15.47, 12.00, and 12.02 mmol of NH3/g, respectively, at STP. Importantly, these near-record capacities are reversible for at least three cycles. These results demonstrate that azolate MOFs are sufficiently thermally and chemically stable to find uses in recyclable sorption, storage, and potentially separation of chemically challenging and/or corrosive gases, especially when designed to exhibit a high density of open metal sites.

Metal-organic frameworks (MOFs) have demonstrated their utility for a variety of applications involving the storage, separation, and sensing of weakly interacting gases of high purity. Exposure to more realistic, impure gas streams and interactions with corrosive and coordinating gases raises the question of chemical robustness, which remains a paramount concern for practical applications of MOFs. However, factors that determine the stability of MOFs remain incompletely understood. Although past researchers attempted to categorize framework materials as either thermodynamically stable or kinetically stable, recent work has elucidated an energetic penalty for porosity for all materials in this class with respect to a dense material. The metastability of porous phases has important implications for the design of materials for gas storage, heterogeneous catalysts, and electronic materials. Here, we focus on two main strategies for stabilization of the porous phase, either by using inert metal ions, or by increasing the heterolytic metal-ligand bond strength, both of which increase the activation barrier for framework collapse. These two strategies have led to exceptionally robust materials for the capture of coordinating and corrosive gases such as water vapor, ammonia, H2S, SO2, NOx, and even elemental halogens, and we review the progress in designing stable materials for these gases. Looking forward, we envision that the continued pursuit of strategies for kinetic stabilization in the synthesis of new MOFs will provide increasing numbers of robust frameworks suited to harsh conditions, and that short-term stability towards these challenging gases will be predictive of long-term stability for applications in less demanding environments.