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There is an almost unlimited number of metal-organic frameworks (MOFs). This creates exciting opportunities but also poses a problem: how do we quickly find the best MOFs for a given application? Molecular simulations have advanced sufficiently that many MOF properties - especially structural and gas adsorption properties - can be predicted computationally, and molecular modeling techniques are now used increasingly to guide the synthesis of new MOFs. With increasing computational power and improved simulation algorithms, it has become possible to conduct high-throughput computational screening to identify promising MOF structures and uncover structure-property relations. We review these efforts and discuss future directions in this new field. [ABSTRACT FROM AUTHOR]

In the past two decades, various microporous materials have been developed as useful adsorbents for gas adsorption for a wide range of industries. Considerable efforts have been made to regulate the pore accessibility in microporous materials for the manipulation of guest molecules' admission and release. It has long been known that some microporous adsorbents suddenly become highly accessible to guest molecules at specific conditions, e.g., above a threshold pressure or temperature. This anomalous adsorption behavior results from a gating effect, where a structural variation of the adsorbent leads to an abrupt change in the gas admission. This review summarizes the mechanisms of the gating effect, which can be a result of the deformation of the framework (e.g., expansion, contraction, reorientation, and sliding of the unit cells), the vibration of the pore-keeping groups (e.g., rotation, swing, and collapse of organic linkers), and the oscillation of the pore-keeping ions (e.g. cesium, potassium, etc.). These structural variations are induced either by the host–guest interaction or by an external stimulus, such as temperature or light, and account for the gating effect at a threshold value of the stimulus. Emphasis is given to the temperature-regulated gating effect, where the critical admission temperature is dictated by the combined effect of the gate opening and thermodynamic factors and plays a key role in regulating guest admission. Molecular simulations can improve our understanding of the gate opening/closing transitions at the atomic scale and enable the construction of quantitative models to describe the gated adsorption behaviour at the macroscale level. The gating effect in porous materials has been widely applied in highly selective gas separation and offers great potential for gas storage and sensing. [ABSTRACT FROM AUTHOR]

The ubiquity of metal–organic frameworks in recent scientific literature underscores their highly versatile nature. MOFs have been developed for use in a wide array of applications, including: sensors, catalysis, separations, drug delivery, and electrochemical processes. Often overlooked in the discussion of MOF-based materials is the mass transport of guest molecules within the pores and channels. Given the wide distribution of pore sizes, linker functionalization, and crystal sizes, molecular diffusion within MOFs can be highly dependent on the MOF-guest system. In this review, we discuss the major factors that govern the mass transport of molecules through MOFs at both the intracrystalline and intercrystalline scale; provide an overview of the experimental and computational methods used to measure guest diffusivity within MOFs; and highlight the relevance of mass transfer in the applications of MOFs in electrochemical systems, separations, and heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

Simulated adsorption isotherms for water in UiO-66 illustrate that defects in the form of missing linkers make this MOF more hydrophilic. Heats of adsorption and density plots further confirm the effect of defects on adsorption of water in UiO-66 at low loadings. In addition, water and CO2 isotherms indicate that not only the amount of defects but their locations within the material affect the loading of guest molecules. [ABSTRACT FROM AUTHOR]

Owing to the vast diversity of linkers, nodes, and topologies, metal–organic frameworks can be tailored for specific tasks, such as chemical separations or catalysis. Accordingly, these materials have attracted significant interest for capture and/or detoxification of toxic industrial chemicals and chemical warfare agents. In this paper, we review recent experimental and computational work pertaining to the capture of several industrially-relevant toxic chemicals, including NH3, SO2, NO2, H2S, and some volatile organic compounds, with particular emphasis on the challenging issue of designing materials that selectively adsorb these chemicals in the presence of water. We also examine recent research on the capture and catalytic degradation of chemical warfare agents such as sarin and sulfur mustard using metal–organic frameworks. [ABSTRACT FROM AUTHOR]

Aiming to elucidate guest-induced structural changes in the coordination polymer CPL-2, grand canonical Monte Carlo (GCMC) simulations were used to predict CO2 loadings in this material, and the results were compared with experimental isotherms. Our calculations suggest that CPL-2 exhibits more pronounced CO2-induced structural changes than previously reported. As the initial evidence, the isotherm simulated in the previously reported CPL-2 structure (experimentally resolved from X-ray diffraction in the “as-synthesized” CPL-2) underestimated the measured CO2 loadings at high pressure, indicating that CPL-2 might undergo structural changes that enable higher pore volumes at high pressure. GCMC simulations in CPL-2 structures considering moderate unit cell expansions reported in the literature still underestimated high-pressure experimental loadings. However, considering an incremental rotation of the CPL-2 bipyridyl pillars with increasing CO2 pressure, we were able to trace the measured isotherm with the simulation data. Computational analysis shows that ligand rotation in CPL-2 enables higher pore volumes, which, in turn, accommodate more CO2 as the gas pressure increases. Desorption measurements suggest that hysteresis in the CO2 isotherm of CPL-2 may also be linked to ligand rotation, and the measured adsorption/desorption cycles show that the rotation is reversible. Based on our simulations for CPL-4 and CPL-5 and previously reported experimental data, it is likely that these materials, which differ from CPL-2 in the bipyridyl ligand, behave similarly in the presence of CO2. Our results help understand the behavior of these materials, which present the kind of structural changes that could be potentially exploited to enhance the CO2 working capacity of ultra-microporous materials for carbon capture applications. [ABSTRACT FROM AUTHOR]

Cu-MOF-74 (also known as Cu-CPO-27) was identified as a sorbent having one of the highest densities of Cu(ii) sites per unit volume. Given that Cu(ii) in the framework can be thermally activated to yield a five-coordinate Cu(ii) species, we identified this MOF as a potential candidate for maximal volumetric uptake of ammonia. To that end, the kinetic breakthrough of ammonia in Cu-MOF-74/Cu-CPO-27 was examined under both dry and humid conditions. Under dry conditions the MOF exhibited a respectable performance (2.6 vs. 2.9 NH3 per nm3 for the current record holder HKUST-1), and under 80% relative humidity, the MOF outperformed HKUST-1 (5.9 vs. 3.9 NH3 per nm3, respectively). [ABSTRACT FROM AUTHOR]

CO2 capture is essential for reducing the carbon footprint of coal-fired power plants. Here we show, both experimentally and computationally, a new design strategy for capturing CO2 in nanoporous adsorbents. The approach involves ‘complementary organic motifs’ (COMs), which have a precise alignment of charge densities that is complementary to the CO2 quadrupole. Two promising COMs were post-synthetically incorporated into a robust metal–organic framework (MOF) material using solvent-assisted ligand incorporation (SALI). We demonstrate that these COM-functionalized MOFs exhibit high capacity and selectivity for CO2 relative to other reported motifs. [ABSTRACT FROM AUTHOR]