Molecular simulation of adsorption in nanoporous materials has become a valuable complement to experimental studies of these materials. In almost all cases, these simulations treat the adsorbing material as rigid. We use molecular simulations to examine the validity of this approximation for the adsorption in metal–organic frameworks (MOFs) that have framework flexibility without change in their unit cells because of thermal vibrations. All nanoporous materials are subject to this kind of framework flexibility. We examine the adsorption of nine molecules (CO2, CH4, ethane, ethene, propane, propene, butane, Xe, and Kr) and four molecular mixtures (CO2/CH4, ethane/ethene, propane/propene/butane, and Xe/Kr) in 100 MOFs at dilute and nondilute adsorption conditions. Our results show that single-component adsorption uptakes at nondilute conditions are only weakly affected by framework flexibility, but adsorption selectivities at both dilute and nondilute conditions can be significantly affected by flexibility. The most dramatic impacts of framework flexibility occur for adsorption uptake in the limit of dilute adsorption. These results suggest that the importance of including framework flexibility when attempting to make quantitative predictions of adsorption selectivity in MOFs and similar materials may have been underestimated in the past.

Finding examples where experimental measurements have been repeated is a powerful strategy for assessing reproducibility of scientific data. Here, we collect quantitative data to assess how often synthesis of a newly reported material is repeated in the scientific literature. We present a simple power-law model for the frequency of repeat syntheses and assess the validity of this model using a specific class of materials, metal-organic frameworks (MOFs). Our data suggest that a power law describes the frequency of repeat synthesis of many MOFs but that a small number of “supermaterials” exist that have been replicated many times more than a power law would predict. Our results also hint that there are many repeat syntheses that have been performed but not reported in the literature, which suggests simple steps that could be taken to greatly increase the number of reports of replicate experiments in materials chemistry.

Nanoporous materials such as metal–organic frameworks (MOFs) have attractive properties for selective capture of chemical warfare agents (CWAs). For obvious reasons, most research on adsorption of CWAs is performed with simulant molecules rather than real agents. This paper examines how effectively common CWA simulants mimic the adsorption properties of sarin and soman. To this end, we perform molecular simulations in the dilute adsorption limit for four simulants [dimethyl methylphosphonate (DMMP), diethyl chlorophosphate (DCP), diisopropyl fluorophosphate, and dimethyl p-nitrophenyl phosphate (DMNP)] and sarin and soman in a set of 2969 MOFs with experimentally known crystal structures. To establish the robustness of the conclusions with respect to the force field used in these simulations, each system was examined with two independent force fields, a “generic” force field and a density functional theory (DFT)-derived force field we established based on extensive dispersion-corrected DFT calculations of adsorption in the well-known MOF UiO-66. Our results show that when judging the performance of adsorbents using the heat of adsorption, DCP and DMMP are the best simulants for the adsorption of sarin, while DMNP is the best simulant for soman. The adsorption properties of DCP or DMMP show a strong correlation with sarin over a range of MOFs, but the correlation between DMNP and soman is considerably weaker. Comparisons of results with both force fields indicate that our main conclusions are robust with respect to the force field used to define adsorbate–MOF interactions.

Systematic collection of replicate experimental data via literature meta-analysis is a powerful approach for assessing the reproducibility of physical properties data. In this paper, we use meta-analysis to examine the adsorption equilibrium of alcohols in porous materials using a collection of more than 500 alcohol isotherm measurements. We report consensus isotherms (after rejecting outliers) using experimentally measured replicates for 11 systems with methanol, ethanol, 1-propanol, or 2-methylpropan-1-ol adsorption as well as assess experimental reproducibility for another 50 systems with these adsorbates, 1-butanol or 2-phenylethan-1-ol. Our analysis indicates that ∼20% of reported adsorption isotherms for alcohols are outliers, an observation that is similar to earlier analyses of CO2 adsorption experiments. We compare a variety of replicate experiments using metal–organic framework adsorbents with predictions from molecular simulations using generic force fields in order to examine the ability of these simulations to predict alcohol adsorption in these materials.

Metal–organic frameworks (MOFs) have shown potential for selective capture of chemical warfare agents (CWAs). To determine characteristic adsorption times, the kinetics of CWA uptake in MOFs must be known. Here, we calculate diffusion coefficients of the CWA sarin and simulants in prototypical MOFs using classical molecular simulations. Sarin can diffuse throughout a one micrometer crystal in less than a second in MIL-47 and Cu-BTC, but this process takes more than 3 h in ZIF-8 and UiO-66. A simple estimate based on Knudsen diffusion is able to describe diffusion of sarin in MIL-47 but fails to do so in other MOFs. This work has implications in designing devices to detect and capture CWAs.