Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer–Emmett–Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro‐ and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already‐measured raw adsorption isotherms were provided to sixty‐one labs, who were asked to calculate the corresponding BET areas. This round‐robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called “BET surface identification” (BETSI), expands on the well‐known Rouquerol criteria and makes an unambiguous BET area assignment possible.

A simple solvent-and catalyst-free method is presented for the synthesis of the large-pore metal−organic framework (MOF) MAF-6 (RHO-Zn(eIm) 2) based on the reaction of ZnO with 2-ethylimidazole vapor at temperatures ≤100°C. By translating this method to a chemical vapor deposition (CVD) protocol, crystalline films of a large-pore material could be deposited for the first time entirely from the vapor phase. A combination of positron annihilation lifetime spectroscopy (PALS) and Kr physisorption measurements confirmed the porosity of these MOF-CVD films and the size of the MAF-6 supercages (diameter ∼2 nm), in close agreement with powder data and calculations. MAF-6 powders and films were further characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), pair distribution function (PDF), and extended X-ray absorption fine structure (EXAFS). The exceptional uptake capacity of MAF-6 in comparison to ZIF-8 is demonstrated by vapor-phase loading of a molecule larger than the ZIF-8 windows. spectra; PALS data and implantation profiles; EDS data; fluorescence emission spectra (PDF)

separation and storage, or catalysis. [3][4][5] In addition, there is tremendous potential in the use of MOF thin films as membranes, active sensor coatings, high-performance dielectrics, and other microelectronic applications that could benefit from the integration of porous functional materials. [6] Routine characterization of MOF powders typically involves N 2 physisorption to investigate their porosity and specific surface area. [7] The characterization of MOF thin films is more challenging due to the low amount of material in sub-micrometer films (Table 1), especially compared to the mass and volume of the substrate (e.g., a Si wafer), and often requires dedicated methods and instruments. Therefore, often only qualitative porosity characterization has been performed, e.g., through intercalation of fluorescent dyes or other labels. [8,9] Thus far, quantitative porosimetry of MOF films has relied on physisorption, by measuring the adsorbed quantity of a probe molecule through manometric/volumetric (e.g., Kr physisorption, KrP), gravimetric (e.g., quartz crystal microbalance, QCM) or spectroscopic (e.g., ellipsometry, EP) methods. [10] When performed as a function of the adsorptive relative pressure at Thin films of crystalline and porous metal-organic frameworks (MOFs) have great potential in membranes, sensors, and microelectronic chips. While the morphology and crystallinity of MOF films can be evaluated using widely available techniques, characterizing their pore size, pore volume, and specific surface area is challenging due to the low amount of material and substrate effects. Positron annihilation lifetime spectroscopy (PALS) is introduced as a powerful method to obtain pore size information and depth profiling in MOF films. The complementarity of this approach to established physisorptionbased methods such as quartz crystal microbalance (QCM) gravimetry, ellipsometric porosimetry (EP), and Kr physisorption (KrP) is illustrated. This comprehensive discussion on MOF thin film porosimetry is supported by experimental data for thin films of ZIF-8.

An effective separation of propylene/propane mixtures is one of the most important processes in the petrochemical industry. Incidentally this separation is challenging due to the extensive similarities between both gases in terms of physicochemical properties such as, but not only limited to, boiling point, kinetic diameter and molecular weight. A drive to switch to less energy consuming processes, like adsorption or membrane separation, has highlighted several microporous metal organic frameworks as promising materials. In this work, we present a combined numerical and experimental investigation on propane and propylene adsorption in Zr-fumarate-MOF (also known as MOF-801), a small pore isoreticular analogue of UiO-66. Here, we demonstrate how the presence of structural defects can completely change the sorptive properties and separation performance of the Zr-fumarate-MOF, with enhanced capacity and gas diffusion rates for C3-sized hydrocarbons at the cost of kinetic selectivity. Extensive GCMC simulations performed on mixed defective supercells show that a percentage of missing cluster defects of around 1/8 th can best account for the experimental results. Furthermore, analysis of low-frequency phonon spectra is used to explain gaseous diffusion in the original pristine material. A slight preference for propane over propylene is highlighted in the defective sample, and confirmed through column breakthrough experiments, suggesting the potential applicability of the Zr-fumarate-MOF in this challenging separation. File list (3) download file view on ChemRxiv manuscript.pdf (3.98 MiB) download file view on ChemRxiv manuscript-SI.pdf (3.63 MiB) download file view on ChemRxiv structures.zip (60.21 KiB)

UiO-66 is known as one of the most robust metal-organic framework materials. Nevertheless, UiO-66 has also been shown to undergo post-synthetic exchange of structural linkers with surprising ease in some solvents. To date, the exchange mechanism has not yet been fully elucidated. Here, we show how timeresolved monitoring grants insight into the selected case of exchanging 2-aminoterephthalate into UiO-66 in methanol. Analysis of both the solid and liquid phase, complemented by computational insights, revealed the active role of methanol in the creation and stabilization of dangling linkers. Similar to monocarboxylate defects that can be introduced during UiO-66 synthesis, such dangling linkers undergo fast exchange. The presence of missing linker or missing cluster defects at the start of the exchange process was shown to have no considerable impact on the equilibrium composition. After the exchange process, the incoming 2aminoterephthalate and remaining terephthalate linkers were distributed homogeneously in the framework for the typical sub-micron size of UiO-66 crystallites.