How reproducible are surface areas calculated from the BET equation?

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

MS37 Advances in Structure determination of new materials by multi-technique approach including imaging techniques MS37-05 Structural elucidation of novel metal-organic frameworks using 3D electron diffraction

International audienceMetal-organic frameworks (MOFs) are hybrid crystalline porous solids demonstrating potential applications in different domains related to energy, environment or health [1]. The structural elucidation of nano-sized MOFs is essential as it provides a better understanding of their unique properties. However, the synthesis of robust MOFs often leads to polycrystalline compounds rendering the structure elucidation by single-crystal and powder X-ray diffraction often challenging. A good alternative is to solve the structure from 3-dimensional electron diffraction (3DED) data [2], a method allowing to solve the structure from much smaller particles by using electrons instead of X-rays. Titanium-based MOFs (Ti-MOFs) are of interest due to their photoactive character, good biocompatibility and tunability in terms of pore engineering, which makes them attractive candidates in photocatalysis or energy-related reactions [3,4]. However, the design of new Ti-MOFs is still driven by serendipity due to the complexity of titanium chemistry in solution [5]. Here, we present a new robust nanoporous nitro functionalized titanium terephthalate MOF labelled MIP-209 (MIP stands for Materials from Institute of Porous Materials of Paris) constructed from Ti12O15 oxo-clusters, similarly to MIP-177 [1] as revealed first by X-ray Pair distribution function analysis (PDF). The structure has been then solved by ab initio methods using continuous rotation electron diffraction (cRED) data and refined kinematically. In this communication, the structural characterization of MIP-209 by 3DED will be presented. in combination with complementary structural characterization methods such as pair distribution function (PDF) analysis and low-dose high-resolution TEM (LD-HRTEM). Due to the high electron beam sensitivity of MOFs, the latter was only made possible by the use of a microscope equipped with a direct detection electron counting camera (DDEC) [6], enabling the imaging of MOFs with low dose rates

Proton-Conducting Phenolate-Based Zr Metal–Organic Framework: A Joint Experimental–Modeling Investigation

International audienc

A robust nanoporous supramolecular metal–organic framework based on ionic hydrogen bonds

International audienceHydrogen-bond assembly of tripod-like organic cations [H3-MeTrip]3+ (1,2,3-tri(4′-pyridinium-oxyl)-2-methylpropane) and the hexa-anionic complex [Zr2(oxalate)7]6− leads to a structurally, thermally, and chemically robust porous 3D supramolecular framework showing channels of 1 nm in width. Permanent porosity has been ascertained by analyzing the material at the single-crystal level during a sorption cycle. The framework crystal structure was found to remain the same for the native compound, its activated phase, and after guest resorption. The channels exhibit affinities for polar organic molecules ranging from simple alcohols to aniline. Halogenated molecules and I2 are also taken up from hexane solutions by this unique supramolecular framework

Tetradihydrobenzoquinonate and Tetrachloranilate Zr(IV) Complexes: Single-Crystal-to-Single-Crystal Phase Transition and Open-Framework Behavior for K4Zr(DBQ)4.

: The molecular complexes K4[Zr(DBQ)4] and K4[Zr(CA)4], where DBQ(2-) and CA(2-) stand respectively for deprotonated dihydroxybenzoquinone and chloranilic acid, are reported. The anionic metal complexes consist of Zr(IV) surrounded by four O,O-chelating ligands. Besides the preparation and crystal structures for the two complexes, we show that in the solid state the DBQ complex forms a 3-D open framework (with 22% accessible volume) that undergoes a crystal-to-crystal phase transition to a compact structure upon guest molecule release. This process is reversible. In the presence of H2O, CO2, and other small molecules, the framework opens and accommodates guest molecules. CO2 adsorption isotherms show that the framework breathing occurs only when a slight gas pressure is applied. Crystal structures for both the hydrated and guest free phases of K4[Zr(DBQ)4] have been investigated