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

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

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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

A phase transformable ultrastable titanium-carboxylate framework for photoconduction

International audiencePorous titanium oxide materials are attractive for energy-related applications. However, many suffer from poor stability and crystallinity. Here we present a robust nanoporous metal–organic framework (MOF), comprising a Ti12O15 oxocluster and a tetracarboxylate ligand, achieved through a scalable synthesis. This material undergoes an unusual irreversible thermally induced phase transformation that generates a highly crystalline porous product with an infinite inorganic moiety of a very high condensation degree. Preliminary photophysical experiments indicate that the product after phase transformation exhibits photoconductive behavior, highlighting the impact of inorganic unit dimensionality on the alteration of physical properties. Introduction of a conductive polymer into its pores leads to a significant increase of the charge separation lifetime under irradiation. Additionally, the inorganic unit of this Ti-MOF can be easily modified via doping with other metal elements. The combined advantages of this compound make it a promising functional scaffold for practical applications