How Reproducible Are Surface Areas Calculated from the BET Equation?

Abstract

Porosity and surface area analysis play a prominent role in modern materials science, where their determination spans the fields of natural sciences, engineering, geology and medical research. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory,[1] 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.[2] Since the BET method was first developed, there has been an explosion in the field of nanoporous materials with the discovery of synthetic zeolites,[3] nanostructured silicas,[4–6] metal-organic frameworks (MOFs),[7] and others. Despite its widespread use, the manual calculation of BET surface areas causes a significant spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, we have brought together 60 labs with strong track records on the study of nanoporous materials. We provided eighteen already measured raw adsorption isotherms and asked these researchers to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values for each isotherm. We demonstrate here that the reproducibility of BET area determination from identical isotherms is a largely ignored issue, raising critical concerns over the reliability of reported BET areas in micro- and mesoporous materials in the literature. To solve this major issue, we have developed a new computational approach to accurately and systematically determine the BET area of nanoporous materials. Our software, called BET Surface Identification (BETSI), expands on the well-known Rouquerol criteria and makes, for the first time, an unambiguous BET area assignment possible.

Metal Organic Frameworks for Bioelectrochemical Applications

“…Biofuel cells that exploit enzymes or microbes as biocatalysts to generate electrical energy offer an eco-friendly energy solution for powering electronic devices [28,29] . Enzymatic biofuel cells are promising for low-power applications such as portable medical devices [30] while microbial biofuel [2] 2450 m 2 g −1 [27] Tris, Phos [15] MAF-7 NU-1006 1730 m 2 g −1 [68] 1440 m 2 g −1 [40] Tris, HEPES [19] UiO-66 ZIF-8 1710 m 2 g −1 [27] 1150 m 2 g −1 [27] Tris [15] MIL-100 (Cr) MIL-53 (Al) 1140 m 2 g −1 [25] 2200 m 2 g −1 [27] Phos [15] HEPES [24] BTP [26] Cr Pore size maximum 3.4 nm [23] 1.1 nm [40] 1.16 nm [17] 2.9 nm [15] Pore size maximum ca. 1.36 nm [2] 6.2 nm [69] 1.2 nm [20] ca.…”

“…Such MOFs may be considered generally appropriate for bioelectrochemical applications although stability is best evaluated on a case-by-case basis. MOF stability should be evaluated based on powder x-ray diffraction (PXRD) and electron microscopy data as well as, where possible, ligands/metal ion leaching and porosity and gas adsorption experiments [27] .…”