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 123 their determination spans the fields of natural sciences, engineering, geology and medical 124 research. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory,[1] which has been 125 a remarkably successful contribution to the field of materials science. The BET method was 126 developed in the 1930s and is now the most widely used metric for the estimation of surface 127 areas of porous materials.[2] Since the BET method was first developed, there has been an 128 explosion in the field of nanoporous materials with the discovery of synthetic zeolites,[3] 129 nanostructured silicas,[4–6] metal-organic frameworks (MOFs),[7] and others. Despite its 130 widespread use, the manual calculation of BET surface areas causes a significant spread in 131 reported areas, resulting in reproducibility problems in both academia and industry. To probe 132 this, we have brought together 60 labs with strong track records in the study of nanoporous 133 materials. We provided eighteen adsorption isotherms and asked these researchers to 134 calculate the corresponding BET areas, resulting in a wide range of values for each one. We 135 show here that the reproducibility of BET area determination from identical isotherms is a 136 largely ignored issue, raising critical concerns over the reliability of reported BET areas in 137 the literature. To solve this major issue, we have developed a new computational approach 138 to accurately and systematically determine the BET area of nanoporous materials. Our 139 software, called BET Surface Identification (BETSI), expands on the well-known Rouquerol 140 criteria and makes, for the first time, an unambiguous BET area assignment possible.

Data-Driven Matching of Experimental Crystal Structures and Gas Adsorption Isotherms of Metal–Organic Frameworks

“…58 In another case, the experimental value of 0.978 cm 3 g −1 slightly exceeds the geometric pore volume of CuBTC, and the manuscript also reports a very high BET surface area of 2327 m 2 g −1 , the largest ever reported to our knowledge. 59 While we are not able to determine in retrospect what led to this large valuefor example, the calibration of the instrument, a material with large defects, or an imprecise BET calculation 60 our analysis points at potential benefits from checking the geometric pore volume of the sample before moving on to measure the adsorption of other gases. 61 Since the indicators of popularity included the number of reports in the NIST-ISODB, their list of the six most studied MOFs, unsurprisingly, contains four of the MOFs listed in Table 1 (UIO-66, CuBTC, ZIF-8, and IRMOF-1).…”

Formulation of Metal–Organic Framework-Based Drug Carriers by Controlled Coordination of Methoxy PEG Phosphate: Boosting Colloidal Stability and Redispersibility

“…48 We next conducted N 2 adsorption experiments at 77 K to investigate the potential impact of incorporating mPEG−PO 3 into the internal porosity of PCN-222. As shown in Figure 2c, PCN-222 and PCN-222@PEG−PO 3 adsorb 526 and 129 cm 3 g −1 N 2 at P/P 0 = 0.8, respectively, with Brunauer−Emmett− Teller (BET) areas, analyzed using BETSI, 49 decreasing from 1151 to 265 m 2 g −1 (see Supporting Information, Section S4). However, the pure mPEG−PO 3 adsorbs a nearly negligible amount of N 2 (Figure S33).…”

Sol-gel processing of a covalent organic framework for the generation of hierarchically porous monolithic adsorbents

“…Analysis of the nitrogen adsorption isotherms (Figures 3A and S3) collected for these pellets, however, revealed a striking trend. Whereas we observed a monotonic increase in Brunauer-Emmett-Teller (BET) area-calculated by BET surface identification (BETSI) 22 -for pellets synthesized in solvent systems containing acetonitrile fractions ranging from 0.000 to 0.750 (v/v), we observed a sharp decrease in BET area to 4 m 2 g À1 for samples prepared at higher acetonitrile fractions (Figure 3C). As a result, the highest BET area that could be obtained for TPB-DMTP-COF with methanol as the activation solvent was 1,122 m 2 g À1 , suggesting the presence of a lower limit in intercrystallite pore size beyond which pore disruption takes place.…”