Experimental methods in chemical engineering: specific surface area and pore size distribution measurements—BET, BJH, and DFT

Abstract

Gas physisorption is an experimental technique based on equilibrium Van der Waals interactions between gas molecules and solid particles, that quantifies the specific surface area (SSA), pore size distribution (PSD), and pore volume of solids and powders. The performance of catalysts, absorbents, chromatography column materials, and polymer resins depends on these morphological properties. Here we introduce the basic principles and procedures of physical adsorption, especially nitrogen physisorption, as a guide to students and researchers unfamiliar with the field. The Brunauer‐Emmett‐Teller theory (BET) is a common approach to estimate SSA that extends the Langmuir monolayer molecular adsorption model to multilayer layers. It relies on an equilibrium adsorption isotherm, measured at the normal boiling point of the adsorbate, eg, 77 K or 87 K for N2 and Ar, respectively. Web of Science indexed 45 400 articles in 2016 and 2017 that mentioned N2 adsorption porosimetry—BET and BJH (Barrett‐Joyner‐Halenda) keywords. The VOSViewer bibliometric tool grouped these articles into four research clusters: adsorption, activated carbon in aqueous solutions for removal of heavy metal ions; synthesis of nanoparticles and composites; catalysts performance in oxidation and reduction processes; and photocatalytic degradation with TiO2. According to the literature, the accuracy of the density function theory (DFT) method is higher than with the BJH theory and it is more reliable.

Electrospun silk fibroin/TiO2 mats. Preparation, characterization and efficiency for the photocatalytic solar treatment of pesticide polluted water

“…Gas physisorption isotherms of nitrogen or argon adsorbates are the basis to measure specic surface area (SSA) of porous material and pore size distribution. 29 In the case of SF (2 m 2 g À1 ) almost no N 2 adsorption is observed, suggesting that the pore structures are very poor. Fig.…”

Activated Carbons and Their Evaluation in Electric Double Layer Capacitors

“… S DFT —the SSA calculated from density functional theory (DFT) based on N 2 and CO 2 adsorption isotherm data. This parameter seems to be more reliable than S BET , and many reports have demonstrated the convergence of S DFT and the real surface areas of materials [ 34 , 35 ]. The DFT method is also commonly used to determine the pore size distribution precisely.…”

General Cluster Sorption Isotherm

“…Often the modeling of type II isotherms is limited in its range. The BET isotherm 28 is practically, in case of surface area evaluation, restricted to the pressure segment between 0.05 and 0.3 29 . More successful are the BET modification by Anderson 30 and the Frenkel-Halsey-HillError: Reference source not found equation.…”