Effects of Molecular Cross-Sectional Areas of Adsorbed Nitrogen on the Brunauer-Emmett-Teller Analysis for Carbon-Based Slit Pores

Brunauer-Emmett-Teller (BET) surface area obtained by nitrogen adsorption is a commonly adopted value to characterize the specific surface area for porous materials. In the BET method, the widely applied cross-sectional area of nitrogen is 16.2 angstrom(2), which has been found to be an oversimplified assumption. The adsorption isotherms of nitrogen simulated with the 2CLJ (Lennard-Jones) + 3q molecular model at 77 K was utilized to determine the cross-sectional area and its behavior as a function of pressure, pore size, and solid affinity. The cross-sectional area shows a negative relation with the pressure and varies with pore size and solid affinity. The overestimation of the BET surface area might arise from the inaccurately determined monolayer adsorption capacity and the cross-sectional area.