A methodology to obtain micropore volume in nanoporous solids based on the Dubinin methods

JHONNY VILLARROEL-ROCHA; JOSE ARROYO GÓMEZ; DEICY BARRERA; KARIM SAPAG

Conferencia; All-Russian Conference with international participation (Dedicated to the 120th anniversary of M.M. Dubinin?s birth) "Physicochemical problems of adsorption, structure and surface chemistry of nanoporous materials"; 2021

According to the IUPAC, gas adsorption is a well-known technique to characterize porous solids and fine powders; this characterization requires the use of various subcritical fluids (e.g., N2 at 77 K, Ar at 87 K, and CO2 at 273 K). After measuring the adsorption isotherm and applying several procedures and models, we can obtain the textural properties in a given sample, i.e., specific surface area, pore volumes, and pore size distribution. Among these properties, the micropore volume (VμP) directly affects the porous material performance, and it can be assessed by Dubinin methods, in particular Dubinin-Radushkevich method (DR), plot methods (αS-plot and t-plot), and microscopic methods based on molecular simulations such as Monte Carlo and Density Functional Theory (DFT). It is well known that microscopic methods provide the best description, at the molecular level, of the adsorption behavior in pore structures. However, access to these methods is still limited, and, to describe a given porous system, an adequate Kernel is required. On the other hand, the plot methods are a suitable option for the calculation of VμP but are susceptible to the selected relative pressures interval. Finally, based on the micropore filling theory and Polanyi potentials, the DR method is commonly used due to its simplicity and reliable results when the studied sample has a Type I isotherm. Nonetheless, it has been demonstrated that when the sample presents mesoporosity, the DR method overestimates the micropore volume. To improve the calculation of VμP, in this work, we propose a more general methodology based on the Dubinin methods and the t concept, naming it the DR_t method, which was evaluated for different nanoporous materials.