NLDFT Pore Size Distribution in Amorphous Microporous Materials

Abstract

The pore size distribution (PSD) is one of the most important properties when characterizing and designing materials for gas storage and separation applications. Experimentally, one of the current standards for determining microscopic PSD is using indirect molecular adsorption methods such as nonlocal density functional theory (NLDFT) and N isotherms at 77 K. Because determining the PSD from NLDFT is an indirect method, the validation can be a nontrivial task for amorphous microporous materials. This is especially crucial since this method is known to produce artifacts. In this work, the accuracy of NLDFT PSD was compared against the exact geometric PSD for 11 different simulated amorphous microporous materials. The geometric surface area and micropore volumes of these materials were between 5 and 1698 m/g and 0.039 and 0.55 cm/g, respectively. N isotherms at 77 K were constructed using Gibbs ensemble Monte Carlo (GEMC) simulations. Our results show that the discrepancies between NLDFT and geometric PSD are significant. NLDFT PSD produced several artificial gaps and peaks that were further confirmed by the coordinates of inserted particles of a specific size. We found that dominant peaks from NLDFT typically reported in the literature do not necessarily represent the truly dominant pore size within the system. The confirmation provides concrete evidence for artifacts that arise from the NLDFT method. Furthermore, a sensitivity analysis was performed to show the high dependency of PSD as a function of the regularization parameter, λ. A higher value of λ produced a broader and smoother PSD that closely resembles geometric PSD. As an alternative, a new criterion for choosing λ, called here the smooth-shift method (SSNLDFT), is proposed that tuned the NLDFT PSD to better match the true geometric PSD. Using the geometric pore size distribution as our reference, the smooth-shift method reduced the root-mean-square deviation by ∼70% when the geometric surface area of the material is greater than 100 m/g.

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

“…Seaton et al were the first to propose the density functional theory (DFT) coupled with Monte Carlo molecular simulations to more precisely calculate pore size distribution from adsorption isotherms. For materials with highly disordered slit‐like micropores and spheres, non‐local density functional theory (NLDFT) apply best . To determine pore size distribution, the BJH and DFT methods are complemented by porosimetry methods on the large size range.…”

“…For materials with highly disordered slit-like micropores and spheres, non-local density functional theory (NLDFT) apply best. [13] To determine pore size distribution, the BJH and DFT methods are complemented by porosimetry methods on the large size range. Low pressure mercury porosimetry applies to macropores (14 μm-200 μm) while high pressure Hg porosimetry measures pore diameters as low as 3 nm (mesopores).…”

Performance of activated carbons synthesized from fruit dehydration biowastes for supercapacitor applications

“…The Brunauer–Emmett–Teller (BET) surface area, in addition to gas adsorption/desorption isotherms of the carbon powders, was analyzed using nitrogen (N 2 ) adsorption in a Micromeritics ASAP 2020 nitrogen adsorption apparatus (Micromeritics Instrument Corporation, Norcross, GA). All samples experienced multiple degassing steps at temperatures up to 115°C for 24 h. Pore size distributions were calculated using SAIEUS Software (http://www.ndlft.com/downloads) according to Non‐Localized Density Function Theory (NLDFT) with nitrogen adsorption data . In the SAIEUS software, L‐curve method was selected because it balances the roughness of the solution and the goodness of the fit to estimate the regularization parameter (λ) for the NLDFT method.…”

Generic Strategy to Synthesize High‐Tap Density Anode and Cathode Structures with Stratified Graphene Pliable Pockets via Monomeric Polymerization and Evaporation, and Their Utilization to Enable Ultrahigh Performance in Hybrid Energy Storages

“…Figure 3d displays the adsorption/desorption isotherms and pore distribution (inset) obtained using the nonlocalized density functional theory method. [ 27 ] The specific surface areas of Sn@GPPs and H@GPPs are 80 and 1351 m 2 g −1 , respectively. The high specific surface area of H@GPPs is considered to be induced by the sublimated S NPs, resulting in the formation of mesopores with sizes of ≈5 and 15 nm.…”