An atomistic model of a disordered nanoporous solid: Interplay between Monte Carlo simulations and gas adsorption experiments

Lorenzo Canti,Leonardo Marchese,Alberto Fraccarollo,Maurizio Cossi,Giorgio Gatti,Mina Errahali

doi:10.1063/1.4982069

Lorenzo Canti, Leonardo Marchese + Show 4 more

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https://doi.org/10.1063/1.4982069

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Abstract

A combination of physisorption measurements and theoretical simulations was used to derive a plausible model for an amorphous nanoporous material, prepared by Friedel-Crafts alkylation of tetraphenylethene (TPM), leading to a crosslinked polymer of TPM connected by methylene bridges. The model was refined with a trial-and-error procedure, by comparing the experimental and simulated gas adsorption isotherms, which were analysed by QSDFT approach to obtain the details of the porous structure. The adsorption of both nitrogen at 77 K and CO2 at 273 K was considered, the latter to describe the narrowest pores with greater accuracy. The best model was selected in order to reproduce the pore size distribution of the real material over a wide range of pore diameters, from 5 to 80 Å. The model was then verified by simulating the adsorption of methane and carbon dioxide, obtaining a satisfactory agreement with the experimental uptakes. The resulting model can be fruitfully used to predict the adsorption isotherms of various gases, and the effect of chemical functionalizations or other post-synthesis treatments.

Highlights

Nanoporous materials are of great interest for applications in gas storage,[7,8,9] molecular separation,[10,11,12] heterogeneous catalysis,[13,14,15] and the properties of such materials are critically affected by their porous structure, whose main parameters are the specific surface area, the micro- and mesoporous volumes and the pore size distribution
The CO2 adsorption is useful for very narrow pores: it clearly indicates the presence of ultramicropores around 5.1 Å, which are confirmed by N2 adsorption, though for this gas such small pores are close to the detection limit
We considered only mesopores up to 80 Å for the comparison with the mPAF models, since wider pores are not likely to arise from atomistic models like ours

Summary

Introduction

Nanoporous materials are of great interest for applications in gas storage,[7,8,9] molecular separation,[10,11,12] heterogeneous catalysis,[13,14,15] and the properties of such materials are critically affected by their porous structure, whose main parameters are the specific surface area, the micro- and mesoporous volumes and the pore size distribution. Hand, the adsorption isotherms can be simulated by Grand Canonical Monte Carlo (GCMC) calculations, if an atomistic, periodic model of a porous material is available;[19,20,21,22,23,24,25,26] both experimental and simulated isotherms can be analyzed with the same DFT-based techniques, obtaining pore size distributions and porous volumes which can be directly compared. The PAF material formed with biphenyl chains (called PAF-1 or PAF-302 in the literature, and synthesized from tetrabromophenylmethane through Yamamoto homo-coupling reaction) has been exploited for gas adsorption, with excellent uptakes of methane[31,32,33] and CO2.34–36

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