Evaluation of carbon nanopores using large molecular probes in grand canonical Monte Carlo simulations and experiments

Nanopores (pores between 1 and 5 nm) have been the object of a great deal of attention because they can selectively adsorb relatively large molecules such as macromolecules and polymer molecules. Conventional methods for analyzing porous structures—such as N₂ adsorption measurements at 77 K—can be used to investigate microporous and mesoporous structures, but there is a lack of investigation of nanopores or the boundary between micropores (<2 nm) and mesopores (2–50 nm). Here, we propose the evaluation method of nanopores using a large probe molecule, SF₆. Grand canonical Monte Carlo simulations for N₂ and SF₆ suggested that SF₆ was adsorbed in 1.5–5 nm nanopores, while there was N₂ adsorption for the wide range of pore sizes. The SF₆ adsorption could therefore be used to confirm existence of the nanopores. To test this, we used single-walled carbon nanohorns as porous carbons with widely distributed pore size. SF₆ was well adsorbed only in the nanopores at 195 K, whereas N₂ adsorption was observed in all micropores and mesopores. This structural analysis of nanopores using a large-molecule probing method complements structural analyses using N₂ adsorption, as well as other techniques.