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.