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Selective Filling of n-Hexane in a Tight Nanopore



Jeffrey Fagan, Haoran Qu, Archith Rayabharam, Narayana Aluru, Xiaojian Wu, Peng Wang, Yunfeng Li, YuHuang Wang


Molecular sieving may occur when two similarly sized molecules compete for a nanopore. This size-selectivity generally favors the adsorption of molecules with smaller kinetic diameter into the pore while excluding larger ones. In nearly all known examples, the nanopores are larger than the molecules that selectively enter the pores. Here, we demonstrate selective filling of n-hexane from a mixture with cyclohexane, two molecules that are nearly identical in size, by single-walled carbon nanotubes with a van der Waals pore size of 0.42 nm. We find that even a trace amount of n-hexane in 99.9 % cyclohexane can be selectively captured and removed from the mixture. Unexpectedly, this selectivity occurs where the n-hexane molecule is larger than the pore size of the nanotube, thus challenging our current understanding of the nanotube pore and how molecules may enter a tight channel. Ab initio molecular dynamics simulation reveals that the molecule stretches by nearly 11.2 % inside the nanotube pore, generating a strain-induced photoluminescence shift in the nanotube that we experimentally observed by photoluminescence spectroscopy and single nanotube hyperspectral imaging. Although at a relatively low probability of only 3 %, the stretched state of n-hexane exists in the bulk solution, allowing the molecule to enter the tight pore even at room temperature. Our work thus provides critical new insights on nanopore selectivity and demonstrates a sensitive spectroscopy method for imaging the molecular filling processes.
Nature Communications


nanopore, nanotube, Single-wall carbon nanotube, separation


Fagan, J. , Qu, H. , Rayabharam, A. , Aluru, N. , Wu, X. , Wang, P. , Li, Y. and Wang, Y. (2021), Selective Filling of n-Hexane in a Tight Nanopore, Nature Communications, [online], (Accessed February 22, 2024)
Created January 12, 2021, Updated February 28, 2023