title: Selective Surface Charge Sign Reversal on Metallic Carbon Nanotubes for Facile Ultrahigh Purity Nanotube Sorting.
abstract: Semiconducting (semi-) single-walled carbon nanotubes (SWNTs) must be purified of their metallic (met-) counterparts for most applications including nanoelectronics, solar cells, chemical sensors, and artificial skins. Previous bulk sorting techniques are based on subtle contrasts between properties of different nanotube/dispersing agent complexes. We report here a method which directly exploits the nanotube band structure differences. For the heterogeneous redox reaction of SWNTs with oxygen/water couple, the aqueous pH can be tuned so that the redox kinetics is determined by the availability of nanotube electrons only at/near the Fermi level, as predicted quantitatively by the Marcus-Gerischer (MG) theory. Consequently, met-SWNTs oxidize much faster than semi-SWNTs and only met-SWNTs selectively reverse the sign of their measured surface zeta potential from negative to positive at the optimized acidic pH when suspended with nonionic surfactants. By passing the redox-reacted nanotubes through anionic hydrogel beads, we isolate semi-SWNTs to record high electrically verified purity above 99.94% ± 0.04%. This facile charge sign reversal (CSR)-based sorting technique is robust and can sort SWNTs with a broad diameter range.
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University , Singapore 637459, Singapore.
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University , Singapore 637459, Singapore.
authors.forename: Tuan Dat
authors.initials: TD
authors.lastname: Nguyen
authors.affiliation: IBM T.J. Watson Research Center , 1101 Kitchawan Road, Yorktown Heights, New York 10598, United States.
authors.forename: Qing
authors.initials: Q
authors.lastname: Cao
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University , Singapore 637459, Singapore.
authors.forename: Yilei
authors.initials: Y
authors.lastname: Wang
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University , Singapore 637459, Singapore.
authors.forename: Marcus Y C
authors.initials: MY
authors.lastname: Tan
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University , Singapore 637459, Singapore.
authors.forename: Mary B
authors.initials: MB
authors.lastname: Chan-Park
keywords: carbon nanotubes; charge sign reversal; gel chromatography; purification; sorting