Selective Surface Charge Sign Reversal on Metallic Carbon Nanotubes for Facile Ultrahigh Purity Nanotube Sorting

• Published in: ACS nano Vol. 10; no. 3; pp. 3222 - 3232
• Main Authors: Wang, Jing, Nguyen, Tuan Dat, Cao, Qing, Wang, Yilei, Tan, Marcus Y.C, Chan-Park, Mary B
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 22-03-2016
• Subjects: carbon nanotubes; charge sign reversal; purification; gel chromatography; sorting
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.5b05795

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.