Sorting of single-walled carbon nanotubes based on metallicity by selective precipitation with polyvinylpyrrolidone

Noncovalent polymer sorting of single-walled carbon nanotubes (SWNTs) was carried out using polyvinylpyrrolidone (PVP) in dimethylformamide (DMF) solvent. With long-term (i.e., 14-day) standing of SWNTs/PVP/DMF in ambient condition, the semiconducting SWNTs remain suspended in solvent while metallic SWNTs precipitated out. The preferential semiconducting nanotube suspension was confirmed by optical absorption spectroscopy, Raman spectroscopy, and field effect transistor measurements. Field-effect transistors made from the enriched semiconducting SWNTs show enhanced switching performance with typical on/off ratios of at least 1000. We propose that noncovalent charge transfer occurs between PVP and SWNTs, and metallic nanotubes with mobile electrons at/near the Fermi level are more susceptible to environmental temperature fluctuations than semiconducting nanotubes, so that with the small temperature increase experienced during 14 days of standing under normal laboratory condition, polymer unwrapping from metallic nanotubes occurs, leading to their selective precipitation.