title: Structure-Dependent Thermal Defunctionalization of Single-Walled Carbon Nanotubes.
abstract: Covalent sidewall functionalization of single-walled carbon nanotubes (SWCNTs) is an important tool for tailoring their properties for research purposes and applications. In this study, SWCNT samples were first functionalized by reductive alkylation using metallic lithium and 1-iodododecane in liquid ammonia. Samples of the alkyl-functionalized SWCNTs were then pyrolyzed under an inert atmosphere at selected temperatures between 100 and 500 °C to remove the addends. The extent of defunctionalization was assessed using a combination of thermogravimetric analysis, Raman measurements of the D, G, and radial breathing bands, absorption spectroscopy of the first- and second-order van Hove peaks, and near-IR fluorescence spectroscopy of (n,m)-specific emission bands. These measurements all indicate a substantial dependence of defunctionalization rate on nanotube diameter, with larger diameter nanotubes showing more facile loss of addends. The effective activation energy for defunctionalization is estimated to be a factor of ∼1.44 greater for 0.76 nm diameter nanotubes as compared to those with 1.24 nm diameter. The experimental findings also reveal the quantitative variation with functionalization density of the Raman D/G intensity ratio and the relative near-IR fluorescence intensity. Pyrolyzed samples show spectroscopic properties that are equivalent to those of SWCNTs prior to functionalization. The strong structure dependence of the defunctionalization rate suggests an approach for scalable diameter sorting of mixed SWCNT samples.
authors.affiliation: Department of Chemistry and R.E. Smalley Institute for Nanoscale Science and Technology, Rice University, 6100 Main Street, Houston, Texas 77005 United States.
authors.forename: Saunab
authors.initials: S
authors.lastname: Ghosh
authors.affiliation: Department of Chemistry and R.E. Smalley Institute for Nanoscale Science and Technology, Rice University, 6100 Main Street, Houston, Texas 77005 United States.
authors.forename: Fang
authors.initials: F
authors.lastname: Wei
authors.affiliation: Department of Chemistry and R.E. Smalley Institute for Nanoscale Science and Technology, Rice University, 6100 Main Street, Houston, Texas 77005 United States.
authors.forename: Sergei M
authors.initials: SM
authors.lastname: Bachilo
authors.affiliation: Department of Chemistry and R.E. Smalley Institute for Nanoscale Science and Technology, Rice University, 6100 Main Street, Houston, Texas 77005 United States.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Hauge
authors.affiliation: Department of Chemistry and R.E. Smalley Institute for Nanoscale Science and Technology, Rice University, 6100 Main Street, Houston, Texas 77005 United States.
authors.forename: W E
authors.initials: WE
authors.lastname: Billups
authors.affiliation: Department of Chemistry and R.E. Smalley Institute for Nanoscale Science and Technology, Rice University, 6100 Main Street, Houston, Texas 77005 United States.
authors.forename: R Bruce
authors.initials: RB
authors.lastname: Weisman
keywords: D/G ratio; covalent functionalization; dodecylation; nanotube fluorescence restoration; pyrolysis