Structure-Dependent Thermal Defunctionalization of Single-Walled Carbon Nanotubes
Saunab Ghosh1, Fang Wei1, Sergei M Bachilo1
1Department of Chemistry and R.E. Smalley Institute for Nanoscale Science and Technology, Rice University, 6100 Main Street, Houston, Texas 77005 United States.
ACS Nano
|June 2, 2015
Summary
Researchers explored defunctionalization of single-walled carbon nanotubes (SWCNTs) by heat treatment. Larger diameter SWCNTs lose attached chemical groups more easily, offering a method for sorting nanotubes by size.
Area of Science:
- Materials Science
- Nanotechnology
- Chemical Engineering
Background:
- Covalent sidewall functionalization of single-walled carbon nanotubes (SWCNTs) is crucial for tuning their properties.
- Reductive alkylation is a common method for SWCNT functionalization.
Purpose of the Study:
- To investigate the defunctionalization of alkyl-functionalized SWCNTs via pyrolysis.
- To assess the influence of SWCNT diameter on the defunctionalization process.
- To explore the potential for diameter-selective sorting of SWCNTs.
Main Methods:
- SWCNTs were functionalized using reductive alkylation (metallic lithium and 1-iodododecane in liquid ammonia).
- Functionalized SWCNTs were pyrolyzed at temperatures ranging from 100 to 500 °C under an inert atmosphere.
- Defunctionalization was analyzed using thermogravimetric analysis, Raman spectroscopy, absorption spectroscopy, and near-infrared fluorescence spectroscopy.
Main Results:
- Defunctionalization rate strongly depends on SWCNT diameter; larger diameters defunctionalize more readily.
- The activation energy for defunctionalization is significantly higher for smaller diameter SWCNTs (0.76 nm) compared to larger ones (1.24 nm).
- Spectroscopic properties of pyrolyzed SWCNTs were restored to their pre-functionalization state.
- Functionalization density impacts Raman D/G ratio and near-infrared fluorescence intensity.
Conclusions:
- The diameter-dependent defunctionalization rate provides a pathway for scalable diameter sorting of mixed SWCNT samples.
- Complete removal of addends restores original SWCNT properties, validating the defunctionalization process.
