Structure analyses of dodecylated single-walled carbon nanotubes

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Single-walled carbon nanotubes (SWNTs) are challenging to process due to aggregation.
• Functionalization can improve SWNT solubility and processability in organic solvents.
• Alkali metal intercalation offers a potential route for sidewall functionalization.

Purpose of the Study:

• To investigate the effect of different alkali metals (lithium, sodium, potassium) on the sidewall alkylation of SWNTs.
• To characterize the resulting functionalized SWNTs and their thermal properties.
• To understand how alkali metal choice influences the dealkylation process and potential addition patterns.

Main Methods:

• Preparation of SWNT salts using lithium, sodium, or potassium in liquid ammonia.
• Alkylation of SWNT salts with 1-iodododecane.
• Characterization using atomic force microscopy (AFM), transmission electron microscopy (TEM), thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy (TGA-FTIR), and solid-state 13C NMR.
• Thermal analysis of dealkylation behavior.

Main Results:

• Sidewall-functionalized, soluble SWNTs were successfully prepared using Li, Na, and K.
• Extensive debundling of SWNT ropes was observed due to alkali metal intercalation.
• Radically different thermal dealkylation profiles were observed: Li-SWNTs at 180-330°C, Na-SWNTs at 380-530°C, and K-SWNTs over 180-500°C.
• Solid-state 13C NMR spectra suggested differences in the addition patterns (1,2- vs. 1,4-) of alkyl groups depending on the alkali metal used.

Conclusions:

• Alkali metal choice in SWNT alkylation significantly influences the thermal stability and dealkylation temperature of the functionalized nanotubes.
• The intercalation of alkali metals leads to effective debundling of SWNT ropes, enhancing solubility.
• The observed differences in dealkylation temperatures and NMR spectra may indicate varying degrees of 1,2- and 1,4-alkylation, offering a method to tune SWNT properties.