Covalent sidewall functionalization of single-walled carbon nanotubes via reduction of benzophenone by potassium metal

Covalent sidewall functionalization of single-walled carbon nanotubes (SWNTs) via addition of diphenylcarbinol (DPC) anions and diphenylcarbinol radicals was reported. The reaction of a potassium atom with a benzophenone molecule results in transferring one electron from the potassium to the benzophenone, forming a radical which adds readily to nanotubes to form functionalized SWNTs (DPC-SWNTs). DPC anions were generated from two- electrons reduction of a benzophenones by two potassium metal. These anions were used to functionalize SWNTs in a different way. First, anions added to the sidewalls of nanotubes to form intermediates DPC
ⁿ
-SWNT
ⁿ⁻
. Finally, oxidation of the intermediates DPC
ⁿ
-SWNT
ⁿ⁻
gives the neutral derivatives DPC-SWNTs. Raman spectroscopy shows that, compared with pristine SWNTs, the disorder mode (1323.1 cm
⁻¹
) of functionalized SWNTs is greatly enhanced, which is indicative of increased number of spa hybridized carbon atoms in the functionalized SWNTs, due to chemically induced disruption of the aromatic system of π-electrons in the hexagonal framework of nanotube walls. UV-Visible spectroscopy shows that functionalized SWNTs lose the van Hove singularities typical for pristine SWNTs, suggesting a significant alteration of the electronic structure of nanotubes through covalent sidewall functionalization. Raman and UV-Visible spectroscopy confirm unambiguously that covalent functionalization has taken place. ATR-FTIR and XPS were utilized to characterize DPC groups grafted onto the sidewalls of carbon nanotubes. ATR-FTIR spectroscopy shows that phenyl and carbinol groups have been grafted onto the nanotubes. X-ray photoelectron spectroscopy (XPS) shows the atomic rate of O/C and number of C-O bands increases after functionalization. Thermo gravimetric analysis (TGA) shows that the degree of functionalization is about 14% and 10% for anion addition and radical addition, respectively. A long chain hydrocarbon marker (n-C
18
H
35
) was grafted onto the functional groups by esterification reaction for high- resolution TEM (HRTEM) visualization. The functional groups (phenyl and carbinol) offer a variety of possible reactions for further derivatization. This process, utilizing reduction of an aromatic molecular by alkali metal, will open a way for covalent sidewall functionalization of SWNTs.