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 DPCⁿ-SWNT^n-. Finally, oxidation of the intermediates DPCⁿ-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 pi-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 hy- - drocarbon marker (n-C₁₈H₃₅) 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.