Spontaneous polymerization of 2-ethynylpyridine with acylated multi-walled carbon nanotubes in supercritical carbon dioxide and their optical and electrochemical performance

A facile and green approach was proposed for the synthesis of multi-walled carbon nanotubes (MWCNTs) covalently functionalized with poly (2-ethynylpyridine) (MWCNT/P2EP) in supercritical carbon dioxide as a reaction medium. The oxidized MWCNTs were refluxed with thionyl chloride to yield COCl terminated MWCNTs, which were subsequently used as an initiator for the spontaneous polymerization of 2-ethynylpyridine to produce the MWCNT/P2EP hybrid. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction confirmed the formation of amorphous MWCNT/P2EP with a large surface area of 38 m² g^-1 and high nitrogen content (up to 8%). Microscopic results revealed that the MWCNTs were well embedded in the polymer matrix and the P2EP chains were wrapped around the carbon nanotube wall. The strong covalent coupling at the interface of the MWCNT/P2EP resulted in high electrical conductivity and enhanced thermal stability. Furthermore, the optical and electrochemical properties were investigated. The hybrid exhibited a photoluminescence peak at 510 nm corresponding to the photon energy of 2.44 eV.