FTIR studies of nitrogen doped carbon nanotubes

Purified and defect free carbon nanotubes have great potential for applications in electronic, polymer composites and biological sciences. The removal of impurities (carbon nanoparticles and amorphous carbon) is an important step before the CNT applications can be realized. We report the results of FTIR and TGA/DTA studies of the impurities present in the carbon nanotubes. The multiwalled CNTs were grown using Microwave Plasma Chemical Vapor Deposition (MPCVD) technique. Fourier transform infrared (FTIR) spectroscopy was carried out in the range of 400–4000 cm− 1 to study the attachment of the impurities on carbon nanotubes. FTIR spectra of the as-grown MWCNTs show dominant peaks at 1026, 1250, 1372, 1445, 1736, 2362, 2851, 2925 cm− 1 that are identified as Si–O, C–N, N–CH3, CNT, C–O, and C–Hx respectively. The peaks are sharp and intense showing the chemisorption nature of the dipole bond. The intensity of the peaks due to N–CH3, C–N and C–H reduces after annealing and the peaks vanish on annealing at high temperature (900 °C). The presence of C–N peak may imply the doping of the CNTs with N in substitution mode. TGA/DTA measurements, carried out under argon flow, show that the dominant weight loss of the sample occurs in the temperature range 400–600 °C corresponding to the removal of the impurities and amorphous carbon.