Carbon nanotube functionalization with carboxylic derivatives: a DFT study

Chemical functionalization of a single-walled carbon nanotube (CNT) with different carboxylic derivatives including -COOX (X = H, CH3, CH2NH2, CH3Ph, CH2NO2, and CH2CN) has been theoretically investigated in terms of geometric, energetic, and electronic properties. Reaction energies have been calculated to be in the range of -0.23 to -7.07 eV. The results reveal that the reaction energy is increased by increasing the electron withdrawing character of the functional groups so that the relative magnitude order is -CH2NO2 >-CH2CN >-H >-CH2Ph >-CH3 >-CH2NH2. The chemical functionalization leads to an increase in HOMO/LUMO energy gap of CNT by about 0.32 to 0.35 eV (except for -H). LUMO, HOMO, and Fermi level of the CNT are shifted to lower energies especially in the case of -CH2NO2 and -CH2CN functional groups. Therefore, it leads to an increment in work function of the tube, impeding the field electron emission.