Functionalization of multi-walled carbon nanotubes with various 4-substituted benzoic acids in mild polyphosphoric acid/phosphorous pentoxide

Functionalization of multi-walled carbon nanotubes (MWCNTs) with various 4-substituted benzoic acids (BAcs) was conducted by using “direct” Friedel–Crafts acylation in mild polyphosphoric acid/phosphorous pentoxide. The degree of functionalization was studied using thermogravimetric analysis, elemental analysis, infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. The overall evidence indicated that the MWCNTs had remained structurally intact as a result of the reaction. The more reactive BAcs showed that the larger arylcarbonyl moieties were covalently attached onto the surface of MWCNTs. The resultant functionalized MWCNTs (F-MWCNTs) formed bundles with average diameters of 40–70 nm depending on the polarity of the surface groups. The diameter dimensions of bundles were closely related to surface polarities of F-MWCNTs. The solubility/dispersibility and thermal properties of F-MWCNTs were also greatly influenced by the nature of the substituted groups.