Characterizing the surface properties of carbon nanotubes by inverse gas chromatography

Inverse gas chromatography (IGC) was used to characterize the surface properties of pristine multi-walled carbon nanotubes (MWNTs), as well as the poly(acrylic acid) sidewall covalently functionalized MWNTs (PAA-g-MWNTs) and hydroxyl group directly grafted MWNTs (MWNTols). The dispersive component of the surface energy ( \( \gamma _S^D \)) and the acid/base character of these samples’ surfaces were estimated by the retention time with different non-polar and polar probes at infinite dilution region. The specific free energy (ΔGAB) and the enthalpy (ΔHAB) of adsorption corresponding to acid–base surface interactions were determined. By correlating ΔHAB with the donor and acceptor numbers of the probes, the acidic (KA) and the basic KD parameters of the samples’ were calculated. The results show that chemical modification successfully reduces the dispersive component of the surface energy of MWNTs. Furthermore, MWNTs grafted with hydroxyl groups exhibit a more basic character, while MWNTs grafted with poly(acrylic acid) show a more acidic character. Overall, IGC provides useful complementary information on the changes resulted from the chemical modifications of the surface.