Investigating the mechanism for the covalent chemical modification of multiwalled carbon nanotubes using aryldiazonium salts

The mechanism involved in the modification of carbon nanotubes (CNTs) functionalized using diazonium salts has been investigated. Bamboo-like and hollow-tube multiwalled carbon nanotubes (MWCNTs) were covalently modified using 4-nitrobenzenediazonium tetrafluoroborate. The MWCNTs were derivatized in the presence and absence of hypophosphorous acid as a mild reducing agent and the resulting materials were characterized using cyclic voltammetry. The obsd. peak potentials for the modified materials were found to differ depending on the derivatization conditions (presence/absence of hypophosphorous acid, diazonium salt concn. and temp.) and these differences were interpreted mech. The exptl. results suggest that, in the absence of hypophosphorous acid, the derivatization mechanism likely proceeds through a cationic intermediate, while in the presence of the hypophosphorous acid the mechanism probably involves either a purely radical intermediate or a mixt. of radical and cationic species depending on the concn. of the hypophosphorous acid reducing agent and the reaction temp. Polymn. of the nitrophenyl groups on the surface of nanotubes was studied using different concns. of 4-nitrobenzenediazonium tetrafluoroborate and was found to increase with increasing concn. of cationic intermediates. The effect of the reaction temp. on the derivatization was explored over a range of temps. from 5 to 50 °C and the optimum derivatization temp. was detd. in the presence and absence of hypophosphorous acid. It was found to be 20 °C and 35 °C in the presence and absence of hypophosphorous acid resp. [on SciFinder(R)]