Thermal Stability Study of Aryl Modified Carbon Black by in Situ Generated Diazonium Salt

The thermal stability of functionalized Vulcan XC72R powders and the chemical species liberated upon their heat treatment in air and nitrogen were investigated by a series of physicochemical techniques. First, Vulcan was modified by a “one pot” synthesis with 4-nitrophenyl, p-azobenzene, and benzene groups by spontaneous reaction with in situ generated aryl diazonium cations, from the corresponding amine, in aqueous solution. The presence of organic moieties at the carbon surface was demonstrated by elemental analysis and X-ray photoelectron spectroscopy (XPS) which yielded a nitrogen content of 1.5 atom % and 3.0 atom %, respectively. The covalent bonding of the organic groups was indirectly evidenced by thermogravimetric analysis (TGA), which revealed that a high temperature (e.g., above 200 °C) is needed to lose a significant weight of grafted groups. Thermogravimetric analysis-mass spectrometry (TGA-MS) and XPS data suggest that the 4-nitrophenyl grafted groups undergo the cleavage of the N−O bond of the nitro group that is followed by the liberation of NO. The liberated NO then reacted with the carbon support to generate pyrrolic and pyridinic type species, as identified by XPS from the lower binding energy components on the N 1s core level spectra.