Voltammetric quantification of the spontaneous chemical modification of carbon black by diazonium coupling

Surface coverage limits obtained through the spontaneous and reductive reaction of 1-diazo-anthraquinone ions with Vulcan XC72 carbon black have been studied using cyclic voltammetry. The effect of modifying the surface structure of the carbon, varying reaction conditions and time, and the use of sequential reactions were studied. The maximum loading of AQ that could be obtained was 1.0 × 10⁻⁴ mol g⁻¹, consisting in the best case of a 3:1 ratio of covalently bound to adsorbed species. Based on literature specific area values for the carbons and measured specific capacitances, it is concluded that only ca. 25% of the BET area of the pristine Vulcan XC72 is accessible to the diazonium ions, and that a loosely packed monolayer of bound and adsorbed species is formed on this accessible area. Carboxylic acid groups on the carbon surface were not found to limit the total loading of AQ, but did significantly favor covalent bonding over adsorption.