The chemical modification of a range of carbon blacks (primary particle diameters ranging from 14 nm to 66 nm) has been investigated and characterised by means of cyclic voltammetry (CV), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and acid-base Boehm titration. An electrochemical probe molecule, 4-nitroaniline, was introduced to the carbon black. Physisorption and intercalation processes were observed and quantified electrochemically. Significantly more 4-nitroaniline per cm2 was present for smaller particles, implying extensive intercalation for particles ca. 14 nm in diameter. The voltammetric reduction of 4-nitroaniline covalently tethered to the carbon black was observed at a potential ca. 0.4 V more negative than the physisorbed and intercalated species, allowing separate quantitative analysis. Nanoscale size effects of carbon black were observed, with an optimum size of 27 nm observed. The electrochemical responses regarding the physisorption process decreased with the increase in surface oxidative pre-treatment time. In contrast, voltammetric signals corresponding to covalently tethered 4-nitroaniline increased with surface oxidation, before decreasing due to over-oxidation of the carbon black. The importance of some oxidation in forming electrochemically stable covalently-tethered groups is noted and discussed. © 2010 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.