Nanoparticle- and Nanotube-Modified Electrodes: Response of Drop-Cast Surfaces

The morphology of electrodes modified by drop casting layers of multi-walled carbon nanotubes (MWCNTs) and platinum nanoparticles (PtNPs) is investigated and shown to exhibit significant heterogeneity, both in the form of ‘patchy’ surfaces and of ‘coffee rings’ formed after evaporation of the carrier solvent. The variation of the heterogeneity with total average coverage is studied and the consequences for quantitative analytical voltammetry assessed. Specifically, the oxidation of bromide in aqueous solution is examined in the case of MWCNTs-modified electrodes and the oxidation of aqueous As(III) in that of PtNPs-modified electrodes. In both cases, significant deviations from the expected voltammetry are observed, even for average coverages that correspond to much in excess of a monolayer of CNTs or NPs. The observed voltammetry is related to the observed structure and the use of such modified electrodes, without concomitant microscopic surface characterization, is caveated.