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

Abstract

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.

Arsenic (III) Detection with Underpotential Deposition and Anodic Stripping Voltammetry

“…According to the optical microscopy images shown in Figure 1b, a ring‐like pattern was formed on the surface of electrode after the drop casting of Pt nanoparticles, so‐called the coffee ring pattern [33] . It was previously characterized by SEM [34] and shown that although most of the particles are deposited as part of the ‘ring’ a few particles remain randomly distributed around the centre of the drop cast (Figure 1c) [34] but which is mostly empty of deposit. The average particle‐particle distances even in the centre for the mass drop casted were shown to be sufficiently small so as to allow diffusional overlap so that analyte diffusion to the full geometric area of the electrode was observed [34] …”

Electro‐Oxidation of Titanium Carbide Nanoparticles in Aqueous Acid Creates TiC@TiO2 Core‐Shell Structures

“…Taking the area of the GCE (7.06 mm 2 ) and the average NP size (35 nm) a 2 μL (1 mg/ml) dispersion (containing NPs of 35–50 nm range) can form ca 1–2 NP layers averaged over a 3 mm diameter GCE assuming close packing and a uniform deposition covering exclusively the entire disc area. However, some unavoidable local NP agglomeration/aggregation is well known [17] to plague the drop‐casting method. Significant heterogeneity was observed for the TiC NP deposits microscopically as detailed in the SI with well‐separated clumps of accumulated particles evident.…”

Diamine Oxidase-Conjugated Multiwalled Carbon Nanotubes to Facilitate Electrode Surface Homogeneity

“…Due to their biocompatibility, MWCNTs are ideal candidates for biomolecule loading, thus significant research is being conducted to advance these models, however, major challenges in the way of nanotube pre-processing remain. The formation of MWCNT agglomerations have been suggested to occur due to the hydrophobicity of the sp 2 carbon sidewalls and the strong π-π stacking interactions between individual carbon nanotubes [25,26]. The surface of unmodified MWCNTs result in a shortage of hydrogen bonding with water molecules.…”