Effect of graphite particle size on the physicochemical properties and dopamine-sensing performance of reduced graphene oxide

Graphene oxide (GO) was synthesised from graphite powders of two different particle sizes (≤50 and ≥149–≤840 μm) using the Hummers’ method and subsequently reduced by thermal shock at 800°C to obtain reduced graphene oxide (rGO). The obtained samples, denoted rGO_1 (from smaller graphite particles) and rGO_2 (from larger graphite flakes), were investigated to evaluate the influence of precursor size on their physicochemical properties and electrochemical performance. Structural characterisation was carried out by X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction, scanning electron microscopy and nitrogen adsorption–desorption analysis. The results confirmed the removal of oxygen-containing groups after thermal reduction and indicated differences in crystallite domains and defect density depending on the size of the graphite precursor. Electrochemical measurements demonstrated that both samples were able to detect dopamine (DA). The electrodes showed linear DA detection in a concentration range of 1–19.96 μM, with detection limits of 61.55 nM for rGO_1 and 98.17 nM for rGO_2. Sensitivities were determined as 6.44 and 12.20 μA μM–1 cm–2, respectively. Our results suggest that the properties of rGO can be tailored by controlling the size of the graphite precursor, which may provide new opportunities for the design of rGO-based electrochemical sensors.