Voltammetric responses of porous Co3O4 spinels supported on MOF-derived carbons: Effects of porous volume on dopamine diffusion processes

Abstract The voltammetric responses of novel porous Co3O4 spinel materials supported on MOF-derived carbons (MOFDC) have been described. The electrocatalysts were prepared using microwave-assisted hydrothermal methods, obtaining both Rich- and Starved-Co3O4 MOF-derived carbons (i.e., R-Co3O4@MOFDC and S-Co3O4@MOFDC). The physicochemical properties of the porous electrode materials were thoroughly characterized via XRD, SEM, BET, EDX and XPS. The R-Co3O4@MOFDC shows low specific surface area and small pore volume, while the S-Co3O4@MOFDC is characterized with high specific surface area and large pore volume, about four times larger than the former. Using dopamine as a model analyte, the study shows the voltammetric response towards the detection of dopamine detection to be strongly dependent on the diffusive and adsorptive/capacitive modes: R-Co3O4@MOFDC exhibits high diffusive mode with enhanced dopamine detection, while S-Co3O4@MOFDC exhibits high adsorptive mode and relatively poor dopamine detection. The overall voltammetric response is interpreted in terms of fast semi-infinite planar diffusion of dopamine towards the electrode surface and the inhibition of the thin layer diffusion process due to the depletion of the electrolyte trapped within pores (leading to disadvantageous adsorption). At higher concentrations (DA > 3 mM) the adsorption behaviour at these porous electrode follows the Langmuir adsorption isotherm with adsorption equilibrium constant (β) of (1.96 ± 0.16) × 105 and (2.53 ± 0.20) × 105 M−1 for R-Co3O4@MOFDC and S-Co3O4@MOFDC, respectively. This study opens doors for rational design and development of transition metal-based MOFDC for the detection of biomolecules.