Synthesis and characterization of glucose-capped CdSe quantum dots. Electrochemical and computational studies of corresponding carbon-ionic liquid electrode for quantitative determination of minoxidil

Abstract

The glucose-capped CdSe quantum dots (QDs) and 1-ethyl-3-methyl-imidazolium:PF6 (EtMIMPF6) ionic liquid (IL) have been incorporated in the graphite paste electrode (GPE) and used for the voltammetric determination of minoxidil. The high permeability of IL as a hydrophilic binder to polar species, in addition to improving the faradaic current, resulted in increased capacitive current. In order to further improvement of the faradaic signal, we employed a glucose-capped CdSe QDs. Cyclic voltammetry and Faradaic impedance spectroscopy (FIS) indicated that incorporating the QDs into the composite matrix although was not able to significantly improve the kinetics of minoxidil oxidation, but remarkably enhanced the magnitude of the anodic peak current. The sluggish expansion of diffusion layer in viscose IL medium and the microdisc-geometry like behaviour of nanoparticles provided a proper condition for transition from the planar semi-infinite diffusion to the thin layer behaviour. Density functional theory (DFT) was found to yield a good description of the enhancement of signal in the presence of nanomaterials. The results of calculation support that the change in diffusion manner, and not improving in the electron transfer capability at electrode/electrolyte interface, is responsible for the observed signal enhancement. A detailed mechanism for oxidation of minoxidil was also proposed.