Properties of octadecylsilyl-coated electrodes in ionic micellar solutions

Abstract

Cyclic voltammetry of ferrocene, hexaammineruthenium(III) and hexacyanoferrate(II) in micellar solution sof sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) was studied at platinum and pyrolytic graphite electrodes treated with octadecyltrichlorosilane. The charge-transfer rates and surface spectra were consistent with near monolayer coverage of the electrodes with an octadecylsilyl (ODS) layer bound to the surface through SiOgroups. Both SDS and CTAB were detected by x-ray photoelectron spectroscopy on ODS-coated electrodes treated with micellar solutions. Compared with bare electrodes, the signal-to-noise ratio and reproducibility were better on ODS electrodes, which were stable when stored in air. Some control over electrochemical selectivity and reversibility was achieved with ODS-coated electrodes in ionic micellar solutions. For surfactant and electroactive ions of the same charge sign, significant inhibition to charge transfer was found. Ions of opposite charge from the surfactant had enhanced charge-transfer rates. The results are qualitatively consistent with the kinetic effects of an adsorbed layer of ionic surfactant on the ODS electrodes.