Electrochemical detection of free glycerol in biodiesel using electrodes with single gold particles in highly ordered SiO2 cavities

In the present work, we report a direct electrochemical glycerol detection method using thermally annealed, facet-specific, single gold particles, Au (1 1 1), located in the cavities of a highly ordered SiO2 cavity array on an indium-doped tin oxide (ITO) electrode. We fabricated an interconnected array structure comprised of SiO2 cavities onto ITO electrodes via monolayer colloidal crustal (MCC) templates. Gold nanoparticles (Au NPs) were electrodeposited at the bottom of the SiO2 cavities in direct contact with the ITO electrodes (Au (poly)/SiO2 cavity/ITO electrode). Upon annealing the electrodes at 700 °C, single gold particles were formed, dominated by the (1 1 1) facet (Au (1 1 1)/SiO2 cavity/ITO electrode). The Au (1 1 1)/SiO2 cavity/ITO electrode exhibited satisfactory electrocatalytic activity to the oxidation of glycerol. More importantly, each cavity of the SiO2 possibly behaves as an independent electrochemical cell in which the glycerol molecules are trapped; this produces a microenvironment advantageous to catalyze electrooxidation. Moreover, Au (1 1 1)/SiO2 cavity/ITO electrode design gave a wide linear range from 0.01 mM to 0.8 mM, and a low detection limit of 1.49 μM. As a glycerol sensor, the electrode displayed good reproducibility and long-term stability. The electrode was applied to directly determine the free glycerol in the biodiesel samples. This strategy might provide an approach to study electrochemical reactions on single particles in a microenvironment and offers a method for constructing alcohols sensors.