Electrochemical sensing of sulphur dioxide: a comparison using dodecanethiol and citrate capped gold nanoclusters

Abstract

A comparison of cyclic voltammograms of dodecanethiol (DDT) capped Au nanoclusters (5.0 ± 0.5 nm) and trisodium citrate (Cit) capped Au nanoclusters (~10-15 nm) modified glassy carbon electrode shows a dramatic variation in the current when exposed to a small amount of sulphur dioxide. This is explained using the electrocatalytic properties of Au nanoclusters towards the oxidation of SO₂, thus facilitating the fabrication of electrochemical sensors for the detection of SO₂. The intrinsic redox changes observed for gold nanocluster-modified glassy carbon electrodes disappear on passing SO₂, despite a dramatic current increase, which indeed scales up with the amount of dissolved SO2. Interestingly, a complete rejuvenation of the redox behavior of gold is also observed on subsequent removal of SO₂ from the solution by passing pure nitrogen for 15 minutes. Further, these nanoclusters when characterized with X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) after SO₂ passage reveal a variety of SO₂ adsorption modes on gold surface. XP spectra also showa shift of 1.03 eV towards higher binding energy indicating a strong adsorption of SO₂ gas, while FTIR gives conclusive evidence for the interaction of SO₂ with gold nanoparticles.