Engineering titanium dioxide-reduced graphene oxide nanocomposite for electrooxidation of nitrite as a surrogate for electrochemical sensing of NO2

Abstract

Nitrogen dioxide (NO2) is a reddish-brown irritating gas characterised by sharp and biting odour. Its detection is imperative as it is harmful to the respiratory system and contributes to the acid rain formation. Aqueous NO2 gas is converted into nitrite (NO2−) ion in solution, which is considered an environmental pollutant with consequential health effects. Oxidation of NO2− has been reported to provide provisional insights for that of NO2 gas in electrolyte. However, detection of NO2− at electrode surface is encountered by difficulty due to high overpotentials. This study presents electrochemical behaviour of a titanium dioxide/reduced graphene oxide-palladium/silver nanocomposite-modified screen-printed carbon electrode (TiO2/rGO-PdAg/SPCE) for the detection of NO2− as a surrogate for NO2 oxidation mechanism in aqueous NaClO4 as electrolyte. Comparative analysis demonstrated superior performance of TiO2/rGO-PdAg/SPCE over bare, TiO2, and TiO2/rGO modified SPCEs due to the synergistic effect of its components. The sensor exhibited a broad detection range of 0.1 – 10 mM and a linear response at 0.1 – 1.4 mM with a limit of detection (LOD) = 1.07 µM NO2− and a sensitivity of 44.38 µA/mM. Simultaneous detection of NO2−and S2O32−demonstrated that the oxidation peak of the former was favoured while the latter was not observed in the investigated potential range. However, adsorption of S2O32− exhibited interference with a decrease in sensitivity to 24.15 µA/mM, which limits the selectivity of the sensor for oxidation of NO2−. Reproducibility exhibited an RSD of 4.18 % at five different electrodes, and stability tests with 74.02 % of peak current retained from initial response for a 12-day period. The recovery of NO2 gas in aqueous medium was studied using calibration curve of NO2−, with average of the triplicate experiments corresponding to 0.4 mM NO2−. These observations present TiO2/rGO-PdAg/SPCE sensor as a potential for reproducible, sensitive, and selective detection of NO2 in environmental monitoring.