A high-performance visual monitoring of trace toxic NO2− and S2− in 100% aqueous based on the superior oxidase-mimic activity of nano CeO2 strengthened by 2D Co3O4 substrate

Abstract

To monitor toxic NO2− and S2− conveniently and effectively in 100% aqueous, nano CeO2 was identified and modified first onto 2-dimensional Co3O4 substrate (CeO2@2D Co3O4) under microwave-assisted conditions at 140 °C. The obtained CeO2@2D Co3O4 expressed excellent stability and superior oxidase-mimic activity with a wide temperature range from 20 to 60 °C. Under the optimized conditions (pH 4.0, 25 °C, 0.07 mM TMB), CeO2@2D Co3O4 could accelerate the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to its blue oxidation (oxTMB) within 12 min at room temperature, whose Michaelis constant (Km) and maximal reaction rate (vmax) were 0.017 mmol/L and 2.17 × 10−7 mol/L·s–1 respectively. Especially, both NO2− and S2− could exclusively make the blue CeO2@2D Co3O4-TMB system into colorless and green respectively, expressing significant visibility. When applied for visual detection of NO2− and S2− in real water, soil, drink and food samples, the recoveries were 97.6~104.6% and 97.5~104.1% with low detection limits of 3.26 × 10−9 mol/L and 6.65 × 10 −8 mol/L (S/N = 3), far below the maxima in drinking water permitted by World Health Organization (WHO). The strengthened oxidase-mimic activity of CeO2@2D Co3O4 and its different recognition mechanisms to NO2− and S2− were studied in detail.