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

To monitor toxic NO 2 − and S 2− conveniently and effectively in 100% aqueous, nano CeO 2 was identified and modified first onto 2-dimensional Co 3 O 4 substrate (CeO 2 @2D Co 3 O 4 ) under microwave-assisted conditions at 140 °C. The obtained CeO 2 @2D Co 3 O 4 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), CeO 2 @2D Co 3 O 4 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 ( K m ) and maximal reaction rate ( v max ) were 0.017 mmol/L and 2.17 × 10 −7 mol/L·s –1 respectively. Especially, both NO 2 − and S 2− could exclusively make the blue CeO 2 @2D Co 3 O 4 -TMB system into colorless and green respectively, expressing significant visibility. When applied for visual detection of NO 2 − and S 2− 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 CeO 2 @2D Co 3 O 4 and its different recognition mechanisms to NO 2 − and S 2− were studied in detail.