A novel selective colorimetric detection of Cr(VI) in environmental water samples based on MnO2-CuO- anchored P-S-doped carbon nanozyme

Chemical sensing, employing nanoparticles, exhibiting intrinsic enzyme-like activity has attracted growing attention. Herein, a novel nanozyme is designed for the selective and sensitive colorimetric sensing of Cr(VI) in environmental water samples. The nanozyme, denoted as MnO2-CuO/CPS, has been synthesised by a one-pot, facile, low-cost method, using glucose-derived carbon matrix doped with phosphorus and sulphur and anchored with mixed transition metal oxides. Many techniques have been employed to characterise the nanozyme. MnO2-CuO/CPS has a heterogeneous morphology composed of sheet-like structure with scattered nano-ellipsoids, with an average particle diameter of 26 nm. The nanozyme has shown to exhibit significant, laccase-mimicking activity, confirmed through efficiently catalysing the chromogenic reaction of phenol with 4-aminoantipyrine, which produces the pink-coloured quinoneimine dye. The activity is inhibited by the addition of Cr(VI), in which a good linear calibration plot is obtained through a concentration range of 0.25–17.50 μM with LOD = 4.26 nM. Cr(VI) detection in environmental water samples is achieved with a recovery and RSD% (n = 3) of 95–103% and 0.23–2.54%, respectively, showing good recoveries, and reliable results. In addition, a smartphone-assisted Cr(VI) quantitative detection is constructed based on the calculation of the greyscale value of RGB (LOD = 0.388 μM, R2 = 0.98).