Spectrofluorimetric determination of Cr(VI) and Cr(III) by quenching effect of Cr(III) based on the Cu-CDs with peroxidase-mimicking activity

The study presents a spectrofluorimetric method for the determination of Cr(III) based on 2,3-diaminophenazine (DAP) as fluorescent nano sensor. With the peroxidase-mimicking activity of copper-doped carbon dots (Cu-CDs), colorless o -phenylenediamine (OPD) was oxidized to fluorescent DAP in the presence of H 2 O 2 via generation of hydroxyl radicals . The Cr(III) was found to decrease the fluorescent intensity of the Cu-CDs-mediated OPD oxidation system. Cr(VI) species were reduced to Cr(III) by employing 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonate) (ABTS) as the reductant, and a novel spectrofluorimetric method for the highly sensitive detection of speciation Cr(VI) and Cr(III) was developed. The Cu-CDs nanozyme was prepared from ethylenediaminetetraacetic acid copper disodium salt (Na 2 [Cu (EDTA)]) by one-step pyrolysis method. Under optimal conditions, the fluorescence intensity of DAP is linearly proportional to the Cr(III) ion concentration in the range of 5 × 10 −6 to 1.5 × 10 −4  mol L −1 and the detection limit is 1.2 × 10 −7  mol L −1 . The method has a good anti-interference performance against some metal ions , such as, Hg 2+ , Co 2+ , Cu 2+ , Mg 2+ , Ba 2+ , K + , Mn 2+ , Ni 2+ , Al 3+ , and Fe 3+ . The proposed method was successfully applied in the determination of Cr(VI) and Cr(III) in water samples.