Highly photoluminescent label free probe for Chromium (II) ions using carbon quantum dots co-doped with nitrogen and phosphorous

Abstract Analytical probe for determination of Chromium (II) ions is almost rare in contrary to tremendous probes for chromium (III) and chromium (VI). Here, highly fluorescent carbon quantum dots (CQDs) doped with nitrogen and phosphorous were prepared solvothermally. Size, morphology, surface structure, chemical composition, and optical properties of the CQDs were characterized. The aqueous solution of CQDs showed high selectivity towards Cr 2+ ions and the fluorescence intensity quenched with Cr 2+ ions. The energy level calculations showed that the quenching mechanism is attributed to the transfer of electron from HOMO orbitals of Cr 2+ to the photo-hole formed in the valence band of CQDs, as the energy levels’ alignment rules out transition of photoexcited electron from the CQDs’ LUMO to the LUMO of Cr 2+ . Due to highly stability of the CQDs under rigorous conditions, such as; low and high pHs, high ionic strength, photostability, and thermal stability, The CQDs will be good candidate nanomaterials for rugged, robust, selective, and sensitive analytical probe. Lower limit of detection as small as 0.1 μM was calculated (with S/N = 3).