Electrochemical synthesis of Ni doped carbon quantum dots for simultaneous fluorometric determination of Fe3+ and Cu2+ ion facilely

A novel Ni doped carbon quantum dots (Ni-CQDs) fluorescence probe was synthesized by facile electrolysis of monoatomic Ni dispersed porous carbon (Ni–N–C). The obtained Ni-CQDs showed a high quantum yield of 6.3% with the strongest excitation and emission peaks of 360 nm and 460 nm, and maintained over 90% of the maximum fluorescence intensity in a wide pH range of 3–12. The metal ions detectability of Ni-CQDs was enhanced by Ni doping and functional groups modification, and the rapid and selective detection of Fe³⁺ and Cu²⁺ ions was achieved with Ni-CQDs through dynamic and static quenching mechanism, respectively. On one hand, the energy band gap of Ni-CQDs was regulated by Ni doping, so that excited electrons in Ni-CQDs were able to transfer to Fe³⁺ easily. On the other hand, the abundant functional groups promoted the generation of static quenching complexation between Cu²⁺ and Ni-CQDs. In metal ions detection, the linear quantitation range of Fe³⁺ and Cu²⁺ were 100–1000 μM (R² = 0.9955) and 300–900 μM (R² = 0.9978), respectively. The limits of detection (LOD) were calculated as 10.17 and 7.88 μM, respectively. Moreover, the fluorescence quenched by Cu²⁺ could be recovered by EDTA²⁻ due to the destruction of the static quenching complexation. In this way, Ni-CQDs showed the ability to identify the two metal ions to a certain degree under the condition of Fe³⁺ and Cu²⁺ coexistent. This work paves the way of facile multiple metal ion detection with high sensitivity.