Carbon dot nanoarchitectonics with high photoluminescence for efficient Cr ion sensors

To overcome that current carbon dots (CDs) can just detect chromium ions in a single valence state, bright N and S co-doped carbon dots (N, S-CDs) were synthesized to respond Cr (III) and Cr (VI) at same time. Sample N, S-CDs with isothiocyanate functional groups were created for quick detection of Cr (III) and Cr (VI). The photoluminescence (PL) of N, S-CDs was adjusted from green to blue emission by changing the doping ratios of N and S. S doping improved the selective recognition ability of CDs to chromium ions. The linear ranges of N, S-CDs for Cr (III) and Cr (VI) are 0-14 and 0-140 µM, respectively, and the detection limits are 0.08 and 0.79 µM, respectively. Through the tests and calculation, the response mechanism of N, S-CDs to chromium ions was proposed. Enhanced PL form chelation resulted in a “turn-on” response mechanism for Cr (III) while the “turn-off” response to Cr (VI) was achieved through a combination of the inner filter effect and static quenching. Sample N, S-CDs were stable for detection of Cr (III) in neutral and weakly alkaline conditions (pH ∼ 7-9) and Cr (VI) in acidic to alkaline conditions (pH ∼ 2-12). In lake water, N, S-CDs maintain specific recognition of Cr (III) and Cr (VI), and the recovery of total chromium content was 100-103%. Due to low cost and simple synthesis method, the N, S-CDs can be used for on-field detection of both Cr (III) and Cr (VI). [Display omitted]