Fluorescence color tuning of dual-emission carbon quantum dots produced from biomass and their use in Fe³⁺ and Cu²⁺ detection

Using simple and eco-friendly ethanol solvothermal treatment, dual-emission biomass carbon quantum dots (D-BCQDs) were synthesized from biomass viburnum awabuki leaves. Under excitation with 413 nm wavelength light two emission peaks appeared at 490 and 675 nm and the dots could be tuned to emit crimson, red, purplish red, purple and blue-gray fluorescence by changing the solvothermal temperature from 140 °C to 160, 180, 200 and 240 °C, respectively. XPS and FTIR characterization indicated that the fluorescence color was mainly determined by surface oxidation defects, elemental nitrogen and sp²-C/sp³-C hybridized structural domains. The D-BCQDs could not only detect Fe³⁺ or Cu²⁺, but also quantify the concentration ratio of Fe³⁺ to Cu²⁺ in a solution containing both, demonstrating their potential applications in the simultaneous detection of Fe³⁺ and Cu²⁺ ions.