Facile fabrication of boron and nitrogen co-doped carbon dots for “ON–OFF–ON” fluorescence sensing of Al3+ and F− ions in water samples

Abstract

Water contamination with harmful ions has grown to be a significant environmental issue on a global scale. Therefore, the fabrication of simple, cost-effective, and reliable sensors is essential for identifying these ions. Herein, co-doping of carbon dots with new caffeine and H₃BO₃-derived boron (B) and nitrogen (N) was performed (BN@CDs). The as-prepared BN@CDs probe was used for the tandem fluorescence sensing of Al³⁺ and F⁻ based on “ON–OFF–ON” switches. The BN@CDs nanoswitch has a high quantum yield of 44.8% with λ_exc. and λ_em. of 360 nm and 440 nm, respectively. The probe exhibited good stability with different pH, ionic-strengths, and irradiation times. The fluorescence emission of BN@CDs was decreased as the Al³⁺ concentration was increased with a linear range of 0.03–90 μM and a limit of detection (S/N = 3) equal to 9.0 nM. Addition of F⁻ restored the BN@CDs emission as F⁻ ions form a strong and stable complex with Al³⁺ ions [Al(OH)₃F]⁻. Therefore, the ratio response (F/F°) was raised by raising the F⁻ ion concentration to the range of 0.18–80 μM with a detection limit (S/N = 3) of 50.0 nM. The BN@CDs sensor exhibits some advantages over other reported methods in terms of simplicity, high quantum yield, and low detection limit. Importantly, the sensor was successfully applied to determine Al³⁺ and F⁻ in various ecological water specimens with accepted results.