Facile fabrication of boron and nitrogen co-doped carbon dots for "ON-OFF-ON" fluorescence sensing of Al and F ions in water samples.

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 HBO-derived boron (B) and nitrogen (N) was performed (BN@CDs). The as-prepared BN@CDs probe was used for the tandem fluorescence sensing of Al and F based on "ON-OFF-ON" switches. The BN@CDs nanoswitch has a high quantum yield of 44.8% with and 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 Al 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 Al ions [Al(OH)F]. Therefore, the ratio response (/°) 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 Al and F in various ecological water specimens with accepted results.