A boron and nitrogen co-doped carbon dot-based “on-off-on” fluorescent probe for the sequential detection of Fe3+ and phoxim

The detection of hazardous contaminants such as heavy metal ions and pesticide residues in water is essential for safeguarding environmental safety and public health. In this study, boron and nitrogen co-doped carbon dots (B,N-CDs) were synthesized via a one-step hydrothermal method using sodium citrate, urea, and boric acid as precursors. The as-prepared B,N-CDs demonstrated good water solubility, uniform dispersion, a maximum fluorescence emission at 445 nm, and reasonable stability. A fluorescence sensing platform based on B,N-CDs was developed for the sequential detection of Fe 3+ and phoxim using an “on-off-on” mode. The fluorescence of B,N-CDs is efficiently quenched by Fe 3+ through a static quenching mechanism (SQE); subsequent addition of phoxim restores the fluorescence due to competitive binding of phoxim with Fe 3+ . The detection limits for Fe 3+ and phoxim are 3.46 μM and 0.5 mg/L, respectively. In spiked environmental water samples, satisfactory recoveries of 82.7%–95.2% for Fe 3+ and 97.5%–112.0% for phoxim were obtained, with relative standard deviations (RSDs) below 15% ( n  = 5). This study presents a promising platform for monitoring Fe 3+ and phoxim in aqueous environments.