Green one-step synthesis of boron and nitrogen co-doped carbon dots based on inner filter effect as fluorescent nanosensors for determination of Fe³⁺

Significant efforts need to be devoted to enhancing the photoluminescence quantum yields (PLQY) of carbon dots (CDs) due to the typically low PLQY (< 10%) of currently synthesized CDs. Moreover, certain special industries such as textiles, paper, and food all have high requirements for water since Fe³⁺ can affect its color, odor, and taste. The traditional detection methods require expensive equipment, so a facile method to detect Fe³⁺ is urgently needed. In this work, the self-doping of nitrogen (N-CDs) has been achieved through tea residues as the carbon source to inhibit the oxygen-deficient state, and the doping of boric acid (BN-CDs) can activate the electron transition at the carbon site, which effectively enhanced the PLQY of CDs from 11.4% to 25.79% compared to N-CDs. Furthermore, as hydroxylated polyphenols in tea residues can adsorb metal ions, stable non-fluorescent matrix state complexes have been established between BN-CDs and Fe³⁺ to quench the FL owing to the inner filter effect. The linear relationship was formed in the concentration range of 0–60 μM, and the detection limit reached 0.07 μM. It demonstrates that along with the effective treatment of waste tea residues, the synthesized high fluorescence property BN-CDs are suitable to detect Fe³⁺ in water for textiles, paper, food, and other special industries.