Lead-Free Cs3Bi2Br9 Perovskite Quantum Dots for Detection of Heavy Metal Cu2+ Ions in Seawater

Seawater pollution caused by heavy metal ions is a growing concern among the public. Perovskite quantum dots (PeQDs) are ideal probes for detecting metal ions due to their exceptional sensing characteristics, including remarkable sensitivity, low detection limit, and good selectivity. However, traditional lead-based PeQDs exhibit drawbacks related to lead toxicity and poor water stability. Herein, lead-free halide PeQDs Cs3Bi2Br9 were synthesized using Bi3+ instead of Pb2+ via the ligand-assisted reprecipitation method. The luminescence performance of the precursor is analyzed with respect to the reaction conditions. The results reveal that the optimal reaction temperature is 80 °C, the ideal octylamine dosage is 35 μL, and the most effective reaction time is 10 min. Photoluminescence spectra of Cs3Bi2Br9 are analyzed at various temperatures and demonstrate that fluorescence intensity decreases as temperature increases. The value of the exciton binding energy (Eb) is determined to be 88.6 meV. Cs3Bi2Br9 PeQDs synthesized under the optimum reaction conditions are utilized as fluorescent probes to detect copper ions in seawater. Results from experiments demonstrate that the presence of copper ions markedly quenched the photoluminescence of Cs3Bi2Br9 owing to the effective transfer of electrons from Cs3Bi2Br9 to Cu2+. A strong linear correlation between the degree of quenching and the contents of Cu2+ is observed. Cs3Bi2Br9 PeQDs demonstrate a sensitivity and detection limit of 1.21 μM−1 and 98.3 nM, respectively. Furthermore, this probe exhibits good photostability, water stability, and selectivity for copper ions, thereby indicating its potential for detecting marine heavy metal contaminants.