Carbon Quantum Dots (CQDs): Synthesis, Rare Earth Elements (REEs) Detection, and DFT Approach for Interaction Energy Calculations

In this work, a novel method has been developed to prepare carbon quantum dots (CQDs) via a hydrothermal process using agricultural biomass waste as a carbon source. The fluorescence quenching effect was observed when La 3+ ions were added to the CQDs solution. The experiment results showed that CQDs have a sensitive response to La 3+ ions at a concentration of nearly 0.1 ppm. The Stern–Volmer constant K sv = 29 × 10 7 L/mol and binding constant K B‐H = 114 × 10 6 L/mol are calculated using the Stern–Volmer equation and Benesi–Hildebrand equation, respectively, which suggests a strong interaction between La 3+ and the CQDs. Also, LOD and LOQ are found to be 118.21 and 358 nM, respectively, indicating the high fluorescence sensitivity of synthesized CQDs towards La 3+ ions allows them to detect trace amounts of La 3+ . From the DFT results for calculating interaction energy, the predominant charge transfer between ─NH 2 and ─OH groups towards La 3+ ion is found, while demonstrating the superior sensing character of CQDs for La 3+ ion. Adsorption free energies of the La 3+ ion at different locations in the CQDs indicate that the La 3+ ion adsorption was thermodynamically feasible with interaction energies ranging between −8.85 and −9.05 eV.