Investigation of Carbon Quantum Dots With Good Optical Properties From Sunflower Seed Shells for Photoluminescence Sensing and DFT Analysis of Cd ²⁺ Quenching

ABSTRACT This study introduces the synthesis, characterization, and utilization of carbon quantum dots (CQDs) from sunflower seed shells for the first time, specifically as a photoluminescence (PL) sensor for cadmium ion detection. CQDs were synthesized by a hydrothermal method. The CQDs were analyzed employing various physicochemical methods, including XRD, FTIR, TEM, UV–Vis spectroscopy, and fluorescence spectroscopy. The green‐source CQDs demonstrated an average nanoscale dimension of 2.1 nm and displayed PL behavior, an emission peak at 497 nm, with a quantum yield (QY) of 33.5%. The synthesized CQDs exhibited significant selectivity for Cd 2+ ion detection, with PL intensity diminishing as Cd 2+ concentrations increased (1–10 μM). The detection limit was established at 0.12 μM, while the limit of quantification was set at 0.38 μM. Selectivity experiments demonstrated that the CQDs displayed a robust response to Cd 2+ ions with negligible interference from other metal ions. The results indicate that the synthesized CQDs are a viable, economical, and eco‐friendly material for the detection of cadmium contamination in water. Additionally, density functional theory (DFT) measurements were employed to investigate the quenching mechanism between CQDs and Cd 2+ ions. The findings indicated that aldehyde groups on the CQD surface demonstrate the most robust interaction with Cd 2+ ions, elucidating the fluorescence quenching mechanism.