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

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 Cd²⁺ ion detection, with PL intensity diminishing as Cd²⁺ 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 Cd²⁺ 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 Cd²⁺ ions. The findings indicated that aldehyde groups on the CQD surface demonstrate the most robust interaction with Cd²⁺ ions, elucidating the fluorescence quenching mechanism.