Hydrothermal Synthesis of Tartaric Acid Functionalized Amino Acid CQD for Sensing of Hg 2+ and Fe 3+ Ions in Aqueous Medium

Abstract Carbon quantum dots (CQDs) are a type of carbon‐based nanoparticles that are typically smaller than 10 nanometres in size. In this study, L‐tryptophan‐mediated CQDs were synthesized using the hydrothermal carbonization (HTC) technique, which is known for its non‐toxic, environmentally friendly, and cost‐effective nature. The synthesized carbon quntum dot was successfully characterized. The HR‐TEM analysis clearly revealed the formation of specific aggregates with a size distribution ranging from 3.0 to 5.1 nm. These L‐tryptophan‐mediated CQDs exhibited remarkable emission behaviour, displaying strong and stable blue fluorescence. Moreover, they were utilized as a sensor for the sensitive detection of Fe 3+ and Hg 2+ ions in an aqueous solution, employing a fluorescence quenching mechanism. The limit of detection for Fe 3+ sensing was determined to be 1.2×10 −5 M, while for Hg 2+ sensing, it was found to be 1.9×10 −5 M. The sensing of Fe 3+ and Hg 2+ ions was also confirmed through visual eye detection, as a significant color change of the CQDs was observed. Additionally, a competitive study was conducted to verify the selectivity of the L‐tryptophan‐mediated CQDs towards Fe 3+ and Hg 2+ metal ions.