Waste to Wealth: Sustainable Synthesis of Green Tea‐Derived Quantum Dots for Nanomolar Detection of Fe³⁺ Ions and Ascorbic Acid

Highly fluorescent carbon quantum dots are synthesized from green tea leaves via microwave pyrolysis and abbreviated as G‐CQDs. This eco‐friendly method utilizes a renewable, low‐cost, and easily accessible carbon source, with water as the solvent, aligning with green and sustainable synthesis. High‐resolution transmission electron microscopy analysis reveals an average particle size of ≈2 nm. The nitrogen content in green tea leaves facilitates surface functionalization of G‐CQDs, confirmed by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy techniques. The G‐CQDs exhibit excitation wavelength‐dependent behavior and a high photoluminescence quantum yield of ≈45%, eliminating the need for surface passivation. The G‐CQDs show excellent photostability and environmental stability when tested under varying pH, irradiation time, and ionic strength. Additionally, they demonstrate high selectivity and sensitivity for detecting Fe³⁺ ions with a detection limit of 2 nM through fluorescence quenching. The fluorescence is restored in the presence of ascorbic acid (AA) due to a redox reaction with Fe³⁺ ions, with a detection limit of 13 nM. This dual‐sensing capability makes G‐CQDs a promising nanoprobe for rapid and on‐site detection of Fe³⁺ ions and AA.