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 were synthesized from green tea leaves via microwave pyrolysis and abbreviated as G‐CQDs. This eco‐friendly method utilized a renewable, low‐cost, and easily accessible carbon source, with water as the solvent, aligning with green and sustainable synthesis. HR‐TEM analysis revealed an average particle size of ~ 2 nm. The nitrogen content in green tea leaves facilitated surface functionalization of G‐CQDs, confirmed by XPS and FTIR techniques. The G‐CQDs exhibited excitation wavelength‐dependent behaviour and a high photoluminescence quantum yield (PLQY) of ~ 45%, eliminating the need for surface passivation. The G‐CQDs showed excellent photostability and environmental stability when tested under varying pH, irradiation time, and ionic strength. Additionally, they demonstrated high selectivity and sensitivity for detecting Fe³⁺ ions with a detection limit of 2 nM through fluorescence quenching. The fluorescence was 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.