Tea Waste‐Derived Carbon Quantum Dots for Rapid Detection of Tea Polyphenols

ABSTRACT This investigation suggests a practical and economical method for producing carbon quantum dots (CQDs) from used oolong tea leaves using microwave and detection of polyphenols and various antioxidants in tea. Polyphenolic compounds and organic matter in oolong tea waste allow CQDs to be synthesized environment friendly and without the need for harmful chemical additives, orlong purification steps. The High‐Resolution Transmission Electron Microscopy, Fourier transform Infrared Spectroscopy, thermogravimetric analysis, x‐ray diffraction, fluorescence, and UV–visible spectroscopy were used to confirm that the synthesized CQDs had a 3–10 nm size, were spherical in appearance, had many types of functional groups, were nanocrystalline graphitic domains, and were capable of absorption and emission. Owing to the exceptional and steady fluorescence of the CQDs, we detected quercetin, gallic acid, and EGCG in samples of both black and oolong tea. The quenching method made it possible to detect the intercalator at a sensitive level, and EGCG was found to have the highest quenching response. We found that black tea contained 16.19 mg/L of quercetin, 3.65 mg/L of gallic acid, and 28.65 mg/L of EGCG, while oolong tea contained 15.77 mg/L of quercetin, 3.27 mg/L of gallic acid, and 50.42 mg/L of EGCG. The fluorescence of CQDs was shown to be highly linear as they responded to calibration curves ( R 2 > 0.93). The research shows that tea waste can be recycled into useful nanomaterials, allowing us to use them for sensing and to reduce the use of conventional techniques. What we found makes it possible to create scalable, environmentally friendly systems for food quality checking and identifying antioxidants with nanomaterials made from agro‐industrial residues.