Optimization of Nitrogen-Doped Carbon Dots from Tea Waste (Camellia sinensis) and Its Application for Metal Ion Sensing

Abstract

Carbon dots (CDs) were synthesized from tea waste extract (Camellia sinensis) as a carbon source via microwave irradiation, with the addition of urea as a nitrogen-doping agent. This study aimed to evaluate the effects of synthesis time and urea mass on the optical properties of CDs and their potential for metal ion sensing. CDs were synthesized with varying irradiation times and urea concentrations. CDs were characterized using a UV-Vis spectrophotometer, a photoluminescent spectrophotometer, and Fourier Transform Infrared (FTIR) spectroscopy to evaluate their optical properties and functional groups. The results showed that the optimal reaction conditions for tea waste extract-based CDs were 10 minutes of irradiation and 0.5 g of urea, yielding the highest fluorescence intensity. The FTIR spectra confirmed the presence of the main functional groups of hydroxyl (–OH) and carbonyl (C=O), which contribute to the stability and formation of CDs. Metal-ion sensing tests with CDs showed selectivity for Fe(III) with a detection limit of 5.91 mM.