Green Synthesis of Various Heteroatom‐doped Carbon Quantum Dots from Urine, Whey, and Their Mixture: The Optimization of Synthesis and Potential Applications

Abstract The employment of biomass waste for the fabrication of carbon quantum dots (CQDs), as a novel fluorescent material with high photoluminescence (PL) activity, has gained intense interest for the last decade. However, the fabrication of CQD from biomass waste encounters challenges including low fluorescence yield, reproducibility, and stability. Therefore, the novel, simple, flexible fabrication routes for CQDs using biomass waste as a precursor are still essential for practical applications. In this study, we reported the employment of human urine (U), sour whey (W), and their mixture (U/W) as precursors for the hydrothermal green synthesis approach. For all cases, CQDs with an excitation‐dependent emission nature were obtained with a quantum yield (QY) value of 48 %, 28 %, and 39 % for U, W, and U/W, respectively. For each case, doping of various heteroatoms such as N, P, S, etc., in the structure of CQDs contributed PL characteristics with high QY, reasonably low cytotoxicity, and, robust pH and storage stability which indicate their high potential in various biomedical applications such as bioimaging and pH sensors. This study proves the utilization of human urine and whey as the precursors for the fabrication of CQDs through a low‐cost, flexible, and eco‐friendly green synthesis procedure.