Development of a Facile and Green Synthesis Strategy for Brightly Fluorescent Carbon Dots from Various Waste Materials.

Carbon dots (CDs) are fluorescent carbon-based nanomaterials with remarkable properties, making them more attractive than traditional fluorophores. Consequently, researchers focused on their development and application in fields such as sensing and bioimaging. One potential advantage of employing CDs is using organic waste as carbon precursors in their synthesis, providing a pathway for waste upcycling for a circular economy. However, waste-based CDs often have low fluorescence quantum yields (QY), limiting their practical applications. So, there is a need for a well-defined strategy to consistently produce waste-based CDs with appreciable QY, irrespective of the starting waste material. Herein, we developed a fabrication strategy based on the hydrothermal treatment of waste materials, using citric acid as a co-carbon precursor and ethylenediamine as N-dopant. This strategy was tested with various materials, including corn stover, spent coffee grounds, cork powder, and sawdust. The results showed consistently appreciable QY, reaching up to ~40 %. A Life Cycle Assessment (LCA) study demonstrated that producing these waste-based CDs has lower environmental impacts compared to CDs made solely from commercial reagents. Thus, we have established a framework for the environmentally friendly production of CDs by upcycling different waste materials without significant sacrifices in performance (QY).