Quantum dots (QDs) are tiny-sized nanoparticles that offer distinct optical and electronic properties tunable with size/shape/composition, resulting from the quantum confinement effect. However, high-performing heavy-metal-based QDs (e.g., CdS, PbS) exhibit toxicity, raising concerns for large-scale applications. Carbon quantum dots (CQDs) and graphene quantum dots (GQDs) offer a safer alternative and possess remarkable properties, including biocompatibility, solution processability, and photostability. In recent years, carbon-rich agricultural and marine waste streams have been explored as effective precursors for synthesizing CQDs and GQDs. Additionally, these sources offer a promising alternative to traditional methods, making the synthesis process more environmentally friendly and cost-effective and promoting the circular economy. This review focuses on CQDs and GQDs derived solely from agricultural and marine waste, using different innovative top-down and bottom-up approaches, emphasizing their potential for scalability and environmental benefits. It provides a comprehensive review of the structural, morphological, optical, and fluorescence properties of CQDs and GQDs synthesized from agricultural and marine waste, emphasizing novel techniques for tuning their emission characteristics. A critical evaluation of the environmental, ecological, and toxicity aspects of CQDs and GQDs is presented. Lastly, the review highlights the applications of these CQDs and GQDs in clean energy technologies such as photovoltaic, green hydrogen production, and supercapacitors. The review concludes by outlining current limitations and future research opportunities for CQDs and GQDs derived from agricultural and marine waste, emphasizing their potential in cost-effective clean energy technologies and their role in promoting a circular economy by converting waste into value-added technologies. Carbon dots derived from agricultural and marine waste and their applications in supercapacitors, photovoltaics, and green hydrogen production via photo/electrocatalytic water splitting.
Chhina et al. (Sun,) studied this question.