State-of-the-art advances in hydrothermally synthesized carbon quantum dots: An extensive review

Fluorescent carbon quantum dots (CQDs) are one of the most recently developed groups of innovative carbon nanomaterials. CQDs possess several unique properties, including low cytotoxicity, excellent photostability, and outstanding biocompatibility that potentially contribute to a wide range of applications. Although numerous synthesis processes have been discovered and reported for CQDs, real-time practical applications and precise controlling of the synthesis process remain difficult. In this regard, the hydrothermal synthesis method is considered to be straightforward and effective due to the high reactivity of the reactants, simplicity of solution control, low environmental impact, and low energy consumption. The synthesis and application of CQDs are covered in several publications; however, there are limited reviews that concentrate on hydrothermal synthesis, their underlying mechanisms, and recent technological developments. Therefore, studying the hydrothermal technique for CQDs using various precursors, characterizations, synthesis affecting factors, and potential applications is provided here. More specifically, this study emphasized the novel contributions, such as systematically summarizing organic molecules, green, animal, human, and industrial waste or byproducts precursors induced CQDs via hydrothermal methods. In addition, this article discusses the underlying reaction mechanisms in depth and provides critical insights into the emerging applications in agricultural, biomedical, environmental, sensing, and energy sectors. This review is expected to provide a strong direction to avoid theoretical doubts and attract more studies into this exciting topic.