Blue-Emitting Carbon Quantum Dots: Insight into the Effect of the Synthesis Parameters of the Hydrothermal Approach

Since their serendipitous discovery in 2004, carbon quantum dots (CDs) gained increasing interest from the scientific community because of their outstanding optical properties, which make them suitable for a plethora of applications, going from sensing to bioimaging, optoelectronics, photovoltaics, etc., as an alternative to the classic chalcogenide-based quantum dots. Their production is simple, low-cost, sustainable, and could employ precursors recycled from biomass and biowaste. Furthermore, through the modulation of the synthesis parameters, it is possible to produce CDs with desired properties, and a recent work by Patel et al. gives an interesting example of the possibility of modulation of the properties of CDs for theranostic applications through the proper setting of the reaction parameters. Starting from those considerations, here we aim to give an insight into the effect of the synthesis parameters on the optical, chemical, and structural properties of blue-emitting CDs. We selected the hydrothermal approach owing to its feasibility for future large-scale industrial applications, and we employed eco-friendly precursors that could be obtained from biowaste, like citric acid (CA) and glucose (Glu) as carbon sources, and urea as both nitrogen source and base (Figure 1). Through spectroscopic, electrochemical, and structural investigations, we studied and discussed the effects of the reaction parameters considering the formation of graphitic nitrogen N-oxides and their role