Abstract
The design of novel carbon dots with ad hoc properties requires a comprehensive understanding of their formation mechanism, which is a complex task considering the number of variables involved, such as reaction time, structure of precursors or synthetic protocol employed. Herein, we systematically investigated the formation of carbon nanodots by tracking structural, chemical and photophysical features during the hydrothermal synthesis. We demonstrate that the formation of carbon nanodots consists of 4 consecutive steps: (i) aggregation of small organic molecules, (ii) formation of a dense core with an extended shell, (iii) collapse of the shell and (iv) aromatization of the core. In addition, we provide examples of routes towards tuning the core-shell design, synthesizing five novel carbon dots that all consist of an electron-dense core covered by an amine rich ligand shell.
Highlights
The design of novel carbon dots with ad hoc properties requires a comprehensive understanding of their formation mechanism, which is a complex task considering the number of variables involved, such as reaction time, structure of precursors or synthetic protocol employed
The MW heating, at each time point, yields a crude reaction mixture (RM) that consists of three isolated species: (i) solid residue recovered on the filter, (ii) dialysate consisting of small particles and polymers removed during dialysis, and (iii) the final purified carbon nanodots (CNDs)
In the paragraphs we will discuss the RM and CNDs obtained from different reaction times (15–240 s), as well as the filter residue and dialysate isolated from the RM
Summary
The design of novel carbon dots with ad hoc properties requires a comprehensive understanding of their formation mechanism, which is a complex task considering the number of variables involved, such as reaction time, structure of precursors or synthetic protocol employed. Clarifying the rather obscure steps involved in the formation of a carbon nanoparticle from small molecular precursors would be of great help in advancing the knowledge of the field and stimulate a rational synthetic approach[15,16,17,18,19,20,21,22,23,24] This formation process in its entirety still remains elusive, recent work has led to hypothesize small molecular weight intermediates[25,26], helping in explaining the formation of molecular fluorophores inside the CD structure or identify heteroatom doping patterns, both usually helpful in improving the photophysical properties of the nanoparticles[26,27,28,29,30,31]. The evolution of these structural aspects of CNDs during synthesis remains elusive
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