Synthesis of Carbon Dots for medical and photocatalytic applications

Carbon dots (CDs) are a novel carbon-based nanomaterial that draws a great attention in the last decade. The easy way of synthesis and the cheapest nature of the precursors used, stimulate a lot of scientist to propose new way of synthesis and applications. Notwithstanding the number of paper published, a systematic and reproducible way of synthesis is not yet been achieved, as well as a common definition of the resulting nanomaterials and their properties. In this thesis, the synthetic protocols and the characterization procedures used for the CDs will be deeply investigated in order to apply the nanomaterials in different applications. In particular, carbon dots synthesized from fully biocompatible precursors such as glucose, fructose and ascorbic acid, are characterized and employed for drug loading applications. The study reveals that the choice of the precursors is a crucial step because it affects the structural properties of the nanomaterials and the biological properties, revealing an unexpected toxicity for the fructose derived CDs, ascribable to its thermal degradation pathway. Furthermore, the drug loading capabilities were found to be correlated to the morphology of the nanoparticles, revealing the crucial role of the π-π interactions in achieving a loading up to 28 %wt for the glucose-based CDs. A second study was conduct on citric acid based CDs, in order to determine the best synthetic approach for photocatalytic applications. The nanoparticles synthesized both by hydrothermal and pyrolysis treatment, from sole citric acid and in combination with a nitrogen doping agent, were deeply characterized. The analysis reveals the difference in chemical, structural, and optical properties between the two synthetic methods. The photoreduction of methylviologen (MV) was used as model reaction to study the photocatalytic ability of the CDs, and the results reveal a relationship between the synthetic methods employed, the structural and optical properties of the CDs and their ability to act as a sensitizer. The amorphous nitrogen doped CDs reveals to be the best choice for this application with an initial rate conversion comparable to other reported in literature. The same CDs were also tested for the photocatalytic cleavage of C-O bonds in activated esters without the use of metals. The study reveals that CDs can successfully catalyze the reaction, with complete conversion and almost total selectivity. In addition, the CDs employed, shows different reactivity depending on the precursors and synthetic methods employed for their synthesis, with the same trend displayed for the MV photoreduction. This study highlights the ability of CDs to act as photosensitizer, without the addition of metals, in an organic reaction, opening a new scenario in the use of this nanomaterial in photocatalytic applications.