Effects of nitrogen, phosphorus, and sulfur doping of carbon dots from sugar on UV absorbance, photoluminescence, phenolic content, stability, and antioxidant activities

Carbon dots (CDs) are nanomaterials with interesting properties and have been used in a wide range of applications, such as cosmetics, composites, and electronics. Their properties are governed by the structure and composition. The presence and amount of heteroatoms in the CD core are known to significantly affect their photoluminescence. To investigate the effects of heteroatoms on other properties, in this work, CDs were synthesized from sugar via hydrothermal method and doped with nitrogen, phosphorus, and sulfur using corresponding nitric acid, phosphoric acid, and sulfuric acid. The amounts of nitrogen, phosphorus, and sulfur were controlled by the amount of acid added with respect to sugar. After purification, the UV absorbance, sun protection factor, photoluminescence, phenolic content, photostability and antioxidant activities of the all CDs were measured. The UV absorbance and sun protection factors of the CDs were also compared with avobenzone and oxybenzone, two well-known UV absorbers in sunscreens. The antioxidant activities of the CDs were tested using 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) assay and compared with that of ascorbic acid a well-known antioxidants. The results from this thesis will be crucial for a number of cosmetic and pharmaceutical applications.