Carbon dots as oxidant-antioxidant nanomaterials, understanding the structure-properties relationship. A critical review

Carbon dots (C-dots) are a large family of nanomaterials characterized by an intense photoluminescence. The origin of the emission is multifaceted and is dependent on a number of factors, including structure, surface, and composition. The term "carbon dots" is quite broad and encompasses a wide range of carbon nanostructures. The multiple properties are a result of this variability, which also makes it difficult to establish a clear structure-property relationship. Photoluminescence is the property of this class of nanomaterials that has garnered the greatest attention due to the possibility of applications in various fields, including biotechnologies, electronics, and energy. Another property of C-dots that has only lately been recognized is their antioxidant activity, i.e., the ability to act as a free radical scavenger. Furthermore, it has been proven that certain types of C-dots function as oxidizing agents when exposed to visible and/or UV radiation. This dual oxidant-antioxidant nature is particularly intriguing and closely related to the C-dot properties. Although many articles have been published on the subject, it still needs to be understood what structure-property relationships regulate the responses to free radicals. This review aims to provide a general overview of the characteristics of C-dots as scavengers or radical emitters by a critical analysis of the relevant studies. Based on their intended application as oxidants or antioxidants, the findings of this review can be used to synthesize C-dots with precisely defined functional properties.