ИСТИНА

Carbon dots (CDs) are a class of carbon nanomaterials with unique optical and chemical properties, such as stable fluorescence, non-toxicity, biocompatibility, etc. Currently, various methods for the synthesis of CDs have been developed. One of the simplest and cheapest new methods is the hydrothermal method, which uses many different precursors. Although CDs have already demonstrated great potential in various applications, the variety of methods for their synthesis necessitates studying the properties of nanoparticles obtained by the new method, in particular, the properties due to the modification of the chemical structures of their surface. As known, functional surface groups significantly affect the optical, chemical, and electronic properties of CDs [1,2]. The presence of certain functional groups on the surface, such as hydroxyl, carboxyl, amino groups, leads to a change in the fluorescence of CDs due to the introduction of new emitting surface states. The study and control of the chemical composition of CDs allow effectively "tune" the optical properties of CDs. Thus, the study of interactions of various functional surface groups with organic, inorganic, polymeric, biological substances provides the use of these nanoparticles in biomedicine and optoelectronics as multimodal nanosensors. In this research, the optical properties of two types of CDs, synthesized by the hydrothermal method from citric acid and ethylenediamine, were studied. The surfaces of CDs were functionalized with carboxyl and hydroxyl groups by treatment with sodium nitride, hydrochloric acid, and NaOH solution. The influence of functional groups on the surface of CDs on their fluorescence was studied using the dependences of the fluorescence spectra of aqueous suspensions of CDs on the pH of the liquid medium.