Facile one-step synthesis and fluorescence performance study of nitrogen-doped carbon quantum dots

A facile strategy is reported to synthesize nitrogen-doped carbon quantum dots (N-CQDs) with fluorescence emission by a one-step hydrothermal treatment under different temperatures with dicyanodiamide and citric acid as precursor materials of nitrogen and carbon sources, respectively. The as-produced N-CQDs display green or blue fluorescence under the ultraviolet lamp was controlled by the reaction temperature. Consequently, the as-prepared sample reacted at 200 degrees C (N-CQDs-200), within the range of 3 nm, exhibits blue fluorescence excited at 365 nm irradiation with the maximum quantum yield (QY) of ca. 30.6%. Moreover, the N-CQDs possess rich functional groups such as nitrous groups and multiple oxygenated groups, which result in a favorable solubility in most hydrophilic solvents. From the characterization and discussion of TEM, HRTEM, FT-IR, XPS, Raman and UV-Vis, it is illustrated that the fluorescence performance was largely related to the nanomorphology, nitrogen concentration, multi-surface emission sites and various forms of transitions derived from the nitrogen doping. With the excellent fluorescence performance and the favorable solubility in solvents, the products are potentially suitable for monitoring organics.