Multicolor photoluminescent carbon nanodots regulated by degree of oxidation for multicolor patterning, invisible inks, and detection of metal ions

A strategy for preparing multicolor photoluminescent carbon nanodots (CNs) has been proposed. Using three types of phenylenediamine and methacrylic acid as raw materials and ethanol as a solvent, a series of novel CNs were synthesized by solvothermal one-pot method. Prepared CNs showed bright green, yellow, and indigo blue fluorescence under ultraviolet (UV) light, respectively. Three types of CNs were spherical-like nano-sized particles, and their particle sizes were approximately 5 nm, 10 nm, and 10 nm, respectively. The optical properties of CNs were characterized using ultraviolet visible spectra and fluorescence spectra. The microscopic morphology was characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The elemental composition was characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectra (XPS). We proposed that the different fluorescence emissions of CNs might be attributed to the surface oxygen content of the CNs. The CNs could also be applied for multicolor patterning and polymer films, invisible inks, and detection of metal ions.