Synthesis of the Cu-Doped Dual-Emission Fluorescent Carbon Dots and Its Analytical Application.

New Cu-doped dual-emission carbon dots (D-CDs) were synthesized rapidly and simply via a one-pot solvothermal method, and its special photoluminescence mechanism was studied. D-CDs have two fluorescence (FL) emission peaks under one-wavelength excitation and can be used as dual-signal sensor which is usually designed with two or more substances. The prepared CDs show excellent water solubility, photostability, salt tolerance, oxidation resistance, and special optical properties. The raw material ratio, solvent, pH, time, and synthesis temperature were optimized. The characterizations of CDs including transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma spectroscopic analysis, X-ray diffraction assignation of phases, thermogravimetric analysis and differential scanning calorimetry, Fourier transform infrared (FTIR) spectroscopy, FL spectrum, and ultraviolet-visible spectrum (UV-vis) were conducted. The investigation on mechanism indicates that the unique dual-emissive property is mainly caused by the energy-level gaps generated by the surface defects of CDs. The prepared D-CDs have good potential in dual-signal analysis and visualization sensing. To demonstrate the practical application, ferric ions, vitamin A acetate, and pH have been determined successfully.