Alcohol Solvent Effect on Fluorescence Properties in the Solvothermal Synthesis of Carbon Quantum Dots

Highly monodisperse carbon quantum dots (CQDs) were synthesized by a solvothermal method using L-ascorbic acid as carbon source and different simple alcohols (methanol, ethanol, ethylene glycol, and isopropanol) as reaction solvents at 180 °C for 4 hours. The performance of CQDs was characterized by transmission electron microscope (TEM), Fourier infrared spectrometer (FTIR), UV-visible spectrophotometer, and fluorescence spectrophotometer. The results show that the prepared CQDs are wavelength-dependent, and have good hydrophilicity and similar surface compositions. However, there are more carbon and oxygen-containing functional groups on the surface of CQDs prepared with ethanol (CQDs-ET), and the type and number of functional groups will directly affect the fluorescence emission of CQDs. Also, it is found that the luminescence mechanisms of CQDs prepared by this solvothermal method are mainly based on the defect state of the oxygen group surface. And alcohol solvents do not directly participate in the formation of carbon nuclei during the reaction process, but it will affect the number and type of surface groups. Therefore, the influence of surface groups on the CQDs performance is greater than that of carbon nuclei in this experiment.