Abstract:

In order to explore their luminescence properties, a series of carbon nanodots were prepared by microwave heating by controlling the microwave power, reaction time, and pH value.The luminescence properties of carbon nanodots were characterized by their fluorescence excitation spectrum and emission spectrum.We present the transformation mechanism of glucose into carbon nanodots during the microwave heating process and the corresponding luminescence mechanism together with the analysis of functional group changes during the reaction as monitored with ultraviolet (UV) absorption and Fourier Transform Infrared (FT-IR) spectra.The results show that the optimal luminescence properties of carbon nanodots were obtained when the glucose was heated under a microwave heating power of 560 W for 2.5 min.When the carbon nanodots were excited with UV radiation with a wavelength of 370 nm, the strongest luminescence appeared at 451 nm.The wavelength of the strongest luminescence peak moved from 350 nm to higher wavelengths significantly, when the pH value was modified from acidic to alkaline, and was accompanied with a significant rise in luminescence peak intensity.We show that polycyclic aromatic hydrocarbons form in the reaction process, as evidenced by UV absorption and FTIR monitoring, indicating that microwave synthesis of carbon nanodots proceeds via polymerization and final carbonization of glucose.Carbon nanodots formed under different pH values exhibit a change in the ratio of carbon-to-carbon double bonds to carbon-to-oxygen double bonds.The optical bandgap and exciton binding energy of the carbon nanodots were also investigated comprehensively.

Key words: Nano carbon dots, Luminescence, Glucose, Microwave synthesis, Carbonation reaction, Optical bandgap