The Preparation And Electron Beam Irradiation Of Graphene Quantum Dots

Graphene quantum dot is a new type of super small carbon nanoparticles with excellent solubility and chemical inert, the stable photoluminescence performance, excellent surface grafting and low toxicity, making graphene quantum dots a promising prospects in cellular fluorescent tags, bio-imaging, drug delivery and thermal treatment application aspects. At present, this domain has drawn close attention of researchers. In this article, we focus on the synthesis method of graphene quantum dots and their optical properties, and then discussed the luminescence mechanism of graphene quantum dots.First, we prepared the graphene quantum dots by the oxidation of carbon fiber using nitric acid and sulfuric acid. The graphene quantum dots have an excellent dispersion in the aqueous. The average size is 4.3 nm and average height is 1.36 nm. There are many oxygen-containing functional groups such as hydroxyl, carboxyl and epoxy groups on surface of graphene quantum dots. The graphene quantum dots almost have none luminescence when excited at different wavelength. And the quantum yields of GQDs are only 0.12%.Secondly, we adopted a method of electron beam irradiation to improve the fluorescence of graphene quantum dot, and explored the best irradiation condition of graphene quantum dots. We selected five different solutions, namely pure water solution system, the DMF solution system, oxidation system, reduction system and neutral system, and explored that the best solution system of electron beam irradiation for graphene quantum dots is the reduction system. Then in reduction system, we set up four different solvents ratio, namely 10:0, 7:3, 5:5 and 3:7. It is concluded that the results of electron beam irradiation are best when under the condition of methanol solution system with solvent ratio 3:7.Finally, we choose different electron beam irradiation doses to irradiate graphene quantum dots, and the irradiation doses are 7 k Gy, 70 k Gy, 140 k Gy, 280 k Gy, 560 k Gy and 1120 k Gy, respectively. The average size of GQDs-560 is 2.7 nm, and average height is 1.8 nm. With the augmentation of the irradiation dose, the oxygen containing groups such as hydroxyl, carboxyl and epoxide groups on the surface of graphene quantum dots reduced gradually. A reduction reaction happened in the process of irradiation, and a large number of hydroxyl methyl(-CH2OH) formed on the surface of GQDs. At the same time, the GQDs could emit strong fluorescence after electron beam irradiation, and the fluorescence intensity of GQDs increases with the increase of irradiation dose. In addition, GQDs irradiated by different irradiation doses can emit different colors of fluorescence under ultraviolet light. GQDs irradiated by the irradiation doses of 70 k Gy, 140 k Gy and 280 k Gy can emit yellow fluorescence, while GQDs irradiated by the irradiation doses of 560 k Gy and 1120 k Gy emit white fluorescence.