Research On Preparation And Modification Of The Graphene Quantum Dots

In recent years, the research of low-dimension nanomaterials has attracted more and more attention from scientists in various fields with the development of science and technology, especially the discovery of graphene. Graphene is quickly becoming the research focus in the fields of biology, sensors, catalyst and photovoltaic devices due to its unique thermal property, mechanical property, electrical property and optical property. In addition, graphene quantum dots(GQDs), a kind of quasi-zero-dimensional materials, are monolayer graphene with lateral dimension inferior to 100 nm. Not only inheriting the excellent properties of graphene, but also they has greater specific surface area, higher electron mobility and stronger mechanical strength on account of their strong quantum confinement and edge effects. Besides that, GQDs also possess good performance of photo-luminescence, better biocompatibility and lower cytotoxicity compared to the semiconductor quantum dots and organic dye. All those properties make GQDs have further application prospect in many new fields, such as biomedicine, cell imaging, optical devices and so on. For improving their photo-luminescent performance better and exploiting their applications widely, this paper carried out the works from innovative preparation and modification of GQDs. The main contents and conclusions are as follows:1. Graphene oxide(GO) is oxidized and cut into GQDs by hydroxyl radical(·OH) produced from the catalytic decomposition of H2O2 catalyzed by the tungsten oxide nanowire(W18O49) catalyst under hydrothermal treatment, which avoid the disadvantages of low environmental protection and poor efficiency producing from traditional acid oxidation. This new preparation method of GQDs are mild, clean, highly efficient and no by-products. The obtained GQD aqueous solution can be directly applied to fluorescence imaging in vitro without any further purifications, indicating that as-prepared solution has better. bio-compatibility and lower cytotoxicity.2. Deep ultraviolet emission photo-luminescent iron modified GQDs(Fe-GQDs) were prepared through a hydrothermal reaction of the mixture、of graphen oxide quantum dots(GOQDs) and iron iron benzoate precursor. The strong negative inductive effect of Fe decreases the π cloud distribution in the Fe-GQDs by the coordination bond between Fe and carboxyl making the blue-shifted photo-luminescent emission wavelength, which can realize the regulation of photo-luminescent property of GQDs.3. Nitrogen-doped graphene quantum dots(N-GQDs) were synthesized under a high temperature range of 800-1200℃ and high pressure of 4.0 GPa through a solid-to-solid process using melamine powder. Without the interference of surface groups, the graphite N in N-GQDs has a strong negative induction effect on the band gap can help us understand the photo-luminescent nature of GQDs. Besides, different photo-luminescent emission wavelength of as-prepared N-GQDs can controlled by N contents regulated by reaction temperature. Based on the recognized PL rules, we synthesised N-GQDs with a higher doping concentration and near ultraviolet light-emittance.