Studies On The N Co-doped Graphene Quantum Dots, Graphene Quantum Dots And Their Properties

In recent years, the carbon nanomaterial with the low-dimension was found gradually along with the development of science and technology. Especially, the unique characteristics and applications of graphene have attracted much attention by the chemical and material communities after it was found in 2004. As a member of quasi zero dimension material, the quantum dots has been gradually applied to the fluorescent probes, bioimaging and other biological, medical aspects. The graphene quantum dots, GQDs, have excellent properties of grapheme such as strength, large specific surface area, and combined with the advantages of quantum dots as the quantum confined effect, size effect, edge effect. In addition, GQDs shows many fascinating properties, such as well biocompatibility, low cytotoxicity, excellent solubility, stable photoluminescence, thus, making them potential application in sensing systems and bioimaging. In this thesis, we mainly through improving the preparation conditions of GQDs and N-GQDs, increased the fluorescence quantum yield of them, and made a detailed research on the nature of GQDs and N-GQDs by various means, explored the application of the N-GQDs in ion and the GQDs in HBV-DNA detection. The main contents can be summarized as follows:(1) The preparation of GQDs by using pyrolysis the organic precursor of citric acid (CA). Explored the optimum preparation conditions by optimizing the reaction time, temperature, pH and other experimental conditions. The PL quantum yield of GQDs reaches 9 %; the mean diameters of GQDs were ～3.0 nm in the optimal conditions. And we reported a facile hydrothermal route to synthesize N-doped GQDs (N-GQDs) with a large number of "pyrrolic-N" by using urea as N sources. Explored the best preparation conditions with different ratio of raw materials, reaction time, and reaction temperature. The PL quantum yield of N-GQDs reaches 24%, the mean diameters of N-GQDs is ～7.5 nm in the optimal conditions. Moreover, the PL lifetime decay of GQDs (1.74 ns) and N-GQDs (7.40 ns) were very well fitted to a single exponential function, indicating that both GQDs and N-GQDs has one single PL origin. Furthermore, the formation mechanism of GQDs and the pyrrolic-N ring in N-GQDs was also discussed.(2) Copper (Cu2+) test of N-GQDs. Cu2+ ion has a higher binding affinity and faster chelating kinetics with N and 0 on the surface of N-GQDs than other transition metal ions, and the fluorescence quenching of N-GQDs might be caused by the facilitation of nonradiative electron/hole recombination annihilation through an effective electron transfer process. When the concentration of Cu2+ in the range from 0 to 100 nM, the limit of detection (LOD) of Cu2+ was 14 nM using the equation LOD=3σ/k, it was better than or at least comparable to the values reported previously.(3) An approach for HBV-DNA detection was described from graphene quantum dots (GQDs) to graphene oxide (GO). The influence of GO with different concentration, response time and incubation time for HBV-DNA detection was studied. Under the optimal conditions, the fluorescence recovery is as high as 96.5%, a detection limit of 5.08 nM (S/N=3). Moreover, the cDNA-GQDs/GO system could differentiate the tDNA, mDNA and HIV DNA, this high sensitivity and good specificity of visual detecting technique has potential applications.