Design, Preparation And Application Of Novel Nitrogen-doped Carbon Dots With High Photoluminescence

Carbon quantum dots, or carbon dots, were a new kind of carbon based nanomaterial with small size and photoluminescence. Carbon dots have widely been used for bioimaging, bio-labeling, sensing, catalysis and photoelectric device due to their low toxicity, environmental friendliness, excellent photoluminescence and non-photobleaching, good solubility and chemical stability, easy modification and low cost. Though the synthesis and application of the carbon dots have rapidly developed, there are still many problems demanding prompt solution in low quantum yield, major emission at blue fluorescence, lack of design strategies and lack of in-depth utilization. In this work, we prepared novel nitrogen-doped carbon dots with high photoluminescence by one step hydrothermal treatment of various carbon sources such as honey, polyacrylamide or waterborne polyurethane emulsion. The size, solubility and emission of the obtained carbon dots could be tuned by changing the reaction condition or the reactant composition. And these carbon dots could be applied in sensing, bioimaging and fluorescent composite films. This thesis includes four major parts as below:(1) The nitrogen-doped carbon dots with a size of 5 nm were synthesized by one step hydrothermal treatment of honey, which showed blue fluorescence under 365 nm irradiation. It was found that the doped nitrogen improved the quantum yield of carbon dots. These carbon dots could be used for fluorescence "off-on" sensor to detect Au(â…¢) and glutathione. The fluorescence of carbon dots could be selectively quenched by the addition of Au(â…¢) and formed the complex of Au(â…¢) decorated carbon dot cluster, whose fluorescence could be specifically restored by biothiols (especially for glutathione). This efficient strategy was successfully applied for the evaluation of intracellular glutathione with/without oxygen stress.(2) The nitrogen-doped carbon dots with quantum yield more than 10% were prepared in one step by hydrothermal carbonization of polyacrylamide, which contained nitrogen element itself. Fluorescent carbon nanoparticles with different sizes (5,20 and 50 nm) were obtained by hydrothermal treatment for 24,72 and 96 h, respectively. The morphology, structure and fluorescent properties of these carbon nanoparticles were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier transform infrared (FT-IR), UV-vis absorption and photoluminescence emission spectra. The obtained carbon nanoparticles were applied for rapid cellular imaging and gave an obvious fluorescence for only one hour. Moreover, it was found that the carbon nanoparticles had a marked size effect on endocytosis and the optimal size was about 20 nm.(3) Aqueous soluble and organic soluble carbon dots were produced by one-pot hydrothermal treatment of designable waterborne polyurethane emulsion. The different solubilities of these two kinds of carbon dots were attributed to the various functional groups on their surfaces. The aqueous soluble carbon dots had good fluorescence with quantum yield more than 20% and showed low cytotoxicity for multicolour bio-imaging. The organic soluble carbon dots processed good solubility in a wide range of organic solvents and were suitable for preparing fluorescent composite films. It was found that the yields of aqueous soluble and organic soluble carbon dots were affected by means of selecting different soft segments in waterborne polyurethane. Furthermore, the emission of the obtained carbon dots could be controlled from blue to blue-green by use of different diisocyanates.(4) Citric acid and cysteamine were chosen as the carbon sources to improve the quantum yield and a novel molecular of 5-oxo-3,5-dihydro-2H-thiazole[3, 2-a]pyridine-7-carboxylic acid (TPCA) with high photoluminescence (quantum yield>90%) was obtained by hydrothermal treatment. The chemical structure and fluorescence property of TPCA were characterized by electrospray ionization mass spectrometry (ESI), nuclear magnetic resonance (NMR) and photoluminescence spectrum (PL).