Preparation Of Carbon Nanocomposites And Studies On The Fluorescence Properties

Carbon nano materials, such as graphene oxide and carbon carbon,have caused extensive concern because of good biocompatible, non-toxic and good water soluble etc. Graphene oxide contains a lot of oxygen groups(such as epoxy groups, hydroxyl, carboxyl, etc) on the surface, which polar functional groups on the surface can form strong polarity interaction or chemical bond with some organic molecules or polymers, thus forming nanocomposites; Carbon dots has strong fluorescence, and its surface is easy to modify, or carbon dots with functional groups can be combined with functional substances to form nanocomposites.The main advantages of fluorescent chemical sensors are its simple operation, high selectivity, high sensitivity, real-time and low detection limit etc., The fluorescence detection technology has been widely used in analytical chemistry, biochemistry, cell biology, and many other fields because of these advantages. Therefore, much attention has been paid to design and synthesize more effective fluorescent molecular probes.In this paper, we focus on the research of carbon nanocomposite material. Firstly, the fluorescent graphene oxide nanocomposites was prepared by graphene oxide covalent bonding with fluorescent dye. The photophysical properties of nanocomposites were studied, and the nanocomposites were applied in the biological cell imaging. Coumarin and perylenediimide which we use as fluorescent dye have many advantages such as higher molar extinction coefficient, higher absorption efficiency, good light stability, and higher quantum yield fluorescence, So they are the widely studied chromophore. Moreover, we prepared carbon dots/manganese dioxide nanocomposite material, and used it as a fluorescent probe of glucose. The paper is divided into five chapters:1. The research background of this work was concisely introduced, it is mainly focused on the following aspects: the research status of graphene oxide and carbon dots, recognition mechanism of fluorescent sensors and fluorescent dye used in this paper.2. The graphene oxide and fluorescent carbon dots were prepared respectively, and the morphology and structure of them were charactered, the spectroscopy properties of them were studied. The results show that graphene oxide nanosheet has weak fluorescence,while carbon nanoparticles has moderate fluorescence. Both of them have good water-solubility.3. A new nanosheet fluorescent chemosensor(GO-NH-COUR) has been prepared based on graphite oxide(GO) covalently functionalized with 4-methyl-7-aminocoumarin(NH2-COUR). The products were characterized by transmission electron microscopy(TEM), X-ray diffraction(XRD) and Fourier transform infrared(FT-IR). The photophysical properties of GO, NH2-COUR and GO-NH-COUR in aqueous and ethanol solution have been investigated by UV/vis spectrophotometry, steady-state and time-resolved fluorometry. In aqueous solution, GO-NH-COUR probes undergo protonation-deprotonation in the acid to basic pH range, producing intensity increases with acid to near-neutral pH range. The advantages of the newly prepared nanoparticles are that they offer good dispersion in aqueous solution and good optical properties. Confocal microscopy experiments showed that GO-NH-COUR can be transfected into the living cells and applied for fluorescence imaging.4. A new visible-light-excite nano fluorescent dye(H2N-PDI-NH-CO-GO) based on graphite oxide(GO) covalently functionalized with non-fluorescent perylenediimide derivatives(H2N-PDI-NH2) has been prepared. The products were characterized by TEM, XRD, and FT-IR. The nanosheet indicator exhibited three acid–base equilibriain in aqueous solution and characterized by pKa values of 3.0, 7.0 and 10.0. On protonation–deprotonation process in acid and the near-neutral pH range(3.0-7.0), UV/Vis absorption and fluorescence spectral shifts of protonated and neutral forms were observed. The protonated and neutral forms of H2N-PDI-NH-CO-GO both have moderately high fluorescence intensity with the fluorescence emission maximum at~550 nm and ~590 nm with excited at 470 nm and 530 nm, respectively. So this nanoindicator emits green fluorescence and red fluorescence when excited at different wavelengths at near-neutral pH range. The time-resolved fluorescence shows the aggregation of the nanoindicator. Laser confocal microscope experiment shows the potential utilization of H2N-PDI-NH-CO-GO in living cells.5. A highly sensitive glucose probe based on MnO2 modified carbon dots has been developed, which is successfully prepared by a simple chemical reduction process. The absorption band of MnO2 nanosheets overlaps well with the fluorescence emission of CDs nanoparticles, resulting in efficient quenching of the fluorescence of carbon dots. In the presence of H2O2, the fluorescence of carbon dots could be recovered due to MnO2 was reduced to Mn2+ by H2O2, and the glucose can thus be monitored based on the enzymatic conversion of glucose by glucose oxidase to generate H2O2 and gluconic acid. The nanocomposite can be use for detecting glucose in blood serum.