Preparation Of Functionalized Carbon Nanomaterials And The Investigation Of Their Fluorescent Properties

Carbon nanomaterials including carbon nanotubes, graphene and carbon nanodots et al have been the research focus of sensors, nanoelectronic devices, catalysis, drug delivery and hydrogen storage due to their extraordinary structure and unusual properties, such as small size effect, quantum effect and surface effect. The photo luminescence property of carbon nanomaterials has drawn a wide attention, since this property could be applied in areas such as biosensor, chemical sensing and biological imaging. Both functionalized carbon nanotubes and graphene are able to show strong NIR fluorescence and visible fluorescence. Being expected to replace the traditional quantum dots to become the most promising and environmentally friendly nanomaterials in the biomedical field, carbon nanodots not only have the similar advantage of efficient, stable and tunable absorption and emission fluorescence to semiconductor quantum dots, but also have the superiority of more stable emission, low toxicity and biocompatibility. The research of functionalized carbon nanotubes, graphene and carbon quantum dots will not only have important significance to the understanding of preparation of fluorescent materials and generation mechanism of fluorescence but also contribute to related chemical and environmental sensors.In this dissertation, we studied the preparation methods and properties of nitrogen-doped carbon nanotubes and nitrogen-doped graphene nanosheets, by chemical modification prepared functionalized carbon nanotubes with highly visible fluorescence, probed the fluorescence mechanism of oxidized carbon nanotubes and graphene oxide using experimental and theoretical simulation method, prepared carbon nanodots with highly efficient fluorescence and made exploration of synthesis of carbon nanodots with low toxicity and good cell imaging performance. The main contents are as follows:(1) Nanosized N-doped GO with visible fluorescence in water was prepared by cutting and unzipping of N-doped carbon nanotubes and used to detect metal ions. The oxidized products with different degrees of oxidation of NCNTs were obtained and characterized, and their fluorescences were found to be bathochromically shifted as the level of oxidation increases. The changes of the fluorescence of N-doped GO is expected to demonstrate the degree of oxidation or degradation of NCNTs, and can also be used to distinguish between normal metal ions and transition metal ions in future.(2) A simple and effective method to prepare highly efficient visible fluorescent MWCNTs well dispersed in water was reported. Carbon nanotubes are shortened and functionalized by several diamines, which leads to high quantum yields, comparative with those of quantum dots and organic dyes. The functionalized carbon nanotubes show good responsivity towards several transition metal ions. It is proposed that the fluorescence quenchingmechanism is due to the complexes formed by carbon nanotubes and metal ions.(3) Dominant components of oxidized products of multi-walled carbon nanotubes were separated by column chromatography, the origin of highly visible fluorescence fromcarbon quantum dots was revealed. The highly visible fluorescence was mainly originated from carbon quantum dots, while short and long oxidized carbon nanotubes only exhibited weak near-UV-Vis fluorescence. It was supported that the fluorescence is dominantly originated from sp2carbon clusters isolated by sp3carbons due to oxidation depending on the comparison between experimental data and calculated values. The results also indicated that carbon nanotubes can be transformed to large graphene oxide during oxidation. This work not only clearly demonstrated the origin of highly visible fluorescence in an oxidized carbon nanotube mixture and a reasonable explanation for fluorescence of oxidized carbon nanotubes, but also provided an example to understand visible fluorescent graphene oxide and carbon quantum dots.(4) We developed a simple and effective method to synthesize halogenated carbon quantum dots.They have unique abilities to identify iron ion and detect slight change in solution viscosity and provided an example that surface-functionalized carbon dots can be easily accomplished through halogenated carbon dots as intermediates. The halogenated carbon quantum dots as a useful reaction intermediate provide an alternative source for further functionalization of carbon quantum dots in future.(5) P-doped carbon quantum dots (P-doped CQDs) were synthesized by solvent-thermal method using phosphorous tribromide and hydroquinone as precursors. The as-prepared P-doped CQDs present strong visble fluorescence with quantum yield up to25%. The toxocity and bioimaging experiments showed that P-doped CQDs have low cell toxicity and excellent biolabelling ability to Hella cells.