Synthesis And Applications Of Fluorescent Carbon Dots From Coal And Its Derivatives

As a kind of novel functional nanomaterials, fluorescent carbon dots (CDs) have attracted extensive research interests across the world in recent years, of which the controllable synthesis is one of the hot topics of nanoscience and nanotechnology. The big challenge on the understanding of the relationship between the structure and characteristics of the fluorescent CDs and their artificial synthesis is how to design them from a superior and low-cost carbon precursor, and how to precisely control the structure, dimensionality and composition of the CDs, further to tailor their intrinsic properties. In the present thesis, the research is primarily focused on low-cost and structure-controllable synthesis and characterization of fluorescent CDs from coal and its derivatives as well as their practical applications, of which the majority results are briefly summarized as follows.Fluorescent CDs can be synthesized from coal via a nitric acid oxidation method. The effects of carbon source, maceral composition, carbonization pre-treatment and oxidation condition were systematically investigated. It is demonstrated that high-coalification coal and the fusinite involved in coal is beneficial to the quantum yield (QY) of CDs. The average size of CDs varies from1.9nm to3.1nm by controlling the carbonization temperature. The species and quantity of the functional groups on the surface of CDs can be modulated by subsequent reduction treatment. The QY of the coal-based CDs increases from1.02%to8.80%after NaBH4reduction. The reduced CDs can be utilized as an effective fluorescent sensing material for label-free and selective detection of Cu2+with a detection limit of as low as2.0nM.Electrochemical oxidation method can be also employed for the synthesis of fluorescent CDs from coal. The effects of carbon source, nitrogenous additive in the electrolyte were investigated, and the fluorescence behavior and aggregate state of the coal-based CDs at high concentrations were revealed in detail. The result shows that the coal-based electrode can be exfoliated more easily than the graphite electrode, resulting in much high yield of coal-based CDs than that of the graphite-based CDs. With the help of ammonia additive in the electrolyte, nitrogen-doped CDs (N-CDs) are successfully synthesized from coal. The coal-based CDs exhibit red-shifted emissions at high concentrations. The N-CDs are demonstrated as effective electrocatalysts for oxygen reduction reaction, as characterized by competitive electrocatalytic activity, negligible crossover effect and better stability in comparison to commercial Pt/C catalyst.Fluorescent CDs can be synthesized from coal tar pitch via a template-assisted method. Coal tar pitch-based CDs with a narrow size distribution and an average diameter of2.2nm can be finally obtained by conducting the reaction in the nanoreactor of the porous channels of the template. It is found that the physicochemical properties of the resultant CDs are significantly influenced by the surface modification with organic ligands, which not only modulates the polarity of the coal tar pitch-based CDs, but also dramatically enhances the fluorescence intensity of the CDs. Specifically, the ethanediamine-modified CDs can be homogeneous dispersed in organic glass matrix, as a light converter for UV InGaN light-emitting diode.