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Study On Solvothermal Synthesis And Application Of Low-dimensional Carbon Nanomaterials

Posted on:2014-03-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:W T WangFull Text:PDF
GTID:1221330503455620Subject:Chemical Engineering and Technology
Abstract/Summary:PDF Full Text Request
With the development of nano-technology, many types of carbon nanomaterials were discovered, such as carbon nanodots(CDs) which show excellent photoluminescent(PL) properties, low toxicity and biocompability and carbon nanosheets(CNS) which exhibit highly ordered defect-free structure, high surface area, good conductivity, high mechanical strength and high stability. However, there were many limitations in the synthesis of CDs and CNS, eg. unsuitable for scale synthesis, complex process, low yield and causing pollution. One of the focuses of research on CDs and CNS is to improve the synthesis method and achieve the green, economic and scale synthesis to get high quality carbon nanomaterials. Hence, the thesis is mainly focused on the improvement of synthesis and application of CDs and CNS, using variety of modern chemical and physical method to characterize the morphology, structure and optical properties.In this paper, organosilane functionalized CDs were synthesized through solvothermal method. The products showed higher quantum yields of 51% and longer average lifetime of 14.99 ns than reported. More importantly, the carbon dots are amphiphilic which can be well dispersed in many kinds of solvents. Carbon dots are sensitive to solvents properties, showing excellent response to temperature, pH value of solution and Fe2+ and Fe3+ ions. Therefore, CDs has great potential to be applied as probe or sensor. Efforts were made to improve the PL stability of solid state samples and found that the fabrication of CDs into salt crystal can provide good protection on PL properties of CDs. NaCl crystal improved the PL stability under UV while KBr crystal increased the thermal stability.Water soluble nitrogen doped carbon dots(N-doped CDs) were successfully synthesized through solvothermal method in ethanol and water as coordinate solvents. The quantum yield of the product synthesized in ethanol(ECNPs) was 24.58% while 17.88% of carbon dots synthesized in water(WCNPs). The optimal synthesis conditions were acquired through evaluation of reaction temperature, reaction time and ratio of reactants. The results indicate that the fluorescent of carbon dots were size dependant, smaller particles emitted stronger luminescence. The carbon dots exhibit good photostability, thermal stability and ion strength stability. Only Fe3+ ions quenched the fluorescence of ECNPs and WCNPs. The fluorescent intensity was strongest at pH value of 3, further increasing or decreasing the pH of solution, the fluorescent intensity decreased gradually. The survival rates of JAR and JEG cells in WCNPs were less than 20%, indicating good anti-cancer function.In addition of CDs, the thesis reported a green, economic and large-scale route to synthesize CNS through solvothermal method and the products were applied into the treatment of water pollutants. As-prepared CNS showed perfect, uniform layer structures of 1~5 nm according to the AFM and HRTEM results. The dye removal experiments showed that many factors influenced the adsorption performance of carbon nanosheets on dye adsorption, including adsorbent dosage, contanct time, initial concentration of dye and pH value of solution. The maximum adsorption amount onto carbon nanosheets was 326.7 mg/g of methylene blue and 113 mg/g of methylene orange. The kinetic study of adsorption indicated that both adsorption of methylene blue and methylene orange onto carbon nanosheets fitted the pseudo-second order well. The adsorption isothermal fitting found that the adsorption can be well described by Langmuir isotherm.
Keywords/Search Tags:Solvothermal synthesis, carbon dots, fluorescence, nitrogen-doping, carbon nanosheets, dye adsorption
PDF Full Text Request
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