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Synthesis of S- and N-doped Carbon Quantum Dots

Minagar, Ava | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53195 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Madah Hosseini, Hamid Reza
  7. Abstract:
  8. In recent years, adjustable optical properties, simple and inexpensive synthesis, and excellent biocompatibility of carbon dots have attracted much attention. However, the widespread use of carbon dots in biomedical diagnostics, photoluminescence, and photocatalysis has been limited due to a lack of emission or excitation in the red or near-infrared region. Studies have shown that doping in carbon dots can affect the displacement and increase the light intensity. This study aims to use the engineering methods of optical properties of carbon points by doping heteroatoms and adjusting the surface state to synthesize biocompatible carbon dots with luminescence at long wavelengths with strong emission. The synthesis of carbon dots was performed by two methods. One of them is pyrolysis, then surface modification with Cysteine, and the other one is the hydrothermal method. The effect of significant parameters in each method, including the concentration of Solvent in the preparation of carbon dots and the concentration of Cysteine in the decomposition of carbon dots in the pyrolysis method, also the presence of nucleating agent and various strong acids in the hydrothermal method, were investigated. Pyrolysis-synthesized carbon dots with a concentration of 0.02 g/l of sodium hydroxide solution had the best stability and fluorescence intensity. After smearing these points with Cysteine, at a concentration of 0.1 mg/l, the luminance wavelength became 511 nm, the fluorescence intensity increased, and the quantum efficiency reached 2.2 times that of the prototype. In the hydrothermal method, strong acid was used as a catalyst, and citric acid was used as a nucleating agent. Samples synthesized with sulfuric acid with a fluorescence wavelength of 526 nm and quantum efficiency of 1.9 times that of the prototype and acetic acid with a wavelength of 514 nm with a quantum efficiency of 2.4 times that of the prototype showed optimal conditions. The structural and optical properties of synthesized carbon quantum dots were studied using PL, UV-Vis, FTIR, DLS, FE-SEM, and HRTEM. Also, the MTT assay was used to evaluate the effect of toxicity. The results of these tests showed that surface modification of carbon dots with Cysteine increased the intensity and fluorescence wavelength by reducing the surface oxide groups and increasing the Carbon dot size. Samples synthesized by hydrothermal method and carbonized with the presence of strong acids showed successful doping of carbon dots with Nitrogen and Sulfur, and it was confirmed that the use of strong acids has an important effect on the dehydration and carbonization of carbon dots. It was observed that proper nucleating agent by forming the first nuclei of luminescence and facilitating the carbonization process could have a significant effect on the size of the conjugated π-domains and luminescent domains of carbon dots
  9. Keywords:
  10. Carbon Nanoparticles ; Biocompatibility ; Fluorescence ; Quantum Dots ; Carbon Dots ; Red Shift

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