Physics of carbon quantum dots for novel optical sensing applications
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Date
2021-09
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E-JUST
Abstract
Carbon quantum dots (C-dots) are cost-effective, environmental-friendly, and biocompatible nanoparticles with many potential applications in sensing and optoelectronics. A simple controllable synthesis of C-dots with different particle sizes using a hydrothermal process, from folic acid source, is investigated in this thesis. Namely, we have synthesized fluorescent carbon dots from Folic Acid as a single precursor in ultra-pure water. The effect of reaction temperature, between 100°C and 230°C, is studied on the dots' sizes and the fluorescence properties. Results show that the reaction temperature can control both the dots' sizes and the fluorescence. Several techniques have been used to confirm that, including X-ray diffractometer XRD, X-ray Photoelectron Spectroscopy XPS, transmission electron microscope TEM, ultraviolet-visible absorption spectroscopy (UV-Vis), fluorescence spectroscopy (FL), and fluorescence lifetime measuring system.
Moreover, the synthesized C-dots were examined as optical-sensor to determine different toxic materials. It was found that the synthesis temperature specifies the appropriate sensor for different hazardous chemicals like pyridine and aniline. Pyridine was realized to quench the fluorescence of the synthesized C-dots that prepared at 300°C effectively. The quenching is explained in terms of the Stern-Volmer relation and confirmed by fluorescence lifetime measurements to have a dynamic character with a predetermined electron transfer. The detection limit for pyridine was found to be 18 nM. To the best of our knowledge, such a small detection limit is more than three orders of magnitude smaller than that obtained so far for pyridine detection using any other facile methods. In addition, whereas aniline can be formed from burning plastics or tobacco and may be use in many industrial sources. Therefore, focus to detect aniline with a sensitive method was one of the aims of this thesis. It was found that C-dots, that was synthesized at low temperature, can be utilized as a turn-off fluorescent chemo-sensor for aniline solution with ultra-law sensitive detection. The fluorescence quenching is described in details by Stern-Volmer relation and was found to have static character as confirmed from nanosecond lifetime fluorescence measurements.