Study On The Synthesis Of Fluorescent Carbon Nanodots And Their Applications

Carbon nanodots was first accidently found by Xu in 2004. They have received wide attention due to their good biocompatibility, low toxicity, excellent fluorescent stability and abundant potential applications. After years’ efforts, a variety of carbon precursors and preparation methods have been proposed. What’s more, CDs have been excellent candidates for myriad applications in biological labeling and imaging, sensors, photocatalysis, and optoelectronic devices. The major researches of the dissertation are as follows:(1) A facile one-step microwave-assisted method is proposed to synthesize carbon nanodots(CDs) by using DL-malic acid and ethylenediamine as the precursors. In addition to excitation-dependent emission behavior and excellent stability, the prepared CDs exhibit a high fluorescence quantum yield of 16.0 %. Moreover, the fluorescence of CDs can be obviously quenched by copper(II) ions through a charge transfer process, then is recovered with the addition of guanine due to its binding with copper(II) ions. Based on this, a novel fluorescence sensing system for the detection of guanine is established. Under optimized conditions, the as-made CDs can be used as highly sensitive fluorescent probes for well quantifying guanine in the range of 1.31×10-8 to 7.27×10-7 mol L-1 with a detection limit of 1.02×10-8 mol L-1. The proposed sensing system has been applied for the determination of guanine in urine and DNA samples with the recoveries from 98.1 % to 103.0 %.(2) The responses of CDs to the 2,4-dinitrophenol has been studied. In this paper, CDs as energy donor and 2,4-dinitrophenol as acceptor, a fast energy transfer process occured. Moreover, the fluorescence spectra of CDs has been investigated. The effects of p H, medium, dosage of reagent and temperature on the system have been discussed. Under optimized conditions, the quenched of fluorescence and the concentration of 2,4-dinitrophenol is proportional in the range of 2.17×10-6 ~ 5.43×10-5 mol L-1with a detection limit of 1.12×10-6 mol L-1. The proposed sensing system has been applied for the determination of 2,4-dinitrophenol in well and tap water samples with the recoveries from 96.0 % ~ 104.0 %.(3) Fluorescence carbon nanodots were synthesized in a one-step process by waste corncob using different methods including hydrothermal carbonization, microwave pyrolysis, ultrasonic assisted and combustion synthesis. The process have been evaluated at different conditions of reaction temperature and time in order to optimize the synthesis. It was found that the as-prepared carbon nanodots with the size of 1.3 nm and a high fluorescence quantum yield of 11.3 % were formed under hydrothermal synthesis, while the microwave irradiation exhibit the characteristic of time-saving. Furthermore, the as-prepared FCNs exhibit excellent stability in high salinity or high temperature environment. we have validated their low toxicity and successfully used for vivo imaging with a zebrafish.