Analytical Applications Of The Functionalized Grapheme Quantum Dots

Optical sensors have advantages of fastness, simplicity, low cost and easy miniaturation, and have been found various applications. Graphene is a material of two-dimensional (2D) crystalline structure with interesting physical and chemical properties. It has great potential applications in electronic devices and molecule sensors. Graphene nanosheets of less than 100 nm in size are known as graphene quantum dots (GQDs) and attracts particular interest owing to their excellent photoluminescence (PL) properties. In this thesis, we focused on the the synthesis of functionalization of grapheme quantum dots and their analytical applications. The major contents are summarized as follows.1、A simple one-pot hydro thermal method for the preparation of N-doped graphene quantum dots was developed. For this, citric acid and ammonia were used as the carbon source and the nitrogen source, respectively. The process gave a 65% yield of the N-GQDs. The as-synthesized N-GQDs exhibited a strong blue emission with a quantum yield of 18.6%, which is 7-fold higher than normal grapheme quantum dots. The N-GQDs are characterized by UV-vis spectroscopy, Fourier transform infrared (FT-IR) Spectroscopy, luminescence, AFM, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The TEM image showed that the average size of the N-GQDs was 6.4 ± 0.3nm, and the AFM image showed a typical topographic height of 0.5 to 1.2 nm. The grapheme quantum dots also exhibit excitation-dependent photoluminescence behavior. When the excitation wavelength changes from 310 to 390 nm, the photo luminescent peak shifts from 424 to 456 nm, and its intensity decreases rapidly. The N-GQDs show luminescence properties having excitation and emission maxima at 360 nm and 430 nm, respectively. The N-GQDs are very stable even in 1M NaCl, and their luminescent properties show pH dependent. It was observed that the blue emission of N-GQDs could be strongly quenched in the presence of Cr(Ⅵ). On this basis, a facile, green, sensitive, and selective chemosensor was developed for the detection of Cr(Ⅵ). It was demonstrated the N-GQDs-based sensing method for Cr(Ⅵ) ions detection in water had improved selectivity and high sensitivity.2、A simple one-pot hydrothermal method for the preparation of L-cysteine functionlization graphene quantum dots was developed. For this, citric acid was used as the carbon source, and mixed with the L-cysteine. The L-Cys@GQDs were characterized by IR, TEM and AFM. The TEM image showed that the average size of the L-Cys@GQDs was 3.0 ± 1.0 nm, and the AFM image showed a typical topographic height of 0.2 to 1.4 nm. The as-synthesized L-Cys@GQDs exhibited a strong blue emission with a quantum yield of 26.4%, which is 14-fold higher than normal grapheme quantum dots. The L-Cys@GQDs exhibit excitation-independent photoluminescence behavior. When the excitation wavelength changes from 300 to 370 nm, the photo luminescent peak shifts not obvious and its intensity decreases rapidly. The L-Cys@GQDs show luminescence properties having excitation and emission maxima at 350 nm and 440 nm, respectively. The 1-Cys@GQDs are very stable even in 1M NaCl, and their luminescent properties show pH dependent. It was observed that the blue emission of L-Cys@GQDs could be strongly quenched in the presence of Au(Ⅲ). On this basis, a new FL method was developed for the detection of Au(Ⅲ).3、A simple one-pot hydrothermal method for the preparation of glutathione functionlization graphene quantum dots was developed. For this, citric acid was used as the carbon source, and mixed with the glutathione. The GSH@GQDs exhibit excitation-independent photoluminescence behavior. When the excitation wavelength changes from 300 to 370 nm, the photo luminescent peak shifts not obvious and its intensity decreases rapidly. The GSH@GQDs show luminescence properties having excitation and emission maxima at 350 nm and 440 nm, respectively. The GSH@GQDs are very stable even in 1M NaCl, and their luminescent properties show pH dependent. It was observed that Hg(Ⅱ) caused quenching of the blue emission of GSH@GQDs. On this basis, a new method was proposed for the detection of Hg(Ⅱ) ions in aqueous solution.