Preparation And Application Of Novel Graphene Quantum Dots And Its Composites

Graphene quantum dots（GQDs）is a new carbon nanomaterial,which is consisted of a single layer or few-layer of carbon atoms in a closely packed honeycomb structure.It can replace the semiconductor quantum dots and dye,with great application prospect in photoelectric device,life detecting,bioimaging,drug delivery due to their excellent fluorescence performance and biocompatibility,good solubility and chemical stability,environmentally friendliness and low toxicity.In this thesis,a series of studies have been directed to the preparation and performance of graphene quantum dots and its composites,in addition to their applications in bioimaging and sensing.The major achievements in the present thesis include the following:（1）The composites（PPy/GQDs）of conducting polymer and GQDs were synthetized by one step pyrolysis citric acid in the presence of polypyrrole（PPy）.We found that the composites exhibited strong fluorescence emission,which was dramatically enhanced as high as three times as pristine GQDs.Meanwhile they had good fluorescence response to DA,presenting a good linearity in range of 5-8000 nM with the detection limit of 10 pM.The results of PPy/GQDs sensor for detecting DA showed the superiority over other published quantum dots-based sensors.（2）Polyindole/GQDs molecular imprinting polymers（MIPs）were prepared by pyrolysis citric acid in the presence of polyindole（PIn）and DA.The MIPs with DA shape cavity were obtained by remove DA molecule in acid solution.It is found that DA had a fluorescence quenching effect on the prepared MIPs based on a photo induced electron transfer process.And by tuning the pH it could adjust the binding interaction between DA and MIPs,which exhibited a high sensitivity with a linear range of 0.5-1200 nM and the limit of detection as low as 0.1 nM in the determination of DA.（3）The polyindole-boronic acid（PIn-BAc）was firstly synthesized by oxidative polymerization,and then a nanocomposite based on PIn-BAc and graphene quantum dots was obtained by the complex between PIn-BAc and pyrolytic citric acid.We developed a novel fluorescent sensor for detecting glucose with excellent sensitivity and selectivity based on the prepared materials.Compared with the reported boric acid-quantum dots sensing system,the prepared sensor shows a wide detection range（5-300 μM and 450-900μM）and lower detection limit（0.5 μM）.（4）The nitrogen-doped graphene quantum dots（N-GQDs）with an average size of 9.4 nm was synthetized by pyrolysis branched polymine with the help of hydrogen peroxide.We found that the prepared N-GQDs had obvious fluorescence excitation independent characteristics and low cytotoxicity,which can be used for cell imaging.At the same time,the fluorescence could be quenched because of the complexation between N-GQDs and Pb²⁺.