Synthesis And Properties Of Doped Carbon Quantum Dots

Carbon Quantum Dots(CQDs)are novel carbon nanomaterials with high fluorescence intensity and stability,and environmentally friendly.CQDs can be combined with inorganic or organic compounds and widely used in biological probes and catalysis.In recent years,it has become a hotspot.The current research is mainly changed the electronic structure and optical properties of the carbon quantum dots by non-metallic element doping.However,usually direct roasting or hydrothermal demand higher temperature,longer time.In view of this,we have developed a highly efficient microwave assisted thermal synthesis method,based on the "bottom-up"method synthesis of both high fluorescence luminescence performance and catalytic activity of carbon quantum dots.The first part of the work developed a high content of nitrogen and sulfur doped carbon quantum dots(N,S-CQDs),discussed its synthesis mechanism,fluorescence luminescence characteristics and enzyme activity.In the second part,boron,nitrogen and fluorine ternary doped carbon quantum dots(B,N,F-CQDs)were prepared by using 1-butyl-3-methylimidazolium tetrafluoroborate as carbon source precursor.The effects of precursor ratio and reaction time on the fluorescence properties of B,N,F-CQDs were studied.Carbon quantum dots with high fluorescence quantum efficiency were obtained.Ⅰ.Synthesis of N,S-CQDs and study the enzyme-like catalytic activity N,S-CQDs with high nitrogen and sulfur doping levels were synthesized by microwave solid-phase pyrolysis method with carbon source of citric acid,nitrogen and sulfur source of thiourea.It is found that thiourea work as weak base can accelerate the reaction rate,reduce the carbonization temperature and reduce the loss of reaction,thus improving the doping level.The N-S-CQDs have higher fluorescence quantum efficiency and enzyme-like catalytic activity compared to free doped CQDs.X-ray photoelectron spectroscopy(XPS)studies have found that the pyridinic structure into the conjugated structure is the predominant doped type and is the center of the enzymatic activity.Pyrrolic structure N at the edge of the N-S-CQDs is the fluorescence emission center.Thus enabling the samples has both high enzymatic activity and photoluminescence quantum yield.Ⅱ.Synthesis of F-doped CQDsF-doped CQDs were synthesized by using the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate([BMIm][BF4])and citric acid.The ternary doped carbon quantum dots of B,N,F-CQDs with diameter ranging from 4nm to 5nm and the maximum quantum yield 41.8%.The analysis of the concentration and structure of each doped element suggesting that fluorine as a fluorescence emission center plays a key role in the luminescent properties of the material.At the same time,C-F semi-ionic bond and C-F covalent bonds exist on the B,N,F-CQDs.