Efficient Preparation And Multifunctional Application Research Of Carbon Dots

Carbon dots（CDs）,is a kind of zero-dimensional carbon nanomaterials,compared with traditional rare-earth fluorescein and semiconductor quantum dots,having superior optical properties,good photostability,good biocompatibility and low toxicity.CDs are widely used in fluorescence sensing,bioimaging and anti-counterfeiting printing.However,there have always been three difficulties that plague researchers:mostly CDs:（1）difficulty in ensuring purity,（2）exhibit low fluorescence quantum yield,（3）difficult for large-scale preparation.These have severely restricted further in-depth research on CDs.Based on the above problems,we try to improve the fluorescence characteristics of CDs and expand their application range by functional regulation of microstructure of CDs.In this thesis,the three kinds of carbon dots and their composites are designed and synthesized by one step in this experiment,the hydrothermal and solvent conditions were adjusted.Their structures and properties are well characterized in detail.These carbon dots are used for fluorescence sensing,fluorescent hybrid film and LED area.The main points of this thesis are outlines as follows:（1）A fluorescent N-doped carbon quantum dots（N-CQDs）is prepared in a hydrothermal way at 200°C,with a carbon source of garlic skins（GSs）and a solvent of ultra-pure（UP）water.The N-CQDs fluorescence quantum yield（QY）of N-CQDs is～9.0%.Maximum excitation wavelength of N-CQDs is 365 nm with an optimal emission wavelength located at 437 nm,with excitation wavelength dependence.By using high resolution transmission electron microscope we can find the N-CQDs have a particle size range from 2.5to 5.5 nm,average particle size is about 3.55 nm.Static quenching was used to explain the fluorescence mechanism.The N-CQDs exhibited a rapid,selective and sensitive response to Fe³⁺with a low detection limit of 4.44μM,which makes them promising potential for Fe³⁺sensing.Furthermore,the N-CQDs is dispersed into poly（vinyl alcohol）（PVA）matrix to make PVA/N-CQDs composite film.The unique optical properties of N-CQDs are inherited by the PVA/N-CQDs composite film,giving cyan fluorescence and high visible transparency,as well as nearly 100%UV-blocking ratio in the UV region.（2）N,P,S-doped carbon dots（N,P,S-CQDs）were synthesized by hydrothermal method by ammonium citrate as carbon source,ammonium dihydrogen phosphate as phosphorus source,ammonium sulfate as sulfur source,and UP water as solvent.N,P,S-CQDs-1 and N,P,S-CQDs-2 quantum yield of 51.0%and 41.0%,respectively.The N,P,S-CQDs is dispersed into PVA matrix to make PVA/N,P,S-CQDs composite film.The UV-A blocking capacity of the PVA/N,P,S-CQDs-2 film can block UV-A up to 77.46%.It provides an attractive solution for the functionalization of PVA materials.Owing to the fluorescence quenching resulted from the static quenching effect,the N,P,S-CQDs can be applied a functional sensor for the detection of Cr⁶⁺.The fluorescent sensors of N,P,S-CQDs have distinct features of simplicity,high sensitivity,and high selectivity.（3）Solid-state fluorescent CDs were acquired by one-step pyrolysis of N,N’-Methylenebisacrylamide（MBA）as carbon source,boric acid as boron source and N,N-Dimethylformamide（DMF）as solvent,having remarkably tunable self-quenching-resistant solid-state FL emissions.By regulating temperature,the particle size and graphitic nitrogen content of CDs are modulated over a wide range,the maximum emission peak of obtained CDs shifts from 469 to 597 nm.The morphology of green（G）,yellow（Y）,orange（O）and white（W）emissive CDs（G-,Y-,O-,W-CDs）were characterized by TEM,which showed the average diameter is approximately 2.53 nm,3.23 nm,7.74 nm and 4.88 nm.The FT-IR spectra displayed the presence of-OH,O=C-N-H and-COOH functional group on the surface of G-CDs,Y-CDs,O-CDs and W-CDs.Typical G-CDs,Y-CDs,O-CDs and W-CDs exhibit solid-state QY of 5.27%,10.49%,36.67%and 1.33%,respectively.Finally,taking advantages of outstanding optical properties of CDs,near white LEDs were prepared.