Preparation Of Multicolor Fluorescent Carbon Quantum Dots And Their Applications In Detection And Composite Materials

Carbon dots(CDs)have been a leader in carbon-based nanomaterials,and it is a new type of carbon material whose size is smaller than 10 nm.CDs can be widely used in biochemical detection,fluorescence imaging,drug delivery,disease diagnosis and treatment because of its many unique photochemical and physicochemical properties,such as excellent water solubility,low cytotoxicity,stable optical properties and so on.So far,there are few methods to effectively regulate the luminous color of CDs,and most of the synthesized CDs mainly emit blue-green fluorescence,which greatly impedes the application of CDs in biomedicine.Most of the long-wavelength luminescent CDs obtained by the preparation strategy have some problems up till the present moment,such as low quantum yield and fuzzy synthesis mechanism,so the scope of application is greatly reduced.In view of the problems raised at this stage,the separation method and solvent control method were studied to prepare CDs,and the synthesis and luminescence mechanism of CDs were also discussed.The prepared CDs were applied to the field of detection and preparation of luminescent compound.The details are as follows:The first chapter mainly describes the properties,preparation method,luminescence mechanism and application of CDs.So far,there have been a lot of related studies on CDs.Because of the diversity of raw materials and preparation methods,the kinds of CDs prepared are also very rich.Owing to the diversity of CDs,researchers have their own ideas on the luminescence principle of CDs.Finally,the applications of CDs in detection,information protection,composite materials and biological imaging are introduced in detail.In the second chapter,1,2,4,5-phenylenetetramine hydrochloride(TAB·4HCl)was used as a precursor to synthesize red emissive CDs(RCDs)with a solvent(ethanol).The influence of anilines with different amino substitution positions on the optical characteristics of CDs was explored.The R-CDs were separated by middle chromatogram isolated gel column chromatography(MCI gel column),and the red,orange and yellow emitting CDs(r-CDs,o-CDs and y-CDs)were obtained,respectively.The fluorescence spectra(FL),transmission electron microscopy(TEM),Fourier transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS)were used to characterize the three kinds of CDs and luminescence mechanism was researched.In the third chapter,the emission wavelength of CDs was controlled by the change of solvent using TAB·4HCl as raw material.Red,pink,orange,yellow and green emitting CDs were prepared by a simple and rapid solvothermal method using anhydrous ethanol,n-butanol,methanol,isopropanol and N,N-dimethylformamide.The effects of dehydration capacity,solubility,boiling point and polarity of solvents on the synthesis of CDs were discussed.In addition,the reason of excitation wavelength dependence and luminescence mechanism of CDs were investigated by means of FL spectrum,TEM,FTIR and XPS.Chapter 4 introduces the application of CDs in detection and optical composites.First of all,methylene blue can effectively quench the fluorescence of R-CDs,so R-CDs were designed as a sensitive detection probe of methylene blue,and its quenching mechanism is inner-filter effect.The prepared multicolor fluorescent CDs can be used in the field of colorful fluorescent inks.Next,CDs can be compounded with gelatin to form CDs/gelatin composites.The experimental results show that the CDs/gelatin composites not only have the properties of fluorescence,but also have the feature of sol-gel conversion.This makes CDs have great potential in the controlled release of drugs and disease treatment.In addition,we also mixed the obtained multicolor fluorescent CDs with epoxy resin,polymethyl methacrylate(PMMA)and polyvinylpyrrolidone K90(PVP-K90)to prepare solid shaped materials and multicolor luminescent films,which effectively solved the problem of solid-state fluorescence quenching of CDs.In summary,using TAB·4HCl as a single reaction precursor,the emission wavelength of CDs was controlled only by changing the type of solvent.A new method of preparing long wavelength multicolor fluorescent CDs was developed.The separation method of MIC gel column chromatography was used to study the luminescence mechanism of CDs for the first time.The fluorescence detection probe of methylene blue was constructed to achieve the purpose of simplicity and rapidity.In addition,a new long-wavelength emission CDs/ gelatin complex has been prepared,which has great potential in biomedical applications.