Preparation Of Heteroatom Doped Carbon Dots And Application Of Optical Sensing

Carbon dots（CDs）has become a hot luminescent material because of its excellent fluorescence properties,but its application was limited by its low fluorescence quantum yield.So far,different methods have been developed to enrich the luminescence properties and fluorescence quantum yield of carbon dots,such as surface passivation,functionalization and heteroatom doping.Among them,heteroatom doping has been widely used as a convenient and common method to enhance the quantum yield of carbon dots.In this paper,we have been synthesized three kinds of high quantum yield carbon dots through the strategy of non-metal or metal heteroatom co-doping,and their applications in the field of fluorescence sensing have been further explored.The specific content of the paper is as follows:Chapter One:The properties,synthesis methods and applications of carbon dots were briefly introduced.The current solutions to low fluorescence quantum yield of carbon points were reviewed,put forward the research direction of this paper according to the problems that still exist.Chapter Tow:A new green fluorescent carbon dots were synthesized from m-phenylenediamine,L-cysteine and phosphoric acid.Due to the co-doping of N,S and P nonmetallic heteroatoms,the prepared N,S,P-CDs not only have excellent fluorescence properties,but also the fluorescence quantum yield（QY）can be as high as 0.41,which greatly promotes its application in fluorescence sensing.The fluorescence intensity of N,S,P-CDs can be sensitized nearly 8 times when the p H of solution was reduced in the range of 2.50-4.75,indicating that the fluorescence of N,S,P-CDs were very sensitive to the fluctuation of extremely acidic p H.Therefore,an excellent fluorescence sensing probe for the accurate monitoring of extreme acidic p H value was constructed.In addition,the fluorescence of N,S,P-CDs were strongly quenched by folic acid,a good linear relationship was established between the fluorescence quenching degree of N,S,P-CDs and the concentration of FA.Therefore,it could be used for the quantitative detection of folic acid,and the detection limit was 0.148μM.The proposed sensing method was applied to the determination of folic acid in orange juice and oatmeal samples with satisfactory results.Chapter Three:Green fluorescent carbon dots（Fe-CDs）were synthesized by using ferric nitrate as metal dopant and 3-aminophenthiophenol as nitrogen and phosphorus sources,QY reached 0.19.The fluorescence quantum yield was higher than that of undoped carbon.Fe-CDs displayed excellent stability in salt resistance,photobleaching resistance and photostability.The fluorescence intensity of Fe-CDs decreased gradually with the increase of the concentration of SudanⅠ,showing a good linear relationship which was used to the detection of SudanⅠin chili powder.The recovery rate was 99.5-103%,showing a promising application prospect in food safety detection.Chapter Four:Blue fluorescent carbon dots（PEI-CDs）were synthesized with polyethylenimine（PEI）and citric acid,the QY was up to 0.39.Because its excitation wavelength was similar to Rhodamine B,a single excited double emission system（PEI-Rh B/CDs）was constructed to detect Cu²⁺.In addition,after adding different concentrations of Cu²⁺to PEI-Rh B/CDs,a smart phone sensor platform was constructed for the detection of Cu²⁺by colorimetric method based on the color change rule of its luminous color under365 nm UV lamp.Finally,the method was applied to the detection of Cu²⁺in tap water and Fenhe River water samples with satisfactory results,which provides a new method for monitoring Cu²⁺in environmental water samples.