Preparation And Analytical Application Of Fluorescent Carbon Quantum Dots

Carbon quantum dots（CQDs）,as environment-friendly nanomaterials,have become a potential alternative to semiconductor quantum dots.Because its synthesis does not require a controllable reaction atmosphere,and it does not contain toxic metals.CQDs also be an alternative to conventional organic dyes owing to their advantages of good biocompatibility,high photostability,chemical inertness and remarkable water-solubility.Based on these advantages,CQDs have been extensively applied in various fields,including biological imaging,catalysis,sensing and electronics.Despite many kinds of CQDs that have been reported up to now,most of them focus on the short-wave region and the quantum yield is relatively low,which restricts their practical applications.In view of the above problems,in this paper,two different types of CQDs were synthesized with different raw materials and methods,after which the prepared CQDs were characterized by transmission electron microscopy（TEM）,Fourier transform infrared spectrum（FTIR）and fluorescence spectroscopy（FL）and then were applied for the analysis and detection of small molecules and the research of bio-imaging.The details are as follows:Chapter 1:The research and applications of CQDs has been comprehensively reviewed.We summarized the research progress,synthesis methods,the physical and chemical properties of CQDs and their applications in the fields of analytical detection,photo-catalysis and bio-imaging.Chapter 2:Nitrogen doped carbon quantum dots（N-CQDs）are produced by one-step hydrothermal treatment of citric acid and p-phenylenediamine.The fluorescence of N-CQDs is significantly enhanced by introducing heteroatoms,which realized yellow fluorescence emission in long-wave region.The as-prepared CQDs possess narrow size distribution,the abundant functional groups,stable luminescent properties and a long fluorescence lifetime.Chapter 3:Based on the above synthesized N-CQDs,a new fluorescent nanosensor for the determination of phoxim was established.On the basis of the fluorescence inner filter effect（IFE）between phoxim and N-CQDs,phoxim can strongly quench the fluorescence of N-CQDs.Notably,the proposed sensing system showed an excellent performance including fast response,wide linear range（1-10μM,10-98μM）,and low detection limit（0.09μM,0.21μM）.What is more,the as-prepared yellow-emitting N-CQDs exhibited low toxicity and good biocompatibility and could be used for Hela cell imaging.Chapter 4:Nitrogen doped carbon quantum dots（N-CQDs）are produced by microwave irradiation of critic acid and tris（hydroxymethyl）aminomethane（Tris）as the carbon source and nitrogen source,respectively.The obtained N-CQDs show excellent water solubility,salt tolerance and photostabiliaty,exhibiting a bright blue fluorescenc(λ_em=432nm)under a 365 nm UV lamp irradiation with quantum yield of 46.5%.It is demonstrated that brilliant blue can show robust quenching effect on blue emission of N-CQDs.On the basis of this quenching effect,a new method for the determination of brilliant blue with high sensitivity was established.The linear range is 0.4-200μM with the detection limit of 0.24μM.The method further exhibited high accuracy and was successfully used to detect brilliant blue in the real sample.