Research On The Synthesis And The Properties Of Polyamine-functionalized N-doped Carbon Dots

As a new type of carbon-based fluorescent nano-material,carbon dots（CDs）has attracted wide attention in the fields of biological imaging,fluorescence labeling,ion detection and catalysis due to its low toxicity,good water solubility and excellent optical performance.The traditional CDs has the disadvantage of relatively low fluorescence quantum yield.It is found that doping nitrogen in CDs can improve its fluorescence performance.Polyamine macromolecules are considered to be ideal nitrogen-doped precursors because of their good water-solubility,high amino content,stable fluorescence properties and the ability to penetrate into carbon skeleton.It has a broad application prospect in the preparation of water-soluble carbon dots with high quantum yield.In this study,polyamine macromolecules with different spatial symmetric structures（1.0G polyamidoamine dendrimers,1.0 G PAMAM;1.0 g hyperbranched polyamidoamine dendrimers,1.0 g h-PAMAM;hyperbranched Polyethylenimine,h-PEI）and Sodium Citrate were used as raw materials,three kinds of polyamine-functional N-doped Carbon Dots（PNCDs）were obtained by hydrothermal method.The following results were obtained through the optimization of synthesis conditions,the characterization of structure and fluorescence properties:1.Under the optimal conditions(T=120℃,p H=3,n_h-PEI:n _Na3Cit=1:3,t=120 min),the blue fluorescent h-PEI CDs was synthesized with h-PEI（Mw=600）as precursor,and the quantum yield was 33%;under the optimal conditions(T=140℃,p H=5,n_h-PAMAM:n _Na3Cit=1:1,t=120 min),the blue fluorescent h-PAMAM CDs was synthesized with 1.0 G h-PAMMA as precursor,and the quantum yield was 45%;under the optimal conditions(T=120℃,p H=5,n _PAMAM:n _Na3Cit=4:3,t=120 min),the blue fluorescent h-PAMAM CDs was synthesized with1.0 G h-PAMMA as precursor,and the quantum yield was 57%.2.The chemical structure,composition and internal carbon core morphology of three kinds of PNCDs were analyzed by means of ¹H NMR,FT-IR,UV-Vis absorb and TEM.The fluorescence mechanism of the three kinds of PNCDs is the surface-state fluorescence,which is produced by the interaction of the surface functional group and the inner carbon core.3.The research focuses on the fluorescence performance of PAMAM CDs with the highest quantum yield.It can be seen that PAMAM CDs belongs to the p H-sensitive CDs.Its relative fluorescence intensity was the highest when the ambient p H was 8.The fluorescence stability of PAMAM CDs was excellent.When the p H was 5,the fluorescence intensity only decreased by 9%after 20 days of shading and airtight storage at 35℃.At the same time,PAMAM CDs has good photostability.Under natural light irradiation,the fluorescence intensity only decreases by 2%after 6 hours,which can adapt to daily operation without avoiding light.4.By studying the quenching of PAMAM CDs,it was found that the concentration of PAMAM CDs,polar solvent and metal ions can cause the quenching.There was a good linear relationship between the fluorescence intensity and the concentration of PAMAM CDs in the range of 0-3m M.The strong polar solvent can enhance the fluorescence emission of PAMAM CDs,and the polar solvent with hydroxyl group is more advantageous to the fluorescence emission.And the PAMAM CDs can identify Cu²⁺specifically.5.High quantum yield PAMAM CDs can be used as fluorescence probe to detect Cu²⁺ion in aqueous phase.There was a good linear relationship between the fluorescence intensity of PAMAM CDs and the concentration of Cu²⁺in the range of 0-80μM,The linear equation was:F₀/F-1=4.311C₂+12.33(F₀ and F were fluorescence intensity of PAMAM CDs before and after quenching respectively,C₂ was concentration of Cu²⁺,the correlation coefficient was R₂²=0.9971).And the detection limit（LOD）was 9 n M（S/N=3）.