Preparation,Characterization And Multifunctional Sensing Of Nitrogen/Boron Doped Carbon Dots

Carbon dots(CDs)was good water solubility,low toxicity,strong chemical stability,high biocompatibility,low preparation cost and easy functionalization,and could be used widely in fluorescence sensing,biomedicine,optoelectronic devices and other fields.In terms of fluorescence sensing,although many CDs had been reported for the detection of different target molecules,they had disadvantages such as poor selectivity,strong interference,and single detection species.Heteroatom doping could improve the targeting ability of CDs for the detection of target substances,and endowed CDs with multifunctional detection performance.In this paper,three kinds of heteroatom-doped CDs with excellent performance were prepared by hydrothermal method,and their properties were analyzed and applied to the analysis and detection of ions and small molecules.The main contents include:(1)Nitrogen-doped carbon dots(N-CDs-1)with a fluorescence quantum yield of 18%was prepared by hydrothermal method using ascorbic acid as carbon source and ethylenediamine as nitrogen source.The N-CDs-1 was characterized by transmission electron microscopy(TEM),ultraviolet-visible absorption spectroscopy(UV-vis),fluorescence spectroscopy(FL)and Fourier transform infrared spectroscopy(FT-IR).The results showed that N-CDs-1 had a particle size of 6.41 nm,and a spherical structure.The N-CDs-1 was good stability in different concentration of salt and pH conditions.N-CDs-1 could be used for the detection of Mn O₄^-with limit of detection of 0.055?M,and had been successfully applied to the analysis of Mn O₄^-in tap water and pond water.Meanwhile,the quenching mechanism of Mn O₄^-on N-CDs-1 was explored.It was found that N-CDs-1 was dynamic quenched by Mn O₄^-,which was caused by electron transfer.(2)Nitrogen-doped carbon dots(N-CDs-2)with a fluorescence quantum yield of 60.2%was prepared by hydrothermal method using citric acid as carbon source and ethylenediamine as nitrogen source.The N-CDs-2 was characterized by TEM,X-ray diffraction(XRD),UV-vis,FL,FT-IR and X-ray photoelectron spectroscopy(XPS).The results showed that N-CDs-2 had an average particle size of 3.5 nm,and a spherical structure.The N-CDs-2 was good stability in different concentration of salt.N-CDs-2 was sensitive to the pH value of the solution,and the fluorescence intensity and color of N-CDs-2 would change at different pH values,which could be used as a pH sensor.In addition,N-CDs-2 simultaneously measured Hg²⁺and GSH based on a fluorescence"on-off-on"approach with limit of detection of 0.014?M and 0.125?M,respectively.The sensitive mechanism was that Hg²⁺could dynamically quench the fluorescence of N-CDs-2,and GSH could coordinate with Hg²⁺to recovery the fluorescence of N-CDs-2.(3)Nitrogen-boron co-doped carbon dots(N,B-CDs)with a fluorescence quantum yield of 32%was prepared by hydrothermal method using citric acid as carbon source,urea and borax as nitrogen and boron sources,respectively.The N,B-CDs was characterized by TEM,XRD,UV,FL,FT-IR,XPS.The results showed that N,B-CDs had an average particle size of5.5 nm,and a spherical structure.The N,B-CDs was good stability in different concentration of salt.N,B-CDs was sensitive to the pH value of the solution,and the fluorescence intensity and color of N,B-CDs would change at different pH values,which could be used as pH sensors.In addition,the introduction of boron atoms enriches the surface of N,B-CDs with boron hydroxyl groups,which improves the selectivity to Fe³⁺.N,B-CDs could sensitively detect Fe³⁺in the detection range of 0-70?M with limit of detection of 0.044?M,and had been successfully applied to the analysis of Fe³⁺content in tap water and pond water.Meanwhile,the quenching mechanism of Fe³⁺on N,B-CDs was explored.It was found that Fe³⁺quenched N,B-CDs statically,and the quenching was caused by electron transfer and the formation of non-fluorescent substances.