Preparation Of Nitrogen-doped Carbon Dots And Their Application In Environmental Analysis

As a new generation of carbon nanomaterials,carbon quantum dots（CDs）have aroused a wave of research in different fields owning to their wide sources,excellent photochemical properties,low toxicity,good biocompatibility,adjustable luminescence,easy functionalization and great application potential.The fluorescence sensing method based on the characteristics of large specific surface area of CD s,abundant surface functional groups,easy modification,high activity and sensitive to environmental changes is an important technical method in environmental monitoring,which is widely used in the detection of various target analytes in the environment.In the face of complex environment and increasing detection demand,the development of new fluorescence sensing method s based on CDs can not only enrich detection methods,but also improve the accuracy,sensitivity and convenience of the detection methods.Moreover,while fluorescence sensing function of the novel synthetic CDs were constructed,its multifunctional application will be further explored,and which could get twice the result with half the effort.In this paper,three kinds of nitrogen-doped fluorescent CDs with different colors were designed and prepared by a one-step synthesis method.And based on their different fluorescence response mechanisms to target analytes in the environment,three kinds of multifunctional fluorescence probes were constructed and were successfully applied to the detection of actual samples in the environment.The research enriches the preparation strategy of carbon quantum dots to a certain extent and expands the application range of CDs,and provides a new idea for fluorescence detection.The main research contents are as follows:1.Water-soluble CDs with strong blue fluorescence（B-CDs）were synthesized by green,simple and economical microwave-assisted pyrolysis.Based on the phenomenon that the fluorescence intensity of B-CDs was significantly quenched in the presence of Cr（VI）and recovered obviously after the introduction of ascorbic acid（AA）,an"on-off-on"type Cr（VI）and AA detection method was established,and the limits of detection（LOD）of Cr（VI）and AA were 0.16μM and 0.10μM,respectively.The fluorescence detection method was simple,rapid and sensitive,and had been successfully applied to the detection of Cr（VI）in actual water and soil samples and AA in various fruit samples.The B-CDs not only has a certain application prospect in environmental monitoring,but also has a potential application in paper sensing,fluorescent film materials,information security and anti-counterfeiting.2.Orange water-soluble fluorescent CDs（O-CDs）was synthesized by one-step hydrothermal method.Based on the fact that the fluorescence intensity of O-CDs was significantly quenched in the presence of curcumin or VB₁₂,an original dual-function detection method for curcumin and VB₁₂ was constructed,and the LOD of curcumin and VB₁₂were 78 n M and 86 n M,respectively.The method had been applied to the detection of curcumin and VB₁₂ in actual water samples,curcumin in human serum samples and VB₁₂ in tablets with satisfactory results.This work provides a novel idea for the design of a portable sensor based on O-CDs to detect curcumin and VB₁₂quickly and sensitively.3.A bright yellow fluorescent CDs（Y-CDs）was synthesized by a simple one-step hydrothermal method,and the prepared Y-CDs was applied to visual detection of Cl O^-and S₂O₃^2-.Based on the effective quenching of the fluorescence intensity of Y-CDs by Cl O^-,a valuable sensing method was constructed for highly selective detection of Cl O^-.The detection range was 0.067～19.33μM and 24.0～98.0μM,and the detection limit was as low as 13 n M.After S₂O₃^2-being added into Y-CDs/Cl O^-system,the fluorescence of Y-CDs partially recovered,and the ratio fluorescence emission(F₅₃₇/F₄₉₂)was displayed in the range of 6.6～100μM.The emission peak at537 nm increased,while emission peak at 492 nm decreased.Therefore,fluorescence sensing method for S₂O₃^2-was constructed,and the LOD was 0.78μM.Based on the phenomenon that the fluorescence color of Y-CDs changed from yellow to green to blue after different concentrations of Cl O^-being added,a simple paper sensor method for recognizing Cl O^-was prepared.The fluorescence color of CDs/Cl O^-also changed from blue to green to yellow after different concentrations of S₂O₃^2-being added.This method could be used as an effective visual method for field detection.