Preparation And Mechanism Of Metal Doped Carbon Dots And Application Of Heavy Metals Detection

Carbon quantum dots（CDs）is a new member of carbon nanomaterials with a size of less than 10 nm.It has the characteristics of easy prepartion,low toxicity,easy to obtain raw materials,good photochemical stability and excellent biocompatibility.It can be widely used in the fields of biosensing,environmental monitoring,photoelectron,photocatalysis,biological imaging and so on.In recent years,researchers have done lots of research on the synthesis and application of high-fluorescence carbon quantum dots which mostly prepared by doping with non-metallic heterogeneous elements.In this project,one step hydrothermal synthesis of carbon quantum dots was used to synthesize zinc doped carbon dots（Zn-CDs）and manganese doped carbon dots（Mn-CDs）,the growth path,morphology,optical properties,chemical structure and composition were also analyzed and studied.The growth mechanism of crystals was studied through simulation.Then,the Mn-CDs was used to establish the fluorescent probe platform for ion Hg²⁺and S^2-detection.The main contents are as follows:1.A simple,rapid,green,low toxicity and environmental friendly,low cost Zn-CDs were synthesized.By optimizing the reaction conditions,the QY of Zn-CDs was as high as 35.5%.Photochemical properties and internal structure analysis of Zn-CDs samples with different reaction times show that with the change of reaction time,the oxidation degree of Zn increases first and then decreases;and zinc element doping plays an important role in the growth of CDs.In view of the fluorescence spectra and combined with density functional theory/theoretical lattice conjugate model analysis,the reason for the enhanced fluorescence of the CDs after doping with the metal element Zn was demonstrated.2.At the presence of sodium citrate,manganese carbonate and citric acid,the reaction time is 2 h,and the reaction temperature is 195°C,the high QY up to 54.4%of Mn-CDs is synthesized by one step hydrothermal method.The Mn-CDs is uniformly dispersed with the average particle size of 4.63 nm.By combining experimental data with electron orbital theory simulation calculations,the mechanism of metal elements Mn doping and addition of citric acid to improve the QY of CDs was studied.In the process of synthesizing Mn-CDs,the conversion phase from metal oxide to metal carbide is present,thus improving the fluorescence properties of CDs,which is also a major factor in the greatly increasing of CDs’QY.A fast,simple and visual Hg²⁺platform is constructed based on the fluorescence property of Mn-CDs,which realizes the linear detection of Hg²⁺in the range of 100～1000 nM.Further analysis of the reasons for fluorescence recovery after adding S^2-is made.