Fabrication Of Carbon Dots Fluorescence Probes And Their Application For Cu(Ⅱ) And Cr(Ⅵ) Detection

Excessive heavy metal ions in drinking water are a serious threat to human health.For example,excessive intake of copper ions(Cu²⁺)can cause headache,stomach pain,vomiting,and even induce Wilson’s disease and Parkinson’s disease,while ingesting excessive chromium ions(Cr⁶⁺).Significantly increase the incidence of illness,so it is necessary to accurately detect the concentration of heavy metal ions in drinking water.As carbon nanomaterials with size less than 10 nm,carbon dots（CDs）have many advantages,such as high fluorescence efficiency,good biocompatibility,excellent stability,good water solubility,low toxicity and simple preparation.The surface of CDs is decorated with abundant functional groups,which can easily interact with heavy metal ions,leading to fluorescence quenching,so CDs are efficient fluorescence probes,but their main disadvantage is the poor fluorescence selectivity.So in this thesis,optimization of CDs preparation method,synthesis of composite fluorescent probes with carbon nitride（C₃N₄）nanosheets and functionalization of CDs surface are used to improve the selectivity of CDs probes,and they are used for highly efficient and selective fluorescence detection of copper ion(Cu²⁺)and chromium ion(Cr⁶⁺).The main contents of the paper are as follows:In chapter 1,the following six aspects are mainly discussed,including the significance of heavy metal ion detection,the preparation,characterization,optical properties of CDs,their development in ions detection and the main r esearch contents of this paper.In Chapter 2,CDs were prepared by the pyrolysis method and used for highly selective Cu²⁺ detection.Citric acid was used to prepared CDs,and the morphology,size distribution and lattice structure of CDs were observed by transmission electron microscopy（TEM）and X-ray diffraction（XRD）.The surface functional groups of CDs were analyzed by Fourier transform infrared spectroscopy（FT-IR）.The fluorescence response characteristics of CDs to Cu²⁺,such as the sensitivity,response time,selectivity,linear response interval,detection limit and stability,were tested.A physical model was established to explain the fluorescence response mechanism of CDs to Cu²⁺ and used to analyze the reasons for their good selectivity.In chapter 3,CDs/C₃N₄ composite fluorescent probe was synthesized for high selectivity Cr⁶⁺ detection.CDs and C₃N₄ nanosheets were prepared by pyrolysis and thermal oxidation method,respectively,and CDs/C₃N₄ composite probes were prepared by ultrasonic mixing.The morphology,size distribution and surface functional groups of CDs/C₃N₄ were analyzed by various characterization methods.The fluorescence response characteristics of CDs/C₃N₄ to Cr⁶⁺ was studied,especially the sensitivity,selectivity,response speed and stability.As a contrast,the fluorescence response characteristics of CDs and C₃N₄ to Cr⁶⁺,especially the selectivity,were also measured,and the effect of C₃N₄ loading amount in CDs/C₃N₄ on their fluorescence response was also evaluated.The effect of Cr⁶⁺ on the functional groups of CDs/C₃N₄,CDs and C₃N₄ was studied by FT-IR technique,and The response model of CDs/C₃N₄ to Cr⁶⁺ was established to explain the fluorescence response process and the corresponding selectivity enhancement.In chapter 4,the functionalization of CDs by hydrothermal method for highly selective Cr⁶⁺ detection.CDs were prepared by electrochemical stripping method,and the functionalization of CDs was realized by hydrothermal method to enhance their fluorescence characteristics.The morphology,size distribution,surface functional groups and optical properties of CDs were measured by TEM,FT-IR,UV-vis and fluorescence spectra.The fluorescence response of CDs probe for Cr⁶⁺ was measured,especially the sensitivity,selectivity,linear response interval,detection limit and stability.The effect of Cr⁶⁺ on the functional groups of CDs was evaluated by FT-IR technique,and the fluorescence response model of CDs to Cr⁶⁺ was established.