Preparation Of Nitrosulfur-doped Carbon Dots And Its Application In The Detection Of Cu²⁺ And Fe³⁺

Carbon dots（CDs）,as a new type of carbon nanomaterial,are composed of three elements:carbon（C）,hydrogen（H）and oxygen（O）,and their particle sizes are generally less than 10 nm.Compared with traditional semiconductor quantum dots,it has aroused increasing concern because of its excellent optical properties,good water solubility,adjustable excitation and emission behavior,low toxicity,and simple synthesis.Based on the above characteristics,carbon dots are widely used in chemical sensing、bioimaging、photocatalysis and other fields.Chapter 1:The synthesis method,optical properties,luminescence mechanism of CDs and the application of CDs in various fields are reviewed briefly（especially the application in chemical sensing）.In addition,the topic background,research content,and innovation points are elaborated.Chapter 2:Nitrogen-sulfur doped carbon dots（N,S-CDs¹）were successfully prepared by hydrothermal method using folic acid and dithioacetamide as reaction precursors,with a fluorescence quantum yield（QY）of 11.42%.Comparing N,S-CDs¹solutions under UV light and ultraviolet irradiation revealed that the former emitted bright blue fluorescence.Secondly,in order to further investigate the elemental composition and content,functional group position and optical characteristics of synthesized N,S-CDs¹,X-ray photoelectron spectroscopy（XPS）,transmission electron microscopy（TEM）,Fourier transform infrared spectroscopy（FT-IR）,UV-vis and fluorescence spectroscopy（FL）were used for characterization tests.The results showed that the morphology of N,S-CDs¹ presented spherical particles（2.9 nm）,with good dispersibility and fluorescence stability in aqueous solution.More importantly,novel sensors capable of selectively detecting Cu²⁺were constructed based on N,S-CDs¹ with a linear range of 3.860-140.2μM and a limit of detection（LOD）of57.32 n M.Compared with other metal ions,N,S-CDs¹ has good selectivity and sensitivity for the detection of Cu²⁺.It was found that the established method could be applied to the determination of Cu²⁺in tap water and lake water,and the recoveries were 99.20%-101.5%and 99.40%-100.8%,respectively.Chapter 3:Nitrogen-sulfur doped fluorescent carbon dots（N,S-CDs²）were synthesized by simple hydrothermal method using paraphenylenediamine and thiosemicarbazide as reaction materials with a quantum yield（QY）of 28.26%.N,S-CDs² exhibits yellow-green fluorescence（λex=393 nm,λem=535 nm）.N,S-CDs²were found to have good dispersibility in aqueous solution by a variety of characterization methods（TEM,XPS,FT-IR,UV-vis,FL）,with a particle size of 3.1nm and functional groups such as hydroxyl and aromatic hydrocarbons on the surface.It was found that N,S-CDs² fluorescence could be selectively quenched by Cu²⁺and had a rapid and good response ability to Cu²⁺,with a response range of 19.89-200.1μM and a LOD of 482.5 n M,thus a sensing system for rapid detection of Cu²⁺was established.The prepared N,S-CDs² can be applied to the determination of copper ions in human serum samples.Chapter 4:Water-soluble nitrogen-doped carbon dots（N,-CDs）were prepared by simple hydrothermal method using o-phenylenediamine and o-aminophenol as reaction materials.This N,-CDs presented yellow fluorescence under UV lamp irradiation（λex=380 nm,λem=560 nm）with a quantum yield QY of 5.21%.The surface morphology,elemental composition and functional group position of N,-CDs were characterized by XPS,TEM,FL and UV-vis spectroscopy.It has a particle size of 2.88 nm and contains functional groups such as hydroxyl and amino groups on its surface.It is shown that N,-CDs can interact with Fe³⁺,when the excitation wavelength is 380 nm,and based on the internal filtration effect（SQE）,a significant quenching of the fluorescence of N,-CDs at the emission wavelength of 560 nm is observed,with a linear response range of 0.9500-50.60μM and a LOD of 32.53 n M.This method provides a new way for the determination of iron ion in environment and the recovery rate is 99.36%-103.2%.