Synthesis Of N-doped Carbon Quantum Dots With Propanedioic Acid And Its Study On Optical Properties

Carbon dots have gain much interest to be used as sensing receptors due to their unique photoluminescence property,ease to prepare,less toxic,and the option to perform surface modification to suit a sensing application.In the water phase,the metal ions can quench the fluorescence produced by CQDs,which enables CQDs to be applied to sensing.High fluorescence quantum yield is a prerequisite for the wide application of CQDs,so it is very important to explore the relatively simple method of improving CQDs yield.and this is a study of the different preparation methods,optical properties and applications of carbon quantum dots,and the main work is as follows:Chapter 1:The experiment with malonic acid as carbon source,respectively by two methods:microwave method and hydrothermal method,for the preparation of carbon quantum dots.Microwave synthesis was optimized by microwave time and microwave power.The hydrothermal law selects the synthesis conditions such as hydrothermal time,hydrothermal temperature and malonic acid concentration.From the particle size,dispersion degree and optical properties to the carbon quantum dots produced by the two methods,the optimal method is obtained for nitrogen doping.Both the carbon quantum dots obtained by the two preparation methods are fluorescence emission dependent excitation,and their particle size distribution is similar.In terms of the fluorescence quantum yield,the hydrothermal method is better than the microwave method,which is 4.25%.Chapter 2:On the basis of the previous experiment,The nitrogen doped carbon quantum dot was obtained by the hydrothermal treatment of propylene diacid as carbon source and ethylenediamine as nitrogen source.The effect of the amount of ethylenediamine on the fluorescence intensity of n-cqds was investigated,and the optimum quantity was selected.The shape of nitrogen doped carbon quantum dots is similar to the shape of a sphere.The particles are dispersed uniformly and the particle size is uniform.The particle size distribution is between 2.06 and 4.62 nm,with an average particle size of 3.32 nm.I The crystal lattice fringes of carbon quantum dots can be seen under high resolution transmission electron microscopy,and the spacing between n-cqds lattice fringes?0.46 nm?is greater than that of undoped carbon quantum dots?0.17 nm?.The fluorescence yield was 36.06%,nearly nine times higher than that of undoped CQDs.The fluorescence emission of N-CQDs was not determined by fluorescence emission.The optimum fluorescence excitation peak was at 330 nm and the fluorescence life was 1.4396 and 5.9081 ns.By IR and XPS characterization of N-CQDs structure,proves that the success of the nitrogen doping.Moreover,solid samples can be obtained,and the water absorption is weaker than CQDs,so that it can be preserved for a longer time,which is beneficial to practical application.The effects of pH value,high salt solution and UV light on the fluorescence of N-CQDs were discussed.It lays the foundation for ion detection.Chapter 3:The N-CQDs was applied to the detection of inorganic ions.By screening the metal cation,the fluorescence quenching of N-CQDs was determined to detect the cobalt ion.The concentration of Co²⁺is in the range of 0.1¹.0 mm,and F/F₀ is linear with c(Co²⁺).The linear equation is F/F₀=-0.1302 c(Co²⁺)+0.9982,and the correlation coefficient R²=0.9935.According to the 3?/k,the detection limit is 0.07?M?18.0?g/L?.A feasible method for determination of cobalt ion concentration was established.In addition,it was applied to the actual sample of vitamin B₁₂ and the detection of cobalt ion in the lake,and obtained satisfactory results.