Preparation Of Water-soluble CdSe/CdS Core-shell Quantum Dots And Determination Of Trace Mercury (Ⅱ)

Quantum dots is a three-dimensional restricted semiconductor nanocrystals,which is constituted by the small number of atoms, referred to as "artificial atoms"sometimes, in which the internal electronic motion in all directions is limited, so thequantum confinement effect is particularly pronounced. It has a wide range of applicationfields for its unique physical and photochemical properties, the special andexcellent fluorescence properties of its make it has an extensive applications inbiology, ions of determination and so on, fields of research involving physics,chemistry, life sciences and other subjects, It is a new materials for which greatpotential for development. Especially in the environment scientific researches,provides a strong technical support for the detection of pollutants and analysis ofelements. Among them, more to study CdE (E=S, Se, Te) quantum dots and used CdEas nuclear to synthesis core-shell quantum dots as researches focus. Compared withthe synthesis in the organic phase, quantum dots synthesized in aqueous solution issimple, moderate, environmentally friendly, low cost, the product of quantum dots ismore stability and higher fluorescence quantum yield.Based on this, this research thesis is based on CdSe quantum dots as main workto synthesis of water-soluble quantum dots which mainly from the three aspects todiscuss and research:1. Preparation and synthesis of CdSe quantum dots in aqueous solution.Preparation of water-soluble CdSe quantum dots in two steps, which includespreparation the precursor and preparation CdSe quantum dots, when prepared theprecursor using the sodium sulfite to restore elemental Se powder where took a longtime, however through the reaction of Se powder with KBH4 reducing agent to getKHSe precursor solution, it only needs about half an hour, time shortens greatly;while prepared CdSe quantum dots using inorganic of cadmium chloride to providecadmium ions and use L-cysteine to modify. This method of preparation is simple,easy operation, the product of the fluorescence properties of CdSe quantum dots isgood, dispersibility is well. By using atomic fluorescence, UV absorptionspectroscopy, transmission electron microscopy (TEM) and so on means werecharacterized of CdSe quantum dots. But requires special attention is, in the preparation of CdSe quantum dots and the preparation of the precursor solution,needing to strictly control the reaction under anaerobic conditions, otherwise, theexistence of oxygen would oxidize CdSe and precursor solution, which will influencethe experimental results.2. Core-shell of CdSe/CdS quantum dots prepared. Based on the preparation ofCdSe quantum dots, preparing the novel type of CdSe/CdS core-shell quantum dots.Compared with the mononuclear CdSe quantum dots, CdSe /CdS core-shell quantumdots'stability is more stable and the fluorescence intensity higher than it. Adoptedseveral ways such as atomic fluorescence spectroscopy,UV absorption spectroscopyand TEM and so on to characterize the core-shell of CdSe/ CdS quantum dots. In thisexperiment, the preparation of size of the CdSe/CdS core- shell quantum dots isapproximately 6nm, diameter slightly larger than the mononuclear CdSe quantum dots,and UV absorption peak and fluorescence emission peak have occurred red-shift.3. CdSe/CdS core-shell quantum dots for the determination of trace Hg²⁺ ions.Using the synthesis of CdSe/CdS core-shell quantum dots as fluorescence probes forthe determination of metallic mercury(Ⅱ) ions, the results of measure showfluorescence quenching, and a new method of determination for trace Hg²⁺ ions isestablished, meanwhile, described the mechanism of fluorescence quenching ofquantum dots. Determination of trace Hg²⁺ ions in this method, when theconcentration of ions in the range of 1.0×10-6-2.5×10-7mol/L, it has a good linearrelationships between the Hg²⁺ ions concentration and the system of the relativefluorescence intensity (F0/F), the linear equation is F0/F = -1.55+0.875c (the unit of c:mol/L), the linear correlation coefficient of r =0.9982, limit of detection is 5.1×10-8mol/L, and about 0.1μg/L. The experimental method provides a new way of methodsfor the quantitative determination of metal Hg²⁺ ions. Compared with other methodsof determination of Hg²⁺ ions, this kind of method is simpler, more efficient, easier,more sensitive, lower cost of experiment, and nearly general laboratories haveequipment needed without using the large and expensive equipment. However, due tolimited experimental conditions, only determine the Hg²⁺ ions in the artificial watersamples in my experiment, where is not used for actual samples in practice, abouttesting actual samples will to be further research and discussion in the future.