Aluminum Reduction Precursor Aqueous Solution Synthesis Of Cdse/Cds Quantum Dots And Determination Of Trace Arsenic

Quantum dots were the nanoparticles composed of III-V or II-VI group elements,also called semiconductor nanocrystals.Their particle size was generally less than10nm. Quantum dots had characteristics of stable structure, relatively high fluorescentintensity, higher quantum yield, resistance to bleaching and so on. Quantum dotscould produce strong fluorescence when they accepted excitation. CdX （X=S, Se, Te）which were studied deeply. CdSe quantum dots owned excellent luminescentproperties. CdSe/CdS core-shell structure quantum dots, because of the strongquantum confinement effect, not only did they have excellent luminescence properties,but also they had high fluorescence quantum yield. So the nanocrystals were expectedto be applied in many fields of biological fluorescent labeling, optoelectronic devices,solar cells, light emitting diodes, and quantitative analysis. Compared the method thatquantum dots synthesized in the organic phase, the method that quantum dotssynthesized in aqueous phase, was easy to operate, low-cost experiments, using thelow toxicity drugs, easy to control the reaction conditions, short reaction time, simplesynthesis method. Moreover, the quantum dots synthesized in aqueous phase whichthe products were more water-soluble.Arsenic and its compounds were highly toxicity, very little requirements tohuman body, which had a close relationship to the environment and human health. InChina, of arsenic were listed as one of the five poisons in water in the environmentaldetection of contamination and also been listed as one of the indicators of the totalemission control. Arsenic has been recognized as a carcinogen and one of the harmfulsubstances by International Cancer Center. How to quick ly and accurately detectarsenic in water pollution and soil has been the hot and focus of research in the fieldof water quality testing and environmental testing. A new method of fluorescenceanalysis developed in recent years, which was employed the qua ntum dot as afluorescent probe with the changes of quantum dots’ fluorescence decreased orenhanced to determine ions. The method had many unmatched advantages to othermethods, such as high sensitivity, the relatively simple instrument, easy operation,relatively mild reaction conditions and so on.In this thesis, the main research work was the preparation of CdSe/CdS quantum dots in the aqueous phase,mainly from the following three aspects:（1）: CdSe quantum dots synthesized in aqueous solution. The synthesis of watersoluble CdSe quantum dots was divided into the preparation of precursor andsynthesis of CdSe two steps. At first, the Na2Se as the precursor has been synthesizedby aluminum powder, selenium powder,sodium hydroxide as raw materials inultrapure water. The second, CdSe quantum dots were compounded by CdCl2solution,the precursor of Na2Se and thioglycolic acid（HSCH2COOH） as the stabilizer in theaqueous solution.Through orthogonal experiment, we found the optimal experimental conditionsfor the synthesis of CdSe quantum dots. The obtained CdSe quantum dots wererelatively high fluorescent intensity under the optimum experimental conditions.Thecharacterization of the CdSe quantum dots was used the TEM, XRD, the Fouriertransformation infrared spectrum, the ultraviolet visible light spectrum, the fluorescentspectrum and so on.We obtained spherical quantum dots in water dispersion withproperties of high light-emitting quantum fluorescent efficiency, stable performanceand saving for a long time. The probability of expanding the application of quantumdots may be provided. Should be noted that, in the preparation of the precursor Na2Sesolution and preparation of CdSe quantum dots solution, the reaction should becarried out under anaerobic conditions, because the oxygen could oxidize CdSe andthe precursor, which affected the experimental results.（2） Preparation of Core-shell CdSe／CdS quantum dots.On the basis of theoptimal experimental program, CdSe quantum dots were synthesized in aqueoussolution,then we synthesized stable, good dispersion and high fluorescent quantumyield core-shell CdSe/CdS quantum dots.The characterization of core-shell CdSe/CdS quantum dots were by atomic fluorescence spectrum, XRD, transmissionelectron microscopy and other several ways. In the synthesis process of CdSe/CdSquantum dots, we examined the reflux time and the core-shell ratio, throughexperiments we had found the proper reflux time and core-shell ratio. Under thesame condition, the fluorescent intensity of Core-shell CdSe／CdS quantum dots wassix times of the single-core CdSe quantum dots. The size of prepared CdSe/CdScore-shell quantum dots were approximately7.0nm. With the thioglycolicacid（HSCH2COOH） as the stabilizer, the aluminum precursor synthesis of CdSe/CdSquantum dots were stable, good dispersion, meeting the need of basic determination.（3） The core-shell CdSe/CdS quantum dots for the determination of trace Asions.Using the synthesis of the core-shell CdSe/CdS quantum dots as fluorescentprobes for the determination of trace arsenic ions, the results of measure showsfluorescent quenching, and a new method of determination for trace arsenic ions hasbeen established, and explained the mechanism of fluorescent quenching of quantumdots. When the trace arsenic ions were determined using this method with ionconcentration in the range of10.0-40.0μg/L, the difference of the fluorescent intensity （F0-F） before and after arsenic ions added showed a good linearrelationship to arsenic ion concentration. The linear regression equation was F0-F=0.5328ρ-1.864（the unit of ρ: μg/L）with the linear correlation coefficient r=0.9980and detection limit0.94ug/L. The arsenic in standard solution Was determined. Thesamples ofarsenic mixed with Cu²⁺，Mn²⁺, Pb²⁺，Hg²⁺，and Fe³⁺and several standardionic were explored at the same time. The results were affected in the presence of Hg²⁺and Cu²⁺which made quantum dots fluorescent quenching, but the existence of othercommon ions were of no significant impact to the determination. Also this method hasbeen applied to actual samples, however,the method needed to be further research andimprove.