Synthesis Of Water-soluble Quantum Dots And Their Application In The Detection Of Cr(Ⅵ)、 Hg(Ⅱ)、Cd(Ⅱ)

Quantum Dots (QDs) have attracted much interest among resesrchers due to their high quantum yield, narrow and tunable emission spectrum and good photostability. With the development of their synthetic methods, surface processability and functional applications, QDs were widely used in chemical and biological analysis. In this thesis, we develop novel methods to synthesize high quality water-soluble QDs, and investigated the applications of the as-synthesized QDs as fluorescent probes in heavy metal ions determination. The main contents are shown as follows:1. We have developed a novel, simple and economical method to synthesize water-soluble CdTe quantum dots (QDs) using hydroxylamine hydrochloride as reduction and L-cysteine (CYS) as the ligand. The maximum photoluminescence quantum yield of the QDs can achieve to47%. What’s more, high quality CdTe nanocrystals could also be obtained using thioglycolic acid as the ligand in this system. By this method, it can obtain high-quality CdTe QDs quickly, there is no need N2protection, buffer solution, special ligands, a large quantity of N2H4or particular treatment (such as microwave, or ultrasonication). The CYS-capped CdTe QDs showed size-dependent sensitivity to metal ions owing to quantum size effect of QDs. The CYS-capped CdTe QDs with the diameter of3.37nm show high selective and sensitive to Cr(VI). So, these QDs were used as fluorescence probe for Cr(VI). Under the optimal conditions, the detection of the Cr(Ⅵ) shows high selectivity and sensitivity. The relative fluorescence intensity decreases linearly proportional to the Cr(Ⅵ) concentration over the range of0.010μmol L-1to4.0μmol L-1with a limit of detection of0.005μmol L-1. The possible mechanism was discussed.2. Through ammonia promoted kinetic growth strategy, thioglycolic acid coated CdTe quantum dots (TGA-CdTe QDs) were successfully synthesized in aqueous phase with a low temperature. Then the TGA-CdTe QDs were characterized by photoluminescence spectra, transmission electron microcopy etcetera. The determination of mercury ions in aqueous solution was investigated using TGA-CdTe QDs as fluorescent probes. The influence factors on the detection system were examined and the optimum conditions were determined. The mercury ions were accurately detected using CdTe QDs as fluorescent probe and they can also be detected visual analysis. The relative fluorescence intensity of CdTe QDs was linearly proportional to the concentration of mercury in the range from0.010μmol L-1to5.0μmol L-1, the correlation coefficient is0.9988, the detection limit was of lnmol L-1. The probe was applied to determine the Hg2+in the practical samples, and the results demonstrate good practicability.3. A facile green synthesis of soluble copper quantum dots is developed, based on reduction of the metal precursor with sodium sulfite in the present of thioglycolic acid ligands. The influences of raw material molar ratio, the amount of reduce, reaction temperature etcetera on the formation of the copper quantum dots were investigated. The optical emission of prepared copper quantum dots was centred at415nm, with a luminescence quantum yield in water of8.1%. The luminescence properties of copper quantum dots keep unchanged in two months at pH2～12. The copper quantum dots can also be used as a fluorescent probes to detect cadmium ion in aqueous solution successfully, the results demonstrate high sensitivity and high selectivity. The relative fluorescence intensity of copper QDs was linearly proportional to the concentration of cadmium in the range from5×10-9mol L-1to5×10-5mol L-1, the correlation coefficient is0.9973, the detection limit was of1×10-9mol L-1.