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Mn-doped ZnS Quantum Dots for Detection of Ions in the Environment

Author: ZhangBaoHua
Tutor: WuFangYing
School: Nanchang University
Course: Applied Chemistry
Keywords: Manganese ion doped zinc sulfide nanocrystals Surface modification Quantum dots Sulfur ions Cadmium Copper ions Silver ions Fluorescent sensing Semiconductor nanocrystals
CLC: X830
Type: Master's thesis
Year: 2010
Downloads: 210
Quote: 1
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Abstract

Molecular recognition is one of the core content of the supramolecular chemistry research, which includes the recognition of neutral molecules, cations and anions. Inorganic ions play an important role in biocatalysis, life sciences, electronics and signal transfer, environmental protection, the establishment of a high sensitivity and high selectivity, easy operation and low cost new method of identifying ion is necessary. Quantum dots as a novel fluorescent probe flurry function of its surface, which can effectively improve the sensitivity and selectivity of identifying objects ions, different ion fluorescence sensor. Related fields of study has attracted extensive attention from scientists. This thesis is divided into five parts, introduced quantum dots as fluorescent probes for the development of recognition molecules, all kinds of photochemical molecular sensing system and mechanism, elaborated on the various types of ion sensing that the proposed new system . The first chapter briefly introduces the concept and composition of the quantum dot system, the advantages of optical properties and light, the development process of the preparation methods, special features, modification and chemical sensors, at home and abroad in recent years related research brief review . The second chapter stabilizer thioglycolic acid, synthesized Mn-doped ZnS semiconductor nanocrystals (ZnS: Mn2) at room temperature and atmospheric pressure, the use of infrared spectroscopy, X-ray diffraction spectra (XRD), fluorescence spectroscopy, UV-visible absorption spectroscopy and particle size distribution curve by means of nano-crystalline structure characterization. The results show that: the nano crystal present sphalerite structure, small particle size and uniform surface modification thioglycolic acid molecules having a good solubility in water. At room temperature, the presence of sulfide ions (S2-) nano-sol system fluorescence quenching phenomenon, and other anions, such as: NO3-, CH3COO-, CO32-, Br-, F-, NO2-, SO42- , S2O32-, I-, SO32-in a certain concentration range, does not interfere with the the S2-determination, pursuant to which the establishment of the new system of aqueous phase identification S2-. Experimental results show that: the nano-sol changes in luminescence intensity at 590 nm with the S2-concentration (in the range of 2.5-37.5μmol · L-1) showed a good linear relationship, the method detection limit of 1.5 × 10-7 mol · L - for the wastewater with S2-determination, the recovery rate of 103%. Chapter III using a similar method with the second chapter, thioglycolic acid as a surface modifier prepared without the aging of the Mn-doped ZnS quantum dots (ZnS: Mn2) applied to the metal cadmium (Cd2 +) identification. PH 7.7 Tris-HCl buffer medium Cd2 join can effectively enhance the system of light-emitting fluorescence intensity of the incremental Cd2 concentration showed a good linear relationship, the linear range of 5.0 × 10-7-8.9 × 10-5mol · L-1, the method detection limit of 3.08 × 10-8 mol · L-1. The methods used for the detection of Cd2 lake, recovery was 93.7-97.4%. While using fluorescence spectroscopy, UV-visible absorption spectroscopy and XRD spectra of ZnS: Mn2 structural characteristics of quantum dots and luminescent properties, and the possible mechanism was discussed. Chapter IV using sodium borohydride and the bovine serum albumin (BSA), disulfide bond reduction, will be modified on the surface of the ZnS: Mn2 quantum dots, in order to improve the luminous efficiency and stability of the quantum dots. Optimized experimental conditions, Cu2 strong quenching effect on the fluorescence of ZnS: Mn2-BSA system has accordingly established a new method for determination of Cu2 linear range of 2.0 × 10-6-7.8 × 10-5 mol · L-1 linear correction equation F0 / F = 1.01 0.06 CCu2 the method detection limit of 2.87 × 10-7 mol L-1, applied to the Determination of Cu2 tap water, the recovery rate was 98.8%. Chapter carbon disulfide (CS2) iminodiacetic acid Zero modification in of ZnS: Mn2 / ZnS core-shell structure of semiconductor nanocrystals on the surface, the modification is not only to solve the water-soluble nanocrystals and nanocrystalline at 590 nm Department orange yellow luminescence enhancement and improved stability. UV-visible absorption spectroscopy, fluorescence spectroscopy, Inductively Coupled Plasma - Atomic Emission Spectrometry (ICP-AES), particle size distribution curve and nuclear magnetic resonance spectroscopy as a means of structural characterization of nanocrystalline synthesis. Optimized experimental conditions, we found that Ag can be very sensitive so obvious quenching of fluorescence and other ions no significant interference showed good selectivity. UV-visible absorption spectroscopy showed that: Ag and nano-crystalline surface with the form of a stable complex, in the light-induced electron transfer occurs, leading to the quenching of fluorescence signal.

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