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Synthesis and Surface Modification of Water-soluble ZnS: Mn Nanocrystals

Author: SunZuo
Tutor: YangWenSheng
School: Jilin University
Course: Physical and chemical
Keywords: Nanocrystalline ZnS Surface modification Silica
CLC: O614
Type: Master's thesis
Year: 2005
Downloads: 370
Quote: 3
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Abstract


Nanotechnology is the creation and utilization of materials, devices, and systems through the control of matter on the nanometer-length scale. Nanoparticles are one of the most important part of nanomaterials. They show size tunable properties due to quantum confine effects and surface effects. These new properties will lead to new, high-performance products and technologies that were not possible before. Since the size of most important biomolecules, such as protein of DNA etc., are similar to the nanoparticles, the using of nanoparticles as biotechnological tool are particularly attractive. one of such application is using fluorescent semiconductor as labels for biological tagging experiments. Biological tagging is one of the most widely employed techniques for diagnostics and visualization. It appears as though for many applications, the colloidal nanocrystals are advantageous as labels, when compared to existing organic dyes. This has led to rapid commercialization of the new nanotechnology. For this reason, the development of a successful synthetic scheme of high quality nanocrystals is very important. My dissertation works aim to develop a versatile synthetic method of doped nanocrystals with high fluorescent properties. In chapter 2, water soluble ZnS:Mn nanocrystals with MPA (3-mercaptopropionic acid) as stabilizer were synthesized. The MPA molecules coordinate with Zn ion on the nanocrystals surface and form negative charge layer which stabilized the nanocrystals in water. TEM, XRD, and absorption spectroscopy are employed to study the structure and optical properties of the obtained ZnS:Mn nanocrystals. The coordination of Zn ion with MPA helps efficient doping of Mn and thus makes the process reproducible as compared to the common co-precipitation method. To obtain a high luminescent intensity, post-preparative treatments are performed. It is found that the surface states of the nanocrystals play important roles in the enhancement of the luminescent intensity. Through surface absorption of oxygen or S2-ion, the 590 nm luminescence of doped Mn can be enhanced while the 420 nm ZnS-related luminescence is quenched. The ZnS:Mn nanocrystals show a pH-sensitive luminescence. Since the changing of pH will affect the coordination between MPA and the Zn ion on the nanocrystals surface. In chapter 3, we presented inorganic molecule of surface modification method on the ZnS:Mn nanocrystals. A two-step silica coating process was used to synthesize “raisin-bun”type composite silica/ZnS:Mn nanocrystals. The ZnS:Mn nanocrystals were first capped with 3-mercaptopropyltrethoxysilane though a ligand exchanging reaction, then were coated with a thin layer of silica in sodium silicate solution. Silica spheres doped with ZnS:Mn nanocrystals were prepared by the modified St?ber synthesis in ethanol-water mixed solution. The chemical and photochemical stability of the silica coated ZnS:Mn nanocrystals are highly enhanced comparing to the bared ZnS:Mn nanocrystals. These characters make the water-soluble core-shell nanocrystals a kind of promising materials for biosensing and biolabeling.

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CLC: > Mathematical sciences and chemical > Chemistry > Inorganic Chemistry > Metal elements and their compounds
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