The Synthesis of One-dimensional Se-silica Bead-like Nanostructures with Solid or Hollow Silica Nanospheres
| Autor: | Liu, Yu-Tzu, 劉語慈 |
|---|---|
| Rok vydání: | 2014 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 102 The synthesis of one-dimensional selenium nanoparticles with unique segmented monoclinic (m) and trigonal (t) cystal phases has been demonstrated previouly. Such segmented crystal phase nanostructure was evidenced while the selenium surface was coated by silica via sol-gel process. The products own a unique nanofloat structure with typically one solid or hollow silica nanosphere located at the middle of individual selenium nanorod. To extend the above findings, we report herein two series of studies : First, the synthesis of dispersed one-dimensional Se-silica bead-like nanostructures (1D-Se@segmented-SiO2 spheres; 1D-Se@s-SS) in more detail, particularly for the cases containing Se nanowires. Meanwhile, we demonstrated the evolution of such bead-like nanostructure from Se nanorods to nanowires in terms of both the number of beads and their mean spacing. Secondly, a series of studies were conducted in order to describing the detailed formation mechanism for the bead-like 1D-Se@s-SS nanostructures with solid or hollow silica nanospheres. In addition, we demonstrated the results of our preliminary studies regarding their selective reactivity towards the selenium removal reactions. In the first part, one-dimensional selenium nanoparticles with the average lengths ranging from 500 nm to 4000 nm were used as the starting material and the bead-like 1D-Se@s-SS nanostructures with good dispersivities were synthesized using sol-gel method. The results indicated that the number of beads increases accordingly to the increase of the length for the 1D nano-Se. Also, the averaged diameters of the silica nanospheres are of 197 ± 24 nm and the averaged spacings between two adjacent silica nanospheres are of 647 ± 276 nm. They provided a more clear picture regarding the segmented cystal-phase of the 1D nsnoSe, (tSe-mSe-tSe)n. In the second part, we demonstrated the formation of the bead-like 1D-Se@s-SS nanostructures with solid or hollow silica nanospheres can be achieved by the use of the starting material (mercaptopropyl trimethoxysilan, MPTMS) for the sol-gel process with a carefully controlled extent of its hydrolysis/condensation prior to the silica coating. It was sensitive to the humidity and pH value, the aging of the starting chemicals, and the trace amount of water/NaOH added. The bead-like 1D-Se@s-SS nanostructures with hollow silica nanospheres can be synthesized by using relatively fresh MPTMS, or less extent of the hydrolysis/condensation, and a subsequent wash by ethanol. Meanwhile, the thickness of the silica shells can be controlled from the sol-gel process to obtain in a range from 13 to 45 nm and the inner diameters are roughly constant in size of ca. 93 nm. This constant averaged inner diameter was attributed to the existence of the condensation of the nanoparticle stabilizing agent (carboxymethylcellulose, CMC) at the m-Se sites. Finally, we demonstrated the results of our preliminary studies of the selective reactivity in the chosen system of the bead-like 1D-Se@s-SS nanostructures with solid silica nanospheres. The reactants were prepared containing different thickness at the surface of t-Se. The Se etching reaction, resulting in the Se removal, was chosen in this demonstration. Our results indicated that the removal of Se occurred at the m-Se while the thickness was less than 5 nm, and at the sites of t-Se while the thickness was greater than 15 nm. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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