具實心或空心二氧化矽球之一維硒奈米串珠核殼結構之合成及奈米金粒於其界面之選擇性鍍層

The Synthesis of SeNW-SiO2 String-of-Beads Core-Shell Nanostructure with Solid or Hollow Beads and the Nanogold Selective Deposition

張秀美(Hsiu-Mei Chang)

指導教授 ： 王崇人

國立中正大學/理學院/化學暨生物化學系/碩士(2015年)

摘要

本實驗室曾報導一維硒區段式差異結晶（symmetry-breaking segmented；SBS）之特殊奈米結構(tq-t-tq)-SeNR or -SeNW之合成，同時將其作為化學模板，透過多種選擇性化學反應可進而合成多種奈米結構，例如含硒奈米棒（SeNR）粒子之SeNR-SiO2奈米魚標狀核殼結構（nanofloats）以及含硒奈米線（SeNW）粒子之SeNW-SiO2奈米串珠核殼結構（nano-string-of-beads; nanoSOBs），其中硒奈米線上具有間隔的二氧化矽球，同時此二氧化矽球可操控得空心或實心兩種。鍍層二氧化矽球是經由前驅物(3-mercaptopropyl) trimethoxy-silane（MPTMS）之溶膠凝膠法而得，然而過去使用庫存已久的MPTMS，嚴重影響合成的再現性。故本計畫旨在使用新鮮的前驅物試藥，重新仔細地探討實心及空心SeNW-SiO2奈米串珠核殼結構之生成機制相關課題，及展示後續奈米金粒選擇性生長於t-Se界面的現象。
實驗結果顯示，前驅物MPTMS之乙醇溶液須加入微量之氫氧化鈉水溶液進行前處理，以提供初期微量之水解縮合。再者，SeNW-SiO2奈米串珠核殼結構中的二氧化矽球的生成是基於硫醇在tq-Se具有選擇性鈍化（selective passivation）衍生而得，至於此二氧化矽球的實心或空心結構操控，我們證實在溶膠凝膠過程中有兩個關鍵性的參數：溶液pH值及反應時間。例如溶液pH值調控在9.2，反應1小時可得空心串珠結構，反應時間增為2小時則可得實心串珠結構。若pH值較低（約9.1）則僅可得空心結構；反之，較高pH值（約9.4）則僅可得實心結構。我們同時亦改良過去形成空心串珠的最後合成步驟，利用甲醇而非乙醇作為移除劑，移除球內僅部分縮合的MPTMS而得。由電顯結果顯示，空心奈米串珠核殼結構產率約80%，而實心奈米串珠核殼結構產率則達約90%。至於空心二氧化矽球的殼層厚度，可藉由調控反應時間而操控介於28 nm至57 nm之間。最後，我們藉由兩個實驗證據：二氧化矽球生成初期的尺寸大小分析以及去除SeNW保護劑（carboxymethyl-cellulose; CMC）之對照組實驗，說明二氧化矽球的生成與CMC並無直接關聯。
第二部分關於奈米金粒選擇性生長於奈米串珠核殼結構t-Se的界面現象，我們再一次地確認四氯金酸乙醇溶液會選擇性地鍍在t-Se與SiO2殼層之間，t-Se上之奈米金粒子明顯多於tq-Se區段的界面，同時粒子平均直徑約7 nm。這結果很明顯地歸因於tq-Se的界面已被MPTMS之硫醇因化學吸附造成鈍化所致。

關鍵字

一維奈米硒

並列摘要

We have previously reported the synthesis of symmetry-breaking segmented selenium nanorods (SeNRs), namely, SBS-SeNRs, show discrete trigonal and quasi-trigonal phases in the form of repeating quasi- trigonaltrigonalquasi-trigonal, (tq-t-tq)n, where tq stands for the quasi-trigonal phase in the space group of P321 and t is the trigonal phase in the space group of P3121. Both SeNR and SeNW served as the chemical templates with distinct chemical reactivities towards compounds containing thiol group. Several unique nanostructures can be thus synthesized, such as SeNR-SiO2 nanofloats and SeNW-SiO2 string-of-beads core-shell nanostructures (nanoSOBs). The SiO2 shell material was prepared by the well-known sol-gel process via a precursor of (3-mercaptopropyl) trimethoxy-silane (MPTMS), and the SiO2 spheres of the nanoSOBs can be controlled in either solid or hollow form. However, the MPTMS used previously was an aged compound in stock for a long time. It turned out to be affecting seriously the synthetic reproducibility. Therefore, my project was set to aim at the use of the fresh MPTMS reagent for carefully investigating the formation mechanism of such SeNW-SiO2 nanoSOBs. Meanwhile, we attempted to confirm the selective deposition of nanogold particles at the SeNW-SiO2 interfacial region of the t-Se segments.
To successfully synthesize the nanoSOBs, it turned out that the fresh MPTMS needed a pretreatment by adding 7 L 0.1 M NaOH(aq) into 1 mL MPTMS ethanol solution (MPTMS : EtOH = 1 : 100) for 1.5 hrs with vigorous stir. Due to the selective passivation of the thiol group of the MPTMS at the tq-Se surface, we demonstrated the synthesis was successful for the SeNW-SiO2 nanoSOBs with SiO2 spheres residing at the t-Se segments. There are two crucial parameters in the formation of SiO2 spheres: The solution pH value and the reaction time. The interplay between these two parameters determines the final structure of SiO2 spheres, either solid or hollow. For examples, at the pH value of 9.2 we obtained the hollow nanoSOBs for 1 hr reaction and the solid nanoSOBs were obtained for 2 hrs reaction time. However, only the hollow nanoSOBs can be produced at lower pH value, such as ca. 9.1. Also, we prepared only solid nanoSOBs if the solution pH value was higher, such as ca. 9.4. Meanwhile, we improved the last step for preparing the hollow nanoSOBs, the ethanol wash, to be more efficient in terms of the product yield. The result showed that the methanol is much more efficient than ethanol to remove the MPTMS and/or its oligomers. The results indicated that the yield of the hollow nanoSOBs was ca. 80%, while the yield of the solid nanoSOBs remains ca. 90% after the same wash. In addition, the shell thickness of the hollow silica spheres can be controlled in the range from ca. 28 nm to 57 nm by varying the reaction time. We also proved that the original stabilizing agent, carboxymethyl-cellulose (CMC) of SeNW plays no role to the formation of the SiO2 spheres in the nanoSOBs. It was evidenced from the results of two separate experiments: first, the time evolution of the mean sizes of the SiO2 spheres and second, the shell coating after removing the majority of CMC.
The goal of the second part of this thesis is to confirm the selective deposition of nanogold particles at the SeNW-SiO2 interfacial region of the t-Se segments. The results nicely indicated that the Au3+ of the tetrachloroauric acid in ethanol solution deposited selectively at the t-Se segments. Relatively much more nanogold particles ca. 7 nm in averaged diameters depositing at the SeNW-SiO2 interfacial region of the t-Se segments than that of the tq-Se segments. This selective reaction again confirmed the passivation by the thiol group of the MPTMS was done on the tq-Se segment surface by chemisorption.

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