標題: 團聯共聚高分子輔助合成新穎貴金屬奈米晶體及其有機分子光學感測之應用
Tri-block copolymer assisted synthesis of novel precious metal nanocrystals for optical sensing of organic molecules
作者: 楊景筌
Yang, Jing-Cyuan
Chen, Chun-Hua
關鍵字: 貴重金屬;團聯共聚高分子;合成;奈米晶體;表面拉曼增強光譜;Precious metal;Tri-block copolymer;Synthesis;Nanocrystals;SERS
公開日期: 2014
摘要: 合成各式尺寸、維度、形貌之新穎金屬奈米結構可謂是奈米科學的起點和基礎,故始終受到廣泛注目而成為熱門的研究領域之一。在相關的研究之中,表面高度分枝、完全中空球型、亦或是半中空金屬奈米結構,由於此些奈米結構均具有高體表比、高結構剛性與安定性、高化學活性、以及高表面穿透性等共同特徵,故展現出有別於結構單純奈米結構之物理與化學特性,可作為高性能觸媒、光子晶體、表面電漿共振或表面拉曼散射感測器之用,而逐漸受到重視,成為極具潛力之奈米結構分類。 本研究論文主要利用各式團聯共聚高分子之特性,水溶液中單步驟合成包括表面高度分枝、半中空球型、中空球型等三大類型之特殊貴金屬奈米結構,並將合成所得之貴金屬奈米結構,應用於各種有機分子之光學感測。 研究初階段主要是在常溫水溶液中利用三嵌段團聯共聚高分子F127(EO100PO70EO100)做為生長誘導劑,輔以维生素C(AsA)還原硝酸銀前趨物成長各種新穎形貌之奈米銀晶體。結果發現,在較低F127濃度可合成三維長程有序分枝之樹枝狀銀奈米晶體。進一步提高F127濃度則能進一步增加分枝的程度。當F127濃度達面心立方(FCC)排列之自組裝模板狀態,則形成三角及六角板狀銀晶體。如果维生素C還原後方加入F127,則可形成表面高度分枝之類石蓮花狀與珊瑚狀之銀奈米晶體。由此可知,除各合成反應物相對濃度直接影響形貌之外,F127之加入時機可間接調控還原之動力學。此外,相較於形貌單純之銀奈米粒子,合成所得之高度分枝銀奈米晶體對水溶液中孔雀綠草酸鹽(MGO)呈顯著之表面增強拉曼散射效應。 第二階段主要利用三嵌段團聯共聚高分子P123(EO20PO70EO20)作為軟模板及還原劑雙重角色,研發一簡便且低毒性之合成法高產率合成兩種具有均勻尺寸及形貌之鳥巢狀金奈米結構,和一種鳥巢狀之金-鉑核殼奈米結構。此外,導入適當之第二金屬源,例如鉑離子,結果證明能有效調控P123之還原位點,進而影響金離子有效成核數,從而導致形成不同晶粒大小與數目之鳥巢狀金奈米結構。相較於球型金奈米粒子,鳥巢狀金奈米結構呈現截然不同之表面電漿共振效應,紅位移達140 nm。此外對微量孔雀綠草酸鹽具顯著表面增強拉曼散射效應。 第三階段主要利用反三嵌段團聯共聚高分子25R4(PO19EO33PO19)作為模板,使用硼氫化鈉還原鉑前趨物,在特定條件下,成功合成球型鉑中空組裝結構,並對此結構之光學特性進行探討。結果發現,特定25R4濃度及低溫為成功合成之必要條件。此外,相較於傳統鉑奈米粒子之單一吸光峰位於不可見光區段(200−250 nm),球型鉑中空組裝結構之吸收峰位移至可見光區段(400−500 nm),並分解成為三個峰。此分峰現象經理論計算可証明是來自於球型鉑中空組裝結構之尺寸分佈。此外,球型鉑中空組裝結構亦具有良好之葡萄糖感測特性。
Synthesis of novel metallic nanostructures with various sizes, dimensions and morphologies is always the most important and interesting topic because it is the threshold to explore distinct physical and chemical phenomena and fundamentals of nanoscience. Among the relevant findings, fabrication of highly branched, full-hollow spherical or hemispherical metallic nanostructures having a high surface-area-to-volume ratio, structural rigidity and stability, chemical activity and surface permeability have attracted growing interest as an important class of nanomaterials that exhibit unusual chemical and physical phenomena for a variety of potential applications such as catalysts, photonic crystals, and localized surface plasmon resonance (LSPR) or surface-enhanced Raman scattering (SERS) sensors. In this thesis, we describe a completely new one-step copolymer-mediated strategy for respectively manufacturing of highly branched, hemispherical and full-hollow spherical metallic nanostructures for optical sensing of various organic molecules. First, silver crystals with various novel nano-scale branched morphologies were synthesized from the reduction of AgNO3 by ascorbic acid (AsA) in aqueous solution with the absence of tri-block copolymer F127 (EO100PO70EO100) which acts as a growth directing agent. At a lower concentration of F127 and in the presence of AsA, we synthesized three-dimensional dendritic Ag crystals with very long and ordered branches. In contrast, the higher AgNO3 concentrations elicited the growth of higher-order dendrites. When the F127 concentration was highly increased up to FCC packing, special hexagonal and triangular Ag prisms were obtained. In addition to these Ag crystals formed in the pre-mixed F127 and AsA, two types of short-branched Ag quasi-spheres, houseleek-like and coral-like structures, were also produced due to the domination of the AsA that was added before the F127. The great variety in morphology is directly correlated with not only the concentration ratio between these reactants but the F127 induced kinetic mechanisms. Moreover, the greatly branched Ag nanocrystals exhibit significant surface-enhanced Raman scattering (SERS) for facilely, rapidly and effectively determining malachite green oxalate (MGO) in aqueous solution. In the second stage, In the second section of this dissertation, a selection of tri-copolymer P123 (EO20PO70EO20) which are easily to formation grape-like copolymer clusters are used as a soft-template. A facile low-toxicity synthesis of two different types of Au nanonests and one binary Au-Pt core-shell nanonest with high yield and excellent uniformity in size and morphology using tri-block copolymer P123 (EO20PO70EO20) as a soft template and the main reductant in an ice/water bath. The introduction of suitable second metallic source, i.e. Pt ions in the present case, was proven as a unique strategy for effectively govern the reduction sites of P123 for Au nucleating and thus lead significant changes especially in the crystalline size of the grown Au nanonests. The Au nanonests exhibited a distinct morphology-dependent surface plasmon resonance (SPR) that is red-shifted by ~140 nm from the spherical particles wavelength, and significant SERS, allowing rapid determination of rare MGO. In the third stage, platinum hollow spherical assemblies have been successfully synthesized in aqueous solutions of H2PtCl6, NaBH4 and the tri-block copolymer 25R4 (PO19EO33PO19) which acts as the soft template at 5 °C. It was found that an optimal concentration of 25R4 and the low temperature are required for the successful synthesis of hollow platinum assemblies. In addition, the absorption band of the obtained platinum hollow spherical assemblies shifts from single invisible band (200–250 nm) generally reported for conventional platinum nanoparticles to the visible band (400–500 nm) and splits into three sharper bands, which could be well understood with the size distributions and the relevant theoretical calculation. The glucose-sensing properties of the platinum hollow spherical assemblies in an aqueous solution are also demonstrated.