Tri-block copolymer assisted synthesis of novel precious metal nanocrystals for optical sensing of organic molecules
|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|
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.