當粒子擁有奈米級之粒徑時，其往往表現出異於塊材之嶄新材料特性。另外，擁有雙成份之金屬奈米粒子，由於具有第二元金屬之配位效應及奈米粒子內之原子分佈效應，使雙金屬奈米粒子展現更豐富之新奇特性，如觸媒特性、光學特性等。本論文主要以X光收光譜分析技術探討雙金屬奈米粒子之生成機構，主要包含四個系統：(1) 膠體還原法製備Pt-Ru雙金屬奈米粒子之生成機制；(2) 逆微胞微乳化系統之Ag-Pt雙金屬奈米粒子之生成機構；(3) 逆微胞微乳化系統之Pd-Pt雙金屬奈米粒子之生成機構; (4)逆微胞乳化系統之Pd-Au雙金屬奈米粒子之生成機構。此外，更進一步以X光吸收光譜適配出來之參數，探討其雙金屬粒子內原子之合金程度與原子分佈情形。此研究將有助於雙金屬奈米粒子之設計與合成，並可提供奈米粒子生產製備程序放大之參考。

在Pt-Ru雙金屬奈米粒子系統，主要是以X光吸收光譜，探討修飾後之Watanabe膠體還原法，在過程中之金屬離子配位環境與其氧化還原狀態之變化。由Pt LIII-edge之邊緣結構發現，當NaHSO3加入H2PtCl6溶液之後，其Pt化合物還原成二價之狀態，且與[Pt(SO3)4]6−化合物之型態相符合，當進一步將過氧化氫加入此溶液，Pt化合物呈現[Pt(OH)6]2−物種。另外、由Ru K-edge之邊緣結構發現，當NaHSO3加入RuIIICl3溶液，Ru化合物被還原成[RuII(OH)4]2−化合物，進一步加入過氧化氫，將使[RuII(OH)4]2−化合物轉化成RuOx物種。其後將[Pt(OH)6]2−物種與RuOx物種混合，並加熱至100℃持續8小時，發現所生成之膠體中包還有Pt與Ru等金屬及金屬氧化物之貢獻。最後，經氫氣還原之PtRu/C雙金屬奈米粒子呈現殼-核型態，而Pt則富於核層，而Ru則富於殼層，且Pt呈現聚集之現象，而Ru之分散性則較佳。

對於Ag-Pd雙金屬奈米粒子系統，其Ag-Pd雙金屬奈米粒子乃於AOT微乳化系統下製備，反應之程序主要分為兩個步驟，首先為Ag奈米粒子之製備，另一步驟則是藉著Ag奈米粒子與Pd2+離子反應生成雙金屬奈米粒子，並以臨場X光吸收光譜探測其生成過程。由Ag與Pd之K-edge邊緣結構分析結果發現，所生成之Ag-Pd雙金屬奈米粒子之結構中，其Ag原子之配位大多是Pd原子，而Pd原子之配位則大多是Pd原子。

對於Pd-Pt雙金屬奈米粒子系統，其主要是利用臨場X光吸收光譜技術研究在逆微胞乳化系統下之Pd-Pt雙金屬奈米粒子初始生成機制。分析結果發現，Pd與Pt離子之還原程序與其所生成之奈米粒子呈現與聯氨還原劑之劑量有一定之相依性。經由Pd K-edge與Pt之LIII-edge邊緣結構解析後，其結構呈現核點為Pd原子，但核層為Pd-Pt雙原子混合分佈，而殼層則是以出現聚集之Pt原子為主。依據X光吸收光譜建立Pd-Pt與Ag-Pd之生成機制探討結果，進一步在逆微胞乳化系統下合成三明治型態Pdnuclei–Aucore–Pdshell雙金屬奈米粒子，並以X光吸收光譜探測其生成機構。首先先成長Pd奈米粒子，而後再以自身氧化還原之置換程序將Au離子還原，結果發現，所生成之奈米粒子，其結構為Pd原子佔據著核點與殼層之部位，而Au原子則佔據著核層部位之三明治型態Pdnuclei–Aucore–Pdshell雙金屬奈米粒子。

上述之結果顯示，在金屬奈米粒子合成程序中，其金屬離子間或金屬離子與還原劑間或奈米金屬粒子與金屬離子間之反應，對合成之金屬奈米粒子之結構及原子分佈扮演極重要之角色。控制製程中之化學反應與奈米粒子間之交互作用參數，便可有效的設計出理想的奈米粒子結構。

Nanoparticles exhibit novel material properties which largely differ from the bulk properties due to their particle sizes at nano-level. Bimetallic nanoparticles can possess improved catalytic and optical properties due to the ensemble with ligand effects of second metal and also alloying extent or atomic distribution play a dominant role in deciding their catalytic activity. Consequently, it is notable that the understanding of formation mechanism of nanoparticles is essential for the successful nanoparticle design and scaling up process. In this context, the main four objectives of the present research work are to explore the X-ray absorption spectroscopy based methods to understand the formation mechanism of bimetallic nanoparticle systems. The first one is the formation mechanism of Pt–Ru bimetallic nanoparticles synthesized by colloidal reduction method. The second study describes the formation mechanism of Ag–Pd bimetallic nanoparticles in AOT reverse micelles. The third one is the formation mechanism of Pd-Pt bimetallic nanoparticles in AOT reverse micelles. And the final one is the formation mechanism of Pd-Au bimetallic nanoparticles in AOT reverse micelles. In all the systems studied the extent of alloying and atomic distribution of core atoms in bimetallic clusters are also discussed based on the calculated XAS structural parameters.

For system of Pt–Ru nanoparticles, Watanabe’s colloidal reduction method is slightly modified to improve homogeneity and atomic distribution in the Pt–Ru nanoparticles and the in situ XAS is utilized to monitor the evolution of Pt and Ru environments and their chemical states. The Pt LIII-edge XAS indicates that when H2PtCl6 is treated with NaHSO3, the platinum compound is found to be reduced to a Pt(II) form corresponding to the anionic complex [Pt(SO3)4]6−. Further oxidation of this anionic complex with hydrogen peroxide forms dispersed [Pt(OH)6]2− species. Analysis of Ru K-edge XAS results confirms the reduction of RuIIICl3 to [RuII(OH)4]2− species upon addition of NaHSO3. Addition of hydrogen peroxide to [RuII(OH)4]2− causes dehydrogenation and forms RuOx species. Mixing of [Pt(OH)6]2− and RuOx species and heat treatment at 100 0C for 8 hrs produced a colloidal sol containing both Pt and Ru metallic as well as ionic contributions. The structural model of the final Pt–Ru/C nanoparticles shows that the structure is similar to Pt-rich core and Ru-rich shell with a considerable amount of segregation in Pt region and with a less segregation in Ru region.

For the system of Ag–Pd bimetallic nanoparticles, a two-step sequential reduction method is employed for the synthesis of Ag–Pd bimetallic clusters within AOT reverse micelles and the formation mechanism probed by in situ XAS. The first step involves the preparation of Ag nanoparticles and the second one is the reaction between Ag nanoparticles and Pd2+ ions. Analysis of Ag and Pd K-edge XAS spectra reveal that in the final stage Ag–Pd clusters in which ‘Ag’ atoms prefer to be surrounded by ‘Pd’ and ‘Pd’ atoms prefer to be surrounded by ‘Pd’ were formed.

For the system of Pd–Pt nanoparticles, the formation mechanism of Pd–Pt bimetallic clusters at the early stage within water-in-oil microemulsion system of water/AOT/n-heptane is investigated by in situ XAS. The reduction of Pd and Pt ions and the formation of corresponding clusters are monitored as a function of dosage of reducing agent, hydrazine. Analysis of both the Pd K-edge and Pt LIII-edge reveal that the Pt atoms are partially segregated and rich in the shell region and the Pd–Pt alloy atoms are preferentially located in the core region and the Pd acts as nuclei to form the bimetallic Pd–Pt clusters in reverse micelles.

In situ X-ray absorption spectroscopy (XAS) investigations are also performed during the growth of Pdnuclei–Aucore–Pdshell sandwich-like bimetallic clusters at the early stage within water-in-oil microemulsion system of water/AOT/n-heptane. The Pdnuclei–Aucore–Pdshell clusters are designed based on knowledge obtained from formation mechanisms of both the Pd–Pt and Ag–Pd clusters as studied by XAS. The Pd nanocluster is grown first and then Au atoms are reduced by redox-transmetalation process. The formation of Pd clusters as nuclei and also in the shell region and Au atoms in the core region is monitored by successive addition of the reducing agent and Au precursor solution. Analysis of both the Pd K-edge and Au LIII-edge reveal that the structure of the Pd-Au bimetallic nanoparticle in reverse micelles is Pdnuclei–Aucore–Pdshell and only few of Au atoms are dispersed on the surface.

Compilation of the studies performed in the present investigation reveals that XAS is an important tool to probe the formation mechanism and chemical states of bimetallic nanoparticles and also with XAS one can study the interaction between nanopaticles and metal ions during the formation of bimetallic nanoparticles. Such studies are of great importance during the synthesis of metal-based nano-engineered clusters. XAS studies during the nanoparticle formation allows judicious control of the nanoparticles interaction parameters and can open up the possibility of a new approach to design and synthesis of structured-controlled bimetallic nanoparticles in the future.

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