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Title:Syntheses and transformations of multimetallic nanoparticles
Author(s):Hofmann, Daniel M
Director of Research:Murphy, Catherine J
Doctoral Committee Chair(s):Murphy, Catherine J
Doctoral Committee Member(s):Gewirth, Andrew A; Lu, Yi; Yang, Hong
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
bimetallic nanoparticle
trimetallic nanoparticle
Abstract:Multimetallic nanoparticles have had increased interest in recent years. In this thesis, we analyze Au, Ag, and Cu nanoparticles and multimetallic nanoparticles containing these three coinage metals. The incorporation of two or more metals together within nanoparticles allows for synergistic enhancements in their properties. Specifically, these nanoparticles containing at least two of the metals Au, Ag, or Cu have been studied for their potential in applications including: imaging, catalysis, sensing, and biomedical uses. With further investigation of these applications, transformations of these nanomaterials can have impact on their overall performance. Cu and Ag nanoparticles specifically are prone to oxidation and dissolution. Multimetallic nanoparticles have the potential to replace their monometallic counterparts but further investigation needs to be completed to see how they are affected by these transformations. Au, Ag and Cu multimetallic nanoparticles have been analyzed for oxidation but dissolution studies have not been completed. In Chapter 1, multimetallic nanoparticles and their properties are introduced. A brief history on the transition of metallurgy from the Bronze Age to the use of multiple metals in nanoparticles is described. The properties of monometallic nanoparticles and the synergistic enhancement that multimetallic nanoparticles display compared to them is outlined. We detail the structures and synthetic strategies for multimetallic nanoparticles. Finally, oxidation and dissolution of Cu nanoparticles are described and the potential for multimetallic nanoparticles to counteract dissolution is hypothesized. Before nanoparticles could be investigated for their transformation, a reproducible, tunable synthesis for monodisperse, multimetallic nanoparticles must be investigated. In Chapter 2, we develop a novel two-phase synthesis for AuCu and AuAg nanoparticles that is inspired by the Brust synthesis for monodisperse Au nanoparticles. The synthesis takes advantage of complex ions to incorporate greater proportions of Cu into the nanoparticles. Nanoparticles were found to be monodisperse in size and shape. The compositions of the nanoparticles were tunable from 100% Au to 100% Cu. The reproducible synthesis for monodisperse, ultrasmall AuCu nanoparticles allowed for the nanoparticles to be analyzed for their transformations without the results being due to polydisperse sizes, shapes, or compositions. The transformations of AuCu nanoparticles including oxidation and dissolution are analyzed in Chapter 3. Oxidation of the Cu within the particles was studied using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and energy electron-loss spectroscopy (EELS). Results found that the particles initially do not display obvious oxidation but some Cu+ may be present in the nanoparticles with higher percentages of Cu. Overtime the particles were found to display more Cu2+ character which can indicate CuO formation. The 1:1 (Au:Cu) composition exhibited increased levels of CuO within the particles compared to the other AuCu compositions and the Cu nanoparticles. The dissolution of the nanoparticles was investigated naturally within purified water and when initiated using cyanide. The dissolution of AuCu in natural waters found that the 1:3 composition displayed the highest levels of Cu ions when compared with the other compositions. The forced dissolution of the particles using cyanide found that Cu nanoparticles had the highest rate of dissolution and Au nanoparticles had the lowest rate. As Cu was added to the Au nanoparticles, the rate of dissolution initially increased but the rate decreased as more Cu was incorporated into the nanoparticles with the 1:3 (Au:Cu) composition having the lowest rate of dissolution. This information details that bimetallic AuCu nanoparticles can lower dissolution of Cu by using specific composition for the suited applications. Development of synthetic methodology was also applied to anisotropic multimetallic nanoparticles. In Chapter 4, we detail a novel synthesis for AuAgCu “miniature” nanorods. This synthesis was inspired by previous research in the Murphy group for Au “miniature” nanorods. The trimetallic “miniature” nanorods were found to have widths of less than 10 nm and aspect ratios that were tuned by the amount of Cu added to the growth solution. Elemental mapping revealed that Au, Ag, and Cu were found throughout the nanorods to indicate the particles were disordered alloys. Finally, the oxidation state of Ag and Cu were analyzed within the particles using XPS. Results found that there may be evidence of Cu+ and Ag+ within the particles synthesized with the highest amount of Cu in the growth solution.
Issue Date:2020-04-23
Rights Information:Copyright 2020 Daniel M. Hofmann
Date Available in IDEALS:2020-08-26
Date Deposited:2020-05

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