Shape and Size Control of Bimetallic PtX (X = Au, Ni, Sn) Nanoparticles

<p>Nanoparticles show interesting and novel properties compared to their bulk materials. These properties range from optical, magnetic, electronic to catalytic and can be influenced by shape, size and elemental composition. As the ability to control nanoparticle morphology is important in materials science these particles are actively researched. Moreover, by combining different metals multiple properties intrinsic to those elements can be accessed within a single system. This thesis describes general synthetic approaches and underlying theory in the formation of nanoparticles. Focusing on organic solution phase synthesis, pathways to control both size and shape of nanoparticles are discussed. The concept behind the formation and possible structures of bimetallic nanoparticles are explained. Additionally, a brief overview about used characterisation techniques such as transmission electron microscopy and x-ray diffraction are given. Metallic nanoparticles were formed using the organic solution phase synthesis within Fischer-Porter bottles. Elevated temperatures and the presence of hydrogen lead to thermal decomposition of the metallic precursor, reduction of formed metal ions and subsequent build-up of nanoparticles. For bimetallic nanoparticles the seed mediated growth technique is commonly used. By utilizing this technique bimetallic AuPt nanoparticles were formed. The impact of different surfactants, hydrogen pressure, precursors and reaction time upon the size, elemental composition and morphology of these bimetallic AuPt nanoparticles is investigated. The bimetallic structure is evaluated and experiments to control the growth of platinum onto the seed structures are conducted. Further research deals with the formation of hexagonal close packed (hcp) nickel nanoparticles. By altering the surfactant type and concentration nickel favours to crystallise in its hcp modification rather than its most common face-centred cubic (fcc) phase. It was found that nickel packing in this hcp crystal system is forming hourglass-shaped nanoparticles. These particles are further used in seed mediated growth experiments with a platinum precursor to achieve bimetallic nanoparticles to both exploit the catalytic activity of platinum as well as the magnetic moment of nickel. It is shown that the choice of reaction conditions is crucial to achieve growth onto the nickel surface. Moreover, it was found that these nanoparticles are only selectively coated by platinum on hcp {001} facets leading to exposure of both nickel and platinum surfaces. The key results are summarised and the exploited parameters evaluated. Also, perspectives for future research are discussed and a brief outlook for the application of the investigated bimetallic systems is given. Bimetallic tin-platinum nanoparticles were formed by coreduction of the respective tin and platinum containing metal precursors. Several metal sources for both tin and platinum were investigated upon their decomposition and the resulting nanoparticle shape and elemental composition. The formation of a bimetallic precursor containing a Pt-Sn bond is discussed. Further reaction parameters such as temperature and time are also investigated to eludicate their impact on the formed nanoparticles. Finally, the key results are summarised and the exploited parameters evaluated. Also, perspectives for future research are discussed and a brief outlook for the application of the investigated bimetallic systems is given. The discussion in Chapter 4 about selectively obtaining hcp Ni nanoparticles is shortened and a major focus is given on the platinum coating of these hourglass-shaped nanoparticles, as Lee et al. published a paper on "Shaped Ni nanoparticles with an unconventional hcp crystalline structure" (Chemical Communications, 2014, 50, 6353-6356) during the course of these studies, describing similar methods and findings as observed in this research.</p>

Shape and Size Control of Bimetallic PtX (X = Au, Ni, Sn) Nanoparticles

<p>Nanoparticles show interesting and novel properties compared to their bulk materials. These properties range from optical, magnetic, electronic to catalytic and can be influenced by shape, size and elemental composition. As the ability to control nanoparticle morphology is important in materials science these particles are actively researched. Moreover, by combining different metals multiple properties intrinsic to those elements can be accessed within a single system. This thesis describes general synthetic approaches and underlying theory in the formation of nanoparticles. Focusing on organic solution phase synthesis, pathways to control both size and shape of nanoparticles are discussed. The concept behind the formation and possible structures of bimetallic nanoparticles are explained. Additionally, a brief overview about used characterisation techniques such as transmission electron microscopy and x-ray diffraction are given. Metallic nanoparticles were formed using the organic solution phase synthesis within Fischer-Porter bottles. Elevated temperatures and the presence of hydrogen lead to thermal decomposition of the metallic precursor, reduction of formed metal ions and subsequent build-up of nanoparticles. For bimetallic nanoparticles the seed mediated growth technique is commonly used. By utilizing this technique bimetallic AuPt nanoparticles were formed. The impact of different surfactants, hydrogen pressure, precursors and reaction time upon the size, elemental composition and morphology of these bimetallic AuPt nanoparticles is investigated. The bimetallic structure is evaluated and experiments to control the growth of platinum onto the seed structures are conducted. Further research deals with the formation of hexagonal close packed (hcp) nickel nanoparticles. By altering the surfactant type and concentration nickel favours to crystallise in its hcp modification rather than its most common face-centred cubic (fcc) phase. It was found that nickel packing in this hcp crystal system is forming hourglass-shaped nanoparticles. These particles are further used in seed mediated growth experiments with a platinum precursor to achieve bimetallic nanoparticles to both exploit the catalytic activity of platinum as well as the magnetic moment of nickel. It is shown that the choice of reaction conditions is crucial to achieve growth onto the nickel surface. Moreover, it was found that these nanoparticles are only selectively coated by platinum on hcp {001} facets leading to exposure of both nickel and platinum surfaces. The key results are summarised and the exploited parameters evaluated. Also, perspectives for future research are discussed and a brief outlook for the application of the investigated bimetallic systems is given. Bimetallic tin-platinum nanoparticles were formed by coreduction of the respective tin and platinum containing metal precursors. Several metal sources for both tin and platinum were investigated upon their decomposition and the resulting nanoparticle shape and elemental composition. The formation of a bimetallic precursor containing a Pt-Sn bond is discussed. Further reaction parameters such as temperature and time are also investigated to eludicate their impact on the formed nanoparticles. Finally, the key results are summarised and the exploited parameters evaluated. Also, perspectives for future research are discussed and a brief outlook for the application of the investigated bimetallic systems is given. The discussion in Chapter 4 about selectively obtaining hcp Ni nanoparticles is shortened and a major focus is given on the platinum coating of these hourglass-shaped nanoparticles, as Lee et al. published a paper on "Shaped Ni nanoparticles with an unconventional hcp crystalline structure" (Chemical Communications, 2014, 50, 6353-6356) during the course of these studies, describing similar methods and findings as observed in this research.</p>

Methionine controlled impediment of secondary nucleation leading to nonclassical growth within self-assembled de novo gold nanoparticles

The conventional key steps for seed mediated growth of noble metal nanostructures involve classical and nonclassical nucleation. Furthermore, the surface of the seed catalytically enhances the secondary nucleation involving Au+ to Au0reduction, thus providing in-plane growth of seed. In contrast to this well-established growth mechanism, herein we report the unique case of methionine (Met) controlled seed mediated growth reaction, which rather proceeds via impeding secondary nucleation in presence of citrate stabilized gold nanoparticle (AuNP). The interaction between the freshly generated Au+ and thioether group of Met in the medium restricts the secondary nucleation process of further seed catalyzed Au+ reduction to Au0. This incomplete conversion of Au+, as confirmed by X-ray photoelectron spectroscopy (XPS), results in a significant enhancement of the zeta (z) potential even at low Met concentration. Nucleation of in situgenerated small-sized particles (nAuNPs) takes place on the parent seed surface followed by their segregation from the seed. Self-assembly process of these nAuNPs arises from the aurophilic interaction among the Au+. Furthermore, the time dependent growth of smaller particles to larger sized particles through assembly and merging within the same self-assembly validates the non-classical growth. This strategy has been successfully extended towards the seed mediated growth reaction of AuNP in presence of three bio-inspired decameric peptides having varying number of Met residues. The study confirms the nucleation strategy even in presence of single Met residue in the peptide and also the self-assembly of nucleated particles with increasing Met residues within the peptide.

Simple Synthesis of Ru Decahedral Hollow Nanocages with Face-Centered Cubic Structure

Metallic nanocrystals with specific morphologies are of great interest to various applications, in particular for nanocages with well-defined and controllable surface due to high surface-to-volume ratio with high utilization efficiency of atoms. In the present work, Ru decahedral nanocages were synthesized via a combination of seed-mediated growth and chemical etching approach over Pd decahedra seeds. To be specific, the Pd decahedra were synthesized via a standard procedure, on which the Ru out layers were grown by seed-mediated growth with a few nanometers. Subsequently, Ru decahedral nanocages were formed with selective chemical etching of Pd cores in acidic aqueous solution. The present work suggests an effective strategy towards synthesis of hollow nanocages.