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>

Microwave-assisted oxidative coupling of thiols using polystyrene supported bromoderivatives of 2-oxazolidone

Polymer-supported reagents have become popular in synthetic organic chemistry over the past decades. But the kinetics of polymer-supported reactions is slow compared to solution phase synthesis because of the poor diffusion of the reactants through the macromolecular polymer matrix. This difficulty can be reduced to a great extent by performing polymer-supported reactions under microwave (MW) conditions. The present work is focussed on the design and development of an innovative, powerful, MW stable and recyclable polymeric reagent prepared by attaching bromoderivative of 2-oxazolidone into the macromolecular matrix of polystyrene. 3% cross-linked polystyrene was prepared by free radical aqueous suspension polymerization technique using tetra ethylene glycol diacrylate as the cross-linking agent and the resulting beads were functionalized by chloromethylation followed by reaction with 2-oxazolidone. Bromine functionality is introduced into the polymer by treating with bromine in carbon tetrachloride. The synthetic utility of the prepared polymeric reagent was demonstrated by the oxidative coupling of thiols to disulfides under MW irradiation. No over oxidation was observed in this protocol and the utilization of polystyrene support simplifies work up and product isolation. The synthesised polymeric reagent displayed good cyclic stability up to five cycles without any substantial decrease in bromine content and satisfactory storage stability under normal laboratory condition. Moreover this may be the first report that uses MW energy for the oxidation of thiols to disulfides using polymer-supported reagents. [Formula: see text]

Solution-Phase Synthesis of Nanoparticles and Growth Study

<p>This thesis is concerned with solution-phase synthesis of nanoparticles and growth of nanoparticles in solution. A facile synthesis route was developed to produce nanoparticles of iron, iron carbide and ruthenium. In general, the synthesis involved the reaction/decomposition of a metal precursor in solution, in the presence of a stabilising agent, in a closed reaction vessel, under a hydrogen atmosphere. The crystallinity, crystal structure, morphology and chemical composition of the nanoparticles obtained were studied primarily by transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDS). Scanning quantum interference device magnetometry (SQUID) was used to characterise the magnetic properties of iron and iron carbide nanoparticles. In situ synchrotron-based XRD was employed to investigate the growth of platinum nanoparticles of different morphologies. The synthesis of iron and iron carbide nanoparticles was investigated at temperatures 80-160 °C. Syntheses at 130 °C and above produced mainly single-crystal α-Fe nanoparticles, whereas those at lower temperatures yielded products consisting of α-Fe and Fe₃C nanoparticles. Nanoparticles of larger than 10 nm oxidised on the surface leading to core/shell structures, and those of smaller size oxidised completely upon exposure to air. Core/shell nanoparticles of larger than 15 nm were observed to be stable under ambient conditions for at least a year, whereas those smaller in size underwent further oxidation forming core/void/shell structures. The magnetic properties of selected samples were characterised. The core/shell nanoparticles were shown to exhibit ferromagnetic behaviours, and saturation magnetisations were obtained at the range of 100-130 emu g⁻¹. Nanoparticle size and size distribution, and morphology were found to be a result of combined effect of precursor concentration and the relative stabiliser concentration. In general, high-precursor concentration resulted in less controlled reaction and produced large nanoparticle size and size distribution. Under the high-concentration condition, the use of stabilisers in reduced amount then led to a diverse range of morphologies, which include dimer, porous and branched structures. As for the synthesis of ruthenium nanoparticles, reactions of different precursors were investigated at temperatures ranging from room temperature to 140 °C. Highly crystalline ruthenium nanoparticles of different sizes and morphologies were obtained through different experimental conditions. The increase in nanoparticle size was found to be a result of increasing reaction temperature and/or decreasing stabiliser to ruthenium ratio. This trend was observed to be independent of the type of stabilisers and precursors used. The use of stabilisers with different binding characteristics has facilitated the formation of non-spherical nanoparticles; these include rod-like structures with high aspect ratios (of up to 12), hexagonal and truncated triangular plate-like structures, and tripods. The growth of faceted and branched structures of platinum nanoparticles was investigated by employing in situ XRD techniques. TEM was used to examine the intermediate structures. The two different morphologies were previously shown to be governed by precursor concentration. It was found that the growth in the low-concentration reaction was characteristic of a thermodynamically controlled regime, whereas that in the high-concentration reaction occurred at much greater rates under a kinetically controlled regime. Based on the observations obtained, different growth mechanisms were proposed and discussed. The former involved an oriented attachment mechanism, while the latter, a novel mechanism involving selective growth and etching processes. The results are followed by an overall discussion comparing and contrasting the various syntheses involved, and relating the results of syntheses to those of the growth studies.</p>

Solution-Phase Synthesis of Nanoparticles and Growth Study

<p>This thesis is concerned with solution-phase synthesis of nanoparticles and growth of nanoparticles in solution. A facile synthesis route was developed to produce nanoparticles of iron, iron carbide and ruthenium. In general, the synthesis involved the reaction/decomposition of a metal precursor in solution, in the presence of a stabilising agent, in a closed reaction vessel, under a hydrogen atmosphere. The crystallinity, crystal structure, morphology and chemical composition of the nanoparticles obtained were studied primarily by transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDS). Scanning quantum interference device magnetometry (SQUID) was used to characterise the magnetic properties of iron and iron carbide nanoparticles. In situ synchrotron-based XRD was employed to investigate the growth of platinum nanoparticles of different morphologies. The synthesis of iron and iron carbide nanoparticles was investigated at temperatures 80-160 °C. Syntheses at 130 °C and above produced mainly single-crystal α-Fe nanoparticles, whereas those at lower temperatures yielded products consisting of α-Fe and Fe₃C nanoparticles. Nanoparticles of larger than 10 nm oxidised on the surface leading to core/shell structures, and those of smaller size oxidised completely upon exposure to air. Core/shell nanoparticles of larger than 15 nm were observed to be stable under ambient conditions for at least a year, whereas those smaller in size underwent further oxidation forming core/void/shell structures. The magnetic properties of selected samples were characterised. The core/shell nanoparticles were shown to exhibit ferromagnetic behaviours, and saturation magnetisations were obtained at the range of 100-130 emu g⁻¹. Nanoparticle size and size distribution, and morphology were found to be a result of combined effect of precursor concentration and the relative stabiliser concentration. In general, high-precursor concentration resulted in less controlled reaction and produced large nanoparticle size and size distribution. Under the high-concentration condition, the use of stabilisers in reduced amount then led to a diverse range of morphologies, which include dimer, porous and branched structures. As for the synthesis of ruthenium nanoparticles, reactions of different precursors were investigated at temperatures ranging from room temperature to 140 °C. Highly crystalline ruthenium nanoparticles of different sizes and morphologies were obtained through different experimental conditions. The increase in nanoparticle size was found to be a result of increasing reaction temperature and/or decreasing stabiliser to ruthenium ratio. This trend was observed to be independent of the type of stabilisers and precursors used. The use of stabilisers with different binding characteristics has facilitated the formation of non-spherical nanoparticles; these include rod-like structures with high aspect ratios (of up to 12), hexagonal and truncated triangular plate-like structures, and tripods. The growth of faceted and branched structures of platinum nanoparticles was investigated by employing in situ XRD techniques. TEM was used to examine the intermediate structures. The two different morphologies were previously shown to be governed by precursor concentration. It was found that the growth in the low-concentration reaction was characteristic of a thermodynamically controlled regime, whereas that in the high-concentration reaction occurred at much greater rates under a kinetically controlled regime. Based on the observations obtained, different growth mechanisms were proposed and discussed. The former involved an oriented attachment mechanism, while the latter, a novel mechanism involving selective growth and etching processes. The results are followed by an overall discussion comparing and contrasting the various syntheses involved, and relating the results of syntheses to those of the growth studies.</p>

Stand-Alone CuFeSe2 (Eskebornite) Nanosheets for Photothermal Cancer Therapy

Two-dimensional CuFeSe2 nanosheets have been successfully obtained via solution-phase synthesis using a sacrificial template method. The high purity was confirmed by X-ray diffraction and the two-dimensional morphology was validated by transmission electron microscopy. The intense absorption in the 400–1400 nm region has been the basis for the CuFeSe2 nanosheets’ photothermal capabilities testing. The colloidal CuFeSe2 (CFS) nanosheets capped with S2− short ligands (CFS-S) exhibit excellent biocompatibility in cell culture studies and strong photothermal effects upon 808 nm laser irradiation. The nanosheets were further loaded with the cancer drug doxorubicin and exposed to laser irradiation, which accelerated the release of doxorubicin, achieving synergy in the therapeutic effect.