The use of metal-containing block-copolymer to fabricate magnetic nanoparticles arranged in desired nanostructure has attracted immense attention in the field of materials science. As a result, a series of FePt-containing block copolymers were synthesized. To begin with, a brief survey on the background of magnetic FePt NPs and the use of both organic and metal-containing block copolymer self-assembly was presented in chapter 1. In chapter 2, a series of FePt-containing polymers were synthesized and characterized. The random copolymer FePt-A exhibited poor solubility and ill-characterized morphology in the bulk state self-assembly. The block copolymer FePt-B2 showed incomplete complexation due to the bulky nature of the FePt-complexes B5 used, whereas the block copolymer FePt-C resulted in insoluble polymeric materials after complexation. Fortunately, when using coordination linkage, FePt-Ds were successfully synthesized and characterized with good solubility in common solvents. To retain the cylindrical (FePt-D-Cy1/2) and spherical (FePt-D-Sp1/2) morphologies of the neat block copolymer, the loading of bimetallic complexes D1 was targeted at 20% of stoichiometry ratio to pyridine. The pyrolysis of bulk samples generated fct FePt nanoparticles with size of 6-13 nm. The results showed the systematic tuning of size of nanoparticles by varying the molecular weight of block copolymers, and hence the total metal content by weight percentage in polymers. In chapter 3, the thin film self-assembly of FePt-Ds was further investigated to demonstrate the potential of our system for thin film fabrication. Three approaches were employed, the first method was solid state self-assembly in thin film, and the morphologies in thin film were consistent to those in the bulk state self-assembly. Solvent annealing of FePt-D-Cy2 and FePt-D-Sp1 showed improvement in the order and orientation of microdomains, despite the presence of some defects in order. With well-defined spherical morphology in FePt-D-Sp1, the pyrolysis in thin film was performed and the result showed the retention of spherical morphology with little defects. In the next stage, nanoimprint lithography directed self-assembly was employed to give the long range order. Both flattened and line array patterned molds were employed to imprint the polymers. The results showed alignment direction with the use of flattened mold. However, the results also showed the deformed and damaged patterns due to high adhesion force between the polymer and mold. Without an appropriate releasing agent covered on mold surface and a remedy to tribological problem, it would be hard to reliably obtain the morphology under the molds during the press and release. Going to the last method, the solution state self-assembly of FePt-D-Cy2 in THF/toluene mixture was demonstrated. By varying polymer concentrations and spinning rate, well-defined spherical micelles are possible to achieve with a better order and distribution. Solvent annealing with slightly selective solvent showed reduction in size distribution and domain size in the FePt spherical micelles with slightly improved packing. Although very nice packings in both solid and solution state self-assembly have not been achieved yet, this study still demonstrated the potential approach to use single bimetallic source-containing block copolymer to self-assemble into desired nanostructures for FePt nanoparticles synthesis. Finally, chapters 4 and 5 presented the concluding remarks, future plans and the experimental details described in chapters 2 and 3.

No description available.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

M.Sc. (Nanoscience) / Please refer to full text to view abstract

The work presented in this dissertation is a composite of experiments in the growth of gold nanoparticles with specific optical properties of interest. The goal is to synthesize these gold nanoparticles using soybean extract for not only shape control, but for propensity as a biocompatible delivery system. The optical properties of these nanoparticles has found great application in coloring glass during the Roman empire and, over the centuries, has grown into its own research field in applications of nanoparticulate materials. Many of the current functions include use in biological systems as biosensors and therapeutic applications, thus making biocompatibility a necessity. Current use of cetyltrimethylammonium bromide leads to rod-shaped gold nanoparticles, however, the stability of these gold nanoparticles does not endure for extended periods of time in aqueous media. In my research, two important components were found to be necessary for stable, anisotropic growth of gold nanoparticles. In the first experiments, it was found that bromide played a key role in shape control. Bromide exchange on the gold atoms led to specific packing of the growing crystals, allowing for two-dimensional growth of gold nanoparticles. It was also discerned that soybean lecithin contained ligands that blocked specific gold facets leading to prismatic gold nanoparticle growth. These gold nanoprisms give a near infrared plasmon absorption similar to that of rod-shaped gold nanoparticles. These gold nanoprisms are discovered to be extremely stable in aqueous media and remain soluble for extended periods of time, far longer than that of gold nanoparticles grown using cetyltrimethylammonium bromide. Since soy lecithin has a plethora of compounds present, it became necessary to discover which compound was responsible for the shape control of the gold nanoprisms in order to optimize the synthesis and allow for a maximum yield of the gold nanoprisms. Many of these components were identified by high performance liquid chromatography and liquid chromatography-mass spectrometry. However, re-spike of these components into growth solutions did not enhance the growth of gold nanoprisms. Upon separating the shapes of the gold nanoparticles using gel electrophoresis, addition of KCN to the separated gold nanoparticles allowed us to extract the culpable ligands for shape control. Analysis of these ligands by mass spectrometry elucidated the identity of PA and upon re-spike of the PA into a growth solution of PC95, the growth of a near-infrared plasmon absorption was seen. The stability of these gold nanoparticles was tested with and without the addition of decane thiol and it was concluded that addition of the thiol allowed for improved stability of the gold nanoparticles towards cyanide. It was determined that at a concentration of 2 μM decanethiol, spherical gold nanoparticles remained stable to cyanide at the expense of the prismatic gold nanoparticles. However, at 5 μM decanethiol, both spherical and prismatic gold nanoparticles retained stability to cyanide in aqueous conditions.

M.Sc. / The main objective of this project was to synthesize carbohydrates that contain a thiol functional group, commonly known as thiocarbohydrates and subsequently employ them as stabilizing agents in the synthesis of gold nanoparticles and as ligands in the synthesis of phosphine thiocarbohydrate gold(I) complexes. In achieving our objective, thiocarbohydrate compounds 62, 64, 69 and 71 were successfully synthesized from acetylated 60 or benzylated glucal 66 using a Ferrier rearrangement reaction. NaHSO4-SiO2 was used as a catalyst for Ferrier rearrangement reaction in the presence of dithiol type nucleophiles (i.e. 1,2-dithiol ethane or 1,5-dithiol pentane) to afford the desired thiocarbohydrate compounds. The S-acetate derivatives 63, 65, 70 and 72 of the corresponding thiocarbohydrates were prepared as a confirmatory test for the presence of the terminal thiol (SH) in the thiocarbohydrate compounds. C-2 modified thiocarbohydrate compounds 78 and 80 were synthesized from C-2 iodomethyl glycoside 77 following a literature reported procedure in the presence of 1,2-dithiol ethane or 1,5-dithiol pentane as nucleophiles. S-acetate derivatives 79 and 81 of the corresponding thiocarbohydrate compounds were synthesized again to confirm the presence of the terminal thiol (SH). All the thiocarbohydrate compounds and their corresponding S-acetate derivatives were characterized with NMR spectroscopy and HRMS. Ethyl thiocarbohydrate compounds 62, 69 and 78 were successfully employed as stabilizing agents in the preparation of gold nanoparticles GNP1-GNP9 following a Brust-Schiffrin procedure. UV-Vis spectroscopy and transmission electron microscopy (TEM) were used to characterize these gold nanoparticles. Phosphine thiocarbohydrate gold(I) complexes 84-94 were synthesized from selected thiocarbohydrate compounds. NMR spectroscopy and HRMS were used to characterize these gold(I) complexes. Having synthesized the target thiocarbohydrate compounds, gold nanoparticles and gold(I) complexes, our aim was to investigate their biological activity against cancer and HIV. However, the biological testing process took considerably longer and as a result this dissertation was submitted without the biological tests results.

Yes / We have synthesised osmium nanoparticles of defined size (1.5–50 nm) on a B- and S-doped turbostratic graphitic structure by electron-beam irradiation of an organometallic osmium complex encapsulated in self-spreading polymer micelles, and characterised them by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and atomic force microscopy (AFM) on the same grid. Oxidation of the osmium nanoparticles after exposure to air was detected by X-ray photoelectron spectroscopy (XPS). / We thank the Leverhulme Trust (Early Career Fellowship No. ECF-2013-414 to NPEB), the University of Warwick (Grant No. RD14102 to NPEB), the ERC (Grant No. 247450 to PJS), and the EPSRC (EP/F034210/1 to PJS). L.M.A.P., J.L., and G.C. acknowledge financial support from the EU through the ERC Consolidator Grant “VISUAL-MS”.

Among various nanomaterials, metal nanoparticles are the widely studied ones because of their pronounced distinct properties arising in the nanometer size regime, which can be tailored easily by tuning predominantly their size and shape. During the past few decades, scientists are engaged in developing new synthetic methodologies for the synthesis of metal nanoparticles which can be divided into two broad categories: i) top-down approach, utilizing physical methods and ii) bottom-up approach, employing chemical methods. As the chemical methods offer better control over particle size, numerous chemical methods have been developed to obtain metal nanoparticles with narrow size distribution. However, these two approaches have their own merits and demerits; they are not complementary to each other and also not sustainable for real time applications. Recent focus on the synthesis of metal nanoparticles is towards the development of green and sustainable synthetic methodologies. A solid state route is an exciting prospect in this direction because it eliminates usage of organic solvents thus, makes the overall process green and at the same time leads to the realization of large quantity of the materials, which is required for many applications. However, the major obstacle associated with the development of a solid state synthetic route is the lack of fundamental understanding regarding the formation mechanism of the nanoparticles in the solid state. Additionally, due to the heterogeneity present in the solid mixture, it is very difficult to ensure the proximity between the capping agent and nuclei which plays the most decisive role in the growth process. Recently, employment of amine–borane compounds as reducing agents emerged as a better prospect towards the development of sustainable synthetic routes for metal nanoparticles because they offer a variety of advantages over the traditional borohydrides. Being soluble in organic medium, amine– borane allows the reaction to be carried out in a single phase and due to its mild reducing ability a much better control over the nucleation and growth processes is realized. However, the most exciting feature of these compounds is that their reducing ability is not only limited to the solution state, they can also bring out the reduction of metal ions in the solid state. With the availability of a variety of amine–boranes of varying reducing ability, it opens up a possibility to modulate the nanostructure in both solid and solution states by a judicious choice of reducing agent. Although our current understanding regarding the growth behavior of nanoparticles has advanced remarkably, however, most often it is some classical model which is invoked to understand these processes. With the recent developments in in situ transmission electron microscopy techniques, it is now possible to unravel more complex growth trajectories of nanoparticles. These studies not only expand the scope of the present knowledge but also opens up possibilities for many future developments. Objectives • To develop an atom economy solid state synthetic methodology for the synthesis of metal nanoparticles employing amine–boranes as reducing agents. • To gain a mechanistic insight into the formation mechanisms of nanoparticles in the solid state by using amine–boranes with differing reducing ability. • Synthesis of bimetallic nanoparticles as well as supported metal nanoparticles in the solid state using ammonia borane as the reducing agent. • To develop a new in situ seeding growth methodology for the synthesis of core@shell nanoparticles composed of noble metals by employing a very weak reducing agent, trimethylamine borane and their transformation to their thermodynamically stable alloy counterparts. • Synthesis of highly monodisperse ultra-small colloidal calcium nanoparticles with different capping agents such as hexadecylamine, octadecylamine, poly(vinylpyrrolidone) and a combination of hexadecylamine/poly(vinylpyrrolidone) using the solvated metal atom dispersion (SMAD) method. To study the coalescence behavior of a pair of calcium nanoparticles under an electron beam by employing in situ TEM technique. Significant results An atom economy solid state synthetic route has been developed for the synthesis of metal nanoparticles from simple metal salts using amine–boranes as reducing agents. Amine–borane plays a dual role here: acts as a reducing agent thus brings out the reduction of metal ions and decomposes simultaneously to generate B-N based compounds which acts as a capping agent to stabilize the particles in the nanosize regime. This essentially minimizes the number of reagents used and hence simplifying and eliminating the purification procedures and thus, brings out an atom economy to the overall process. Additionally, as the reactions were carried out in the solid state, it eliminates use of organic solvents which have many adverse effects on the environment, thus makes the synthetic route, green. The particle size and the size distribution were tuned by employing amine–boranes with differing reducing abilities. Three different amine–boranes have been employed: ammonia borane (AB), dimethylamine borane (DMAB), and trimethylamine borane (TMAB) whose reducing ability varies as AB > DMAB >> TMAB. It was found that in case of AB, it is the polyborazylene or BNHx polymer whereas, in case of DMAB and TMAB, the complexing amines act as the stabilizing agents. Several controlled studies also showed that the rate of addition of metal salt to AB is the crucial step and has a profound effect on the particle size as well as the size distribution. It was also found that an optimum ratio of amine–borane to metal salt is important to realize the smallest possible size with narrowest size distribution. Whereas, use of AB and TMAB resulted in the smallest sized particles with best size distribution, usage of DMAB provided larger particles that are also polydisperse in nature. Based on several experiments along with available data, the formation mechanism of metal nanoparticles in the solid state has been proposed. Highly monodisperse Cu, Ag, Au, Pd, and Ir nanoparticles were realized using the solid state route described herein. The solid state route was extended to the synthesis of bimetallic nanoparticles as well as supported metal nanoparticles. Employment of metal nitrate as the metal precursor and ammonia borane as the reducing agent resulted in highly exothermic reaction. The heat evolved in this reaction was exploited successfully towards mixing of the constituent elements thus allowing the alloy formation to occur at much lower temperature (60 oC) compared to the traditional solid state metallurgical methods (temperature used in these cases are > 1000 oC). Synthesis of highly monodisperse 2-3 nm Cu/Au and 5-8 nm Cu/Ag nanoparticles were demonstrated herein. Alumina and silica supported Pt and Pd nanoparticles have also been prepared. Use of ammonia borane as the reducing agent in the solid state brought out the reduction of metal ions to metal nanoparticles and the simultaneous generation of BNHx polymer which encapsulates the metal (Pt and Pd) nanoparticles supported on support materials. Treatment of these materials with methanol resulted in the solvolysis of BNHx polymer and its complete removal to finally provide metal nanoparticles on the support materials. An in situ seeding growth methodology for the synthesis of bimetallic nanoparticles with core@shell architecture composed of noble metals has been developed using trimethylamine borane (TMAB) as the reducing agent. The key idea of this synthetic procedure is that, TMAB being a weak reducing agent is able to differentiate the smallest possible window of reduction potential and hence reduces the metal ions sequentially. A dramatic solvent effect was noted in the preparation of Ag nanoparticles: Ag nanoparticles were obtained at room temperature when dry THF was used as the solvent whereas, reflux condition was required to realize the same using wet THF as the solvent. However, no such behavior was noted in the preparation of Au and Pd nanoparticles wherein Au and Pd nanoparticles were obtained at room temperature and reflux conditions, respectively. This difference in reduction behavior was successfully exploited to synthesize Au@Ag, Ag@Au, and Ag@Pd nanoparticles. All these core@shell nanoparticles were further transformed to their alloy counterparts under very mild conditions reported to date. Highly monodisperse, ultrasmall, colloidal Ca nanoparticles with a size regime of 2-4 nm were synthesized using solvated metal atom dispersion (SMAD) method and digestive ripening technique. Hexadecylamine (HDA) was used as the stabilizing agent in this case. Employment of capping agent with a longer chain length, octadecylamine afforded even smaller sized particles. However, when poly(vinylpyrrolidone) (PVP), a branched chain polymer was used as the capping agent, agglomerated particles were realized together with small particles of 3-6 nm. Use of a combination of PVP and HDA resulted in spherical particles of 2-3 nm size with narrow size distribution. Growth of Ca nanoparticles via colaesence mechanism was observed under an electron beam. Employing in situ transmission electron microscopy technique, real time coalescence between a pair of Ca nanoparticles were detected and details of coalescence steps were analyzed.

M.Sc.(Nanoscience) / The synthesis and application of gold nanoparticles (AuNPs) has been intensively studied worldwide. However, the toxicity of these nanoparticles is still a concern. We considered that various physiochemical methods used to synthesize AuNPs are energy driven, costly and require the use of harmful chemicals. Thus, this makes them not environmentally-friendly. The aim of this study was therefore to synthesize AuNPs via a greener route using Aspalathus linearis tea leaves. The AuNPs were used to coat eight commercial antifungal discs (i.e. amphotericin B, fluconazole, clotrimazole, econazole, flucytosine, ketoconazole, miconazole and nystatin) against four Aspergillus spp. for enhanced antifungal activity. The aqueous extract of A. linearis was characterized by high performance liquid chromatography and liquid chromatography–mass spectroscopy. The AuNPs were characterized using ultravioletvisible (UV-vis) spectroscopy, dynamic light scattering, nanoparticle tracking analysis, Fourier transforms infrared spectroscopy (FTIR), high-resolution transmission electron microscopy and X-ray diffraction. The toxicity of the synthesized AuNPs was studied by 3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay and xCELLigence test on HepG-2 cell lines and results revealed very little to no toxicity of the AuNPs. The pristine antifungal and AuNPs coated antifungal discs were characterized by FTIR, scanning electron microscopy (SEM) and antifungal activity performed using the disc diffusion method. A strong resonance peak was observed at 529 nm of the AuNPs measured using UV-vis spectroscopy. Average size of AuNPs was ~44±1 nm and demonstrated excellent in-vitro stability under various solutions (5% NaCl, phosphate buffered saline) at varying pH levels. The SEM images revealed that the AuNPs were attached onto the coated antifungal discs when compared with the pristine antifungal discs. Antifungal results indicated that AuNPs significantly (p<0.001) enhanced the antifungal activity of the coated antifungal discs against the tested fungi when compared to the pristine antifungal discs. The AuNPs coated econazole disc exhibited the greatest (broad spectrum) activity than other antifungal agents tested. In conclusion, A. linearis can be used as a reducing agent in the synthesis of stable AuNPs. Furthermore, the AuNPs coated antifungal discs demonstrated considerable antifungal activity over the pristine antifungal discs...

Nanomateriais de fct-FePt, SmCo e Carbeto de Cobalto têm sido bastante estudados para a aplicação em gravação magnética e imãs de elevado desempenho, devido as suas energias magnetocristalinas e coercividades elevadas. Nanopartículas de FePt unidimensionais foram propostas na tentativa de obter melhora no alinhamento magnético das estruturas auto-organizadas. Neste trabalho, a formação de nanobastão e nanofios de FePt foi estudada através da presença de oleilamina e pequena quantidade de monóxido de carbono liberado pelo pentacarbonilferro(0). Estes dois parâmetros foram estudados a fim de analisar a influência no alongamento das nanopartículas e verificou-se que ambos atuam sinergicamente. Foram obtidos tanto nanofios de FePt ramificados de comprimento de 20-100 nm quanto nanobastões de FePt de 20-60 nm de comprimento, ambos com diâmetro de 2-3 nm. Todas as nanopartículas sintetizadas foram obtidas na fase cúbica de face centrada e o processo de tratamento térmico nas temperaturas de 450 oC e 560 oC levou a conversão para a fase tetragonal de face centrada, com custo da sinterização das nanopartículas. Os nanobastões, entretanto, apresentaram maior estabilidade térmica se comparado com o nanofio ramificado, obtendo propriedade ferromagnética na amostra. Alternativamente, têm sido obtidos satisfatoriamente nanobastões de platina para posterior recobrimento com ferro para a formação da liga FePt após o processo de recozimento. Na síntese de SmCo, foi estudada a formação da liga diretamente por via química através do uso de redutores comumente utilizandos em síntese de nanopartículas, porém foi possível observar apenas uma pequena quantidade da liga Sm2Co17 quando se utiliza o boroidreto de sódio. Isto se deve, principalmente, ao alto potencial de redução de Sm3+ e a sua instabilidade química. Entretanto, foram desenvolvidos métodos promissores para a obtenção de nanopartículas de CoO e SmCoO com tamanho e forma controlada. Além destes sistemas, tem sido obtidas diretamente através de síntese química nanopartículas de carbeto de cobalto com coercividade de até 2,3 kOe e magnetização de 45 emu/g, além de desenvolver um método geral de síntese de carbetos de outros metais. / SmCo, fct-FePt and CoC nanomaterials have been studied for application in magnetic recording and permanent magnets due to theirs high coercivity and magnetocrystalline anisotropy. One-dimensional FePt nanoparticles were proposed to improve the magnetic alignment of self-assembled system. In this work, the formation of FePt nanorods and nanowires was studied by using a small amount of carbon monoxide from the precursor pentacarbonyliron(0) and oleylamine. Both parameters of synthesis were studied and was verified that they influence the one-dimensional growth of FePt. In fact, branched FePt nanowires with 20 - 100 nm of length and nanorods with 20 - 60 nm were obtained, both with 2-3 nm of diameters. The FePt nanoparticles were obtained in face centered cubic phase and the transformation to face centered tetragonal phase was carry out in the temperatures of 450 oC and 560 oC, which led the formation of sintered nanoparticles. FePt nanorods have better thermal stability than nanowires according the results obtained. The platinum nanorods covered with iron oxide also were obtained to formation of FePt by thermal treatment. In concern of SmCo syntheses, the formation of SmCo phase directly by chemical synthesis was investigated by using some reduction agent, but was obtained a small amount of smco phase only if the sodium borohydrate was used in the synthesis. This could be occurred due to high reducing potential of Sm3+ and its chemical instability. However, some methods were obtained to obtain CoO and SmCoO nanoparticles with size and shape control. Furthermore, cobalt carbide nanoparticles were well obtained with coercivity of 2,3 kOe and magnetization of 45 emu/g, and a new general method to obtain metals carbides was developed.