Rozprawy doktorskie na temat „Core-shell Nanomaterials”

Magister Scientiae - MSc (Chemistry)
This work involves the synthesis of copper telluride-polypropylenimine tetra(5-(2-thienyl) salicylaldimine) (CuTe@PPI) and copper antimonide-polypropylenimine tetra(5-(2-thienyl) salicylaldimine) (CuSb@PPI) core-shell nanoparticles (NPs), using two-pots and one-pot synthesis methods, respectively. Their morphology was studied by X-ray diffraction spectroscopy (XRD), high resolution transmission electron microscopy (HRTEM) and high resolution scanning electron microscopy (HRSEM); while their structures were characterized by Fourier transform infrared spectroscopy (FTIR) and elemental analysis. Photophysical properties of the core-shell NPs were determined from ultraviolet-visible absorption spectroscopy (UV-Vis) and photoluminescence spectroscopy (PL). For core-shell NPs produced via two-pots method only CuTe@PPI exhibited ? ? ?* and n ? ?* which indicate that CuSb@PPI produced via two-pots method was unsuccessfully synthesized. The ? ? ?* and n ? ?* transitions indicate the presence of polypropylenimine tetra(5-(2-thienyl) salicylaldimine) (PPI) on the surface of CuTe NPs and CuSb NPs. FTIR confirmed coordination of PPI on the surface of CuTe NPs and CuSb NPs by showing a shift in wavenumber of C=N group bands from PPI. HR-TEM showed that the CuTe@PPI synthesized via one-pot method have a wide particles sizes distribution with an average particles size of 13.60 nm while for CuTe@PPI synthesized via two-pots it was impossible to determine the particles size due to aggregation. CuSb@PPI synthesized via twopots method and one-pot method has a wide particles sizes distribution with an average size of 7.98 nm and 11.61 nm respectively. The average particles sizes determined by HR-SEM were found to be 35.24 nm (CuTe@PPI two-pots method), 33.90 nm (CuTe@PPI one-pot method), 18.30 nm (CuSb@PPI two-pots method), and 16.18 nm (CuSb@PPI one pot method).
2021-08-31

In recent years, employing advanced oxidation processes (AOPs) as a means of wastewater remediation has emerged as a promising route towards maintaining a sustainable global water management program. The heterogeneous photocatalytic oxidation process has been of particular interest due to the prospective of utilizing solar radiation as the driving force behind the degradation of pollutants. Of the photocatalyst studied to date, TiO2 remains the most attractive material for environmental applications due to its affordability, stability, biocompatibility and high quantum yield. A key draw back however is roughly only 5% of solar radiation incident on earth can provide the energy required (3.0-3.2 eV) to generate the electron-hole pairs necessary for photo-oxidation. As a means to improve the process under solar irradiance, optical properties such as surface plasmon resonance of metallic nanoparticles and upconversion luminescence of rare earth ions have been exploited for improved light harvesting as well as the generation of more usable UV light from lower energy photons. In order to explore these phenomena and their role in the enhancement of this AOP, the photocatalytic degradation of organic dyes was studied under various conditions employing Degussa P25 TiO2 as the photocatalyst. Ag nanocubes, Ag-Pd core-shell nanoparticles and YAG:Yb+3,Er+3 served as the dopants for the various studies which resulted in enhanced degradation rates, insight into the applicability of utilizing Yb+3 as sensitizing ion under solar radiation and a novel core-shell nanoparticle synthesis.

The objective of this study is to examine core-shell type plasmonic metamaterials aimed at the development of materials with unique electromagnetic properties. The building blocks of metamaterials under study consist of gold as a metal component, and silica and precipitated calcium carbonate (PCC) as the dielectric media. The results of this study demonstrate important applications of the core-shells including scattering suppression, airborne obscurants made of fractal gold shells, photomodification of the fractal structure providing windows of transparency, and plasmonics core-shell with a gain shell as an active device. Plasmonic resonances of the metallic shells depend on their nanostructure and geometry of the core, which can be optimized for the broadband extinction. Significant extinction from the visible to mid-infrared makes fractal shells very attractive as bandpass filters and aerosolized obscurants. In contrast to the planar fractal films, where the absorption and reflection equally contribute to the extinction, the shells' extinction is caused mainly by the absorption. This work shows that the Mie scattering resonance of a silica core with 780 nm diameter at 560 nm is suppressed by 75% and only partially substituted by the absorption in the shell so that the total transmission is noticeably increased. Effective medium theory supports our experiments and indicates that light goes mostly through the epsilon-near-zero shell with approximately wavelength independent absorption rate. Broadband extinction in fractal shells allows as well for a laser photoburning of holes in the extinction spectra and consequently windows of transparency in a controlled manner. Au fractal nanostructures grown on PCC flakes provide the highest mass normalized extinction, up to 3 m^2/g, which has been demonstrated in the broad spectral range. In the nanoplasmonic field active devices consist of a Au nanoparticle that acts as a cavity and the dye molecules attached to it via thin silica shell as the active medium. Such kind of devices is considered as a nano-laser or nano-amplifier. The fabricated nanolasers were studied for their photoluminescence kinetic properties. It is shown that the cooperative effects due to the coupling of dye molecules via Au nanoparticle plasmons result in bi-exponential emission decay characteristics in accord with theory predictions. These bi-exponential decays involve a fast superradiant decay, which is followed by a slow subradiant decay. To summarize, this work shows new attractive properties of core-shell nanoparticles. Fractal Au shells on silica cores prove to be a good scattering suppressor and a band pass filter in a broadband spectral range. They can also be used as an obscurant when PCC is used as the core material. Finally, gold nanoparticles coated with silica with dye results in bi-exponential decays.

Thesis (Ph. D.)--University of New Orleans, 2005.
Title from electronic submission form. "A dissertation ... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry"--Dissertation t.p. Vita. Includes bibliographical references.

Nanotechnology as a field has the potential to answer some of the major challenges that mankind faces in regards to environmental sustainability, energy generation and health care. Though, solutions to these concerns can not necessarily rely on our current knowhow. Instead, it is reasonable to expect that humanity must adapt and learn to develop new materials and methods to overcome the adversities that we are facing. This master thesis has involved developing novel materials, serving as a small step in the continuous march towards a bright future where this is possible. More specifically, this work sought to combine mesoporous magnesium carbonate with various metal-organic frameworks to utilize the beneficial aspects from each of these constituents. The ambition was that these could be joined to render combined micro-/mesoporous core-shell structures, with high surface areas and many active sites whilst maintaining a good permeability. Numerous different synthesis routes were developed and explored in the pursuit of viable routes to design novel materials with potential future applications within for instance drug delivery, water harvesting from air and gas adsorption. Coreshell structures of the hydrophilic mesoporous magnesium carbonate covered with the hydrophobic zeolitic imidazole framework ZIF-8 was successfully synthesized for the first time, and practical studies demonstrated a dramatically enhanced water stability, which is perceived to have an impact on further research on these materials. ZIF-67 was also combined with mesoporous magnesium carbonate in a similar manner. Further, Mg-MOF-74 was grown directly from mesoporous magnesium carbonate, where the latter acted as a partially self-sacrificing template, with the aim of rendering a porous hierarchical structure with contributions from the micro- and mesoporous ranges. The outcomes of all these syntheses were characterized using several analyzing methods such as scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy and nitrogen sorption analysis.

Abstract Template assisted deposition was used to produce various nanomaterials including simple nanowires, nanorods, multi-segmented metal nanowires, core-shell nanowires, alloy and polymer wires and tubes. Anodized aluminum oxide (AAO) membranes were used as templates for the growth of the various structures using an electrochemical deposition method and also by wetting the porous templates. In the electrochemical deposition method, the pore size of the templates affects the rate of synthesis and the structures of the nanomaterials while in the wetting method, the viscosity and reaction time in the polymer solution influence the structures of the nanomaterials. A conventional two-step anodization procedure was used to synthesize thick AAO templates with porous hexagonal channels at a constant applied voltage and temperature. A maximum thickness of over 180 µm oxide layer could be fabricated using mild anodization at 60 V and 80 V. Compared to conventional mild anodization, these conditions facilitated faster growth of oxide layers with regular pore arrangement. Polyethylene glycol (PEG) containing ferromagnetic nanowires were synthesized using template assisted electrochemical deposition method. During the synthesis, simultaneous deposition of polymer and metal ions resulted nanowires coated with a uniform layer of PEG without interfering with the structure and magnetic properties of the nanowires. PEG-coated Ni nanowires were embedded in polyethylene diacrylate (PEGDA) matrix after the removal of the AAO templates. Comparison of results with and without a magnetic field during embedding showed that the presence of magnetic field supported embedding of nanowire arrays in polymer. Influence of using AAO templates with several pore diameters for the synthesis of bimetallic nanowires were studied by growing Ni-Fe and Ni-Co bi-metallic nanowires. At a constant applied current by using templates with a pore diameters of 60 nm alloy formed while with a pore diameter of 130 nm core-shell nanowires formed. Polyvinylidene fluoride (PVDF) films and nanotubes were synthesized using a solution recrystallization method that favored the formation of piezoelectric β phase thin films. Variation in the concentration of polymer in the mixture solution allowed synthesis of different types of structures such as PVDF composites, nanorods and nanocrystals with tunable morphologies. Keywords: One-dimensional structures, electrodeposition, porous alumina, ferromagnetic nanostructures, magnetic core-shell nanowires, alloys, polymer composite, stimuli-active, PEGDA, azobenzene, and PVDF.

This thesis explores how the carrier dynamics within semiconductor nanocrystals can be directly engineered through specific core-shell design. Emphasis is placed on how material characteristics, such as strain or alloying at a core-shell interface, can influence the exciton energies and the recombination dynamics within semiconductor nanocrystals. This study synthesises type-II heterojunction ZnTe/ZnSe core-shell nanocrystals via a diethyl zinc-free synthesis method, producing small size distributions and quantum yields as high as 12%. It was found that the 7% lattice mismatch between the core and shell materials places limitations on the range of structures in which coherent growth is achieved. By developing compositional and strained atomistic core-shell models a variety of physical and optical properties could be simulated and has led to a clear picture of the core-shell architecture to be built. This characterisation provides evidence that the low bulk modulus ZnTe cores are compressed by the higher bulk modulus smaller lattice constant ZnSe shells. Further studies show how strain is manifested in structures with 'sharp' core-shell interfaces and how intentional alloying the interface can influence the growth and exciton energies. A (2-6)-band effective mass model was able to distinguish between the as-grown 'sharp' and 'alloyed' interfaces which indicated that strain accentuates the redshift of the excitonic state whilst reduced strain within an alloyed interface sees a reduced redshift. Single nanocrystal spectroscopy investigations of brightly emitting single graded alloyed nanocrystals and of a size series of commercially available CdSe/ZnS nanocrystals showed almost no fluorescence intermittency (nearly 'non-blinking'). These investigations also identified trion recombination as the main mechanism within the blinking 'off' state. Ultimately this thesis adds to the growing understanding of how specific core-shell architectures manipulate the electronic structure and develops techniques to identify specific material characteristics and how these characteristics influence the physical and optical properties within semiconductor nanocrystals.

Le remplacement du carbone graphite, matériau commercial dans les batteries au lithium ion, par du silicium est un axe privilégié afin d’augmenter la capacité des anodes au sein de ces accumulateurs. En revanche, le silicium micrométrique souffre de puissants effets de dégradation au cours du cyclage. L’expansion volumique des particules lors de la formation des alliages lithiés et la réduction des électrolytes en contact avec la matière active, sous forme de produits de dégradation appelés SEI, induisent une diminution importante de la durée de vie de ces anodes. La communauté scientifique a donc émis l’idée de stabiliser le silicium en diminuant la taille des particules à l’échelle nanométrique, limitant fortement le risque de pulvérisation. De plus, le contact direct entre la matière active et les solvants peut être très largement diminué via la formation d’une coquille de carbone autour des particules de silicium. La problématique est alors la suivante : obtenir un matériau dit « cœur-coquille » à base de silicium nanométrique enrobé de carbone, à l’aide d’un procédé facilement industrialisable.Le Laboratoire Edifices Nanométriques (LEDNA) possède une grande expertise en synthèse de nanomatériaux par pyrolyse laser en phase gaz. Cette méthode de synthèse est souple, possède un rendement de production élevé et offre un contrôle important sur les conditions de réaction. Afin de répondre à la problématique posée, un nouveau réacteur de synthèse à deux étages de réaction a été développé. A l’aide de cette expérience originale, des nanomatériaux à base de silicium cristallin ont été synthétisés, ainsi que leur équivalent enrobé de carbone. Des cœurs de silicium amorphes ont également été enrobé de carbone, permettant l’obtention d’une structure cœur-coquille encore inédite dans la littérature. La microscopie révèle que les matériaux sont sous forme de chainette de particules, une structure obtenue de façon classique par les méthodes de synthèse en phase gaz mais qui se pourrait se révéler bénéfique aux propriétés de conduction électronique et ionique. Les coquilles carbonées caractérisées par spectroscopie Raman révèlent une organisation riche en liaisons sp2 mais peu graphitique. Une étude par spectroscopie des électrons Auger (AES) montre que l’homogénéité de l’enrobage carboné varie selon les matériaux, les plus petits cœurs de silicium bénéficiant d’un meilleur recouvrement. Par diffraction des neutrons, nous avons montré que le silicium amorphe enrobé est très peu sensible à l’oxydation contrairement aux autres matériaux non enrobés.Les matériaux ont été utilisés en tant que matériaux d’anode dans des batteries au lithium métal. Une étude par balayage voltamétrique a montré que les matériaux à base de silicium cristallin nécessitent plusieurs balayages avant d’être lithiés jusqu’au cœur. En revanche, le silicium amorphe enrobé subit une lithiation profonde immédiate, phénomène dont la littérature ne fait pas mention faute de pouvoir obtenir ce composite non oxydée selon les méthodes de synthèses traditionnelles. Une étude par spectroscopie d’impédance électrochimique résolue en potentiel a été réalisée afin de déterminer les mécanismes de dégradation de ces électrodes. Nous avons montré que ce phénomène est principalement entretenu par la dissolution des composés de la SEI lors de la délithiation des matériaux. De plus, l’intensité de ce phénomène de dissolution semble corrélée avec la quantité de surface de silicium potentiellement en contact avec l’électrolyte. Enfin, testés galvanostatiquement, les matériaux enrobés de carbone ont démontré des performances très supérieures au carbone graphite. Au régime élevé de 2C, difficilement accessible au matériau d’anode commerciale, le matériau amorphe enrobé a supporté près de 500 cycles en maintenant une capacité et une efficacité coulombique élevée, supérieure à 800 mAh.g-1 et 99,99%
The replacement of carbon graphite, the commercial anode material in Li-ion batteries, by silicon is one of the most promising strategies to increase the capacity of anode in these devices. However, micrometric silicon suffers from strong degradation effect while cycling. The volume expansion of the lithiated particles and the direct contact between the active material and the solvents induce the continuous formation and pulverization of a solid electrolyte interphase (SEI) leading to the rapid fading of the capacity. Many research groups suggest decreasing the size of the particle to the nanoscale where pulverization of the particles is almost inexistent. Furthermore, the formation of a carbon shell around these silicon nanoparticles is cited as the most efficient way to isolate the material from the direct contact with the solvent. The main issue is to obtain these core shell nanocomposites with a process able to meet industrial requirement.The Nanometric Structure Laboratory (LEDNA) is experimented in the synthesis of nanomaterial thanks to the gas phase laser pyrolysis method. This versatile process is characterized by a high yield of production and permits an efficient control over the reaction parameters. In order to obtain core shell structures, a new reactor has been developed by the combination of two stages of reaction. Thanks to this original setup, crystalline silicon cores covered or not with a carbon shell were achieved in one step for the first time. Likewise, amorphous cores were covered with a carbon shell, leading to the synthesis of a novel nanocomposite. Microscopic study reveals that these materials are obtained in a chain-like structure that can be beneficial to the electronic and ionic conduction properties. The carbonaceous compound were characterized by Raman spectroscopy and appeared to be non-graphitic sp2 rich species known in the literature as basic structural units (BSU). Auger electron spectroscopy study highlights the homogeneity of the carbon covering, in particular over smaller silicon cores. Neutron diffraction showed that the amorphous silicon cores covered with carbon are protected against passive oxidation unlike bare amorphous cores.The nanocomposites were used as anode materials in lithium-metal coin cell configuration. A cyclic voltammetry study highlights that crystalline silicon cores embedded into carbon need many sweeps before their full lithiation whereas amorphous core shell nanocomposites deeply lithiated from the first sweep, a phenomena yet not described in the literature. A potential resolved electronic impedance spectroscopy technic was used to determine the main degradation process of the core shell materials. We showed that the capacity fading can be mainly attributed to SEI dissolution and reformation through cycling, obstructing the porous structure of the electrode and limiting the cyclability. Finally, galvanostatically tested the core-shell nanocomposites reveal enhanced performance compared to graphite carbon. At the high charge/discharge rate of 2C, hardly reachable to the commercial anode material, the amorphous core-shell nanocomposite was cycled up to 500 cycles while maintaining a high capacity of 800 mAh.g-1 and outstanding coulombic efficiency of 99,99 %

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Human skin is constantly exposed to the harmful effects of solar radiation due to the presence of ultraviolet (UV) radiation, and skin cancer is more frequent in Brazil. Another effect caused by excess sun exposure besides skin cancer is photoaging which motivates the population to use sunscreens. Sunscreens can be classified into chemical (organic) filters and/or physical (inorganic) filters. Physical UV filters are filters containing a broad spectrum that absorb, reflect and disperse UV light so they have a wider range of protection. Titanium dioxide and zinc oxide, classified as inert particles, are singled out as the best way to protect the skin against the harmful effects of ultraviolet UVB and UVA radiation, respectively. One of the disadvantages of these constituents is that they have white coloration on the skin, decreasing its acceptability. With the use of nanotechnology, they allow the product to form a more transparent film possible on the skin thus increasing its acceptability. In this work, the physico-chemical characteristics and the ability to form a core-shell system between TiO2 and ZnO were constructed and evaluated by constructing a nanostructured system for the absorption and scattering of UV radiation. Samples of titanium dioxide, titanium dioxide coated with silicon dioxide, zinc oxide, titanium dioxide and zinc, zinc oxide and the TiO2 / SiO2/ZnO compound were synthesized. The analysis of X-ray diffraction that allowed the observation of the crystalline phase of the oxides, was used the UV/VIS spectrophotometry to analyze in which UV/VIS region the oxides are absorbing, the diffuse reflectance spectrophotometry technique in which it was observed The region in which TiO2 and TiO2/SiO2, defining the SiO2 critical thickness, and the transmission electron microscopy for visualization of the TiO2 and TiO2/SiO2layers. The studies were complemented with the evaluation of the photostability of the materials. The material is promising for an effective and safe sunscreen, whereby toxicity testing as well as assessing the permeation profile are required.
A pele está em constante exposição aos efeitos nocivos das radiações solares devido a presença de radiação ultravioleta (UV), sendo o câncer de pele muito frequente no Brasil. Outro efeito causado pelo excesso de exposição solar além do câncer de pele é o fotoenvelhecimento o que motiva a população a utilizar protetores solares. Os filtros solares podem ser classificados em filtros químicos (orgânicos) e/ou filtros físicos (inorgânicos). Os filtros UV físicos são filtros contendo um amplo espectro que absorvem, refletem e dispersam a luz UV por isso têm uma gama mais ampla de proteção. O dióxido de titânio e o óxido de zinco, classificados como partículas inertes, são apontados como a melhor maneira de proteger a pele contra os efeitos nocivos das radiações UVB e UVA, respectivamente. Uma das desvantagens destes constituintes é que apresentam coloração branca sobre a pele, diminuindo sua aceitabilidade. Com o auxílio da nanotecnologia, é possível que o produto forme uma película mais transparente sobre a pele aumentando assim sua aceitabilidade. Nesse trabalho, foram produzidos e avaliados as características físico-químicas e a capacidade de formação de um sistema core-shell entre TiO2 e ZnO, construindo um sistema nanoestruturado para a absorção e espalhamento da radiação UV. Foram preparadas amostras de dióxido de titânio, dióxido de titânio recoberto com dióxido de silício, óxido de zinco, dióxido de titânio e zinco, óxido de zinco e o composto TiO2/SiO2/ZnO. As análises de difratometria de raios X que permitiram a observação da fase cristalina dos óxidos. Além disso empregou-se a espectrofotometria no UV/VIS para analisar em qual região UV/VIS que os óxidos estão absorvendo, enquanto que a técnica de espectrofotometria de reflectância difusa em que foi utilizada para observar a região em que o TiO2 e TiO2 SiO2 absorvem, definindo a espessura crítica de SiO2. Ainda, e a microscopia eletrônica de transmissão foi utilizada para a visualização das camadas de TiO2 e TiO2 SiO2. Os estudos foram complementados com a avaliação da fotoestabilidade dos materiais. O material é promissor para a preparação de um filtro solar eficaz e seguro, sendo necessária para essa condição a realização de testes de toxicidade, bem como avaliar o perfil de permeação.

As diversas aplicações tecnológicas de nanopartículas magnéticas (NPM) vêm intensificando o interesse por materiais com propriedades magnéticas diferenciadas, como magnetização de saturação (MS) intensificada e comportamento superparamagnético. Embora MNP metálicas de Fe, Co e bimetálicas de FeCo e FePt possuam altos valores de MS, sua baixa estabilidade química dificulta aplicações em escala nanométrica. Neste trabalho foram sintetizadas NPM de Fe, Co, FeCo e FePt com alta estabilidade química e rigoroso controle morfológico. NPM de óxido metálicos (Fe e Co) também foram obtidas. Dois métodos de síntese foram empregados. Usando método baseado em sistemas nanoheterogêneos (sistemas micelares ou de microemulsão inversa), foram sintetizadas NPM de Fe3O4 e Co metálico. Foram empregados surfactantes cátion-substituídos: dodecil sulfato de ferro(III) (FeDS) e dodecil sulfato de cobalto(II) (CoDS). Para a síntese das NPM, foram estudados e determinados a concentração micelar crítica do FeDS em 1-octanol (cmc = 0,90 mmol L-1) e o diagrama de fases pseudoternário para o sistema n-heptano/CoDS/n-butanol/H2O. NPM esferoidais de magnetita com3,4 nm de diâmetro e comportamento quase-paramagnético foram obtidas usando sistemas micelares de FeDS em 1-octanol. Já as NPM de Co obtidas via microemulsão inversa, apesar da larga distribuição de tamanho e baixa MS, são quimicamente estáveis e superparamagnéticas. O segundo método é baseado na decomposição térmica de complexos metálicos, pelo qual foram preparadas NPM esféricas de FePt e de óxidos metálicos (Fe3O4, FeXO1-X, (Co,Fe)XO1-X e CoFe2O4) com morfologia controlada e estabilidade química. O método não mostrou a mesma efetividade na síntese de NPM de FeAg e FeCo: a liga FeAg não foi obtida enquanto que NPM de FeCo com estabilidade química foram obtidas sem controle morfológico. NPM de Fe e FeCo foram preparadas a partir da redução térmica de NPM de Fe3O4 e CoFe2O4, as quais foram previamente recobertas com sílica. A sílica previne a sinterização inter-partículas, além de proporcionar caráter hidrofílico e biocompatibilidade ao material. As amostras reduzidas apresentaram aumento dos valores de MS (entre 21,3 e 163,9%), o qual é diretamente proporcional às dimensões das NPM. O recobrimento com sílica foi realizado via hidrólise de tetraetilortosilicato (TEOS) em sistema de microemulsão inversa. A espessura da camada de sílica foi controlada variando-se o tempo de reação e as concentrações de TEOS e de NPM, sendo então proposto um mecanismo do processo de recobrimento. Algumas amostras receberam um recobrimento adicional de TiO2 na fase anatase, para o qual foi empregado etilenoglicol como solvente e ligante para formação de glicolato de Ti como precursor. A espessura da camada de TiO2 (2-12 nm) é controlada variando as quantidades relativas entre NPM e o precursor de Ti. Ensaios de hipertermia magnética foram realizados para as amostras recobertas com sílica. Ensaios de hipertermia magnéticas mostram grande aumento da taxa de aquecimento das amostras após a redução térmica, mesmo para dispersões diluídas de NPM (0,6 a 4,5 mg mL-1). Taxas de aquecimento entre 0,3 e 3,0oC min-1 e SAR entre 37,2 e 96,3 W g-1. foram obtidos. A atividade fotocatalítica das amostras recobertas foram próximas à da fase anatase pura, com a vantagem de possuir um núcleo magnético que permite a recuperação do catalisador pela simples aplicação de campos magnéticos externos. Os resultados preliminares dos ensaios de hipertermia magnética e fotocatálise indicam um forte potencial dos materiais aqui relatados para aplicações em biomedicina e em fotocatálise.
The most diverse technological applications of magnetic nanoparticles (MNP) have intensifiedthe interest for materials with different magnetic properties such as enhanced saturationmagnetization (MS) and superparamagnetic behavior. Despite the high MS values of metalparticles of Fe, Co, FeCo and FePt, their low chemical stability hinders most applications at thenanoscale. This thesis reports the synthesis of metallic Fe and Co and bimetallic FeCo and FePtMNP with high chemical stability and strict morphological control. MNP of iron oxide and mixediron-cobalt oxide were also synthesized. Two methods were employed. The first method, basedon nanoheterogeneous systems (micellar or reverse microemulsion systems), was used toprepare magnetite and metallic Co NPM. The method applies cation-substituted surfactants:iron(III) dodecyl sulfate iron (FeDS) and cobalt(II) dodecyl sulfate (CoDS). Before the MNPsyntheses, it were studied e determined the critical micelle concentration of FeDS in 1-octanol(cmc = 0.90 mmol L-1) and the pseudo-ternary phase diagram of n-heptane/CoDS/nbutanol/H2O. Spheroidal MNP of magnetite with 3.4 nm in diameter and quasi-paramagneticbehavior were prepared in octanolic FeDS micellar systems. Despite their broad sizedistribution and low MS, metallic Co MNP were produced in reverse microemulsions withchemical stability and superparamagnetic behavior. The second synthesis method, based onthermal decomposition of metal complexes, was employed to prepare spherical FePt and metaloxides (Fe3O4, FeXO1-X, (Co, Fe)XO1-X and CoFe2O4) MNP. Strict morphological control and highchemical stability were reached. Such method does not show the same effectiveness tosynthesize FeAg and FeCo MNP: the FeAg bimetallic alloy was not obtained while FeCo MNPwith chemical stability and compositional control were prepared with no morphological control.Fe and FeCo MNP were produced by thermal reduction of silica-coated Fe3O4 and CoFe2O4 MPN. The coating, beyond to prevent inter-particle sintering, provides biocompatibility andhydrophilic character. The reduced samples showed a significant increase in MS values(between 21.3 and 163.9%), which is directly proportional to MNP size. The silica coating wasaccomplished by tetraethylorthosilicate (TEOS) hydrolysis in reverse microemulsions. Thethickness of the silica layer is controlled by varying the reaction time and concentration of TEOSand NPM. The observations during coating process allowed to propose its probable mechanism.An additional coating of TiO2 (anatase phase) was performed onto silica layer for somesamples. Anatase coating was achieved by using ethylene glycol as both solvent and ligand toproduce an intermediate complex Ti precursor. The variation of the relative amounts of NPMand the Ti precursor allows to control the thickness of the anatase layer between 2 and 12 nm. Assays of magnetic hyperthermia were performed for silica-coated samples. The heating rate of the reduced samples increases after thermal reduction, even for dilute MNP dispersions (0.6 to4.5 mg mL-1). Heating rates between 0.3 and 3.0o C min-1 and SAR in the range of 37.2 96.3 Wg-1 were obtained. The photocatalytic activities of pure anatase particles and TiO2 -coated MNPwere close, but the magnetic samples has the advantage of being recovered from reactionmedia by applying the external magnetic fields. The preliminary results of magnetichyperthermia and photocatalysis assays indicate such materials have strong potential forapplications in biomedicine and photocatalysis.

Nanomaterials were adorned with recognition molecules and combined with surface-enhanced Raman scattering to selectively separate, identify, and quantify trace amounts of bioactive molecules from within a complex mixture. This work is presented as a rapid, portable, and cost-effective method that complements existing biomolecule analysis techniques, with potential in-field applications in clinical diagnostics, environmental monitoring, and forensic science.

In recent times, plasmonics has been a hallmark in improving optoelectronic device performance as well as in improving sensing. Confining light in dimensions below the diffraction limit and subsequently converting the incident photons into localized charge-density oscillations called localized surface plasmons, optical enhancements of the local fields by many orders of magnitude is possible. This dissertation explores the use of such surface plasmon resonances in core multishell nanostructures and demonstrates the values of such structures in energy harvesting and sensing. Additionally, it also shows the use of emerging plasmonic materials like metal nitrides (TiN, ZrN) instead of traditional plasmonic materials (Au, Ag) in the nanostructure designs. Utilizing the localized surface plasmon resonance (LSPR) in metallic components of core multishell nanowires, calculations of the local density of states as a measure of emission were made using a Green’s function method, while the absorption and scattering were simulated using the Mie formalism. Combining both the absorption and the emission, the quantum efficiency of white LEDs was calculated and the optimal material/dimensions for maximal performance was determined for different phosphor components in a white LED. Additionally, the use of ZrN as a plasmonic cloak for noise cancellation in Si photodetectors is shown and the performance is compared with an Au cloak. Using the developed methodology, it is proved that ZrN cloaks can outperform Au cloaks in a certain region of the visible spectrum, showing the benefit of using such plasmonic systems in place of traditional materials. The fabrication of the different components of the core multishell nanowires is also presented, and in particular, fabrication of ultra-thin (sub-10 nm) plasmonic TiN is achieved. Utilizing plasmon hybridization, a tunable double resonance feature is observed in Au/SiO2/Au core shell shell (CSS) nanoparticles, which have been then demonstrated to improve the photocatalytic performance in hematite. In particular, the double resonance peak allows absorption of light beyond the band gap of hematite and subsequent conversion into photocurrent through hot electron injection. Comparison has been made with Au nanoparticles, and it has been shown that the CSS nanoparticles outperform Au nanoparticles significantly. These CSS nanoparticles have also been used for bioimaging, in particular for Raman spectroscopy, with strong results at high densities of the nanoparticles. Utilizing stronger scattering SiO2/Au Nanoshells, it has been possible to work towards single particle imaging of molecules and demonstration of this phenomenon has been shown here through the use of coherent Raman scattering spectroscopy.

碩士
逢甲大學
化學工程學系
102
Magnetic Fe3O4, NiCo2O4 and CoFe2O4 nanoparticles were used as core materials. A ZnS shell layer is synthesized with zinc acetate and thiourea as precursors by a solvothermal process. Fe3O4@ZnS, NiCo2O4@ZnS and CoFe2O4@ZnS core-shell nanoparticles were used as hydrogen production photocatalysts, which can be recycled by magnetic force for repeated hydrogen generation. The morphology, crystalline property, magnetic property, photocatalytic activity, and magnetic separation capability of the core-shell photocatalysts were studied. The photocatalytic activity of the catalysts was evaluated by splitting Na2S/Na2SO3 solution into H2. Fe3O4@ZnS core-shell nanoparticles exhibit better magnetic separation capability than NiCo2O4@ZnS and CoFe2O4@ZnS analog. The optimized photocatalytic hydrogen production rates of Fe3O4@ZnS, NiCo2O4@ZnS and CoFe2O4@ZnS core-shell nanoparticles reach 3900 μmol h-1 g-1, 880 μmol h-1 g-1 and 900 μmol h-1 g-1, respectively. All the photocatalysts can be recycled by magnetic force. Recycled photocatalysts exhibit good hydrogen generation performance after being recycled for three times. Besides that, Ni-doped stainless steel@ZnS wire mesh photocatalysts for photocatalytic hydrogen production was also prepared by a solvothermal method. The effects of wire mesh density, doping, and surface texture on the photocatalytic activity were studied. The effects of surface texture and doping on the surface wettability and photocatalytic activity were investigated. Energy- III FCU e-Theses &; Dissertations (2014) dispersive X-ray spectroscopy (EDX) analysis and Ni mapping images indicated that a small amount of Ni is loaded on the ZnS. Because of increased surface area of ZnS layer, enhanced separation of the photoinduced carriers by Ni-doping, and effective contact among sacrificial aqueous solution and the ZnS shell, the highest hydrogen evolution is obtained for the Ni-doped SS60@ZnS- Ni1 photocatalyst. Photocatalytic activity and photocurrent of three repeated tests of recycled photocatalysts were also investigated.

M.Sc.
This dissertation describes the synthesis and characterization of CdSe/ZnO and Ag/ZnO core/shell nanoparticles using water as a solvent. The effects of the concentration of the shell precursor, pH, and stabilizing agents on the properties of the nanoparticles were investigated. In general, the type of capping agents had an influence on the crystallite size of the core nanocrystals. The particle size distributions which were calculated from TEM images show that thioglycolic acid as a capping agent produced larger particle sizes compared to thioglycerol. For example, thioglycolic acid produced on average 5.0 nm CdSe nanoparticles while 4.0 nm average CdSe particle size was obtained when using thioglycerol as stabilizer. This observation was confirmed by UV/Vis absorption results which showed that thioglycerol capped CdSe NCs exhibited excitonic peaks positioned at lower wavelength than thioglycolic capped CdSe NCs. XRD results showed that the capping agents used in the current work had no influence upon crystal structure of the CdSe nanocrystals as the cubic structure was obtained with both stabilizers. The effect of shell precursor concentration at pH 12 showed heterogeneous formation of ZnO nanoparticles at high shell precursor concentrations. Various ZnO morphologies including nanoflowers and nanotriangles were observed on TEM images when 50 mL and 25 mL of zinc nitrate solution were used as shell precursors. UV/Vis absorption results also confirmed the presence of ZnO absorption peaks for samples prepared with 50 mL and 25 mL of zinc nitrate solution as shell precursors. PL results showed an increase in peak intensity as a function of precursor volumes. XRD results showed diffraction patterns due to the wurtzite structure of ZnO. CdSe diffraction patterns in these samples were not detected by the XRD instrument. At low volume of the shell precursor, which was 5 mL of 0.05 M zinc nitrate, TEM results showed that spherical CdSe/ZnO core/shell nanoparticles were obtained at pH 12 with 5 mL of 0.05 M zinc nitrate solution and 0.1 M sodium hydroxide used as shell precursor solutions, and thioglycerol as a stabilizer. XRD analysis of the v sample exhibited ZnO diffraction patterns and the CdSe patterns were not detected owing to their low peak intensities compared to those of the ZnO. Similar results were obtained when thioglycolic acid was used a stabilizing agent. However, TEM images showed the hexagonal shape of the CdSe/ZnO core/shell nanoparticles. The pH level was found to influence the photoluminescence properties of the CdSe/ZnO core/shell nanoparticles. The enhanced PL intensity was obtained with CdSe/ZnO core/shell nanoparticles with pH 9 in comparison with CdSe/ZnO core/shell nanoparticles prepared at pH 12. TEM images showed the presence of a thin ZnO shell on the surface of CdSe cores for CdSe/ZnO prepared at pH 9 which could be attributed to the PL enhancement. Although EDS results confirmed the presence of elements such as Cd, Se, Zn and O for both the CdSe core and ZnO shell, the XRD results confirmed the presence of only CdSe diffraction patterns, which suggested the ZnO shell had low peak intensity or was amorphous. A similar effect of these capping agents was observed for Ag nanoparticles as thioglycerol produced average particle size of 16.0 nm whereas 31.0 nm as the average particle size was obtained with thioglycolic acid as stabilizing agent. The crystal phase of Ag NPs was independent of the type of stabilizer. The Ag NPs precipitated in face centred cubic phase. Core/shell Ag/ZnO nanoparticles were produced with 5 ml of zinc nitrate as shell precursor. Higher volumes (50 ml and 25 ml) of zinc nitrate shell precursor induced heterogeneous precipitation of ZnO nanoparticles. XRD patterns confirmed peaks due to ZnO and Ag for Ag/ZnO core/shell nanoparticles.

碩士
逢甲大學
化學工程學系
107
In the first part of this study, the ZnO@ZnS core shell nanorods decorated Ni foam as an immobilized photocatalyst for hydrogen production was prepared by a two-step process, including the formation of ZnO nanorod core by a hydrothermal method and the fabrication of ZnS shell by a sulfidation method. The crystal lattice was analyzed by XRD. FESEM and FETEM were applied to observe the surface morphology and ZnO@ZnS core-shell structure. The surface chemisty and band gap were investigated by XPS and UV-Vis spectra. The surface wetting properties were evaluated by photoluminescence, photocurrent respone and EIS analysis. Formation of the ZnO@ZnS core-shell structure and the incorporation of conductive Ni foam help to decrease the band gap and enhance the separation of photogenerated electron-hole pairs. The porous structure of the Ni foam facilitate the effective contact between the sacrificing agent and the immobilized photocatalyst. These factors contributed to improve the photocatalytic hydrogen production activity. The photocatalyst prepared with a sulfidation time for four hours exhibites the highest activity of 5860 μmol g-1 h-1, and still retaines 90% of hydrogen production activity. For the second part, dendritic PbS@CuS core-shell photocatalyst were synthesized by a two-step process, including the fabrication of a dendritic PbS nanomaterial as a core by hydrothermal method, followed by the formation of the CuS shell through an ion-exchange method. The morphology, surface chemisty, and crystal lattice properties of the core-shell nanomaterials were investigated. The effects of Copper(II) nitrate hydrate precursor concentration on the optical property, carrier separation, and the hydrogen production activity of the photocatalysts were studied. The hydrogen production activity of the photocatalyst prepared by 0.025M Copper(II) nitrate hydrate precursor reaches a maximum of 1736μmol g-1 h-1. PbS@CuS core-shell structure can effectively improve the photocatalytic activity.

博士
逢甲大學
化學工程學系
103
In this study, hierarchical ZnO photocatalyst and stainless steel wire mesh-based hierarchical ZnO photocatalyst were synthesized by a hydrothermal route and used for photocatalytic degradation and hydrogen production applications. By changing the reaction conditions and dopant concentration, nanostructure, chemical and crystalline properties of the photocatalysts can be adjusted to optimize the photocatalytic degradation and hydrogen production efficiency. Effects of reaction conditions on the nanostructure, surface chemistry, crystalline properties, photocatalytic degradation activity and hydrogen production activity were investigated by FESEM, TEM, XRD, XPS, DRS, GC and SECM. The energy gap and light absorption characteristics of the photocatalyst can be tuned by doping. It helps the separation of photogenerated electron-hole pairs. The UV-Visible DRS spectra indicates that the direct energy gap (Eg) decreases with increasing dopant concentration. The PEC-SECM was used to evaluate the photocurrent response and the photocatalytic activity. This study can be divided into two parts, including photocatalytic degradation and hydrogen production. In photocatalytic degradation section, the methyl orange dye can be completely degraded within 50 min by sliver decorated hierarchical ZnO photocatalyst under UV light irradiation. For the sliver decorated hierarchical ZnO photocatalysts, the effects of nanostructure, chemical and crystalline properties on the photocatalytic degradation activity were investigated. For the silver doped stainless steel wire mesh-based hierarchical ZnO photocatalyst, degradation of methyl orange can be achieved within 60 min under visible light irradiation. For the silver doped ZnO decorated stainless steel wire mesh-based hierarchical photocatalysts, the effects of nanostructure, chemical and crystalline properties on the photocatalytic degradation activity were investigated. The photocatalytic hydrogen production performances of sulfur doped stainless steel wire mesh-based hierarchical ZnO phtotcatalysts reached 3400 μmol g-1h-1 when the Na2S precursor concentration is 15 mM. The photocatalytic hydrogen production performances of core-shell stainless steel wire mesh-based hierarchical ZnO/ZnS phtotcatalysts reached 55.67 μmol g-1h-1 when the Na2S precursor concentration is 30 mM under visible irradiation.

With the emergence of smart electronic devices, we have witnessed a rapid surge in the growth and subsequent drive-in for the miniaturization of electronic interfaces. Any electronic gadget that transmits, distributes, or uses electrical energy creates electromagnetic interference (EMI), has harmful impacts on device performance. This increase in unrestricted EM pollution can also affect human wellbeing as well as the surrounding environment if proper shielding is not provided. Various EM screeners are designed in the last few decades, such as metals and metallic architectures, ferrite pads, ferritic paints and so on. While each one of them efficient in certain terms but also suffers some serious drawbacks such as corrosion, high weight structure, reflection-driven mechanism and so on. Polymer nanocomposites evolved rapidly as one of the promising EM absorbers as they address all the drawbacks of previously mentioned materials. Among the various nanocomposites, Polyvinylidene fluoride (PVDF)-based nanocomposites have been studied for EMI shielding applications involving various kinds of fillers. Heterogeneous dispersion of conducting and magnetic nanoparticles in the polymer matrix leads to synergistic absorption of microwave radiation in these systems. However, materials derived out of these nanocomposites are often encountered with few drawbacks such as high filler loading and large thickness, making them unsuitable for smart, sophisticated and high-end applications. However, the inclusion of only a single component (such as conducting, magnetic, or dielectric) in a polymer matrix to design EM shields failed to provide significant shielding values at smaller thicknesses. However, though satisfactory shielding may be achieved by increasing the filler loading, it may result in processing difficulties and poor structural properties in the case of composites. To address all the discussed, this thesis titled “Polyvinylidene fluoride(PVDF) based nanocomposites with multi-layered architecture containing core-shell nanomaterials for electromagnetic interference shielding” features the systematic studies of key requirement properties to sort out the challenges. This thesis attempts to provide various synthesis and fabrication techniques of core-shell nanomaterials and core-double-shell nanomaterials based polymer nanocomposites for EMI shielding and some other associated applications. This work also provides some physical insight into the materials design and mechanism of shielding at high frequency in polymer composite systems with the proper design choices. Under this framework, current work discusses few strategies to design and synthesize multicomponent core-shell heterostructures, composited with PVDF to make multi-layered architectures, which have the potential to deliver better shielding values at relatively lower filler loading and low thickness, extremely desired as per state key requirement. Designed core-shell nanostructures when composited with PVDF matrix, led to maximum attenuation of incoming electromagnetic radiation ‒ a remarkable 42 dB (> 99.99% attenuation) dominated by absorption (82%) for 600-micron thickness. Additionally, these composites were effective in blocking ultraviolet radiation (both UVA and UVB) up to 99.9%. Apart from being an effective shield, these composites were also able to dissipate heat very quickly, were durable at very high service temperatures, and under mechanical stresses.
MHRD, DST

This thesis is devoted to the investigation of mechanical properties and self-assembly process of materials at the nanoscale. Various nanostructured materials such as nanoparticles, nanotubes, nanowires and thin films are used as constituent elements of nanodevices. Hence, knowledge of the mechanical properties of materials at the nanoscale is extremely important for understanding their functionality in nanodevices. Mechanical properties of nanostructured materials may significantly differ from those of their bulk counterparts due to the high surface to volume ratio in nanostruc-tures. We particularly focus on the role of the surface region on the stiffness of nanomaterials. We have shown that the stiffness of a nanomaterial can be tuned over a wide range by introducing appropriate coating on the nanostructure surface. We have also explored the effects of the surface region on the stability of various phases in a nanostructure. In the second part of this thesis, we have described the self-assembly process of nanostructures mediated by drendrimers. Self-assembly techniques are frequently used to decorate nanostructures into specific networks. The motivation of this study is to investigate the mechanisms which control the effective interaction and the inter-particle distance between nanoparticle-dendrimer compos-ites. Control over the inter-particle separation is very important since it has a strong influence on the electronic and optical properties of the nanostructures. In the following paragraphs, we sum-marize the results of our study. We start with a brief introduction to the mechanical properties and self-assembly process of nanostructures in the first chapter. A brief review of the work done on these topics in the recent past is presented in this chapter. We discuss the results and conclusions of various experimental and numerical studies on these topics. We also mention the motivation for the studies we have carried out. At the end, we briefly describe the numerical methods (molecular dynamics (MD) and density functional theory (DFT)) which have been used in our investigations. In the second chapter, we discuss the effects of the surface region on the mechanical properties of nanostructures. We have investigated the size and growth direction dependence of the mechanical properties of ZnS nanowires and thin films as a case study. We observe that the Young’s modulus of nanowires and thin films strongly depends on their size and growth direction. This size and growth direction dependence of the stiffness of nanostructured materials can be explained in terms of their surface modifications. Since the energy of the surface region is usually higher than that of the core region in a nanostructure, the surface atoms move their positions to minimize the surface energy. As a result, bond lengths at the surface region are usually different from their bulk values. We observe that in ZnS nanowires and thin films, the average bond length at the surface region is lower than that in the core region which remains unchanged from its bulk value. This decrease in the bond length (or equivalently increase in the bond energy) increases the effective stiffness of the entire nanostructure. As the size of the nanowire/thin film increases, the effect of the surface region gradually decreases and hence the Young’s modulus value converges to the bulk value. Since the surface region has a strong influence on the mechanical properties of nanostructures, the stiffness of a nanostructure can be tuned by modifying the surface region with other materials. In chapter three, we have shown that the stiffness of ZnS nanowires can be tuned by introducing a thin CdS shell on top of the ZnS surface. In general, the stiffness of a nanostructure can be increased (decreased) by coating the surface region with a stiffer (less stiff) material. However, the stiffness of the core/shell nanostructures strongly depends on the properties of the interface between the core and the shell. We observe that the binding energy between the core and shell regions is relatively low due to the lattice mismatch at the interface region of core/shell nanostructures. This lower binding energy strongly affects the stiffness of core/shell nanostructures. We have also shown that thermal properties such as thermal conductivity and melting temperature of core/shell structures can be tuned by changing the coating material. In chapter four, we discuss the effects of the surface region on the stability of various phases in a nanostructure. The surface atoms may stabilize a particular phase in a nanostructure which is not a stable phase in the bulk material. In this chapter, we investigate the stability of the h-MgO phase, an intermediate structure found during the wurtzite to rock salt transformation, in CdSe nanostructures. We observe that this five-fold coordinated phase is more stable at lower temperatures and smaller sizes of the nanowires. The appearance of this phase has not been observed till now in experiments. We show that this phase is not stable for larger CdSe nanocrystals on which the experiments have been done. In the rest of the thesis, we have presented the results of our studies of self-assembly of nanostructures mediated by DNAs and dendrimers. First we describe in chapter five the nature of the effective interaction between two PAMAM dendrimers. Dendrimers are frequently used to coat surfaces of nanoparticles to prevent the nanoparticles from aggregation. The interaction between such nanoparticle-dendrimer composites depends strongly on the nature of the effective interac-tion between dendrimers. We have used fully atomistic MD simulations to calculate the potential of mean force (PMF) between two PAMAM dendrimers. We show that the effective interaction strongly depends on the size (generation) and protonation level of the dendrimers. The PMF profiles of nonprotonated dendrimers show a global minimum which represents the attractive nature of the interaction between the dendrimers up to a certain center-to-center distance. On the other hand, the interaction between protonated dendrimers is repulsive throughout their interaction re-gion. The PMF profiles are fitted very well by a sum of an exponential and a Gaussian function. This observation is in contradiction with some of the results of existing coarse-grained simulations which predicted the effective interaction between dendrimers to be Gaussian. Our atomistic simulation which includes all the local fluctuations is expected to give more accurate results. Information about the effective interaction between two dendrimers helps in understanding how dendrimer molecules can be used to control the interaction strength and the preferred inter-particle distance between two nanostructures. In chapter six, we discuss the effective interaction between two dendrimer grafted gold nanoparticles. We observe that dendrimer molecules can get adsorbed spontaneously on the surface of a gold nanoparticle. These grafted dendrimers significantly alter the interaction between the gold nanoparticles. We have explored the effects of proto-nation level and the density of the grafted dendrimers on the effective interaction between two gold nanoparticle-dendrimer composites. We observe that these nanoparticle-dendrimer composites at-tract each other at low grafting density. However, the interaction strength and the inter-particle distance at the minimum of the potential are much lower and higher, respectively than those between two bare gold nanoparticles. Interestingly at higher grafting density, the nature of the interaction between the nanocomposites depends on the protonation level of the grafted dendrimers. Nanoparticles grafted with nonprotonated dendrimers still attract each other but with lower inter-action strength and higher inter-particle distance compared to the values for low grafting density. On the other hand, nanocomposites grafted with protonated dendrimers repel each other at high grafting density. Thus we show that the effective interaction and the optimal inter-particle distance between the nanostructures can be tuned over a wide range by using a suitable grafting density and protonation level of the dendrimers. In the seventh chapter, we describe a strategy to assemble dendrimers with the help of sin-gle stranded DNA (ssDNA). We attach an ssDNA to one dendrimer and a complementary ssDNA to a second dendrimer. These two complementary ssDNAs bind with each other through base pair formation to assemble the dendrimers into a single structure. The complementary ssDNAs form a dsDNA which is rigid enough to maintain the inter-dendrimer distance almost the same as the length of the DNA. The inter-dendrimer distance can be tuned by changing the DNA length. However, this method strongly depends on the protonation level of the dendrimers. It works well only for nonprotonated dendrimers. Since the protonated dendrimers are positively charged, they strongly interact with the negatively charged ssDNAs through electrostatic interaction. As a result, ssDNAs wrap the dendrimer surface and hence the inter-dendrimer distance can not be controlled. We have also verified that this method works for multiple nonprotonated dendrimers as well. In the final chapter of this thesis, we summarize the main results and conclude with a brief discussion of future directions of research on the problems considered in the thesis.

This thesis is devoted to the investigation of mechanical properties and self-assembly process of materials at the nanoscale. Various nanostructured materials such as nanoparticles, nanotubes, nanowires and thin films are used as constituent elements of nanodevices. Hence, knowledge of the mechanical properties of materials at the nanoscale is extremely important for understanding their functionality in nanodevices. Mechanical properties of nanostructured materials may significantly differ from those of their bulk counterparts due to the high surface to volume ratio in nanostruc-tures. We particularly focus on the role of the surface region on the stiffness of nanomaterials. We have shown that the stiffness of a nanomaterial can be tuned over a wide range by introducing appropriate coating on the nanostructure surface. We have also explored the effects of the surface region on the stability of various phases in a nanostructure. In the second part of this thesis, we have described the self-assembly process of nanostructures mediated by drendrimers. Self-assembly techniques are frequently used to decorate nanostructures into specific networks. The motivation of this study is to investigate the mechanisms which control the effective interaction and the inter-particle distance between nanoparticle-dendrimer compos-ites. Control over the inter-particle separation is very important since it has a strong influence on the electronic and optical properties of the nanostructures. In the following paragraphs, we sum-marize the results of our study. We start with a brief introduction to the mechanical properties and self-assembly process of nanostructures in the first chapter. A brief review of the work done on these topics in the recent past is presented in this chapter. We discuss the results and conclusions of various experimental and numerical studies on these topics. We also mention the motivation for the studies we have carried out. At the end, we briefly describe the numerical methods (molecular dynamics (MD) and density functional theory (DFT)) which have been used in our investigations. In the second chapter, we discuss the effects of the surface region on the mechanical properties of nanostructures. We have investigated the size and growth direction dependence of the mechanical properties of ZnS nanowires and thin films as a case study. We observe that the Young’s modulus of nanowires and thin films strongly depends on their size and growth direction. This size and growth direction dependence of the stiffness of nanostructured materials can be explained in terms of their surface modifications. Since the energy of the surface region is usually higher than that of the core region in a nanostructure, the surface atoms move their positions to minimize the surface energy. As a result, bond lengths at the surface region are usually different from their bulk values. We observe that in ZnS nanowires and thin films, the average bond length at the surface region is lower than that in the core region which remains unchanged from its bulk value. This decrease in the bond length (or equivalently increase in the bond energy) increases the effective stiffness of the entire nanostructure. As the size of the nanowire/thin film increases, the effect of the surface region gradually decreases and hence the Young’s modulus value converges to the bulk value. Since the surface region has a strong influence on the mechanical properties of nanostructures, the stiffness of a nanostructure can be tuned by modifying the surface region with other materials. In chapter three, we have shown that the stiffness of ZnS nanowires can be tuned by introducing a thin CdS shell on top of the ZnS surface. In general, the stiffness of a nanostructure can be increased (decreased) by coating the surface region with a stiffer (less stiff) material. However, the stiffness of the core/shell nanostructures strongly depends on the properties of the interface between the core and the shell. We observe that the binding energy between the core and shell regions is relatively low due to the lattice mismatch at the interface region of core/shell nanostructures. This lower binding energy strongly affects the stiffness of core/shell nanostructures. We have also shown that thermal properties such as thermal conductivity and melting temperature of core/shell structures can be tuned by changing the coating material. In chapter four, we discuss the effects of the surface region on the stability of various phases in a nanostructure. The surface atoms may stabilize a particular phase in a nanostructure which is not a stable phase in the bulk material. In this chapter, we investigate the stability of the h-MgO phase, an intermediate structure found during the wurtzite to rock salt transformation, in CdSe nanostructures. We observe that this five-fold coordinated phase is more stable at lower temperatures and smaller sizes of the nanowires. The appearance of this phase has not been observed till now in experiments. We show that this phase is not stable for larger CdSe nanocrystals on which the experiments have been done. In the rest of the thesis, we have presented the results of our studies of self-assembly of nanostructures mediated by DNAs and dendrimers. First we describe in chapter five the nature of the effective interaction between two PAMAM dendrimers. Dendrimers are frequently used to coat surfaces of nanoparticles to prevent the nanoparticles from aggregation. The interaction between such nanoparticle-dendrimer composites depends strongly on the nature of the effective interac-tion between dendrimers. We have used fully atomistic MD simulations to calculate the potential of mean force (PMF) between two PAMAM dendrimers. We show that the effective interaction strongly depends on the size (generation) and protonation level of the dendrimers. The PMF profiles of nonprotonated dendrimers show a global minimum which represents the attractive nature of the interaction between the dendrimers up to a certain center-to-center distance. On the other hand, the interaction between protonated dendrimers is repulsive throughout their interaction re-gion. The PMF profiles are fitted very well by a sum of an exponential and a Gaussian function. This observation is in contradiction with some of the results of existing coarse-grained simulations which predicted the effective interaction between dendrimers to be Gaussian. Our atomistic simulation which includes all the local fluctuations is expected to give more accurate results. Information about the effective interaction between two dendrimers helps in understanding how dendrimer molecules can be used to control the interaction strength and the preferred inter-particle distance between two nanostructures. In chapter six, we discuss the effective interaction between two dendrimer grafted gold nanoparticles. We observe that dendrimer molecules can get adsorbed spontaneously on the surface of a gold nanoparticle. These grafted dendrimers significantly alter the interaction between the gold nanoparticles. We have explored the effects of proto-nation level and the density of the grafted dendrimers on the effective interaction between two gold nanoparticle-dendrimer composites. We observe that these nanoparticle-dendrimer composites at-tract each other at low grafting density. However, the interaction strength and the inter-particle distance at the minimum of the potential are much lower and higher, respectively than those between two bare gold nanoparticles. Interestingly at higher grafting density, the nature of the interaction between the nanocomposites depends on the protonation level of the grafted dendrimers. Nanoparticles grafted with nonprotonated dendrimers still attract each other but with lower inter-action strength and higher inter-particle distance compared to the values for low grafting density. On the other hand, nanocomposites grafted with protonated dendrimers repel each other at high grafting density. Thus we show that the effective interaction and the optimal inter-particle distance between the nanostructures can be tuned over a wide range by using a suitable grafting density and protonation level of the dendrimers. In the seventh chapter, we describe a strategy to assemble dendrimers with the help of sin-gle stranded DNA (ssDNA). We attach an ssDNA to one dendrimer and a complementary ssDNA to a second dendrimer. These two complementary ssDNAs bind with each other through base pair formation to assemble the dendrimers into a single structure. The complementary ssDNAs form a dsDNA which is rigid enough to maintain the inter-dendrimer distance almost the same as the length of the DNA. The inter-dendrimer distance can be tuned by changing the DNA length. However, this method strongly depends on the protonation level of the dendrimers. It works well only for nonprotonated dendrimers. Since the protonated dendrimers are positively charged, they strongly interact with the negatively charged ssDNAs through electrostatic interaction. As a result, ssDNAs wrap the dendrimer surface and hence the inter-dendrimer distance can not be controlled. We have also verified that this method works for multiple nonprotonated dendrimers as well. In the final chapter of this thesis, we summarize the main results and conclude with a brief discussion of future directions of research on the problems considered in the thesis.

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.

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.

[ES] La fabricación de nanopartículas con tamaños por debajo de los 100 nm ha permitido el desarrollo de innovadores nanodispositivos capaces de interactuar de forma directa con sistemas vivos a nivel celular y molecular, convirtiéndose en una parte fundamental dentro del campo de la nanomedicina. Uno de los principales retos a los que se enfrenta la ingeniería de nanopartículas es el desarrollo de nanodispositivos con propiedades físico-químicas bien definidas, ya que de ellas depende el comportamiento y biodistribución de dichos sistemas una vez introducidos en el organismo. No menos importante es el desarrollo de protocolos de síntesis reproducibles y optimizados, indispensables para la fabricación y escalado de nanodispositivos que puedan ser trasladados a futuras aplicaciones biomédicas. El principal objetivo de este proyecto de doctorado es el estudio y fabricación de nanopartículas magnéticas mesoporosas de sílice con estructura "core-shell" para su aplicación como agentes teranósticos en el campo de la nanomedicina. En este estudio se analiza en profundidad la síntesis y caracterización de dichos nanomateriales con el objetivo de producir nanopartículas con unas propiedades físico-químicas bien definidas de forma controlada y reproducible. La obtención de dichas nanopartículas supondría un gran avance de cara al desarrollo de nanodispositivos más complejos y sofisticados. El contenido de la tesis se ha estructurado en distintos capítulos que se detallan brevemente a continuación: ¿El capítulo 1 es una introducción a la nanomedicina, destacando el papel fundamental que tienen las nanopartículas en el desarrollo de nuevas aplicaciones biomédicas. A continuación se presentan las nanopartículas de sílice mesoporosa, mostrando la gran versatilidad de dichos nanomateriales para el desarrollo de dispositivos teranósticos así como sistemas para la liberación controlada de fármacos. Por último, se destaca la importancia de fabricar nanodispositivos con unas propiedades físico-químicas bien definidas como requisito indispensable para la traslación de los resultados experimentales hacia el campo clínico. ¿El capítulo 2 incluye los objetivos principales de la tesis. ¿El capítulo 3 se centra en la síntesis y caracterización de nanopartículas superparamagnéticas de óxido de hierro (USPIONs), siendo estas utilizadas en capítulos posteriores para la síntesis de las nanopartículas mesoporosas tipo "core-shell". Las USPIONs son preparadas a través de un método sencillo de coprecipitación en el que se emplean condiciones de reacción moderadas. Las nanopartículas obtenidas son caracterizadas en profundidad, analizando sus propiedades magnéticas para su aplicación en hipertermia magnética y como agentes de contraste dual en imagen por resonancia magnética (MRI). ¿El capítulo 4 está dedicado a la preparación de nanopartículas magnéticas mesoporosas de sílice con estructura "core-shell". Los conceptos fundamentales relacionados con los mecanismos de formación de este tipo de nanomateriales son ampliamente analizados, así como los parámetros de reacción involucrados en la síntesis. Como punto de partida, se propone un protocolo de síntesis general para la obtención de las nanopartículas tipo "core-shell". A continuación, se analiza en profundidad el efecto que los distintos parámetros de reacción tienen en las propiedades físico-químicas de dichas nanopartículas. Para la fase de optimización se utiliza un modelo semi-empírico como referencia, racionalizando los resultados experimentales observados en base a un posible mecanismo de formación. ¿El capítulo 5 se centra en el análisis y caracterización de la estructura mesoporosa de las nanopartículas tipo "core-shell". Además, se analiza el efecto que los distintos parámetros de reacción tienen sobre la estructura final de las nanopartículas, aportando información adicional sobre su posible mecanismo
[CAT] La fabricació de nanopartícules amb grandàries per davall dels 100 nm ha permés el desenvolupament d'innovadors nanodispositius capaços d'interactuar de forma directa amb sistemes vius a nivell cel¿lular i molecular, convertint-se en una part fonamental dins del camp de la nanomedicina. Un dels principals reptes als quals s'enfronta l'enginyeria de nanopartícules és el desenvolupament de nanodispositius amb propietats físic-químiques ben definides, ja que d'elles depén el comportament i biodistribució d'aquests sistemes una vegada introduïts en l'organisme. No menys important és el desenvolupament de protocols de síntesis reproduïbles i optimitzats, indispensables per a la fabricació a gran escala de nanodispositius que puguen ser utilitzats en futures aplicacions biomèdiques. El principal objectiu d'aquest projecte de doctorat és l'estudi i fabricació de nanopartícules magnètiques mesoporoses de sílice amb estructura "core-shell" per a la seua aplicació com a agents teranòstics en el camp de la nanomedicina. En aquest estudi s'analitza en profunditat la síntesi i caracterització d'aquests nanomaterials amb l'objectiu de produir nanopartícules amb unes propietats físic-químiques ben definides de forma controlada i reproduïble. L'obtenció d'aquestes nanopartícules suposaria un gran avanç de cara al desenvolupament de nanodispositius més complexos i sofisticats. El contingut de la tesi s'ha estructurat en diferents capítols que es detallen breument a continuació: ¿El capítol 1 és una introducció a la nanomedicina, destacant el paper fonamental que tenen les nanopartícules en el desenvolupament de noves aplicacions biomèdiques. A continuació es presenten les nanopartícules de sílice mesoporosa, mostrant la gran versatilitat d'aquests nanomaterials per al desenvolupament de dispositius teranòstics així com sistemes per a l'alliberament controlat de fàrmacs. Finalment, es destaca la importància de fabricar nanodispositius amb unes propietats físic-químiques ben definides com a requisit indispensable per a la translació dels resultats experimentals al camp clínic. ¿El capítol 2 inclou els objectius principals de la tesi així com els objectius específics proposats per a cada capítol de la tesi. ¿El capítol 3 està dedicat a la síntesi i caracterització de nanopartícules superparamagnétiques d'òxid de ferro (USPIONs), sent aquestes utilitzades en capítols posteriors per a la síntesi de les nanopartícules mesoporoses tipus "core-shell". Les USPIONs són preparades a través d'un mètode senzill de coprecipitació en el qual s'empren condicions de reacció moderades. Les nanopartícules obtingudes són caracteritzades en profunditat, analitzant les seues propietats magnètiques per a la seua aplicació en hipertèrmia magnètica i com a agents de contrast dual en imatge per ressonància magnètica (MRI). ¿El capítol 4 està dedicat a la preparació de nanopartícules magnètiques mesoporoses de sílice amb estructura "core-shell". Els conceptes fonamentals relacionats amb els mecanismes de formació d'aquest tipus de nanomaterials són àmpliament analitzats, així com els paràmetres de reacció involucrats en la síntesi. Com a punt de partida, es proposa un protocol de síntesi general per a l'obtenció de les nanopartícules tipus "core-shell". A continuació, s'analitza en profunditat l'efecte que els diferents paràmetres de reacció tenen en les propietats físic-químiques d'aquestes nanopartícules. Per a la fase d'optimització s'utilitza un model semi-empíric com a referència, racionalitzant els resultats experimentals observats sobre la base d'un possible mecanisme de formació. ¿El capítol 5 està dedicat a l'anàlisi i caracterització de l'estructura mesoporosa de les nanopartícules tipus "core-shell". A més, s'analitza l'efecte que els diferents paràmetres de reacció tenen sobre l'estructura final de les nanopartícules, aportant informació
[EN] The fabrication of nanoparticles with sizes below 100 nm has opened the door to the development of innovative nanodevices that directly interact with living systems at the cellular and molecular level, becoming an essential part of nanomedicine. One of the main challenges that nanoparticle engineering is currently facing is the design of nanodevices with well-defined physico-chemical properties, which ultimately determine the fate and function of these systems inside the organism. Similarly, the development of reproducible and versatile synthetic protocols is of great importance for manufacture purposes, a fundamental requirement for an efficient translation of this technology into the clinic. The main objective of this PhD thesis is the study and fabrication of core-shell-type magnetic mesoporous silica nanoparticles (M-MSNs) for their application as theranostic nanodevices in the field of nanomedicine. A comprehensive study about the synthesis and characterization of this type of nanomaterials is presented with the aim of obtaining core-shell M-MSNs with well-defined physico-chemical properties in a robust and reproducible way. The fabrication of such particles would provide a versatile and reliable platform for the development of more complex nanodevices with advanced functionalities. The thesis has been structured into several chapters that are briefly summarized as follows: ¿Chapter 1 is an introduction to the topic of nanomedicine, highlighting the importance of nanoparticles in the development of new biomedical applications. Mesoporous silica nanoparticles are then introduced, showing the great versatility that this nanomaterials offer for the development of theranostic nanodevices and smart drug delivery systems. Finally, the development of nanodevices with well-defined physico-chemical properties is identified as a crucial requirement for overcoming biological barriers and facilitate the translation of nanomedicines from the bench to bedside. ¿Chapter 2 presents the aims of this thesis and the specific objectives that are addressed in the following chapters. ¿Chapter 3 is devoted to the synthesis and characterization of ultrasmall superparamagnetic iron oxide nanoparticles (USPIONs), which are later used as magnetic seeds for the synthesis of core-shell M-MSNs. USPIONs are prepared through a simple coprecipitation method using mild reaction conditions. The obtained nanoparticles are fully characterized and their magnetic properties are analyzed focusing on magnetic hyperthermia and dual MR imaging applications. ¿Chapter 4 is a comprehensive study about the preparation of monodisperse core-shell M-MSNs. The main concepts related to the synthesis and formation mechanisms of this type of nanomaterials are revised, together with the reaction parameters that are expected to have a major contribution on the reaction. As a starting point, a general synthetic protocol for the synthesis of core-shell M-MSNs is presented. Then, specific reaction parameters are investigated in order to understand their effect on the physico-chemical properties of the obtained nanoparticles. The application of a semi-empirical model to the optimization stage is presented in an attempt to provide an adequate reference framework to understand the formation of this complex nanodevices. ¿Chapter 5 presents a detailed analysis about the characterization of mesoporous silica materials and, in particular, the assessment of the mesoporous structure of MSNs with a radial distribution of wormhole-like channels. The effects that specific reaction parameters have on the mesoporous silica structure of core-shell M-MSNs are also analysed, providing additional information about the formation of this type of nanoparticles. ¿Chapter 6 gathers the main conclusions of this thesis.
Sánchez Cabezas, S. (2019). Development of a reproducible and optimized synthetic protocol for the preparation of monodisperse core-shell-type magnetic mesoporous silica nanoparticles [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/129878
TESIS