Engineered nanomaterials (ENMs) are currently used in a wide range of manufacturing processes and applications thanks to the numerous technical and economic benefits derived from the incorporation of ENMs in these processes. Accompanying these benefits are the potential toxicity of ENMs to humans and the environment. Previous research has shown that ENMs display strong toxicity to plants. Earlier research suggested that physicochemical properties of ENMs such as their size, shape, and surface properties considerably affect toxicity; however, the unique physicochemical properties of ENMs affect their phytotxicity to plants is still unknown. This research evaluated the phytotoxicity of silver and gold nanoparticles to lettuce plants in both sand and hydroponic conditions by monitoring a wide range of plant physiological parameters after their exposure to these nanoparticles with two coating materials (citrate and polyvinylpyrrolidone) and three shapes (sphere, wire and plate) at 200 and 1000 µg/L concentrations. The result from lettuce in hydroponics showed that spherical silver or gold nanoparticles with both coatings did not affect biomass significantly, but both of silver and gold nanoparticles at 1000 µg/L slightly reduced the biomass compared to the control lettuce. The effect on root leakage was similar, but spherical silver nanoparticles had slightly higher damage due to root leakage than gold nanoparticles at the same concentration. The lettuce treated to citrate-coated gold nanoparticles significantly reduced chlorophyll content compared to citrate-coated silver nanoparticles. Secondly, when it came to the surface coating, the plant exposed to 1000 µg/L spherical citrate- coated silver or gold nanoparticles had higher root leakage compared to PVP-coated nanoparticles. Both of 1000 µg/L spherical citrate-coated silver nanoparticles and gold nanoparticles significantly reduced chlorophyll content compared to PVP-coated nanoparticles. Thirdly, for different shapes of PVP-coated silver nanoparticles, the plant exposed to plate shaped and sphere shaped silver nanoparticles had significantly lower biomass compared to the wire shaped silver nanoparticles. The plant exposed to spherical silver nanoparticles had the lowest chlorophyll content between plate shaped and wire shaped silver nanoparticles. In addition, the result from lettuce in sand medium showed that the biomass production and the root leakage showed no significant difference between spherical citrate-coated, spherical PVP-coated, and silver ions at 200 µg/L. In conclusion, different nanoparticles affected different physiological processes of plants differently.

xvii, 183 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / In recent years, nanoscience has evolved from a multidisciplinary research concept to a primary scientific frontier. Rapid technological advancements have led to the development of nanoscale device components, advanced sensors, and novel biomimetic materials. However, potential negative impacts of nanomaterials are sometimes overlooked during the discovery phase of research. The implementation of green chemistry principles can enhance nanoscience by maximizing safety and efficiency while minimizing the environmental and societal impacts of nanomaterials. This dissertation introduces the concept of green nanosynthesis, demonstrating the application of green chemistry to the synthesis of nanornaterials. A comprehensive review of the synthesis of metal nanomaterials is presented, demonstrating how individual green chemistry principles can improve traditional synthetic routes as well as guide the design of new materials. Detailed examples of greener syntheses of functionalized gold nanoparticles with core diameters of 2-10 nm are described in subsequent chapters, beginning with a method for functionalizing citrate-stabilized gold nanoparticles that are desirable for advanced applications. Although citrate-stabilized gold nanoparticles can be easily produced from a classic procedure using mild reagents and benign methods, functionalization via ligand exchange is often unsuccessful. It was discovered that an ill-defined layer comprised of citrate and other ligands interferes with functionalization processes. By removing excess citrate in a manner where overall structure and stability is maintained, gold cores produced by this route are readily functionalized by incoming thiols, affording unprecedented control over surface composition and functionality. A direct route to functional nanomaterials using Bunte salt precursors is discussed next, describing the use of easily synthesized shelf-stable alternatives to thiols in the preparation of water-soluble gold nanoparticles. Control of core size and surface chemistry is demonstrated through simple manipulation of reagent ratios, yielding products similar to those produced by traditional direct syntheses which rely on the use of thiols. The use of functionalized nanoparticles as "building blocks" for more complex structures was demonstrated in self-assembly processes. Cationic gold particles were deposited upon DNA scaffolds to create linear arrays. A discussion of the future outlook of green nanosynthesis concludes this work, identifying immediate challenges and long-term goals. This dissertation contains previously published and co-authored materials. / Adviser: James E. Hutchison

Made available in DSpace on 2016-03-07T19:20:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-02-27. Added 1 bitstream(s) on 2016-03-07T19:24:00Z : No. of bitstreams: 1 000858098.pdf: 1377224 bytes, checksum: 7b94c05d71eb0b0a82596fe9940bb370 (MD5) / No presente trabalho foram estudadas as reações de oxidação do glicerol, em meio alcalino (KOH), sobre a superfície dos materiais Au/C, AuSn/C e Au2Bi/C, sintetizados por microemulsão, e AuSn/C e Au2Bi/C, sintetizados por redução por poliol. A caracterização física dos materiais foi realizada por DRX e EDX. Pelos difratogramas obtidos, foi verificado que, através do método da microemulsão, ligas AuSn/C e Au2Bi/C foram formadas, e que pelo método de redução por poliol ocorreu formação de cluster, constituído por Au e Sn, e de um material formado pela liga Au2Bi/C e por Bi. A liga AuSn/C não apresentoyu variação significativa na composição atômica obtida por EDX em relação a razão atômica nominal, indicando que o método de microemulsão foi eficiente na preparação desse material. Já o cluster, apesar de ter tido reprodutividade nos diferentes pontos analisados, não apresentou a composição atômica esperada. Em relação aos materiais formados por Bi, estes não mostraram coerência nos resultados obtidos por EDX. A caracterização eletroquímica da superfície foi realizada por voltametria cíclica. O desempenho eletroquímico dos materiais frente ao processo eletro-oxidação do glicerol foi avaliado tanto por voltametria como por cronoamperometria. Todos os materiais apresentaram desempenho eletroquímico, porém a liga AuSn/C foi a que apresentou os melhores resultados devido a um efeito eletrônico e um possível efeito bifuncional / In the present work, we studied the oxidation reaction of glycerol, in alkaline medium (KOH), on the surface of Au/C, AuSn/C e Au2Bi/C materials, synthesized by microemulsion, and Au/Sn/C and Au2Bi/C, by reduction of polyol. The physical characterization of materials was performed by XRD and EDX. By diffractograms obtained it was found that, by the microemulsion method, AuSn/C and Au2Bi/C alloys have been formed, and by the polyol reduction method, occurred cluster formation consisting of Au and Sn, and a material formed by the Au2Bi/C alloy and Bi. The AuSn/C alloy showed no significant variation in the atomic composition obtained by EDX in relation to the nominal atomic ratio, indicating that the microemulsion method was effective in preparing this material. However, the cluster, despite having reproducibility from various points analyzed did not show the expected atomic composition. In relation to the materials formed by Bi, these showed no coherence in the results obtained by EDX. The electrochemical characterization of the surface was accomplished by cyclic voltammetry. The electrochemical performance of the material against glycerol electrooxidation was assessed both by voltammetry and by chronoamperometry. All materials presented electrochemical performance, but the AuSn/C showed the best results, probality due to an electronic effect, and a possible bifunctional effect

Made available in DSpace on 2014-06-11T19:25:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-05-20Bitstream added on 2014-06-13T18:29:02Z : No. of bitstreams: 1 santos_na_me_araiq_parcial.pdf: 107047 bytes, checksum: 6ab4a09755a1002babf2aaad1bf894e9 (MD5) Bitstreams deleted on 2015-05-28T14:25:10Z: santos_na_me_araiq_parcial.pdf,. Added 1 bitstream(s) on 2015-05-28T14:26:14Z : No. of bitstreams: 1 000719118.pdf: 2090606 bytes, checksum: 5c9626436fc671dfbfafc881dab966c0 (MD5) / Nesse trabalho foi realizado um estudo comparativo das propriedades físicas e eletrônicas e das atividades catalíticas para a oxidação de etanol de nanopartículas bi e trimetálicas suportadas em pó de carbono. Para a obtenção dos catalisadores as nanopartículas foram preparadas inicialmente em estado coloidal pelo método de poliol e posteriormente suportadas em carbono (Vulcan XC-72), utilizando quantidades adequadas para obter catalisadores com composição metal:carbono de 20:80 (em massa). Nanopartículas dos sistemas binários e ternários PtSn, PtRh, PtRu, PtSnRu e PtSnRh com composições atômicas nominais 70:30 e 70:15:15, respectivamente, foram preparadas misturando-se os precursores metálicos no início da síntese. Os sistemas ternários PtSn-PtRh e PtSn-PtRu foram sintetizados pela mistura de nanopartículas bimetálicas em estado coloidal antes da etapa de suporte em carbono. Os catalisadores foram caracterizados por difração de raios X (DRX), microscopia eletrônica de transmissão (TEM) e espectroscopia de absorção de raios X (DXAS). O comportamento eletroquímico geral dos catalisadores foi avaliado por voltametria cíclica em solução de H2SO4 (0,5 mol L-1). A atividade catalítica para a oxidação de etanol foi avaliada por varreduras de potencial e cronoamperometria em solução ácida de etanol (0,5 mol L-1). Para a avaliação das áreas dos catalisadores foram realizadas medidas de oxidação de CO adsorvido. Experimentos de espectroscopia no infravermelho in situ (FTIRAS in situ) foram realizados para verificar a distribuição dos produtos da reação de oxidação de etanol. O estudo mostrou que os catalisadores têm atividades catalíticas significativamente diferentes tanto para a oxidação de etanol quanto para a oxidação de CO adsorvido, sendo o material PtSn/C o mais ativo para... / In this work, a comparative study of physical and electronic properties and catalytic activities for ethanol oxidation of carbon-supported binary and ternary metallic nanoparticles was carried out. For the catalysts, the nanoparticles were initially synthesized in colloidal state by a polyol method and subsequently supported on carbon powder (Vulcan XC-72) in amounts adequate to obtain catalysts with nominal composition metal:carbon 20:80 (in mass). The nanoparticles of the binary and ternary systems PtSn, PtRh, PtRu, PtSnRu and PtSnRh with nominal atomic compositions 70:30 and 70:15:15, respectively, were prepared from the mixture of the metal precursors at the beginning of the synthesis. The ternary systems PtSn-PtRh and PtSn-PtRu were synthesized by mixing the binary nanoparticles in colloidal state before the supporting step. The catalysts were characterized by X-ray diffraction (XRD), transmission electronic microscopy (TEM) and Dispersive X-ray absorption spectroscopy (DXAS). The general electrochemical behavior was evaluated by cyclic voltammetry in H2SO4 solution (0.5 mol L-1). The catalytic activity for ethanol oxidation was evaluated by potential sweeps and chronoamperometry in acid solutions of ethanol (0.5 mol L-1). Experiments of oxidation of adsorbed CO were done for the evaluation of the catalysts active areas. Infrared spectroscopy (FTIRAS in situ) measurements were performed to study the product distribution of the ethanol oxidation reaction. All these studies showed that the catalysts have catalytic activities substantially different for ethanol oxidation reaction as well as for the oxidation of adsorbed CO, and that while the PtSn/C catalyst is the most active for ethanol oxidation PtSnRh/C and PtSnRu/C are more effective for CO oxidation. FTIRAS measurements evidenced formation of adsorbed CO for PtRh/C indicating... (Complete abstract click electronic access below)

Made available in DSpace on 2014-06-11T19:32:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-06-12Bitstream added on 2014-06-13T20:42:54Z : No. of bitstreams: 1 viali_wr_dr_araiq_parcial.pdf: 179609 bytes, checksum: 68e5a99dde6434bab353339a79011194 (MD5) Bitstreams deleted on 2014-06-27T19:00:48Z: viali_wr_dr_araiq_parcial.pdf,Bitstream added on 2014-06-27T19:02:03Z : No. of bitstreams: 1 viali_wr_dr_araiq.pdf: 3191221 bytes, checksum: 5e42b7cc78f22390a5f4a9c125271374 (MD5) / A proposta deste trabalho foi a síntese e caracterização de nanoestruturas caroço@casca de cobalto@paládio através do método de crescimento mediado por sementes. Foram utilizados como caroços magnéticos nanopartículas de cobalto obtidas pelo método da decomposição térmica assistida por redutores, utilizando alcanodiois e trietilborohidreto de lítio como redutores. Foram avaliados os efeitos do redutor utilizado para a síntese dos núcleos magnéticos, assim como os efeitos da taxa de aquecimento, concentração do precursor metálico, razão molar entre percussor metálico e agentes de superfície. O diâmetro médio das nanopartículas utilizando alcanodiol como redutor variou entre 9 e 12 nm, estas nanopartículas apresentam forte interação magnética e se mostraram não adequadas para a realização da etapa de crescimento da casca de metal nobre. O diâmetro médio das nanopartículas utilizando trietilborohidreto de lítio como redutor variou entre 3 e 7 nm. Neste método foi avaliada a influência da presença de precursor de metal nobre no meio reacional e crescimento do núcleo magnético através da metodologia de crescimento de sementes. As nanopartículas de cobalto obtidas por este método apresentaram comportamento superparamagnético em temperatura ambiente se mostrando adequadas para a etapa de formação da casca de metal nobre. Algumas nanoestruturas caroço@casca foram obtidas através da metodologia de crescimento via sementes, onde foram utilizados como sementes de nucleação as nanopartículas de cobalto e também nanoestruturas Co@Pd. A formação da casca de paládio foi avaliada em função da concentração de precursor de paládio no meio reacional. Também foi avaliada a obtenção de nanoestruturas caroço@casca utilizando etapas consecutivas para melhor ajuste do diâmetro final. Essas... / The aim of this work was the synthesis and characterization of core@shell nanostructures through seed mediated growth, in which the magnetic cores were cobalt nanoparticle obtained by thermal decomposition of organometallic compounds in the presence of reductants, namely alkanediol and lithium triethylborohydride. The effects of reductant used in the magnetic cores were evaluated, as well as the effect of heating rate, the concentration of the metal precursor, the molar ratio between metal precursor and surfactants. The average diameter of the nanoparticles using alkanediol as reductant varied from 9 to 12 nm, these nanoparticles exhibit strong magnetic interactions and proved not suitable to carry out the formation of noble metal shell layer. The average diameter of nanoparticles using triethylborohydride as reductant varied from 3 to 7 nm. Using this synthetic route, the presence of noble metal compounds during the reduction step and the seed mediated grown of magnetic cores were evaluated. The cobalt nanoparticles synthetized showed superparmagnetic behavior at room temperature allowing its use as magnetic cores in the synthesis of noble metal shell. The core@shell nanostructures were synthetized by seed mediated route, using as seed the cobalt nanoparticles and other Co@Pd nanostructures. The palladium shell formation was evaluated as a function of concentration of palladium precursor in the reaction medium. The increase of palladium content of shell was evaluated repeating the step of formation of palladium layer, obtaining onion like structures. The nanostructures exhibited lower average diameters in comparison with their magnetic cores. Nonetheless the average diameter can be adjusted by tuning the experimental conditions, like increasing in palladium precursor contents. The average diameter of... (Complete abstract click electronic access below)

The synthesis, spectroscopic characterization, and studies of the photophysicochemical behaviour of selective anionic, cationic and neutral metallophthallocyanine (MPc) complexes were carried out and the results are presented herein. Studies on the effect of the central metal ion, the solvent used and the presence of nanoparticles on the photophysicochemical properties were conducted. The findings showed that the photophysicochemical parameters were mostly enhanced in the presence of central metal ions of high atomic numbers and also in the presence of nanoparticles. It was also observed that solvents that encouraged the monomericity of the MPc complexes also lead to improved photophysical and photochemical behaviour. CdTe quantum dots (QDs) stabilized with mercaptocarbonic acids were also observed to cause stimulated emission of the MPcs through Förster resonance energy transfer (FRET) thus acting as energy donors while the respective MPc acted as energy acceptors in all the FRET studies. FRET was observed following the photoexcitation of QDs for all monomeric anionic MPcs but it was also shown to occur for some cationic MPcs in organic media. Both the substituent and solvent used were found to exert a strong influence on the occurrence of FRET. Other cationic MPcs however showed different behaviour in the presence of the meraptocarbonic stabilized CdTe QDs; with the cationic porphyrazine giving clear indications of Pc ring reduction. The rest of the cationic MPcs did not give clear evidence of Pc ring reduction, instead they showed signs of aggregate formation possibly from the assembly of electrostatic ion pair complexes which could result in reduction of the quaternized pyridinium ring of the substituent. Both the QDs and the MPc complex emission spectra were significantly quenched for each in the presence of the other. Stern-Volmer quenching studies indicated that both static and dynamic quenching of the QDs in the presence of MPcs took place. The fluorescence lifetimes of the mercaptopropionic acid (MPA) capped CdTe QDs in the presence of various MPc complexes showed quenching of mostly the longer lifetimes of the QDs in the presence of MPcs suggesting that the surface defects and states are involved in the interaction of the QDs and MPcs. An MPc complex terminating in thio tethers was employed in the conjugation to AuNPs. Spectroscopic and microscopic studies confirmed the formation of the MPc-AuNP conjugate which was also shown to exhibit improved photophysicochemical properties compared to the free MPc.

The potential toxicity of seven different types of quantum dots without shell (L-cysteine-CdTe, TGA-CdTe, MPA-CdTe, TGA-CdSe) and with the shell (GSH-CdSe@ZnS, GSH-CdTe@ZnS,) with different capping agents were evaluated. The growth inhibitory effects of the various quantum dots on human pancreatic BON cancerous cells were determined. The least cytotoxic of the various quantum dots synthesized and the one displaying the lowest growth inhibitory potential and no embryotoxicity was determined to be the GSH-CdSe@ZnS quantum dots. The GSH-CdSe@ZnS quantum dots were then conjugated to gallium, aluminium and indium octacarboxy phthalocyanine and the photophysical behaviour of the conjugates studied for potential use in photodynamic therapy and imaging applications. The sizes, morphology, thermal stability and confirmation of successful conjugation was determined using X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR), respectively. The study was extended by conjugating amino functionalized magnetic nanoparticles (Fe₃O₄) to indium octacarboxy phthalocyanine to study the photophysical behaviour of the conjugate as a potential bi-functional anti-cancer agent (hyperthermia and photodynamic therapy applications). A three-in-one multifunctional nanocomposite comprising of the quantum dots, magnetic nanoparticles and indium octacarboxy phthalocyanine was developed with the aim of developing a multifunctional composite that is able detect, monitor and treat cancer. All conjugates showed improved and enhanced photophysical behaviour. Finally, GSH-CdSe@ZnS conjugated to aluminium octacarboxy phthalocyanine was applied in human pancreatic carcinoid BON cells. The conjugates induced cell death dose-dependently.

La synthèse de nanoparticules (NPs) d’or fonctionnalisées en phase aqueuse est encore aujourd’hui un enjeu majeur de la recherche dans le domaine des nanomatériaux. Depuis les travaux de J. Turkevich de 1951, la synthèse utilisant le citrate comme ligand et agent réducteur est la méthode de choix pour obtenir des NPs d'or. Cependant cette synthèse nécessite une étape supplémentaire de modification de surface par échange de ligand, pour pouvoir accrocher des molécules d’intérêt. Afin de simplifier la procédure, notre projet propose de synthétiser en une seule étape des NPs qui possèdent un groupement permettant une post-fonctionnalisation. La nouvelle voie de synthèse fait intervenir des composés bifonctionnels de la famille des 1-hydroxy-1,1-méthylène bisphosphonates (HMBP). Ainsi la base conjuguée de l'acide (1-hydroxy-1-phosphonopent-4-ènyl) phosphonique (HMBPène), qui possède une fonction éthylénique terminale nous a permis d'obtenir des dispersions de nanosphères de tailles contrôlées et nous avons pu rationaliser le mécanisme de synthèse utilisant ce type de molécules. Nous avons ensuite évalué plusieurs modalités de post-fonctionnalisation de notre nanoplateforme et validé une approche par chimie « Click » la via cycloaddition de composés tétrazine. En utilisant une nouvelle classe de HMBP couplés à une chaine polyéthylène glycol, des NPs stables en milieu physiologique ont pu être synthétisées selon le même modèle. Elles offrent également des possibilités de post-fonctionnalisation par couplage carbodiimide, que nous avons illustré par le couplage d'un fluorophore. Nous développons en dernière partie les résultats préliminaires sur deux types NPs d'or synthétisées à l'aide des HMBP pour des applications thérapeutiques. / In the ever growing fields of nanoscience the control of the synthesis of gold nanoparticles (GNPs) owing to their large variety of applications has emerged as an important domain. Among all methodologies Turkevich-Frens synthesis using citrates that act as ligand and reducing agent remains a method of choice for the obtaining of water soluble GNPs. Nevertheless, in post-synthesis, citrates are often exchanged with other ligands to enhanced stabilization and allow further functionalisation. In our work we present a new class of bi-functional molecules (1-hydroxy-1,1-methylene bisphosphonates HMBP) that can both reduce Au(III) and act as an efficient stabilizer of the formed GNPs in water. The first size controlled GNPs “one pot” synthesis was achieved by using an alkene conjugated HMBP, the (1-hydroxy-1-phosphonopent-4-enyl)phosphonic acid (HMBPene). We moreover, rationalized the mechanism of the GNPs synthesis using this type of molecule. We then, evaluated several methodologies for the post-functionalization of our nanoplateform and developed a « Click » chemistry approach to nanoparticle coating by tetrazine cycloaddition. Other nanoplatforms were synthesized using pegylated hydroxyl methylene bisphosphonates. This new class of bisphosphonate coated GNPs showed an improved stability in biological media and brought reactive groups available for post-functionalization as well, illustrated by the coupling of a fluorescent dye. The last part of this was dedicated to our latest results on GNPs synthesis for biomedical applications with HMBP compounds.

Orientador: Miguel Jafelicci Junior / Banca: Elisete Aparecida Batista / Banca: Dário Antonio Donatti / Banca: Emilia Celma de Oliveira Lima / Banca: Mario Roberto Meneghetti / Resumo: A proposta deste trabalho foi a síntese e caracterização de nanoestruturas caroço@casca de cobalto@paládio através do método de crescimento mediado por sementes. Foram utilizados como caroços magnéticos nanopartículas de cobalto obtidas pelo método da decomposição térmica assistida por redutores, utilizando alcanodiois e trietilborohidreto de lítio como redutores. Foram avaliados os efeitos do redutor utilizado para a síntese dos núcleos magnéticos, assim como os efeitos da taxa de aquecimento, concentração do precursor metálico, razão molar entre percussor metálico e agentes de superfície. O diâmetro médio das nanopartículas utilizando alcanodiol como redutor variou entre 9 e 12 nm, estas nanopartículas apresentam forte interação magnética e se mostraram não adequadas para a realização da etapa de crescimento da casca de metal nobre. O diâmetro médio das nanopartículas utilizando trietilborohidreto de lítio como redutor variou entre 3 e 7 nm. Neste método foi avaliada a influência da presença de precursor de metal nobre no meio reacional e crescimento do núcleo magnético através da metodologia de crescimento de sementes. As nanopartículas de cobalto obtidas por este método apresentaram comportamento superparamagnético em temperatura ambiente se mostrando adequadas para a etapa de formação da casca de metal nobre. Algumas nanoestruturas caroço@casca foram obtidas através da metodologia de crescimento via sementes, onde foram utilizados como sementes de nucleação as nanopartículas de cobalto e também nanoestruturas Co@Pd. A formação da casca de paládio foi avaliada em função da concentração de precursor de paládio no meio reacional. Também foi avaliada a obtenção de nanoestruturas caroço@casca utilizando etapas consecutivas para melhor ajuste do diâmetro final. Essas... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The aim of this work was the synthesis and characterization of core@shell nanostructures through seed mediated growth, in which the magnetic cores were cobalt nanoparticle obtained by thermal decomposition of organometallic compounds in the presence of reductants, namely alkanediol and lithium triethylborohydride. The effects of reductant used in the magnetic cores were evaluated, as well as the effect of heating rate, the concentration of the metal precursor, the molar ratio between metal precursor and surfactants. The average diameter of the nanoparticles using alkanediol as reductant varied from 9 to 12 nm, these nanoparticles exhibit strong magnetic interactions and proved not suitable to carry out the formation of noble metal shell layer. The average diameter of nanoparticles using triethylborohydride as reductant varied from 3 to 7 nm. Using this synthetic route, the presence of noble metal compounds during the reduction step and the seed mediated grown of magnetic cores were evaluated. The cobalt nanoparticles synthetized showed superparmagnetic behavior at room temperature allowing its use as magnetic cores in the synthesis of noble metal shell. The core@shell nanostructures were synthetized by seed mediated route, using as seed the cobalt nanoparticles and other Co@Pd nanostructures. The palladium shell formation was evaluated as a function of concentration of palladium precursor in the reaction medium. The increase of palladium content of shell was evaluated repeating the step of formation of palladium layer, obtaining onion like structures. The nanostructures exhibited lower average diameters in comparison with their magnetic cores. Nonetheless the average diameter can be adjusted by tuning the experimental conditions, like increasing in palladium precursor contents. The average diameter of... (Complete abstract click electronic access below) / Doutor

Orientador: Miguel Jafelicci Júnior / Banca: Antonio Tallarico Vicente Adorno / Banca: Humberto Osorio Stumpf / Banca: Adelino de Aguiar Coelho / Banca: Herbert Winnischofer / Resumo: A proposta deste estudo foi introduzir novos namomateriais para avaliar o efeito magnetocalórico (EMC). O EMC foi obtido a partir de medidas de uma família de isotermas de magnetização em um intervalo de temperatura e a mudança de entropia do sistema (ΔS) foi calculado usando as relações de Maxwell. Três tipos de materiais foram obtidos neste trabalho. O primeiro marterial foi as ferritas de gadolinío sintetizadas pelo processo poliol usando acetilacetonato de gadolínio e acetilacetonado de ferro como precursores metálicos e tetraetilenoglicol como solvente. O valor de mudança de entropia alcançou o valor máximo de 0,16 J Kg-1K-1 para campo de 2T, a baixa temperatura (30K). As propriedades magnéticas dos nanomateriais obtidos (Gd50FeOx, Gd5FeOx, Gd3FeOx e Gd1FeOx) foram obtidos em função da composição dos materiais. Moagem de alta energia foi empregada para produzir particulas pequenas de Gd5Si2Ge2. As propriedades magnéticas e magnetocalóricas das amostras bulk e moídas de Gd5Si2Ge2 foram investigadas a partir de medidas magnéticas. Quando comparado com o material bulk primitivo, diminuições significativas nos valores de magnetização de saturação e efeito magnetocalórico são observadas mesmo depois de pouco tempo de moagem, com 4h que produz partículas com distribuição de tamanho de 0,5μm. As amostras moídas parecem perder a transição estrutural de primeira ordem que aparece no Gd5Si2Ge2 bulk. Em baixas temperaturas as amostras moídas passam por uma transição de vidro de spin. Nanopartículas de FeAg foram sintetizadas através de modificações no processo poliol, usando acetilacetonato de prata e acetilacetonato de ferro como precursores e diferentes razões molares de Fe:Ag (1:1, 1:0,5 e 1:0,1, respectivamente). Os dados de difração de raios X mostram picos somente da prata na fase cúbico de face centrada. Os espectros de infravermelhos mostram... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The purpose of this study was to introduce new nanomaterial to evaluate magnetocaloric effect. The MCE was obtained by measuring a family of magnetization isotherms curves at set temperature intervals and calculating the entropy change (ΔS) for this system using the Maxwell relation. Three kinds of materials were made in this work. First material was gadolinium ferrites synthesized by polyol process using gadolinium acetilacetonate and iron acetilacetonate as metal precursors and tetraethileneglycol as solvent. The magnetic entropy change reaches the maximum values of 0.16 J Kg-1K-1 for the field of 2T, at low temperature (30K). The magnetic properties of the produced nanomaterials (Gd50FeOx, Gd5FeOx, Gd3FeOx and Gd1FeOx) were determined as a function of their composition. Highenergy ball milling was employed to produce small particles of Gd5Si2Ge2. Magnetic and magnetocaloric properties of the ball-milled and bulk Gd5Si2Ge2 samples were investigated through the magnetization measurements. When compared to the pristine bulk material, a significant decrease in saturation magnetization and magnetocaloric effect is observed even after the relatively short ball milling time of 4 h which produced particles with an average size of ca. 0.5 μm. The ball-milled samples appear to lose a first-order structural transition, present in bulk Gd5Si2Ge2, and display a superparamagnetic behaviour below the corresponding Curie temperatures. At very low temperatures, the Gd5Si2Ge2 ball-milled samples undergo a spin-glass transition. FeAg nanoparticles are synthesized by modified... (Complete abstract click electronic access below) / Doutor