Com o desenvolvimento de novos nanomateriais têm-se descoberto propriedades eletrônicas, elétricas, ópticas e catalíticas únicas para aplicações nanotecnológicas. Entre estes nanomateriais com caraterísticas singulares, estão as nanopartículas (Np) CoreαShell, as quais combinam propriedades físico-químicas de dois materiais diferentes, provendo maior eficiência em aplicações como nanoeletrônica, sensoreamento, biossensoreamento e biomédicas. Neste trabalho, Np CoreαShell são sintetizada com núcleo (Core) de Np Fe₃O₄ e com casca (Shell) de Np Au, formando as Nps Fe₃O₄αAu na presença do dendrímero poli(amidoamina) geração 4.0 (Pamam G4). As propriedades físico-químicas do nanomaterial core-shell são estudadas através de análises espectroscópicas, microscopias e eletroquímicas, além de medidas de magnetização. Essas técnicas revelam a formação das Nps Au nas cavidades do Pamam G4 e as interações eletrostáticas entre os grupos funcionais do Pamam G4 e os grupos OH ⁻ e H ⁺ da superfície das Nps magnéticas, as quais dão uma forte estabilidade na configuração da Np Fe₃O₄αAu. Evidencia-se propriedades óticas da Np Au e propriedades superparamagnéticas da Np Fe ₃ O ₄, as quais podem ser usadas para aplicações em nanomedicina. As propriedades electrocatalíticas das Nps são utilizadas na detecção de dopamina (DA). Foram fabricados sensores eletroquímicos das Nps Fe₃O₄αAu, Nps Fe₃O₄ e Nps Au, e caracterizados por técnicas de voltametria cíclica e voltametria de pulso diferencial. A fabricação dos sensores consistiu na deposição de camadas alternadas entre as nanopartículas com o poliânion poly(ácido vinil sulfônico) (PVS) no eletrodo de ITO, levando à configuração de três arquiteturas; ITO - (Fe₃O₄αAu ⁄ PV S), ITO - (Fe₃O₄ ⁄ PV S) e ITO - (Au ⁄ PV S). Um problema encontrado na detecção de DA é que esta tem potenciais de oxidação aproximadamente iguais ao ácido ascórbico (AA) e ao ácido úrico (AU). Portanto, os sensores utilizados na detecção de DA, devem ser altamente seletivos a DA em relação a seus interferentes. Os sensores desenvolvidos aqui mostraram uma boa seletividade e velocidade de resposta na detecção de DA, sendo o sensor ITO - (Fe₃O₄αAu ⁄ PV S) o mais eficiente. As Nps Fe₃O₄αAu revelam maior citotoxicidade nas células cancerígenas comparadas com as células saudáveis, já que as células cancerígenas são mais sensíveis ao estresse oxidativo produzido pelas nanopartículas no interior da célula. / Along with the development of nanomaterials came the knowledge and design of their unique eletronic, optical and catalitycal properties which may be used for a variety of nanotecnological applications. A special class of nanomaterials with interesting characteristics is represented by the CoreαShell nanoparticles, which combine the physicochemical properties of two differerent nanomaterials (including oxides, metals, semiconductors or polymers). This combination provides greater efficiency in applications such as nanoelectronics, sensing, biosensing and biomedical areas. This study reports the synthesis of Fe₃O₄ Np, which in the presence of the polyamido amine generation 4.0 (Pamam G4), is covered with Au Np forming the Fe₃O₄αAu Nps. The nanomaterials had been characterized using spectroscopic, microscopic and electrochemical techniques. The results revealed the formation of Au Nps in the cavities of PAMAM G4 and showed that the electrostatic interactions between the PAMAM functional groups and the OH ⁻ and H ⁺ groups on the surface of the magnetic nanoparticles lead to a strong stability in the configuration of Fe₃O₄αAu Nps. The optical properties of the Au Np (namely the Plasmon resonance band at 542 nm) as well as the superparamagnetic properties of the Fe₃O₄ Np were present in the core-shell nanostrutures. Due to their electrocatalytical properties, the core-shell nanoparticles were employed as active elements for dopamine (DA) detection. The fabrication of the modified electrodes for DA detection consisted in the deposition by LbL technique of alternating layers of nanoparticles and poly(vinyl sulfonic acid) (PVS) on the ITO eletrode, in three distinct architectures: ITO - (Fe₃O₄αAu Fe₃O₄ PV S), ITO - (Fe₃O₄ ⁄ PV S) and ITO - (Au ⁄ PV S). We found a good selectivity and rapid response toward the detection of DA, being the sensor ITO - (Fe₃O₄αAu ⁄ PV S) the most efficient. The effect of Fe₃O₄αAu Nps showed a higher cytotoxicity in cancer cells compared to healthy cells, because cancer cells are more sensitive to oxidative stress produced by the nanoparticles.

A controlled assembly of natural beta-cyclodextrin modified Au NPs mediated by dopamine is demonstrated. Furthermore, a simple and sensitive colorimetric detection for dopamine is established by the concentration-dependent assembly.

Die Kombination aus anorganischen Nanopartikeln und Mikrogelen in einem hybriden System erlaubt die Herstellung von Materialien mit vielseitigen neuen Eigenschaften. Im Idealfall weisen solche hybriden Materialien neben den Eigenschaften von beiden indivduellen Systemen zusätzlich synergetische Effekte auf, welche aus den Interaktionen zwischen dem anorganischen Nanopartikel und dem Mikrogel resultieren. Im ersten Teil dieser Arbeit wird eine neuartige und eingängige Methode zur Herstellung von Cu2O@PNIPAM Kern-Schale Nanoreaktoren präsentiert. Die PNIPAM Schale schützt dabei die Cu2O Nanopartikel effektiv vor Oxidation. Die Cu2O@PNIPAM wurden als Photokatalysator zum Abbau von Methylorange unter sichtbarem Licht eingesetzt. Im Vergleich zu den reinen Cu2O Nanopartikeln konnte eine signifikante Steigerung der katalytischen Aktivität festgestellt werden. Desweiteren kann die photokatalytische Aktivität mittels Temperatur durch die thermosensitive PNIPAM Schale abgestimmt werden. Verhältnismäßig geringe Konzentrationen einer Cu2O@PNIPAM wässrigen Lösung (1,5 Gew%) können direkt als neuartige Tinte genutzt werden. Keine zusätzlichen Additive oder organische Lösungsmittel sind für die Strahldruckprozesse vonnöten. Gedruckte Bauelemente bestehend aus den Cu2O@PNIPAM wurden als Gas Sensoren eingesetzt und zeigten eine geringere Nachweisgrenze für NO2 als die reinen Cu2O Nanowürfel. Im zweiten Teil der Arbeit wurden katalytisch aktive Au Nanopartikel an copolymerisierten α –Cyclodextrin (α-CD) Einheiten in einem Poly(N-vinylcaprolactan) (PVCL) Mikrogel immobilisiert. Diese hybriden Partikel sind sehr aktive Katalysatoren für die Reduktion von aromatischen Nitroverbindungen. Die Reduktion von 4-Nitrophenol (Nip) und 2,6-Dimethyl-4-nitrophenol (DMNip) wurden als Modellreaktionen ausgewählt. Durch selektive Bindungseingenschaften der Nitroverbindungen an die α-CD Einheiten konnten verschiedene katalytische Aktivitäten für Nip and DMNip festgestellt werden. / The combination of inorganic nanoparticles and organic microgels in one hybrid system allows for the preparation of new materials with multifunctional properties. Ideally, such hybrid materials reflect both the properties of its individual components and synergetic effects due to the interaction between inorganic nanoparticles and microgels. In the first part of this thesis, the fabrication of Cu2O@Poly(N-isopropylacrylamide) (PNIPAM) core-shell nanoreactors has been presented. It was found that the PNIPAM shell effectively protects the Cu2O nanocubes from oxidation. The core-shell microgels have been used as photocatalyst for the decomposition of methyl orange and a significant enhancement in the catalytic activity has been observed compared with the bare Cu2O nanocubes. Most importantly, the photocatalytic activity of the core-shell nanoreactors can be further tuned by the thermosensitive PNIPAM shell. The aqueous solution of Cu2O@PNIPAM core-shell nanoparticles with quite low solid content (1.5wt. %) can be also directly used as a novel ink material for the inkjet printing without adding any other surfactants and organic solvents. The gas sensor device printed by core-shell nanoparticles is more sensitive to NO2 than that made from the bare Cu2O nanocubes. In the second part, a kind of hybrid microgel has been fabricated by immobilization of catalytically active Au nanoparticles in the α-cyclodextrin (α-CD) modified poly(N-vinylcaprolactam) (PVCL) microgels without addition of reducing agent and surfactant. The hybrid microgels can work efficiently as catalyst for the reduction of aromatic nitro-compounds by using the reduction of 4-nitrophenol (Nip) and 2,6-dimethyl-4-nitrophenol (DMNip) as model reactions. Due to the selective binding property of α-CDs to nitro compounds, the synthesized hybrid microgels show different catalytic activity for the target compounds, 4-nitrophenol (Nip) and 2,6-dimethyl-4-nitrophenol (DMNip), during the catalytic reactions.

Surfactant bound stable colloids of Au, Ag, and Pd were prepared by the solvated Metal Atom Dispersion (SMAD) method, a method involving co-condensation of metal and solvent vapors on the walls of a reactor at 77 k. The as=prepared dodecanethiol-capped Au and Ag colloids consisting of polydisperse nanoparticles were transformed into colloids consisting of highly monodisperse nanoparticles by the digestive ripening process. In the case of Pd colloids, digestive ripening led to the formation of thiolate complexes. The [Pd(SC12H25)2]6 complex formed from the dodecanethiol-capped Pd nanoparticles was found to be a versatile precursor for the synthesis of a variety of Pd nanophases such as Pd(0), PdS, and Pd@PdO by soventless thermolysis. Co-digestive ripening of as-prepared dodecanethiol-capped Au or Ag colloids with Pd colloid resulted in Au@Pd and Ag@Pd core-shell nanoparticles, respectively; attempts to transform the core-shell structures into alloy phases even at high temperatures were unsuccessful. Phosphine-capped Au nanoparticles were also prepared by the SMAD method and refluxing of this colloid resulted in an Ostwald ripening process rather than the expected digestive ripening due to the labile nature of bound PPh3. The labile nature of the bound phosphine was studied using 31P NMR spectroscopy and utilized in the adsorption of CO. Palladium nanoparticles obtained from the SMAD Pd-butanone colloids and Pd@PdO nanoparticles prepared by the solventless thermolysis of Pd-dodecanethiolate complex were found to be good catalysts for the generation of H2 from AB via either hydrolysis and methanolysis. The active hydrogen atoms produced during the hydrolysis and methanolysis diffuse into the Pd lattice. It was also noticed that hydrogen atoms that were buried deep inside the Pd lattice cannot be removed completely by heating the sample even at 600°C. Wet chemical reduction method was employed for the synthesis of PVP capped, nearly monodisperse, spherical Ir nanoparticles which undergo a polymer driven self-assembly at 80°C to afford rectangular structures and interlinked particles.

Recent advancements in nanotechnology and emerging applications of nanomaterials in various fields have stimulated interest in fundamental scientific research dealing with the size and structure controlled synthesis of nanoparticles. The unique properties of nanoparticles are largely size dependent which could be tuned further by varying shape, structure, and surface properties, etc. The preparation of monodisperse nanoparticles is desirable for many applications due to better control over properties and higher performance compared to polydispersity nanoparticles. There are several methods for the synthesis of nanoparticles based on top-down and bottom-up approaches. The main disadvantage of top-down approach is the difficulty in achieving size control. Whereas, uniform nanoparticles with controllable size could be obtained by chemical methods but most of them are difficult to scale up. Moreover, a separate step of size separation is necessary in order to achieve monodispersed which may lead to material loss. In this context, a post-synthetic size modification process known as digestive ripening is highly significant. In this process, addition of a capping agent to poly disperse colloid renders it highly monodisperse either under ambient or thermal conditions. In addition to size control, digestive ripening is also effective in controlling the structure of nanoparticles in colloidal solution comprising two different elements. Use of co-digestive ripening strategy in conjunction with solvated metal atom dispersion (SMAD) method of synthesis resulted in hetero structures such as core–shell, alloy, and composite nanoparticles. Despite the versatility of digestive ripening process, the underlying mechanism in controlling size and structure of nanoparticles are not understood to date. The aim of this thesis is to gain mechanistic insight into size control of digestive ripening as well as to investigate structure control in various binary systems. Objectives  Study digestive ripening of Au nanoparticles using various alkyl amines to probe the mechanism  Study co-digestive ripening of binary colloids consisting of two metals, Pd and Cu prepared separately by SMAD method  Study co-digestive ripening of binary colloids consisting of a metal (Au) and a semiconductor (CdS) prepared separately by SMAD method  Study vaporization of bulk brass in SMAD reactor and analyse phase, structure, and morphology of various Cu/Zn bimetallic nanoparticles obtained from bulk brass under various experimental conditions Significant results In chapter 1, fundamental processes of nanoparticle formation and common synthetic techniques for the preparation of monodisperse nanoparticles are briefly discussed. Chapter 2 presents a mechanistic study of digestive ripening process with regard to size control using Au nanoparticles as a model system. Three long chain alkyl amine molecules having different chain length were used as digestive ripening agents. The course of digestive ripening process was analysed by UV-visible spectroscopy and transmission electron microscopy. The experimental conditions such as concentration of digestive ripening agent, time, and temperature were found to influence the size distribution of nanoparticles. The average particle size was found to be characteristic of metal-digestive ripening agent combination which is considered as the optimum size preferred during digestive ripening under a given set of experimental conditions. This study discusses stabilization of optimum sized particles, surface etching, and reversibility in digestive ripening. Chapter 3 describes the synthesis and characterization of PdCu alloy nanoparticles by co-digestive ripening method. Syntheses of individual Pd and Cu colloids were carried out by SMAD method. Pd nanoparticles obtained using THF as solvent and in the absence of any capping agent resulted in an extended small Pd nanowire network assembly. Morphological evolution of spherical Pd nanoparticles from Pd nanowire network structure was observed with the use of capping agent, hexadecyl amine (HDA) in SMAD method. Co-digestive ripening of Pd and Cu colloids was studied at various temperatures. This study revealed temperature dependent diffusion of Cu atoms into Pd lattice forming PdCu alloy nanoparticles. Next, co-digestive ripening of a colloidal system comprising a metal and a semiconductor was explored. Au-CdS combination was chosen for this study owing to its interesting photocatalytic properties. Chapter 4 deals with the synthesis of Au and CdS nanoparticles by SMAD method and Au/CdS nanocomposite by co-digestive ripening. CdS nanoparticles of size 4.0 + 1.2 nm and Au nanoparticles of size 5.6 + 1.1 nm were obtained as a result of digestive ripening process. Au/CdS nanocomposite obtained by co-digestive ripening was characterized by a matrix-like structure made up of CdS nanoparticles in which Au nanoparticles were embedded. CdS nanoparticles were found to establish an intimate surface contact with Au nanoparticles and the matrix of CdS surrounding Au was developed via aggregation during digestive ripening. Chapter 5 describes a comprehensive study on various Cu/Zn bimetallic nanoparticles obtained from bulk brass. Vaporization of bulk brass in SMAD reactor led to a deploying process and further growth of nanoparticles from phase separated Cu and Zn atoms formed a composite structure. The characterization of Cu/Zn nanocomposite revealed covering of composite surface with Cu resulting in a core-shell structure, Cu/Zn@Cu. Post-synthetic digestive ripening of these core-shell composite particles showed diffusion of Zn atoms to the composite surface in addition to size and shape modification. Annealing of Cu/Zn nanocomposites prepared in THF resulted in α-CuZn alloy nanoparticles via sequential transformation through η-CuZn5, γ-Cu5Zn8, and β-CuZn (observed as marten site) phases.