Zinc oxide (ZnO) is a versatile environmentally benign II-VI direct wide band gap semiconductor with several technologically plausible applications such as transparent conducting oxide in flat panel and flexible displays. Hence, ZnO thin films have to be processed below the glass transition temperatures of polymeric substrates used in flexible displays. ZnO thin films were synthesized via aqueous polymeric precursor process by different metallic salt routes using ethylene glycol, glycerol, citric acid, and ethylene diamine tetraacetic acid (EDTA) as chelating agents. ZnO thin films, derived from ethylene glycol based polymeric precursor, exhibit flower-like morphology whereas thin films derived of other precursors illustrate crack free nanocrystalline films. ZnO thin films on sapphire substrates show an increase in preferential orientation along the (002) plane with increase in annealing temperature. The polymeric precursors have also been used in fabricating maskless patterned ZnO thin films in a single step using the commercial Maskless Mesoscale Materials Deposition system.

This thesis presents a novel ZnO-hydrogel based fluorescent colloidal semiconductor nanomaterial system for potential bio-medical applications such as bio-imaging, cancer detection and therapy. The preparation of ZnO nanoparticles and their surface modification to make a biocompatible material with enhanced optical properties is discussed. High quality ZnO nanoparticles with UV band edge emission are prepared using gas evaporation method. Semiconductor materials including ZnO are insoluble in water. Since biological applications require water soluble nanomaterials, ZnO nanoparticles are first dispersed in water by ball milling method, and their aqueous stability and fluorescence properties are enhanced by incorporating them in bio-compatible poly N-isopropylacrylamide (PNIPAM) based hydrogel polymer matrix. The optical properties of ZnO-hydrogel colloidal dispersion versus ZnO-Water dispersion were analyzed. The optical characterization using photoluminescence spectroscopy indicates approximately 10 times enhancement of fluorescence in ZnO-hydrogel colloidal system compared to ZnO-water system. Ultrafast time resolved measurement demonstrates dominant exciton recombination process in ZnO-hydrogel system compared to ZnO-water system, confirming the surface modification of ZnO nanoparticles by hydrogel polymer matrix. The surface modification of ZnO nanoparticles by hydrogel induce more scattering centers per unit area of cross-section, and hence increase the luminescence from the ZnO-gel samples due to multiple path excitations. Furthermore, surface modification of ZnO by hydrogel increases the radiative efficiency of this hybrid colloidal material system thereby contributing to enhanced emission.

A presença de defeitos intrínsecos na estrutura do óxido de zinco possibilita a sua dopagem com outros materiais, como o bismuto. O óxido de zinco dopado com bismuto (BZO) preparado via síntese hidrotermal assistida por microondas (MAHS) foi estudado em relação à sua concentração de dopante e caracterização morfológica. Para a síntese do BZO foi realizada pela reação de uma solução de nitrato de zinco (precursor) e nitrato de bismuto, usando com hidróxido de amônio para ajuste do pH. Para realizar a reação, a solução de nitrato de zinco foi foi aquecida em um microondas por intervalos de 5, 10 e 20 minutos a 200ºC. A dopagem foi realizada com 3 diferentes teores em massa nitrato de bismuto (1, 3 e 6%). Os produtos obtidos foram caracterizados por DRX, MEV e PL, assim como pelo cálculos de band gap por espectroscopia de transmissão. A atividade fotocatalítica foi analisada por ensaios de fotocatálise utilizando corantes orgânicos, azul de metileno (AM) e Rodamina B (RhB). Os resultados indicam que as nanoestruturas de BZO obtidas apresentam tamanhos de cristalitos variando de 5,82 a 8,37 nm. A estrutura morfológica, tipo flor, foi formada com diferentes concentrações de dopantes. Os resultados do PL demonstram que os defeitos aumentam com a dopagem do bismuto. O intervalo de band gap encontrado foi de 2,79 a 3,3 eV e tem potencial de uso em aplicações de fotodegradação. Neste sentido a dopagem de bismuto modificou positivamente o óxido de zinco, já que nos ensaios de fotocatálise, o BZO degradou ambos os corantes, sendo a amostra com 3% de dopagem de bismuto a que obteve os melhores resultados, chegando a degradar 68% do corante de Rodamina B em 1 hora. / Zinc oxide, due to the presence of intrinsic defects, allows doping with other materials, such as bismuth. BZO (zinc oxide doped bismuth), prepared by microwave assisted hydrothermal synthesis (MAHS), was studied dopant concentration and morphological characterization. For the synthesis, zinc nitrate was used as a precursor; for pH control, ammonium hydroxide was used. After the solution was heated in a microwave for 5, 10 and 20 minutes at 200 ° C. Doping was performed with 3 different mass contents of bismuth nitrate (1, 3 and 6%). The products were characterized by DRX, MEV and PL; Band gap calculations by transmission spectroscopy. The photocatalytic activity was analyzed by photocatalysis using organic dyes, methylene blue (AM) and Rhodamine B (RhB). The results indicate that BZO nanostructures were obtained with crystallite sizes ranging from 5.82 to 8.37 nm. The same morphological structure, flower type, was formed with different dopants concentrations. PL demonstrates that defects increase with doping of bismuth. The band gap found was from 2.79 to 3.3 eV and has potential use in photodegradation applications. In this sense, the bismuth doping positively modified the zinc oxide, in the photocatalysis tests BZO degraded both dyes, being the sample with 3% doping of bismuth that obtained the best results, reaching to degrade 68% of the Rhodamine B dye in 1 hour.

Orientador: Julio Ricardo Sambrano / Banca: Miguel Angel San-Miguel Barrera / Banca: Rogério Custódio / Banca: Ieda Maria Garcia dos Santos / Banca: Luis Vicente de Andrade Scalvi / Resumo: A química computacional tem se mostrado uma ferramenta muito útil no meio científico e tem sido cada vez mais utilizada na pesquisa de novos materiais. Dentre os muitos sistemas estudados com o auxílio da química computacional, destaca-se o óxido de zinco (ZnO), muito utilizado em diversos dispositivos eletrônicos tais como, sensores, células solares, diodos de emissão de luz UV e diodos a laser. À temperatura e pressão ambientes, a estrutura cristalina mais estável do ZnO é hexagonal do tipo wurtzita, na qual os átomos de zinco estão coordenados a quatro átomos de oxigênio. Devido a coordenação tetraédrica e falta de centro de simetria dessa estrutura, o ZnO apresenta propriedades piezoelétricas podendo ser aplicado em sensores piezoelétricos, por exemplo. Atualmente, existem muitos trabalhos científicos relacionados com o ZnO, porém o número de trabalhos teóricos em relação aos trabalhos experimentais ainda é pequeno. Neste sentido, este projeto teve como objetivo a análise das propriedades do ZnO em três morfologias diferentes, bulk, superfícies e nanotubos, aplicando as principais técnicas de modelagem computacional aplicada ao estado sólido tais como escolha do funcional de densidade e funções de base, otimização da geometria, dopagem por substituição de átomos, cálculo de constantes elásticas e piezoelétricas, simulação de pressão hidrostática aplicada a célula unitária, secção do bulk para gerar superfícies, substituição de átomos para formar interfaces, nanotubos e ad... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Computacional chemistry has proved to be a very useful tool in the scientific field and has been incrasingly used in the research of new materials. Among the many systems studied with the aid of computacional chemistry, we highlight zinc oxide (ZnO), widely used in many electronic devices such as sensors, solar cells, UV light emitting diodes and laser diodes. At room temperature and pressure, the most stable crystalline structure of ZnO is hexagonal of the wurtzite type, in the zinc atoms are coordinated to four oxygen atoms. Due to the tetrahedral coordination and lack of center of symmetry of this structure, the ZnO presents piezoelectric properties and can be applied in piezoelectric sensors, for example. Currently, there are many papers related to ZnO, however the number of theoretical articles in relation to the experimental works are still small. In this sense, this project aimed the analysis of ZnO properties in three different morphologies, bulk, surfaces and nanotubes, applying the main techniques of computational modeling to solid state such as the choise of density functional and basic functions, optimization of geometry, doping by atom replacement, calculation of elastic and piezoelectric constants, hydrostatic pressure simulation applied to unit cell, bulk section to generate surfaces, replacement of atoms to form interfaces, nanotubes and adsorption of molecules in nanotubes. The calculations were performed applying th Density Functional Theory, with the help of the CRYSTAL14 program, using the hybrid function B3LYP, with the ste of all-electron base functions. The applied methodology preserves the periodicity of the crystalline system (1D for nanotubes, 2D for surfaces or 3D for bulk), in which the building blocks are composed of unit cells and can be replicanted by the symmetry operator. The topological reviews were performed applying the Quantum Theory... (Complete abstract electronic access below) / Doutor

Orientador: César Renato Foschini / Resumo: O óxido de zinco (ZnO) apresenta uma grande versatilidade física, elétrica, mecânica e propriedades químicas que podem ser exploradas em uma variedade de aplicações, tais como fotocatálise, nanoadsorventes e sensoriamento de gases. Os materiais nanoestruturados têm atraído a atenção da ciência e tecnologia nos últimos anos porque podem melhorar suas propriedades em nanoescala. A prata em escala nanométrica tem gerado interesse de pesquisadores de diferentes áreas, pois a prata é moldável e maleável, possui elevada condutividade térmica e elétrica, além de ser um forte oxidante. Neste trabalho, foram desenvolvidos filmes de óxido de zinco puro e dopados com nanopartículas de prata, visando aplicação em sensores de gás. Os filmes de óxido de zinco foram fabricados pelo método dos precursores poliméricos e utilizados como matriz devido a sua interatividade com os gases. As nanopartículas de prata foram produzidas por meio de reação em emulsão, explorando sua alta condutividade elétrica. Dessa forma, por meio das propriedades de ambos os materiais, desenvolveu-se um sensor de gás composto de óxido de zinco na forma de filmes em substratos de Al2O3, com diferentes camadas dopadas e não dopadas com nanopartículas de prata. Notou-se que o desenvolvimento de um material compósito do tipo filme de ZnO dopado com as nanopartículas de prata, apresentou propriedades melhoradas, como por exemplo, a resposta elétrica do material quando comparada com o filme contendo apenas o filme de ZnO p... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Zinc oxide (ZnO) presents a great physical, electrical, mechanical and chemical versatility that can be exploited in a variety of applications, such as photocatalysis, nanoadsorbents and gas sensing. Nanostructured materials have attracted the attention of science and technology in recent years because they can improve their nanoscale properties. The silver in nanoscale has generated interest of researchers of different areas, because the silver is moldable and malleable, has high thermal and electrical conductivity, besides being a strong oxidant. And this project was developed based on the production of silver nanoparticles and zinc oxide films for the application in gas sensors. The zinc oxide films were manufactured by the method of the polymeric precursors and used as matrix due to its interactivity with the gases. The silver nanoparticles were produced by means of emulsion reaction, exploring their high electrical conductivity. Thus, through the properties of both materials, a gas sensor composed of zinc oxide in the form of films on substrates of Al2O3, with different layers doped and not doped with silver nanoparticles was developed. It was noted that the development of a ZnO film-like composite material doped with the silver nanoparticles exhibited improved properties, such as the electrical response of the material as compared to the film containing only the pure ZnO film. / Mestre

Understanding the size dependent dissolution of engineered nanoparticles is one important aspect in addressing the potential environmental and health impacts of these materials as well as their long-term stability. In this study, experimental measurements of size dependent dissolution of well-characterized zinc oxide (ZnO) nanoparticles with particle diameters in the range of 4 to 130 nm have been measured and compared at circumneutral pH (pH 7.5). Enhanced dissolution was found for the smaller particles with the largest enhancement observed in Zn2+(aq) concentrations for 4 nm diameter ZnO nanoparticles compared to larger-sized particles. Interestingly, size dependent dissolution was observed even though the nanoparticles aggregated with hydrodynamic diameters on the order of 1-3 m in diameter. Although these results are found to be in qualitative agreement with theoretical predictions used to predict the dissolution of solids, a linearized form of the Kelvin equation to calculate a bulk dissolution value for ZnO and a surface free energy yielded quantities inconsistent with known literature values. It is therefore concluded that deviations from solubility behavior from classical thermodynamics are due to a lack of the detailed knowledge of the surface free energy as well as its dependence on the details of the surface structure, surface properties, including the presence of different surface crystal facets and adsorbed ligands, as well of aggregation state. The presence of citric acid significantly enhances the extent of ZnO dissolution for all sizes such that no significant differences were observed for total Zn2+(aq) concentrations for nanoparticles between 4 to 130 nm. This can be attributed to ligand enhanced dissolution of ZnO nanoparticles where there is no dependence on size. Adsorption of citrates onto ZnO nanoparticles was observed using ATR-FTIR spectroscopy. A reversal of surface charge of ZnO nanoparticles was observed upon adsorption of citrates. Adsorption of negatively charged Cit3- onto ZnO nanoparticles make the surfaces negatively charged and this result in a repulsion between nanoparticles eventually leading to a lesser extent of aggregation. Formation of a stable suspension was also observed in the presence of citric acid. These trends observed in aggregation pattern are of great environmental and biological importance as citric acid is abandon in the environment as well as in human body.

This diploma thesis is about ZnO nanowires growth, their doping and analysis. High temperature and pressure oxidation of brass foil and deposition from effusion cell in oxidative atmosphere utilized for nanowires growth. The growth is affected by different temperature and pressure. It has been shown that under certain experimental conditions nanowires can be prepared by the former method. However, the growth was hindered when effusion cell was used.

Polymeric materials are widely used in diverse applications. However, a major weakness in the majority of the thermoplastic polymers is their lack of ability to resist fire. Most of the chemicals and additives currently used to improve fire retardancy have deleterious effects on the environment. This research focuses on developing an environmentally safe and effective fire-retardant system for high density polyethylene (HDPE), using cellulose nanocrystals (CNCs) and zinc oxide (ZnO). The effect of CNCs coated with nano ZnO has been investigated for improving the fire resistance properties of the HDPE. Improved dispersion of CNCs into HDPE matrix was achieved by employing maleic anhydride as a coupling agent. It was found that addition of CNCs-ZnO can introduce a reasonable level of flame retardancy in HDPE matrix in addition to improving the maximum tensile strength and elongation at break.

Zinc oxide (ZnO) is a well-known II-VI semiconductor material that has gained renewed interest in the past decade due to the developments of growth technologies and the availability of high-quality ZnO bulk single crystals. Owing to a wide direct band gap (3.37 eV), large exciton binding energy (60 meV), and high electron mobility (440 cm2 V-1 s-1), ZnO has been used for applications including actuators, optoelectronics, and sensors. ZnO nanoparticles can be synthesized in a broad variety of morphologies, such as nanotetrapods, nanotubes, and nanowires. Among these nanostructures, the tetrapods have attracted significant attention due to their unique morphology consisting of four legs connected together in a tetrahedral symmetry. Recently, it has been reported that nano-microstructured ZnO tetrapods (ZnO-Ts) can be synthesized by flame transport synthesis (FTS) in a rapid and up-scalable approach. Compared to conventional ZnO nanoparticles, the nano-microstructured ZnO-Ts can reduce cellular uptake, while still exhibiting specific nanomaterial properties due to the nanoscale tips. Moreover, the anisotropic ZnO-Ts have the advantages of multiple electron transfer paths, chemical stability, and biocompatibility, which make the ZnO-Ts promising candidates for biomolecule sensing applications. This work herein reports a systematical study on the structural, optical and electrochemical properties of the ZnO-Ts, which were synthesized by FTS using precursor Zn microparticles. The morphology of the ZnO-Ts was confirmed by scanning electron microscopy (SEM) as joint structures of four single crystalline legs, of which the diameter of each leg is 0.7-2.2 μm in average from the tip to the stem. The ZnO-Ts were dispersed in glucose solutions to study the photoluminescence as well as photocatalytic activity in a mimicked biological environment. The photoluminescence (PL) intensity in the ultraviolet (UV) region decreased with linear dependence on the glucose concentration up to 4 mM. The ZnO-Ts were also attached with glucose oxidase (GOx) and over coated with Nafion® to form the active media for electrochemical glucose sensing. The active layers were confirmed by Fourier transform infrared spectroscopy (FT-IR). Furthermore, the current response of the active layers to glucose was studied by cyclic voltammetry (CV) in various glucose concentration conditions. Stable current response to glucose was detected with linear dependence on the glucose concentration up to 12 mM, which confirms the potential of ZnO-Ts for biomolecule sensing applications.

Thermographic phosphors are useful compounds to determine temperature, due to their luminescence characteristics being a function of temperature. In this research, Zinc Oxide: Gallium was evaluated for its ability to measure the temperature of an impact event in a drop weight apparatus. Different solids loadings of the phosphor were placed in a sylgard binder and these samples were then excited by a 355 nm laser as they were impacted. Images of the event were captured through two separate filters with a high-speed camera, from which intensity ratios were formed. These intensity ratios correlated to a temperature, revealing the change in temperature of the sample throughout the impact. Initial testing at a repetition rate of 500 kHz provided insignificant data, due to difficulties with timing. The whole impact event was not able to be captured, and the imprecise timing of the drop did not allow for imaging of a specific area of the impact. Moving to a slower repetition rate of 50 kHz, the entire impact was captured on the high-speed camera, showing three separate areas of interest. The first section of this area was where the impact was first initiated, resulting in a temperature increase. Next, there was a temperature decrease, where the energy from the drop weight transitioned to deforming, rather than heating the sample. Lastly, there was a final temperature rise when the sample was fully compressed, but the impact was still occurring. This trend presented itself in all of the samples, supporting the idea that when combined with the intensity ratio method, ZnO:Ga embedded in a sylgard binder is an appropriate method to determine the temperature changes in a high-speed impact event.