Nonaqueous sol-gel routes to doped metal oxide nanoparticles: synthesis, characterization, assembly and properties

The results presented in this thesis have been achieved under the Ph.D. project entitled “Nonaqueous Sol-Gel routes to doped metal oxide nanoparticles: Synthesis, characterization, assembly and properties”. The purpose of this study is the investigation of metal oxide nanostructures doped with metals of a diverse nature, leading to different type of applications. The easier control over the reaction kinetics in solvothermal routes, compared to aqueous methods, allows to better match the reactivity between metal oxide precursors, paving the way to a facile and low temperature production of doped oxides. In this manuscript diverse examples of the exploitation of the “Benzyl Alcohol Route” are discussed. Such a powerful pathway was utilized for the synthesis of transition metal doped zirconia, hafnia and various perovskites, and the study of their magnetic properties, as well as the synthesis of rare earth doped zirconium oxide. A further extension, proving the solidity of the synthetic method, is shown for the preparation of Li4Ti5O12 nanocrystals carrying excellent electrochemical properties for lithium-ion battery applications. Finally, the effect of doping and other reaction parameters on the assembly of the nanocrystals is discussed. These studies were carried out principally at the University of Aveiro, as well as at the University of Montpellier II and at the Seoul National University due to complementary available expertises and equipments.

Híbridos orgânicos-inorgânicos para aplicações de baixo custo em óptica integrada

O objectivo desta tese é a utilização de materiais híbridos orgânicos-inorgânicos, designados por di-ureiasis modificados pela adição de tetra-propóxido de zircónio (Zr(i-OPr)4) estabilizado com ácido metacrílico (CH2=C(CH3)COOH), obtidos pela via sol-gel, para aplicações em dispositivos ópticos integrados de baixo custo. A estrutura local dos di-ureiasis com diferentes concentrações de propóxido de zircónio (20 a 80 % mol) foi estudada por difracção de raios-X, espalhamento de raios X a baixos ângulos, microscopia de força atómica, ressonância magnética nuclear dos núcleos dos átomos de 29Si e 13C, espectroscopia no infravermelho por transformada de Fourier, espectroscopia de Raman por transformada de Fourier e termogravimetria. A influência dos parâmetros de síntese, concentração de tetra propóxido de zircónio e rácio tetra propóxido de zircónio: ácido metacrilico na estrutura e propriedades das amostras em monólito e filmes finos (depositados pela técnica de deposição por rotação do substrato) foram avaliadas, permitindo obter amostras transparentes, fotopolimerizáveis e estáveis termicamente até aos 100 ºC. Foram determinadas as propriedades dos guias planares em substratos de vidro borosilicato e silício oxidado (1

Síntese de ésteres catalisada por fosfatos e fosfonatos metálicos(IV)

No âmbito do Mestrado em Química, com especialização em Química Orgânica e Produtos Naturais, será apresentado nesta dissertação o trabalho desenvolvido sobre a síntese e caracterização de fosfatos e fosfonatos metálicos tetravalentes, assim como a avaliação da sua capacidade catalítica em reações de esterificação. Iniciou-se este trabalho pela síntese de vários fosfatos e fosfonatos metálicos tetravalentes, que apresentam a fórmula geral MIV(HXO4)2.nH2O e MIV(RXO3)2.nH2O, respetivamente, onde MIV = Zr, X = P, W, Mo e R = grupo orgânico. Os compostos sintetizados foram caracterizados por espetroscopia de infravermelho, difração de raios-X de pós e por análise elementar e termogravimétrica. Os fosfatos e fosfonatos metálicos tetravalentes foram avaliados como catalisadores em reações de esterificação de Fischer entre os ácidos acético, ou benzóico, e diferentes álcoois. Após esta avaliação foram efetuados estudos de otimização das condições reacionais para a síntese de cada éster. Em cada um dos casos foi utilizado o catalisador com o qual se obtiveram os melhores rendimentos nos estudos iniciais, ou seja com o molibdato-fenilfosfonato de zircónio(IV), ZrMoPhP. Todas as reações foram monitorizadas por cromatografia gasosa ou por cromatografia líquida de alta pressão. Todos os ésteres foram identificados por comparação com os padrões correspondentes.

Catalytic routes to convert saccharides to furanic aldehydes

The conversion of plant biomass-derived carbohydrates (preferably non-edible) into added-value products is envisaged to be at the core of the future biorefineries. Carbohydrates are the most abundant natural organic polymers on Earth. This work deals with the chemical valorisation of plant biomass, focusing on the acid-catalysed conversion of carbohydrates (mono and polysaccharides) to furanic aldehydes, namely 2-furaldehyde (Fur) and 5-hydroxymethyl-2-furaldehyde (Hmf), which are valuable platform chemicals that have the potential to replace a variety of oil derived chemicals and materials. The investigated reaction systems can be divided into two types depending on the solvent used to dissolve the carbohydrates in the reaction medium: water or ionic liquid-based systems. The reaction temperatures were greater than 150 ºC when the solvent was water, and lower than 150 º C in the cases of the ionic liquid-based catalytic systems. As alternatives to liquid acids (typically used in the industrial production of Fur), solid acid catalysts were investigated in these reaction systems. Aiming at the identification of (soluble and insoluble) reaction products, complementary characterisation techniques were used namely, FT-IR spectroscopy, liquid and solid state NMR spectroscopy, TGA, DSC and GC´GC-ToFMS analyses. Complex mixtures of soluble reaction products were obtained and different types of side reactions may occur. The requirements to be put on the catalysts for these reaction systems partly depend on the type of carbohydrates to be converted and the reaction conditions used. The thermal stability is important due to the fact that formation of humins and catalyst coking phenomena are characteristically inherent to these types of reactions systems leading to the need to regenerate the catalyst which can be effectively accomplished by calcination. Special attention was given to fully inorganic nanoporous solid acids, amorphous or crystalline, and consisting of nano to micro-size particles. The investigated catalysts were silicoaluminophosphates, aluminosilicates and zirconium-tungsten mixed oxides which are versatile catalysts in that their physicochemical properties can be fine-tuned to improve the catalytic performances in the conversion of different substrates (e.g. introduction of mesoporosity and modification of the acid properties). The catalytic systems consisting of aluminosilicates as solid acids and water as solvent seem to be more effective in converting pentoses and related polysaccharides into Fur, than hexoses and related polysaccharides into Hmf. The investigated solid acids exhibited fairly good hydrothermal stabilities. On the other hand, ionic liquid-based catalytic systems can allow reaching simultaneously high Fur and Hmf yields, particularly when Hmf is obtained from D-fructose and related polysaccharides; however, catalyst deactivation occurs and the catalytic reactions take place in homogeneous phase. As pointed out in a review of the state of the art on this topic, the development of truly heterogeneous ionic liquid-based catalytic systems for producing Fur and Hmf in high yields remains a challenge.

Effect assessment of nanoparticles toxicity in the terrestrial compartment

Over 11 million tons of nanomaterials (NMs) have been produced in 2012 and predictions point the increase in production. Despite predictions and extended usage via consumer products and industry, the understanding of the potential impact of these materials on the environment is virtually absent. The main aim of this thesis is to understand how a selected group of nanomaterials (metal based particles) may impact soil invertebrates, with special focus on the mechanisms of response. Since a case-by-case Environmental Risk Assessment (ERA) of all the emerging contaminants (particularly NMs) is impossible, among others due to time and cost reasons, to gain understanding on the mechanism of action and response is very important to reach a common paradigm. Understanding the modes of action provides predictive characters in cross particle extrapolation. Besides, it also provides insight for the production of new and sustainable materials. Overall, the effects of the selected NMs (Copper and Silver, Titanium and Zirconium oxides) and the respective salt forms, were investigated at the gene expression (using high-throughput tools, microarray and qPCR technology), biochemical (using enzymatic assays for analysis of oxidative stress markers) and organism (survival and reproduction as in OECD test guidelines) levels, this using standard soil species (Enchytraeus albidus, Enchytraeus crypticus, Eisenia fetida). Gene expression analysis provided valuable information on the mechanisms affected by each of the NMs. The gene expression profile highlighted a (nano)material signature and the effect of the duration of exposure. The functional analyses integrated with the biochemical and organism data, revealed a good understanding power. The biochemical parameters (oxidative stress related) were distinct across the materials and also influenced by duration of exposure and concentration. The standardized organismal responses differed the least between the various materials. The overall outcome is that, in this context of NMs effect assessment, gene expression and enzymatic assays introduced a very important knowledge gap, which could not had been achieved by the standard organismal effects alone. A reoccurring issue with some metal based NMs is the possible dissolution and subsequent release of ions that then causes toxicity e.g. Cu-NPs or Ag-NPs release Cu2+ or Ag+. The oxidation state of the particles was investigated, although this was not the focus of the thesis. The study of fate, e.g. dissolution of NPs, is also only in its beginning and the appropriate techniques are currently being developed. The results showed a specific nanoparticle effect. The UV exposure with titanium dioxide nanoparticles increased its effect.

Alkaline-earth aluminosilicate-based glass and glass-ceramic sealants for functional applications

The planar design of solid oxide fuel cell (SOFC) is the most promising one due to its easier fabrication, improved performance and relatively high power density. In planar SOFCs and other solid-electrolyte devices, gas-tight seals must be formed along the edges of each cell and between the stack and gas manifolds. Glass and glass-ceramic (GC), in particular alkaline-earth alumino silicate based glasses and GCs, are becoming the most promising materials for gas-tight sealing applications in SOFCs. Besides the development of new glass-based materials, new additional concepts are required to overcome the challenges being faced by the currently existing sealant technology. The present work deals with the development of glasses- and GCs-based materials to be used as a sealants for SOFCs and other electrochemical functional applications. In this pursuit, various glasses and GCs in the field of diopside crystalline materials have been synthesized and characterized by a wide array of techniques. All the glasses were prepared by melt-quenching technique while GCs were produced by sintering of glass powder compacts at the temperature ranges from 800−900 ºC for 1−1000 h. Furthermore, the influence of various ionic substitutions, especially SrO for CaO, and Ln2O3 (Ln=La, Nd, Gd, and Yb), for MgO + SiO2 in Al-containing diopside on the structure, sintering and crystallization behaviour of glasses and properties of resultant GCs has been investigated, in relevance with final application as sealants in SOFC. From the results obtained in the study of diopside-based glasses, a bilayered concept of GC sealant is proposed to overcome the challenges being faced by (SOFCs). The systems designated as Gd−0.3 (in mol%: 20.62MgO−18.05CaO−7.74SrO−46.40SiO2−1.29Al2O3 − 2.04 B2O3−3.87Gd2O3) and Sr−0.3 (in mol%: 24.54 MgO−14.73 CaO−7.36 SrO−0.55 BaO−47.73 SiO2−1.23 Al2O3−1.23 La2O3−1.79 B2O3−0.84 NiO) have been utilized to realize the bi-layer concept. Both GCs exhibit similar thermal properties, while differing in their amorphous fractions, revealed excellent thermal stability along a period of 1,000 h. They also bonded well to the metallic interconnect (Crofer22APU) and 8 mol% yttrium stabilized zirconium (8YSZ) ceramic electrolyte without forming undesirable interfacial layers at the joints of SOFC components and GC. Two separated layers composed of glasses (Gd−0.3 and Sr−0.3) were prepared and deposited onto interconnect materials using a tape casting approach. The bi-layered GC showed good wetting and bonding ability to Crofer22APU plate, suitable thermal expansion coefficient (9.7–11.1 × 10–6 K−1), mechanical reliability, high electrical resistivity, and strong adhesion to the SOFC componets. All these features confirm the good suitability of the investigated bi-layered sealant system for SOFC applications.