Pigmentary titanium dioxide (TiO2) is the most important white pigment used in several industries, including those that manufacture plastic, coatings and paper. To achieve maximum efficiency in light scattering and to deliver the required opacity to the medium in which the TiO2 is present, the TiO2 particles must be fully dispersed throughout this medium. The particle dispersion in a cured, dry, or solid medium depends on the dispersion efficiency in the wet state, which depends on the effectiveness of the deagglomeration process. Based on the existing technical knowledge, the objective of this study is to investigate fundamental aspects in the dispersion process and to understand the effect of these processes on the required energy to deagglomerate pigmentary TiO2 particles in water. The fundamental aspects of particle wetting, dispersion and stability are reviewed as well as the theories of the tensile strength of agglomerates, particle roughness and liquid surface tension and viscosity. Although liquid surface tension and viscosity are the main factors that influence deagglomeration, some particle-related properties (particle radius, particle shape factor, agglomerate pore volume and specific surface area) play an important role in wetting behavior. The maximum mass of water adsorbed by the agglomerates is proportional to the liquid surface tension. The liquid adsorption rate is a function of the ratio between the liquid and solid surface tensions as well as the shape factor. In the present study, for any shape factor value, the lower the liquid surface energy is in relation to the solid surface tension, the larger the water adsorption rate. After characterizing the particles, the agglomerates and the liquid medium, and obtaining correlations between all properties and the energy to achieve maximum dispersion, a predictive model is proposed to describe the influence of liquid surface tension and the particle roughness on the energy required to produce liquid dispersions with minimum particle size. This model applies to different particles with similar surfaces and to particles with different surfaces but similar sizes. / Dióxido de titânio é o pigmento branco mais importante de diversas indústrias incluindo as de tintas, plásticos e papel. Para atingir sua máxima eficiência no espalhamento de luz, prover a opacidade requerida ao meio em que se encontra presente, as partículas devem estar completamente dispersas neste meio. A dispersão no meio sólido, seco ou curado dependerá da eficiência de dispersão no estado úmido, a eficiência da dispersão no estado úmido dependerá de quão efetivo foi o processo de desaglomeração. O objetivo deste trabalho é compreender como as propriedades do líquido e do sólido impactam a energia requerida para desaglomerar às partículas de dióxido de titânio pigmentário em um meio líquido. As teorias de umectação de partículas, dispersão e estabilidade foram revisadas assim como as teorias de tensão de coesão de aglomerados, rugosidade da partícula e viscosidade e tensão superficial de líquidos. O objetivo destas revisões foi determinar os fatores que influenciam o processo de desaglomeração e a energia requerida para que isso ocorra. Apesar das propriedades do líquido serem os principais fatores que influenciam o processo de desaglomeração (viscosidade e tensão superficial do líquido), as propriedades da partícula, ainda que sempre associadas a propriedades do líquido, desempenham um papel importante no comportamento de umectação (raio da partícula, rugosidade, volume dos poros do aglomerado e área superficial específica). Após a caracterização das propriedades das partículas, dos aglomerados e do meio, e analisar as correlações entre as propriedades e a energia necessária para atingir o máximo da dispersão um modelo preditivo foi desenvolvido para descrever a influencia da tensão superficial e da rugosidade na energia necessária para atingir o tamanho de partícula mínimo. Este modelo se aplica a diferentes partículas com superfícies similares e partículas com superfícies diferentes com tamanhos similares.

L’objectif principal de ce travail est d’étudier les mécanismes d’oxydation lors de la photocatalyse (TiO2 irradié sous UV-A) appliquée à la dégradation des microorganismes et leurs effets sur les composants cellulaires. L'étude de l'efficacité antimicrobienne de TiO2 sur un panel de microorganismes (bactéries, spores, champignons) réalisée dans différents milieux (TiO2 en milieu riche, 'sec', en phase liquide) montre l’influence des méthodes d’évaluation, de test et de comptage sur les efficacités d’inactivation. Des études menées en présence de molécules scavengers d’anions superoxydes (O2°-) mettent en évidence l’implication des O2°- dans l’effet antibactérien et dans la peroxydation lipidique. Au niveau protéomique, diverses cibles d’action potentielles du TiO2 sont aussi proposées. Enfin, une partie applicative détermine l’efficacité antimicrobienne de dispositifs photocatalytiques équipés de mousses alvéolaires de β-SiC et de diodes électroluminescentes, et met en avant les propriétés auto-désinfectantes sous lumière solaire de textiles photocatalytiques fonctionnalisés par la technique layer-by-layer. / The main objective of this work is to study the oxidation mechanisms of UV-A photocatalysis on TiO2 applied to the degradation of microorganisms and their effects on cellular components. The study of the antimicrobial efficiency of TiO2 towards a panel of microorganisms (bacteria, spores, fungi) in different media (TiO2 in rich or 'dry' environment, in liquid phase) shows the influence of the evaluation methods, test and counting on the inactivation efficiency. Studies carried out in the presence of scavenger molecule of superoxide anions (O2°-) highlight the involvement of O2°- in the antibacterial effect and lipid peroxidation. Proteomics analysis leads to propose various potential targets of the TiO2 action. Finally, an application part deals with the design of photocatalytic devices based on LEDs and β-SiC alveolar foams for air disinfection, and of sunlight active self-disinfecting layer-by-layer functionalized photocatalytic textiles.

Neste trabalho foram desenvolvidos e avaliados sistemas integrados de fotodegradação de material orgânico precedendo a determinação voltamétrica, em batch e em fluxo, de metais pesados em níveis de traço, em amostras de água e outras matrizes. Em particular, pela primeira vez, foi proposto, para a abertura das amostras, o método da degradação fotocatalítica mediada por TiO2 (Degussa P-25, via de regra 0,1% em peso) em suspensão. O quelato Cd(II)-EDTA atuou como sistema modelo nesta investigação baseada na recuperação do sinal voltamétrico do metal, inicialmente suprimido, através da parcial ou total destruição do ligante orgânico. Mostrou-se que a degradação fotocatalítica permite acelerar significativamente o processo, especialmente na presença de scavengers de elétrons, como O2 e a temperaturas acima da ambiente. Além disso, o maior aproveitamento da região próxima ao visível do espectro de emissão das lâmpadas, proporciona uma serie de vantagens práticas, como o uso de bobinas de PTFE, no lugar das de quartzo, para a exposição das amostras à radiação ou o emprego de lâmpadas de fluorescência no lugar das de vapor de mercúrio. Observou-se que a presença de partículas de TiO2 não afeta significativamente o sinal polarográfico (NPP) e voltamétrico (ASV) do Cd(II), apesar da deposição de certa quantidade deste óxido na superficie do eletrodo, ocasionando redução na sobretensão de H2 em meio ácido. Para metais com potencial redox menor que o Cd(II), a troca de eletrólito (em fluxo) representa uma elegante solução para contornar o problema. Já, fenômenos de adsorção do analito na superfície do TiO2, observado com Pb(II) mas não com Cd(II), puderam ser prevenidos no caso do Pb(II) com o uso de eletrólitos com pH<2. Examinou-se amplamente a operação em fluxo monosegmentado (MSFA), em sistemas integrados de injeção, fotodigestão, remoção de bolhas, desoxigenação, pré-concentração na superfície do EGPM e determinação, após eventual troca do eletrólito até níveis de Cd(II) da ordem de &#181;g L-1 e excessos de EDTA de até 1:500. Em particular, avaliou-se sistematicamente o uso de adaptadores FIA-EGPM. Estes estudos serviram de base para a idealização e a montagem de um sistema mecanizado prático e compacto, com operação de rotina controlado por software. Aplicações iniciais a alguns tipos de amostras ou matrizes reais (enriquecidas com padrão de Cd(II) e outros metais) que se seguiram ao aprofundado estudo do sistema modelo demonstraram a potencialidade da técnica, que passa a constituir atraente alternativa a ser considerada num leque de aplicações reais. / The present work aimed to develop and assess integrated devices for the photodegradation of organic matter prior to the voltammetric determination of trace heavy metals in water samples as well as in other matrixes, in batch and flowing systems. In particular, for the first time, for the sample digestion step a TiO2-mediated photocatalytic degradation method is proposed. This is based on the use of suspensions of Degussa P-25 TiO2, usually 0.1% w/w in the samples to be treated. The chelate Cd(II)-EDTA acted as a model system in investigations in which the voltammetric signal, suppressed at first, was recovered upon partial or total destruction of the organic ligand. Significant process enhancement speed is obtained with the photocatalytic degradation, especially in the presence of electron scavengers, such as dissolved O2, and at temperature above ambient values. In addition to this, thanks to this UV-TiO2-mediated method, it is possible not only to make use of a broader portion of the radiation but also to benefit from other advantages, such as the use of PTFE rather than quartz for the manufacture of the reactor coil and the utilisation of fluorescent lamps instead of mercury ones. It was observed that the presence of colloidal particles of TiO2 does not significantly affect the polarographic (NPP) nor the voltammetric (ASV) Cd(II) signal, even if a small amount is deposited onto the electrode surface. This causes the reduction of the H2 overvoltage in acidic medium. For metals with redox potential lower than cadmium\'s, the electrolyte exchange under flowing conditions represents an elegant way to overcome the problem. Phenomena of analyte adsorption on TiO2, observed for Pb(II) but not for Cd(II), were prevented in the case of Pb(II) bu operating at pH lower than 2. Monosegmented Flow Analysis systems (MSFA), integrating the injection, photodigestion, bubbles removal, degassing, preconcentration on the HMDE, determination and electrolyte exchange (as needed) steps, were thoroughly examined for Cd(II) levels of as little as few &#181;g L-1 in the presence of EDTA 1:500 (w/w). More notably, a number of FIA-MDE adaptors were systematically assessed. The investigations resulted in the design and construction of a practical and compact mechanised system, controlled by software, for routine analysis. Some applications on real samples or spiked real matrixes have shown the potentials of the technique which seems to represent an attractive alternative for a wider range of real applications.

Os processos oxidativos avançados (POAs) têm sido apontados como alternativa eficiente para a degradação de poluentes recalcitrantes. Entre os POAs, a fotocatálise utilizando luz solar vem sendo muito estudada tendo em vista sua aplicação no tratamento de efluentes aquosos contendo pesticidas. No presente trabalho, estudou-se a degradação do herbicida amicarbazona (AMZ) por meio do processo TiO2/UV em um reator com coletores parabólicos compostos irradiados por luz solar. Os experimentos foram realizados segundo uma matriz Doehlert para o estudo da influência da concentração inicial de AMZ (20-100 mg L-1), da concentração de catalisador (0,1-1 g L-1) e do número de tubos expostos à luz solar (1-9). Amostras retiradas ao longo do tempo foram analisadas quanto às concentrações de AMZ e de carbono orgânico total (TOC). As medidas radiométricas realizadas indicaram que a radiação UVB-UVA correspondeu em média a ca. 4% da radiação solar total incidente entre 310-2800 nm; a actinometria de ferrioxalato indicou fluxo fotônico médio de 3,58×10-5 mol fótons m-2 s-1 para dias ensolarados típicos. O processo TiO2/UV mostrou-se eficiente para degradação do pesticida, que foi totalmente removido antes de 45 minutos de tratamento, para as seguintes condições: [AMZ]0=21,3 mg L-1; [TiO2]=0,5 g L-1; e 7 tubos. Contudo, nesse caso houve apenas ca. 24% de mineralização e na grande maioria dos casos os valores de TOC permaneceram praticamente constantes, o que indica a formação de sub-produtos recalcitrantes, cuja toxicidade e biodegradabilidade devem ser caracterizadas. A análise estatística dos resultados confirma os efeitos importantes da concentração inicial do pesticida e do número de tubos expostos (volume irradiado), cujo aumento permite compensar a menor incidência de radiação solar. Em alguns experimentos os resultados sugeriram que a degradação da AMZ foi favorecida pela maior concentração de TiO2. Na grande maioria dos casos os valores de ACM foram inferiores a 50 m2 kg-1, o que torna este parâmetro interessante para aumento de escala de processos fotocatalíticos irradiados por luz solar empregados no tratamento de efluentes aquosos contendo amicarbazona. / Advanced oxidative processes (AOP) have been considered as an efficient alternative for the degradation of recalcitrant pollutants. Photocatalysis using solar radiation has been studied for the treatment of wastewaters containing pesticides. In this work, the degradation of the herbicide amicarbazone (AMZ) by the TiO2/UV process was studied in a reactor equipped with compound parabolic collectors irradiated by solar light. The experiments were carried out according to a Doehlert matrix to study the effects AMZ initial concentration (20-100 mg L-1), catalyst concentration (0.1-1 g L-1), and number of tubes exposed to solar light (1-9). Samples were analyzed for AMZ and total organic carbon (TOC) concentrations. Radiometric measurements indicated that UVB-UVA radiation corresponded in average to about 4% of the solar radiation between 310-2800 nm; ferrioxalate actinometry resulted in an average photonic flux of 3.58×10-5 mol fótons m-2 s-1 for typical sunny days. The TiO2/UV process showed to be efficient for the degradation of the pesticide, which was completely removed before 45 minutes of treatment, for the following conditions: [AMZ]0=21.3 mg L-1; [TiO2]=0.5 g L-1; and 7 tubes. However, in this case only ca. 24% of mineralization was achieved, and in most cases TOC values remained practically constant, indicating the formation of recalcitrant by-products whose toxicity and biodegradility should be characterized. Statistical analysis of the results confirmed important effects of pesticide initial concentration and number of tubes exposed (irradiated volume), whose increase enables to compensate the lower incidence of solar radiation. Some experimental results suggested that AMZ degradation was favored by higher TiO2 concentrations. In most cases the values of ACM were lower than 50 m2 kg-1, in such a way that this parameter is interesting for scale-up of solar irradiated photocalytic processes used in the treatment of amicarbazone-containing wastewaters.

Made available in DSpace on 2014-12-17T15:41:57Z (GMT). No. of bitstreams: 1 RobertaPMM_DISSERT.pdf: 3172444 bytes, checksum: 159d519d0473cdce848696ecb3f8e8f6 (MD5) Previous issue date: 2011-02-24 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Hybrid systems formed from polymers and transition metals have now their physical and chemical properties extensively investigated for use in electronic devices. In this work, Titanium Dioxide (TiO2) from the precursor of titanium tetrabutoxide and the composite system Poly(Ethylene Glycol)-Titanium Dioxide (TiO2-PEG) were synthesized by sol-gel method. The PEG as acquired and TiO2 and composites powders were analyzed by X-Ray Diffraction (XRD), Spectroscopy in the Infrared region with Fourier transform (IRFT), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and Electrochemical Impedance Spectroscopy (EIS). In the XRD analysis were observed in the TiO2 crystal faces of one of its polymorphs - anatase phase, crystal planes in Poly (Ethylene Glycol) with considerable intensity and in the composite systems the mixture of crystal faces of their precursors isolated and reduction of crystallinity. The TG / DTG suggested increasing the thermal instability of PEG in the composite powders as TiO2 is incorporated into the system. Spectral analysis presented in the infrared overlapping bands for the polymer and metal oxide, reducing the intensity of symmetric stretching of ligand groups in the main chain polymer and angular deformations; were observed using SEM micrographs of the morphological changes suffered by composite systems with the variation of the oxide concentration. Analyses by impedance spectroscopy indicated that the increased conductivity in composite occurs in line with the addition of the metal oxide concentration in the composite system / Sistemas h?bridos formados a partir de pol?meros e metais de transi??o atualmente t?m suas propriedades f?sicas e qu?micas extensivamente investigadas para aplica??o em dispositivos eletr?nicos. Neste trabalho, o Di?xido de Tit?nio (TiO2) a partir do precursor Tetrabut?xido de Tit?nio e o sistema comp?sito Poli (Etileno Glicol)-Di?xido de Tit?nio (PEG-TiO2) foram sintetizados pelo m?todo sol-gel. O PEG como adquirido e os p?s de TiO2 e comp?sitos obtidos foram analisados por Difra??o de Raios X (DRX), Espectroscopia de Absor??o na regi?o do Infravermelho com Transformada de Fourier (EIV-TF), An?lise Termogravim?trica (TG), Microscopia Eletr?nica de Varredura (MEV) e Espectroscopia de Imped?ncia Eletroqu?mica (EIE). Nas an?lises por DRX foram observadas no TiO2, faces cristalinas de um de seus polimorfos fase anat?sio, planos cristalinos no PEG com intensidade substancial e nos sistemas comp?sitos a mistura de faces cristalinas dos seus precursores na forma isolada, bem como, redu??o da cristalinidade. As curvas TG/DTG sugeriram o aumento da instabilidade t?rmica do PEG nos p?s comp?sitos ? medida que TiO2 ? incorporado ao sistema. A an?lise espectral na regi?o do infravermelho apresentou sobreposi??o de bandas relativas ao pol?mero e ao ?xido met?lico, redu??o da intensidade de estiramentos sim?tricos dos grupos ligantes da cadeia principal polim?rica e deforma??es angulares; foram observadas atrav?s das micrografias de MEV modifica??es morfol?gicas sofridas pelos sistemas comp?sitos com a varia??o da concentra??o do ?xido. As an?lises por imped?ncia eletroqu?mica indicaram que o aumento da condutividade nos comp?sitos ocorre em conson?ncia com a adi??o da concentra??o do ?xido met?lico no sistema comp?sito

En raison des problèmes d'instabilité à moyen termes des cellules solaires à colorant (DSSC), l'électrolyte liquide à base d'iodure a été remplacé par plusieurs types de matériaux solides transport de trous (HTM) pour obtenir des DSSCs à l'état solide (s-DSSCs). Parmi ces matériaux, l’utilisation des polymères conducteurs(PC) a attiré une attention considérable en raison de leur bonne stabilité, de leur haute conductivité et de la facilité de leur dépôt sur le semi-conducteur mésoporeux TiO2. Dans ce travail de thèse, plusieurs s-DSSCs basées sur des PC utilisés comme HTM ont été développés dans le but d'améliorer leurs performances photovoltaïques en tenant compte des deux objectifs suivants: (i) l'optimisation des processus de transfert inter facial de charge dans la cellule solaire, et (ii) l'optimisation du transport de charge dans le semi-conducteur d'oxyde de type n. Pour atteindre ces objectifs, chaque composant de la s-DSSC a été modifié afin d'étudier son effet sur les performances du dispositif final. En première tentative, une étude analytique est réalisée en faisant varier le sensibilisateur afin de déterminer les fragments de la structure du colorant, qui ont un effet important sur le processus de photopolymérization électrochimique in-situ (PEP) à la fois en milieu organique et en milieu aqueux mais aussi sur les performances des s-DSSCs. Sur la base de ces résultats, un nouveau concept a été développé et consiste en la suppression totale de l'interface entre le colorant et le HTM. Ceci est obtenu par la synthèse de nouveaux colorants liés de façon covalente à un monomère électroactif qui est co-polymérisé par la PEP in-situ. Le copolymère résultant, utilisé comme HTM, est lié de manière covalente au colorant. En outre, la nature de la liaison chimique, reliant le résidu triphénylamine TPA au monomère, est également étudiée comme un facteur clé dans les performances de s-DSSC. En outre, et pour optimiser les processus de transport de charges dans ce type de s-DSSC, de nouvelles s-DSSC basées sur ZnO ont été réalisées et étudiées. / Due to instability problems of dye sensitized solar cells (DSSCs) in longtime uses, the iodine based liquidelectrolyte has been replaced by several types of solid hole transporting materials (HTM) to perform solidstate DSSCs (s-DSSCs). Among them, the substitution by conducting polymers (CP) has attractedconsiderable attention because of their good stability, high hole-conductivity and simple deposition withinthe mesoporous TiO2 semiconductor. In this thesis work, several s-DSSCs based on CPs used as HTM havebeen developed in order to improve their photovoltaic performances taking into account the following twoobjectives: (i) the optimization of the interfacial charge transfer processes within the solar cell, and (ii) theoptimization of the charge transport within the n-type oxide semiconductor. To reach these goals, eachcomponent that constitutes the device was varied in order to investigate its effect on the device’sperformances. As first attempt, an analytical study is carried out by varying the sensitizer in order todetermine the fragments of the dyes structures, that have an important effect on the in-situ photoelectrochemical polymerization process (PEP) both in organic and in aqueous media and hence on theperformances of the s-DSSCs. Based on these results, a new concept of removing completely the interfacebetween the dye and the HTM is developed. This is achieved by the synthesis of new dyes covalently linkedto an electroactive monomer which is co-polymerized by in-situ PEP. The resulting co-polymer, used asHTM, is covalently linked to the dye. In addition, the nature of the chemical bond linking the triphenylamineresidue TPA to the monomer is also investigated as a key factor in the s-DSSCs performances. Besides, andto optimize the charge transport processes within this type of s-DSSC, the elaboration of novel ZnO baseds-DSSCs has been achieved and investigated.

Ce travail de thèse a consisté en l’étude de catalyseurs ultradispersés, composés de clusters nanométriques ou d’atomes isolés (single-atom catalysts, SACs) de métal, une nouvelle classe de catalyseurs faisant actuellement l’objet d’un engouement mondial. Les systèmes Pt/?-Al2O3 et Pt/TiO2 ont été préparés, caractérisés et testés en oxydation de CO et photogénération d’hydrogène, respectivement. Plusieurs méthodes d’imprégnation et de traitement thermique ont été comparées, notamment grâce à l’analyse de la dispersion du platine par microscopie électronique en transmission à balayage (STEM). Pour la préparation de SACs, notre choix s’est finalement porté sur l’imprégnation à humidité naissante d’une faible charge de précurseur Pt(NH3)4(NO3)2, suivie d’une calcination à l’air. L’étude des performances catalytiques et de l’évolution structurale des catalyseurs au cours des réactions a permis de montrer que les atomes isolés (cations) de platine étaient moins actifs que les clusters (réduits) pour les deux systèmes catalytiques étudiés. Dans le cas de Pt/?-Al2O3, des suivis par spectroscopie d’absorption X (XAS) operando en rayonnement synchrotron, spectroscopie infrarouge par réflexion diffuse (DRIFTS) operando et microscopie environnementale (E-STEM) ont montré la formation et la déstabilisation des SACs, cette dernière étant toutefois moindre en conditions oxydantes. En effet, l’oxygène stabilise le platine isolé via la formation de plusieurs liaisons Pt-O-Al comme montré par modélisation DFT, alors que la présence d’un composé réducteur (CO, H2) conduit à la formation de clusters, mobiles sur leur support. Ce travail met en évidence les limites possibles concernant la stabilisation et la mise en œuvre des SACs dans des réactions catalytiques impliquant des conditions réductrices / This PhD work is focused on the study of ultradispersed catalysts, composed of nanometer-sized clusters or isolated atoms (single-atom catalysts, SACs) of metal, a new class of catalysts which are currently the object of worldwide interest. The Pt/?-Al2O3 and Pt/TiO2 systems were prepared, characterized and evaluated for CO oxidation and hydrogen photogeneration, respectively.Several methods of impregnation and thermal treatment were compared, in particular through platinum dispersion analysis using scanning electron microscopy (STEM). For the preparation of SACs, our choice finally turned to the incipient wetness impregnation of Pt(NH3)4(NO3)2 precursor at low loading, followed by calcination in air.For the two catalytic systems of interest, the study of the performances and the structural evolution of the catalysts during the reactions shows that isolated Pt atoms (cations) are less active than their (reduced) cluster counterparts.In the case of Pt/?-Al2O3, operando X-ray absorption spectroscopy (XAS) using synchrotron radiation, operando diffuse reflectance infrared spectroscopy (DRIFTS), and environmental microscopy (E-STEM) allowed us to monitor the SAC formation and destabilization, the latter being however limited in oxidizing conditions. Indeed, the presence of oxygen stabilizes single Pt atoms via the formation of several Pt-O-Al bonds as shown by DFT modeling, whereas the presence of a reducing compound (CO, H2) leads to the formation of Pt clusters, mobile on their support.This work highlights the possible limitations in the stabilization and implementation of SACs for catalytic reactions involving reducing conditions

En raison de leur petite taille, les nanoparticules (NP) (< 100 nm) peuvent coaguler très rapidement ce qui favorise leur pénétration dans l’organisme sous forme d’agglomérats. L’objectif de cette recherche est d’étudier l’influence de l’état d’agglomération de NP de dioxyde de titane (TiO2) de trois tailles de départ différentes, 5, 10-30 ou 50 nm sur la toxicité pulmonaire chez le rat mâle (F344) exposé à des aérosols de 2, 7 ou 20 mg/m3 pendant 6 heures. Dans une chambre d’inhalation, six groupes de rats (n = 6 par groupe) ont été exposés par inhalation aiguë nez-seulement à des aérosols ayant une taille primaire de 5 nm, mais produits sous forme faiblement (< 100 nm) ou fortement (> 100 nm) agglomérée à 2, 7 et 20 mg/m3. De façon similaire, quatre autres groupes de rats ont été exposés à 20 mg/m3 à des aérosols ayant une taille primaire de 10-30 et 50 nm. Les différents aérosols ont été générés par nébulisation à partir de suspensions ou par dispersion à sec. Pour chaque concentration massique, un groupe de rats témoins (n = 6 par groupe) a été exposé à de l’air comprimé dans les mêmes conditions. Les animaux ont été sacrifiés 16 heures après la fin de l’exposition et les lavages broncho-alvéolaires ont permis de doser des marqueurs d’effets inflammatoires, cytotoxiques et de stress oxydant. Des coupes histologiques de poumons ont également été analysées. L’influence de l’état d’agglomération des NP de TiO2 n’a pu être discriminée à 2 mg/m3. Aux concentrations massiques de 7 et 20 mg/m3, nos résultats montrent qu’une réponse inflammatoire aiguë est induite suite à l'exposition aux aérosols fortement agglomérés. En plus de cette réponse, l’exposition aux aérosols faiblement agglomérés à 20 mg/m3 s’est traduite par une augmentation significative de la 8-isoprostane et de la lactate déshydrogénase. À 20 mg/m3, les effets cytotoxiques étaient plus importants suite à l’exposition aux NP de 5 nm faiblement agglomérées. Ces travaux ont montré dans l'ensemble que différents mécanismes de toxicité pulmonaire peuvent être empruntés par les NP de TiO2 en fonction de la taille de départ et de l’état d’agglomération. / Given their small size, nanoparticles (NP) (< 100 nm) can coagulate quickly, which promotes their entry into the body in the form of agglomerates. The objective of this study is to evaluate the influence of the agglomeration state of three different primary particle sizes (5, 10-30 and 50 nm) of titanium dioxide (TiO2) NP on the pulmonary toxicity of male rats (F344) exposed to aerosols at 2, 7 or 20 mg/m3 for 6 hours. In an inhalation chamber, six groups of rats (n = 6 per group) were acutely exposed by nose-only inhalation to aerosols with a 5-nm primary particle size, produced in the form of small agglomerates (< 100 nm) (SA) or large agglomerates (> 100 nm) (LA) at 2, 7 and 20 mg/m3. Similarly, four other groups of rats were exposed to aerosols at 20 mg/m3 with a primary particle size of 10-30 and 50 nm. The different aerosols were generated by nebulization of suspensions or by dry dispersion. For each mass concentration, one group of control rats (n = 6 per group) was exposed to compressed air under the same conditions. The animals were sacrificed 16 hours after the end of exposure, and analysis of the bronchoalveolar lavage fluids was used to measure markers of inflammatory, cytotoxicity and oxidative stress effects. Lung sections were also analyzed for histopathology. The influence of the agglomeration state of TiO2 NP (5 nm) could not be determined at 2 mg/m3. For mass concentrations of 7 and 20 mg/m3, our results showed that an acute inflammatory response was induced following exposure to LA aerosols. In addition to this response, exposure to SA aerosols resulted in a significant increase in 8-isoprostane and lactate dehydrogenase. At 20 mg/m3, the cytotoxic effects were greater after exposure to the 5-nm NP in the SA aerosol. This study showed that TiO2 NP use different mechanisms to induce their pulmonary toxicity as a function of their primary particle size and their agglomeration state.

Στην παρούσα διατριβή ειδίκευσης παρασκευάσθηκαν νανοσύνθετα υλικά αργιλικών ορυκτών/διοξειδίου του τιτανίου (TiO2) για την περιγραφή και μελέτη των νέων βελτιωμένων χαρακτηριστικών τους και την εφαρμογή τους σαν φωτοκαταλύτες στη διάσπαση ανόργανων αέριων ρύπων οξειδίων του αζώτου (NOX). Τρία αργιλικά ορυκτά (σαπωνίτης, παλυγορσκίτης και αλλοϋσίτης) χρησιμοποιήθηκαν για την διεξαγωγή των πειραμάτων. Δείγματα σαπωνίτη και παλυγορσκίτη συλλέχθηκαν από τη λεκάνη του Βεντζίου στα Γρεβενά και αλλοϋσίτη από τη νήσο Λήμνο. Δύο διαφορετικές μορφές νανοσύνθετων αργιλικού ορυκτού/TiO2 παρήχθησαν με δύο διαφορετικές μεθόδους και χρησιμοποιήθηκαν για τη μελέτη της φωτοαποικοδόμησης ανόργανων αέριων ρύπων NOX : Υποστυλωμένα με TiO2 νανοσύνθετα σαπωνίτη (Ti-sap1, Ti-sap2) παρήχθησαν με τη μέθοδο της «solvothermal synthesis” χρησιμοποιώντας TiCl3 σαν πρόδρομο TiO2 και νανοσύνθετα TiO2/ παλυγορσκίτη (Ti-pal) και TiO2/ αλλοϋσίτη (Ti-hall) παρήχθησαν με τη μέθοδο κολλοειδούς διαλύματος σε πήκτωμα (sol-gel) χρησιμοποιώντας Titanium Tetraisopropoxide (Ti(OC3H7)4) σαν διάλυμα διασποράς-επικάθησης. Για τον χαρακτηρισμό των ιδιοτήτων των φυσικών και τροποποιημένων δειγμάτων εφαρμόστηκαν διαφορετικές τεχνικές (XRD, FTIR-ATR, SEM-EDS, TEM, DLS, BET, porosimetry). Τα νανοσύνθετα αποδείχθηκαν αρκετά αποτελεσματικά για τη φωτοδιάσπαση των αέριων ρύπων NOX συγκριτικά με τον standard τύπο διοξειδίου του τιτανίου, Degussa P25, που χρησιμοποιείται γιαυτό το σκοπό. Tα υποστυλωμένα νανοσύνθετα Ti-sap1 και Ti-sap2 (με αναλογίες μάζας TiO2:σαπωνίτη = 0.2:1 και 0.1:1 αντίστοιχα) έδειξαν αύξηση της ειδικής τους επιφάνειας συγκριτικά με το φυσικό δείγμα σαπωνίτη και μεσοπορώδη δομή με κατανομή πόρων 5.7-9.8nm για το Ti-sap1 και 3.8nm για το Ti-sap2. Και τα δύο νανοσύνθετα απέκτησαν αυξημένη φωτοκαταλυτική ικανότητα βάση του περιεχόμενου ποσοστού TiO2 συγκριτικά με τον standard P25 λόγω της ομοιογενούς διασποράς των σωματιδίων TiO2 στον σαπωνίτη αλλά συγκρίνοντας τα δύο δείγματα Tisap1 και Tisap2, το Tisap2 είχε καλύτερη φωτοκαταλυτική δράση από το Tisap1. Όσον αφορά τα νανοσύνθετα TiO2-pal και TiO2-hall τα αποτελέσματα έδειξαν τη δημιουργία μεσοπορώδους δομής με πόρους 6.5 και 5.6 nm αντίστοιχα για το κάθε υλικό ενώ η μακροπορώδης δομή (lumen) του αλλοϋσίτη δεν υπήρχε στο τροποποιημένο δείγμα λόγω του ότι καλύφθηκε από τα νανοσωματίδια του TiO2 με αποτέλεσμα να προκύψει ένα υλικό με μικρότερο μέγεθος πόρων. Τα δύο δείγματα έδειξαν υψηλή φωτοκαταλυτική ικανότητα στη διάσπαση των αέριων ρύπων NOX υπό την επίδραση ορατής (λ>510nm) και υπεριώδους (λ>290nm) ακτινοβολίας σε σύγκριση με τα αποτελέσματα που έδωσε ο standard τύπος TiO2 P25. / In this thesis TiO2/clay nanocomposites have been synthesized and characterized as photocatalysts in the decomposition of NOx gases. Three different clay minerals (saponite, palygorskite and halloysite) have been used. The saponite and palygorskite samples were collected from Western Macedonia (Grevena, Ventzia basin) and halloysite from Lemnos island. The two different forms of nanocomposites that synthesized by two different methods were: TiO2 -pillared saponite (Ti-sap1, Tisap2) were successfully prepared by solvothermal synthesis using titanium trichloride as the precursor and TiO2- Palygorskite (Ti-pal) and TiO2-Halloysite (Ti-hall) nanocomposites were prepared by deposition of anatase form of TiO2 on the clay surfaces using a sol–gel method with titanium isopropoxide as a precursor. The characterization of the natural and modified samples was done by using different techniques (XRD, FTIR-ATR, SEMEDS, TEM, DLS, BET, porosimetry) The photocatalytic properties of the TiO2-clay nanocomposites were found to be better than that of the standard titania, Degussa P25 in decomposing NOX gases. The pillared TiO2 nanocomposites Ti-sap1, Tisap2 (mass ratio of TiO2:saponite= 0.2:1 and 01:1 respectively) showed a mesoporous structure compared to the natural saponite, with the distribution of pore diameters centered at 5.7-9.8 and at 3.8 nm, with high specific surface areas. Both TiO2-saponite nanocomposites showed higher photocatlytic activity than the standard (Degussa P25) based on TiO2 content because the TiO2 was well dispersed on saponite. By comparing the two modified samples Ti-sap1, Ti-sap2, the second one showed better photocatalytic activity than Ti-sap1 The results of the other two nanocomposites, Ti-hall and Ti-pal, showed mesopores of about 5.6 and 6.5 nm, respectively, while the macropores of halloysite (lumen) disappeared. The latter is attributed to the covering of the lumen of halloysite tubes by TiO2 nanoparticles and for that reason the pore size of the TiO2–treated halloysite was significantly smaller. The clay minerals- TiO2 samples showed significantly higher activity in decomposing NOx gas under visible-light irradiation (λ> 510 nm) and UV light irradiation (λ> 290 nm) compared to that of the standard commercial TiO2, P 25.

Το Η2 είναι το ελαφρύτερο και πλέον άφθονο στοιχείο στη φύση. Βρίσκεται παντού στη γη, στο νερό, στα ορυκτά καύσιμα και σε όλα τα έμβια όντα. Αν το Η2 αξιοποιηθεί κατάλληλα και χρησιμοποιηθεί για τροφοδοσία των κελιών καυσίμου, θα ελαχιστοποιηθεί η εξάρτηση του σύγχρονου πολιτισμού από τα ορυκτά καύσιμα, με συνεπακόλουθο τη μείωση των εκπομπών βλαβερών αερίων στην ατμόσφαιρα. Η χαμηλή θερμοκρασία λειτουργίας των κελιών καυσίμου πολυμερούς ηλεκτρολύτη (PEMFCs) προσφέρει πολλά πλεονεκτήματα και σε συνδυασμό με την υψηλή πυκνότητα ισχύος που αποδίδουν, τα καθιστά κύριους υποψήφιους για εφαρμογή στην αυτοκίνηση. Ωστόσο, η χαμηλή θερμοκρασία εγείρει και σημαντικά προβλήματα, όπως η χρήση ευγενών μετάλλων για την επιτάχυνση των αντιδράσεων και η ευαισθησία σε φαινόμενα δηλητηρίασης. Το κυριότερο δηλητήριο είναι το CO, βασικό παραπροϊόν των διεργασιών παραγωγής H2 από τους υδρογονάνθρακες, οι οποίοι προς το παρόν αποτελούν την κύρια πηγή του. Στην παρούσα διδακτορική διατριβή εξετάστηκαν τα φαινόμενα δηλητηρίασης από το CO της ανόδου του PEMFC. Καθώς το CO δεσμεύεται ισχυρότερα στην επιφάνεια του Pt από το καύσιμο Η2, η παρουσία του στην τροφοδοσία ακόμα και σε ίχνη απενεργοποιεί δραματικά τη λειτουργία της ανόδου. Έτσι, μελετήθηκαν διμεταλλικά και τριμεταλλικά καταλυτικά συστήματα, βασισμένα στο Pt, για την πιθανή αντιμετώπιση του προβλήματος, διαμέσου εξασθένισης του δεσμού Pt-CO ή ενίσχυσης της ηλεκτροχημικής οξείδωσής του από το Η2Ο, που είναι άφθονο στο περιβάλλον ενός PEMFC. Στο κεφάλαιο 1 περιγράφονται οι βιβλιογραφικές πληροφορίες για την τεχνολογία του Η2, όπως μέθοδοι παραγωγής του, καθαρισμού του και αποθήκευσης/μεταφοράς του. Στο κεφάλαιο 2 αναφέρονται οι βασικές αρχές λειτουργίας των κελιών καυσίμου, όσον αφορά στη θερμοδυναμική και στην κινητική, στα είδη τους και στις πιθανές εφαρμογές τους. Στο κεφάλαιο 3 γίνεται εκτενής περιγραφή των δομικών στοιχείων που απαρτίζουν ένα PEMFC, και βιβλιογραφική ανασκόπηση των καταλυτικών συστημάτων που έχουν μελετηθεί για τις βασικές αντιδράσεις. Στο κεφάλαιο 4 περιγράφονται συνοπτικά οι μέθοδοι χαρακτηρισμού και ανάλυσης καθώς και οι πειραματικές διατάξεις που χρησιμοποιήθηκαν. Στο κεφάλαιο 5 εξετάστηκε η επίδραση του υποστρώματος TiO2 στα χαρακτηριστικά του Pt, όσον αφορά την αλληλεπίδρασή του με το CO, σε διάταξη μονής κυψέλης καυσίμου. Παρουσιάστηκε αυξημένη ενεργότητα για την ηλεκτροοοξείδωση του CO και ασθενέστερη αλληλεπίδρασή του με την επιφάνεια του Pt, συντελώντας σε ενεργοποιημένη ρόφηση. Στο κεφάλαιο 6 με φασματοσκοπία υπερύθρου μελετήθηκαν τα χαρακτηριστικά της ρόφησης/εκρόφησης του CO σε μια σειρά καταλυτών Pt-Mo σε υπόστρωμα TiO2. Παρουσία των οξειδίων του Mo η θερμοκρασία εκρόφησης του CO ήταν σημαντικά μειωμένη σε σχέση με μονομεταλλικό Pt, υποδεικνύοντας ασθενέστερο δεσμό του CO με την καταλυτική επιφάνεια. Ωστόσο, παρουσία H2 ο δεσμός ισχυροποιείται, με αποτέλεσμα η εκρόφηση να πραγματοποιείται σε υψηλότερη θερμοκρασία. Αυτό εξηγήθηκε με βάση την ανταγωνιστική αντίδραση του H2 με τις οξειδικές ομάδες, τόσο του υποστρώματος TiO2, όσο και των οξειδίων του Mo. Στο κεφάλαιο 7 εξετάστηκε η οξείδωση του CO σε καταλύτη Pt4Mo/C, δεδομένου του αποσταθεροποιητικού ρόλου του Mo στα χαρακτηριστικά της αλληλεπίδρασης με το CO. Έτσι, αναγνωρίστηκε η ικανότητα των οξειδίων του Mo να διασπούν το Η2Ο σε δυναμικά που συμπίπτουν με τη λειτουργία της ανόδου ενός PEMFC, ενώ παρουσίασαν ενεργότητα για την οξείδωση του CO σε συνθήκες ανοιχτού κυκλώματος διαμέσου της αντίδρασης μετατόπισης με ατμό σε χαμηλή θερμοκρασία μέχρι και 60οC. Ωστόσο, η παραπάνω ιδιότητες δεν ήταν κατανεμημένες ομοιόμορφα στην καταλυτική επιφάνεια, παρά μόνο στη διεπιφάνεια Pt/MoOx, ενώ οι θέσεις μονομεταλλικού Pt παρουσίασαν έντονα φαινόμενα δηλητηρίασης. Επιπλέον, το Mo παρουσιάστηκε ευαίσθητο σε φαινόμενα διάλυσης στο όξινο υδατικό περιβάλλον του PEMFC για δυναμικά μεγαλύτερα από 0.2 V. Στο κεφάλαιο 8 μελετήθηκε η αλληλεπίδραση του CO με τριμεταλλικό καταλύτη Pt-Ru-Co σε σύγκριση με εμπορικό PtRu/C. Ο τριμεταλλικός καταλύτης παρουσιάστηκε ενεργότερος, με χαμηλότερη φαινόμενη ενέργεια ενεργοποίησης για την οξείδωση ροφημένου CO, εμφανίζοντας ισχυρότερη εξάρτηση από το εφαρμοζόμενο δυναμικό. / Hydrogen is the lighter and more abundant element in nature. It is everywhere in earth, water, fossil fuels and in all the living creatures. If H2 can be properly extracted and utilized as a fuel in fuel cells, the dependence of the global economy on fossil fuels will be minimized, resulting in significant attenuation of the greenhouse gases emissions in the atmosphere. The low operation temperature of the polymer electrolyte membrane fuel cells (PEMFCs) offers a lot of advantages. In combination with the high power density yielded by the PEMFCs renders them as the main candidates for application in automotive industry. However, the low temperature raises significant problems, such as the use of noble metals for the acceleration of the basic reactions and the susceptibility in poisoning phenomena. The basic poison is carbon monoxide (CO), one of the main side-products of H2 production from fossil fuels, which for the moment is the main source of H2. In this thesis, the poisoning phenomena of the PEMFCs anode electrocatalysts from CO were investigated. Since CO is bounded on the surface of Pt stronger than the H2 fuel, its presence in the fuel feed in ppm levels deactivates the anode electrocatalyst. In order to eliminate this problem, bimetallic and ternary catalytic systems, based on Pt, were studied with the aim to reduce the Pt-CO bond strength or to promote the electrocatalytic oxidation of CO by water, which is abundant in the PEMFC environment. In chapter 1 is reported the literature information about H2 technology, such as H2 production and cleaning methods and the transport and storage infrastructure. In chapter 2, the basic thermodynamic and kinetic rules of fuel cells operation are referred together with the types of fuel cells and the possible applications. In chapter 3 the structural characteristics of the PEMFCs are outlined and the basic catalytic systems that have been studied for the fuel cell reactions are reviewed. The catalysts’ characterization methods, as well as the experimental procedures utilized in this thesis, are briefly described in chapter 4. In chapter 5 the effect of TiO2 support on the CO chemisorption’s and oxidative properties of Pt was investigated in a single PEMFC configuration. The activity of the CO electrooxidation reaction was enhanced and the Pt-CO bond was destabilized comparing to a commercial Pt/C catalyst. In chapter 6 the CO adsorption/desorption properties were studied by Infrared Spectroscopy, on a series of Pt-Mo catalysts supported on anatase TiO2. The presence of Mo oxides on the catalyst surface reduces significantly the CO desorption temperature in comparison to monometallic TiO2 supported Pt, suggesting the weak CO bonding on the catalytic surface. However, in the presence of H2, the Pt-CO bond strengthens, resulting in higher CO desorption temperature for all the catalysts tested. This was explained on the basis of competitive reaction of H2 with the oxidic surface species, originating from the TiO2 support and the surface Mo oxides. The CO electrooxidation activity of a Pt4Mo/C catalyst is described in chapter 7, considering the destabilizing effect of Mo on the Pt-CO bond. The surface Mo oxide species were able to dissociate H2O at potential values that coincide with the potential window of the PEMFC anode operation. This catalyst oxidized CO under open circuit conditions through the water gas shift reaction and at temperature as low as 60oC. However, the catalytic activity was not homogeneously distributed on the entire catalyst surface, but it was located at the Pt/MoOx interface, with the monometallic Pt sites to be strongly susceptible to CO poisoning. Furthermore, Mo was sensitive to dissolution phenomena in the hydrous acidic environment of the PEMFC for potentials higher than 0.2 V vs. rhe. Finally, in chapter 8 is described the interaction of CO with a ternary Pt-Ru-Co catalyst surface, in comparison to a commercial PtRu/C catalyst. The ternary catalyst was more active for the adsorbed CO electrooxidation, with a lower apparent activation energy than the bimetallic commercial one. The ternary catalyst exhibited zero reaction order with respect to CO partial pressure, while the PtRu/C showed negative reaction order due to competitive adsorption of CO and oxidic species for the same catalytic sites. The kinetic rate constant of the CO electrooxidation reaction for the ternary catalyst showed stronger dependence on the applied potential.