Os eletrocatalisadores PtSnRh suportados em carbono-Sb2O5.SnO2, com 20% de massa de metal, foram preparados pelo método de redução por álcool, utilizando H2PtCl6.6H2O (Aldrich), RhCl3.xH2O (Aldrich) e SnCl2.2H2O (Aldrich), como fontes de metais; Sb2O5.SnO2 (ATO) e carbono Vulcan XC72, como suporte; e etileno glicol como agente redutor. Os eletrocatalisadores obtidos foram caracterizados fisicamente por difração de raios-X (DRX) e microscopia eletrônica de transmissão (MET). Por meio dos difratogramas observou-se que os eletrocatalisadores PtSnRh/C-ATO possuem estrutura CFC para a Pt e ligas de Pt, além de vários picos associados ao SnO2 e ATO. Os tamanhos médios dos cristalitos ficaram entre 2 e 4 nm. Por meio das micrografias verificou-se uma boa distribuição das nanopartículas sobre o suporte. Os tamanhos médios das partículas ficaram entre 2 e 3 nm, com boa concordância para os tamanhos médios dos cristalitos. Os desempenhos dos eletrocatalisadores foram analisados por meio de técnicas eletroquímicas e em condições reais de operação utilizando uma célula a combustível unitária alimentada diretamente por etanol. Na cronoamperometria, a temperatura de 50ºC, os eletrocatalisadores com proporção de 85%C+15%ATO para o suporte, apresentaram a melhor atividade, e as proporções atômicas que obtiveram os melhores resultados foram PtSnRh(70:25:05) e (90:05:05). Nos experimentos em célula, o eletrocatalisador PtSnRh(70:25:05)/85C+15ATO apresentou o melhor desempenho. / PtSnRh electrocatalysts supported on carbon-Sb2O5.SnO2, with metal loading of 20 wt%, were prepared by an alcohol-reduction process, using H2PtCl6.6H2O (Aldrich), RhCl3.xH2O (Aldrich) and SnCl2.2H2O (Aldrich), as source of metals; Sb2O5.SnO2 (ATO) and carbon Vulcan XC72, as support; and ethylene glycol as reducing agent. The electrocatalysts obtained were characterized physically by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The diffractograms showed which PtSnRh/C-ATO electrocatalysts had FCC structure of Pt and Pt alloys, besides several peaks associated with SnO2 and ATO. The average sizes of crystallites were between 2 and 4 nm. TEM micrographs showed a good distribution of the nanoparticles on the support. The average sizes of particles were between 2 and 3 nm, with good agreement for the average size of the crystallites. The performances of the electrocatalysts were analyzed by electrochemical techniques and in real conditions of operation using single direct ethanol fuel cell. In the chronoamperometry at 50ºC, the electrocatalysts with carbon (85 wt%) and ATO (15 wt%) support, showed the best activity, and the atomic proportions which achieved the best results were PtSnRh(70:25:05) e (90:05:05). PtSnRh(70:25:05)/85C+15ATO electrocatalysts showed the best performance in a direct ethanol fuel cell.

Dans le domaine de la santé, l’analyse de l'haleine expirée offre un outil simple et non invasif pour le diagnostic précoce des maladies. Les capteurs de gaz à base de SnO2 modifies semblent être des dispositifs prometteurs pour détecter les gaz polaires tels que l'ammoniac. Dans cette étude, la fonctionnalisation de la surface de SnO2 a été réalisée afin d'obtenir un capteur de gaz sensible et sélectif à l'ammoniac, qui fonctionne à température ambiante. La première étape de la fonctionnalisation est la fixation covalente d’un film de 3-aminopropyltrethoxysalane (APTES) sur SnO2 en phase vapeur ou liquide. Les caractérisations effectuées par Spectroscopie Infrarouge et Spectrométrie photoélectronique X montrent qu’une quantité plus importante d'APTES a été greffée en phase liquide hydratée. La deuxième étape consiste à fonctionnaliser le SnO2-APTES avec des molécules contenant du chlorure d'acyle avec différents groupes tel que des groupes alkyle, acide et ester. Les capteurs modifiés par des acides et des esters sont sensibles à l’ammoniac entre 0,2 et 10 ppm à température ambiante. Cependant, le SnO2 APTES modifié par l’ester s'est révélé être plus sélectif que le capteur modifié par l'acide pour l’ethanol et le mondxyde de carbone. Ces résultats impliquent que la réponse est générée par les groupes fonctionnels acide et ester, NH3 modifie le moment dipolaire de la couche moléculaire greffée, ce qui entraine une modification de la conductance de SnO2. Le fonctionnement à température ambiante est l'un des avantages de ces capteurs, tout comme leur sélectivité à l'ammoniac en regard d'autres gaz tels que l'éthanol, le monoxyde de carbone et l'acétone. / One of the major challenges in the modern era is how we can detect the disease when we are still feeling healthy via noninvasive methods. Exhaled breath analysis is offering a simple and noninvasive tool for early diagnosis of diseases. Molecularly modified SnO2 sensors seem to be promising devices for sensing polar gases such as ammonia. SnO2 surface functionalization was performed in order to obtain sensitive and selective ammonia gas sensor that operates at room temperature. The first step of functionalization is the covalently attachment of 3-aminopropyltriethoxysilane (APTES) film on SnO2 in vapor or liquid phases. The characterization performed by the Infrared Spectroscopy and X-ray Photoelectron Spectroscopy, show that more APTES were grafted by hydrous liquid phase silanization. The second step was the functionalization of APTES modified SnO2 with molecules having acyl chloride of end functional groups molecules such as alkyl, acid and ester groups. Pure SnO2 and APTES modified SnO2 sensors did not show any significant sensitivity to ammonia (0.2-100 ppm) at 25 °C. On the contrary, acid and ester modified sensors are sensitive to ammonia between 0.2 and 10 ppm at room temperature. However, ester modified SnO2 was more selective than acid modified sensor regarding the ethanol and carbon monoxide gases. Ammonia variates the attached molecular layer’s dipole moment which leads to change in SnO2 conductance. Working at ambient temperature is also one of the advantages of these sensors in addition to the selectivity to ammonia regarding other gases such as ethanol, carbon monoxide and acetone.

Les nano-composés de type Sn1-xTaxO2 (0 ≤ x ≤ 0,03) ont été étudiés en vue de leurs propriétés thermoélectriques. Une méthode de co-précipitation a été utilisée pour synthétiser des nano-poudres ayant une taille des grains moyenne d’environ 3 nm. L’étude structurale et microstructurale a suggéré une limite de solubilité pour le Ta de 0,008 ≤ x < 0,010. Ces nano-poudres ont été ensuite densifiées par Spark Plasma Sintering, avec des compacités atteignant ~ 95%. Le dopage en Ta a permis une amélioration des propriétés thermoélectriques du SnO2 et, en accord avec la limite de solubilité, une valeur maximale du facteur de mérite de 4,7x10-5 K-1 a été observée pour l’échantillon x = 0,008. De plus, nous avons démontré qu’une diminution de la taille des grains permettait d’améliorer le coefficient Seebeck, de diminuer la conductivité thermique, mais conduisait à une diminution de la conductivité électrique. La stabilité des oxydes, notamment à l'échelle nanométrique, est remise en question par des caractérisations physico-chimiques. Partant de ces matériaux à base de SnO2, un nano-composite (ZnO-SnO2) a été étudié. Le composé Zn1-xGdxO (0 ≤ x ≤ 0,03) a été préparé par la méthode de Péchini et caractérisé en comparant avec d’autres matériaux à base de ZnO. Un premier test de nano-composite M30 (30% en masse Sn0.996Ta0.004O2 et 70% en masse Zn0.997Gd0.003O) a été mené. Le résultat obtenu a montré qu’une concentration de nano-inclusion Sn0.996Ta0.004O2 de 30 % ne permettait pas d’améliorer les propriétés thermoélectriques du nano-composite M30, par rapport aux matériaux de départ. / The nano-compound Sn1-xTaxO2 (0 ≤ x ≤ 0.03) was studied with a view to their thermoelectric properties. A method of co-precipitation was used to synthesize nano-powders having an average grain size of about 3 nm. The structural and microstructural study suggested a solid solubility limit of 0.008 ≤ x < 0.010. These nano-powders were then densified by Spark Plasma Sintering, with density reaching ~ 95%. The doping of Ta improved the thermoelectric properties, and in good agreement with the solubility limit, a maximum value of the factor of merit of 4.7x10-5 K-1 was observed for the sample x = 0.008. The stability of oxides, particularly at the nanoscale, is questioned by physicochemical characterizations. From these SnO2-based materials, a nano-composite (ZnO-SnO2) was studied. The compound Zn1-xGdxO (0 ≤ x ≤ 0.03) was prepared by the method of Pechini and characterized by comparing with other ZnO-based materials. A first test of nano-composite M30 (30 wt% Sn0.996Ta0.004O2 and 70 wt% Zn0.997Gd0.003O) was conducted. The result showed that a concentration of 30% nano-inclusion Sn0.996Ta0.004O2 did not allow to improve the thermoelectric properties of nano-composite M30, compared to the starting materials.

O presente trabalho teve como objetivo utilizar a técnica nuclear de Correlação Angular &gamma;-&gamma; Perturbada (CAP) para a medida de interações hiperfinas em filmes finos e amostras em pó de óxidos semicondutores SnO2 e TiO2 puros e dopados com metais de transição para uma investigação sistemática de defeitos estruturais e do magnetismo sob o ponto de vista atômico tendo como principal motivação a candidatura à aplicação desses óxidos em spintrônica. O trabalho também teve como foco a preparação e caracterização das amostras por meio de técnicas convencionais, como difração de raios X, microscopia eletrônica de varredura, espectroscopia de energia dispersiva e medidas de magnetização. Amostras puras dos filmes foram medidas mediante a variação sistemática da temperatura de tratamento térmico e do campo magnético aplicado. Tais medidas foram realizadas no HISKP, na Universidade de Bonn (Rheinische Friedrich-Wilhelms-Universität Bonn), através de implantação de íons de 111In(111Cd) ou 181Hf(181Ta); no IPEN, por sua vez, essas medidas foram realizadas após a difusão dos mesmos núcleos de prova. Outra parte das medidas CAP foram feitas através de implantação de íons de 111mCd(111Cd) e 117Cd(117In) no Isotope Mass Separator On-Line (ISOLDE) do Centre Européen Recherche Nucléaire (CERN). As medidas foram realizadas nos intervalos de temperatura de 8 K a 1173 K. Para análise de ferromagnetismo, medidas foram feitas à temperatura ambiente com e sem aplicação de campo magnético externo. Após a comparação dos resultados das medidas macroscópicas e atômicas das amostras, foi possível concluir que há uma correlação entre os defeitos, o magnetismo e a mobilidade dos portadores de carga nos semicondutores aqui estudados. Um passo adiante na busca de semicondutores, cujo ordenamento magnético possibilite o seu uso na eletrônica baseada em spin. Alguns resultados já foram publicados, incluindo resultados obtidos na Universidade de Bonn durante o período de doutorado sanduíche [1-7]. / This study aimed the use of nuclear technique Perturbed &gamma;-&gamma; Angular Correlation Spectroccopy (PAC) to measure the hyperfine interactions in thin films and powder samples of SnO2 and TiO2 pure and doped with transition metals to obtain a systematic investigation of defects and magnetism from an atomic point of view with the main motivation the application in spintronics. The work also focused on the preparation and characterization of samples by conventional techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and magnetization measurements. Pure samples of the films were measured by the systematic variation of thermal treatment and applied magnetic field. These measurements were performed in HISKP at the University of Bonn (Rheinische Friedrich-Wilhelms-Universität Bonn) using 111In(111Cd) or 181Hf (181Ta); at IPEN, in turn, these measurements were performed after the diffusion of the same probe nuclei. Another part of PAC measurements were carried out using 111mCd(111Cd) and 117Cd (117In) in Isotope Mass Separator On-Line (ISOLDE) at Centre Européen Recherche Nucléaire (CERN). The measurements were performed from 8 K to 1173 K. After comparing results from macroscopic techniques with those from PAC, it was concluded that there is a correlation between the defects, magnetism and the mobility of charge carriers in semiconductors studied here. A step forward in the search for semiconductors, whose magnetic ordering allows its use in electronics based on spin. Some results have been published, including results obtained at the University of Bonn for the sandwich doctorate period [1-7].

Orientador: Alexandre José de Castro Lanfredi. / Dissertação (mestrado) - Universidade Federal do ABC. Programa de Pós-Graduação em Nanociências e Materiais Avançados.

O presente trabalho teve como objetivo utilizar a técnica nuclear de Correlação Angular &gamma;-&gamma; Perturbada (CAP) para a medida de interações hiperfinas em filmes finos e amostras em pó de óxidos semicondutores SnO2 e TiO2 puros e dopados com metais de transição para uma investigação sistemática de defeitos estruturais e do magnetismo sob o ponto de vista atômico tendo como principal motivação a candidatura à aplicação desses óxidos em spintrônica. O trabalho também teve como foco a preparação e caracterização das amostras por meio de técnicas convencionais, como difração de raios X, microscopia eletrônica de varredura, espectroscopia de energia dispersiva e medidas de magnetização. Amostras puras dos filmes foram medidas mediante a variação sistemática da temperatura de tratamento térmico e do campo magnético aplicado. Tais medidas foram realizadas no HISKP, na Universidade de Bonn (Rheinische Friedrich-Wilhelms-Universität Bonn), através de implantação de íons de 111In(111Cd) ou 181Hf(181Ta); no IPEN, por sua vez, essas medidas foram realizadas após a difusão dos mesmos núcleos de prova. Outra parte das medidas CAP foram feitas através de implantação de íons de 111mCd(111Cd) e 117Cd(117In) no Isotope Mass Separator On-Line (ISOLDE) do Centre Européen Recherche Nucléaire (CERN). As medidas foram realizadas nos intervalos de temperatura de 8 K a 1173 K. Para análise de ferromagnetismo, medidas foram feitas à temperatura ambiente com e sem aplicação de campo magnético externo. Após a comparação dos resultados das medidas macroscópicas e atômicas das amostras, foi possível concluir que há uma correlação entre os defeitos, o magnetismo e a mobilidade dos portadores de carga nos semicondutores aqui estudados. Um passo adiante na busca de semicondutores, cujo ordenamento magnético possibilite o seu uso na eletrônica baseada em spin. Alguns resultados já foram publicados, incluindo resultados obtidos na Universidade de Bonn durante o período de doutorado sanduíche [1-7]. / This study aimed the use of nuclear technique Perturbed &gamma;-&gamma; Angular Correlation Spectroccopy (PAC) to measure the hyperfine interactions in thin films and powder samples of SnO2 and TiO2 pure and doped with transition metals to obtain a systematic investigation of defects and magnetism from an atomic point of view with the main motivation the application in spintronics. The work also focused on the preparation and characterization of samples by conventional techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and magnetization measurements. Pure samples of the films were measured by the systematic variation of thermal treatment and applied magnetic field. These measurements were performed in HISKP at the University of Bonn (Rheinische Friedrich-Wilhelms-Universität Bonn) using 111In(111Cd) or 181Hf (181Ta); at IPEN, in turn, these measurements were performed after the diffusion of the same probe nuclei. Another part of PAC measurements were carried out using 111mCd(111Cd) and 117Cd (117In) in Isotope Mass Separator On-Line (ISOLDE) at Centre Européen Recherche Nucléaire (CERN). The measurements were performed from 8 K to 1173 K. After comparing results from macroscopic techniques with those from PAC, it was concluded that there is a correlation between the defects, magnetism and the mobility of charge carriers in semiconductors studied here. A step forward in the search for semiconductors, whose magnetic ordering allows its use in electronics based on spin. Some results have been published, including results obtained at the University of Bonn for the sandwich doctorate period [1-7].

Cette thèse a été effectuée dans le cadre dun contrat Européen « Nanosensoflex » au sein du laboratoire LAAS-CNRS de Toulouse, qui visait à améliorer la technologie capteur et à optimiser la sélectivité grâce notamment à un nouveau mode opératoire associé à une nouvelle technique de traitement des réponses. Pour cela, nous avons démontré expérimentalement que la forme de la réponse transitoire de ces capteurs, au cours de variations très rapides de température, était fonction du mélange gazeux environnant de manière très reproductible. Aussi, nous avons pu définir un profil thermique adapté à la détection du CO dans le mélange de NO2 et propane. Il comporte 6 paliers de température compris entre 100°C et 500°C et nexcède pas au total 12s. Par la prise en compte des formes et temps associés issus des réponses normalisées dun capteur et dune méthode multifactorielle, nous avons discriminé chaque mélange gazeux et quantifier le CO entre 1 et 200 ppm indépendamment du taux dhumidité.

La present tesi doctoral tracta la modelitzacio de diferents estats de la materia: clusters o agregats, superficies i cristalls d'oxids metal.lics. Els metodes disponibles per abordar cada sistema han estat breument descrits, per justificar la seua utilitzacio en diverses aplicacions a materials. Primer, s'han proposat geometries per als agregats de V2O5 cations i neutres en fase gas, i s'han caracteritzat els estats electronics, estructura, espectre de vibracio i enllac quimic. Segon, s'han simulat superficies d'oxids metal.lics i processos d'adsorcio de molecules o atoms metal.lics: CH3OH i O2 sobre SnO2, Cu sobre ZnO. La interaccio adsorbat-superficie te lloc per un mecanisme acid/base, i s'ha caracteritzat la geometria i energia de cada supersistema (mode d'adsorcio, paper dels defectes de superficie). Finalment, s'ha estudiat el cristall de TiO2 en fase anatasa des de multiples punts de vista: descripcio de l'estructura en poliedres, estructura electronica (bandes i densitat d'estats), termodinamic (equacio d'estat) i d'enllac quimic ("Atoms In Molecules"). Les superficies mes estables han estat construides i els efectes de relaxacio avaluats.

Semiconductor metal oxides can be induced by light with proper wavelength resulting in oxidation and reduction reactions for the transformation of water and oxygen molecules into active radicals. With this method, it is possible to obtain self-cleaning surfaces and products having antimicrobial properties. The aim of this study is to develop semiconductor metal oxide thin films for multifunctional glass products and the characterization of photocatalytic self cleaning and antimicrobial properties. As semiconductor metal oxides / titanium dioxide (TiO2), tin oxide (SnO2) and their binary mixtures (TiO2-SnO2) are selected because of their abundancy, non toxic properties, stability and the ability of absorbing light close to visible range. Also the effect of metal dopants such as praseodymium (Pr), palladium (Pd), silver (Ag) and iron (Fe) was examined with these metal oxides. The colloidal solutions were synthesized by using sol-gel method in order to apply the developed method to industrial usage as applying on large surfaces. The glass substrates were coated with the colloidal solutions by dip coating and the dried samples were calcined under air flow. The best calcination condition for pure TiO2 coated thin film was determined as 400oC for 45 minutes. Surface characterization studies were performed by using UV-Visible Spectrophotometer for band gap measurement, CAM for contact angle measurement, SEM for surface morphology and tophology. The methylene blue adsorption tests were carried out and the effective surface area of the samples were predicted by the Langmuir adsorption isotherm of samples. The photocatalytic activities of the coated thin films were measured with the degradation of organic materials as red wine and methylene blue, and with the antimicrobial activity tests as counting the number of viable E.coli cells. 61.2% deactivation of methylene blue stain was achieved over SnO2 coated thin films while this was 22.1% over TiO2 coated thin films after irradiation for 180 minutes. The superior photocatalytic activity was observed with TiO2 samples doped with Pd and Ag ions. The TiO2-SnO2 coated samples performed limited photocatalytic activity which is less than the activity of SnO2 coated samples which was confirmed with surface area measurements as SnO2 coated samples had higher surface area (9.81 cm2/cm2) than TiO2-SnO2 coated samples. Surface area increased with increasing the amount of SnO2 and it was in the following order: SnO2 &gt / 80% SnO2 + 20% TiO2 &gt / 50% SnO2 + 50%TiO2 &gt / 35% SnO2 + 65%TiO2 &gt / 20% SnO2 + 80% TiO2 &gt / TiO2.

Effects of urban air pollution on health and environment have lead researchers to find economic air quality monitoring regulations. Since tin dioxide (SnO2) was demonstrated as a gas sensing device in 1962, tin oxide based thin film sensors have been widely studied due to their high sensitivity and fast response. The main advantages of using tin oxide sensors are their low cost, small size and low power consumption for mobile system applications. But, in order SnO2 based sensors to meet low concentration of gases they should be highly upgraded in sensitivity, selectivity and stability. This study was focused on the capacity of dopants in the SnO2 layer to increase the sensitivity of the sensor in detecting carbon monoxide. 1 wt. % Pd promoted and 0.1 wt. % Na-1 % Pd promoted SnO2 multilayer thin films were produced by sol-gel technique followed by spin coating route on soda-lime glass substrates. The EDX and SEM studies showed the surface composition and the surface structure is homogeneous throughout the films. The film thickness was determined app. 450 nm from the SEM image of the cross-section, after coating 8 layers. The experiments conducted at several temperatures namely 150, 175 and 200oC, in oxygen free and 1% oxygen containing atmospheres showed that the responses at higher temperatures in the presence of oxygen were much sharper with respect to others. Besides, Na promoted test sensors showed larger responses with shorter response time in oxygen free atmospheres at relatively lower temperatures. The results showed that the sensor signal is not directly correlated with the carbon dioxide production in oxygen free atmospheres.