A atrazina (ATZ) é um herbicida utilizado em larga escala no Brasil de forma intensiva em culturas de cana-de-açúcar, milho e sorgo. A ATZ possui caráter persistente e recalcitrante, de forma que os tratamentos convencionais de efluentes não são capazes de removê-lo. Nesse contexto, os processos oxidativos avançados, como a fotocatálise heterogênea, têm se mostrado eficientes para remoção deste poluente. Este trabalho tem por objetivo avaliar o desempenho dos fotocatalisadores TiO2 P25 e C-TiO2 Kronos vlp 7000 modificado com carbono para a degradação do pesticida atrazina em solução aquosa, utilizando um reator fotoquímico com coletor parabólico composto irradiado por um simulador solar. Os catalisadores TiO2 P25 e C-TiO2 Kronos foram caracterizados por meio de difração de raios-X, espectroscopia de infravermelho, área superficial específica BET e análise de reflectância difusa. As concentrações de TiO2 P25 e C-TiO2 Kronos empregadas foram 500 e 100 mg L&-1, respectivamente. Os resultados obtidos mostraram significativa remoção de ATZ ao final de 120 minutos (100; 98; 98; 93; 86% para concentrações iniciais de ATZ de 1; 5; 10; 20 e 30 mg L-1, respectivamente) com emprego do catalisador TiO2 P25. No entanto, as análises de carbono orgânico total (COT) indicaram que não houve mineralização significativa da ATZ, com valores inferiores a 20% com o uso do TiO2 P25. Para o catalisador C-TiO2 Kronos não se obteve remoção importante da ATZ ao final de 120 minutos de experimento, quando comparado com o TiO2 P25. Neste caso, o catalisador C-TiO2 Kronos permitiu obter remoções do pesticida de 37; 35; 38; 39 e 45%, aproximadamente, para as concentrações iniciais de ATZ de 1; 5; 10; 20 e 30 mg L-1, respectivamente. Apesar disso, o catalisador C-TiO2 Kronos apresentou melhor desempenho em mineralizar a ATZ a CO2 e H2O em relação ao proporcionado pelo TiO2 P25, com aproximadamente 38% de mineralização. O modelo de Langmuir-Hinshelwood (LH) constitui uma aproximação adequada para a cinética de degradação da atrazina para ambos os catalisadores estudados, com valores de Kr e Kads iguais a 1,54 mg L-1 min-1 e 15,47 L mg-1, respectivamente, para o catalisador TiO2 P25 e de 1,34 mg L-1 min-1 e 132,95 L mg-1, respectivamente para o catalisador C-TiO2 Kronos vlp 7000. / Atrazine (ATZ) is a widely used herbicide in Brazil, where it is intensively applied in sugarcane, corn and sorghum cultivations. However, conventional wastewater treatments are not able to remove ATZ due to its persistent and recalcitrant properties. Advanced oxidation processes, such as heterogeneous photocatalysis, have been proved effective for the removal of this pollutant. This study aims to evaluate the performance of TiO2 P25 and carbon-modified TiO2 Kronos vlp 7000 photocatalysts in the degradation of ATZ in aqueous systems using a tubular photochemical reactor equipped with a compound parabolic collector (CPC) irradiated by simulated solar light. Catalysts TiO2 P25 and C-TiO2 Kronos were characterized by X-ray diffraction, infrared spectroscopy, BET analysis and diffuse reflectance analysis. The concentrations of TiO2 P25 and C-TiO2 Kronos were 500 and 100 mg L-1, respectively. For TiO2 P25, the results showed significant ATZ removals after 120 minutes of irradiation (100; 98; 98; 93; 86% for initial ATZ concentrations of 1; 5; 10; 20, and 30 mg L-1, respectively). In contrast, the total organic carbon (TOC) analyses indicated that no significant ATZ mineralization occurred, with values lower than 20% for TiO2 P25. In comparison with TiO2 P25, C-TiO2 was not able to completely remove ATZ at the end of 120 minutes of irradition. In this case, pesticide removals of about 37; 35; 38; 39 and 45% were obtained for initial ATZ concentrations of 1; 5; 10; 20, and 30 mg L-1, respectively. Nevertheless, C-TiO2 Kronos showed better performance for ATZ mineralization to CO2 and H2O in comparison with TiO2 P25, with approximately 38% total carbon organic removal. The Langmuir-Hinshelwood (LH) model was shown to be an appropriate approximation for the degradation kinetics of atrazine for both catalysts, with values of Kr and Kads equal to 1.54 mg L-1 min-1 and 15.47 mg L-1, respectively, for the P25 TiO2 and 1.34 mg L-1 min-1 and 132.95 mg L-1, respectively, for C-TiO2 Kronos vlp 7000.

A redução da emissão de compostos nitrogenados tem sido um dos grandes desafios da área de proteção ambiental e o tratamento catalítico pode reduzir significativamente tal emissão. Neste caminho, têm sido testadas várias categorias de catalisadores. Considerando-se o potencial de utilização de catalisadores de cobre e de cobalto nos processos de abatimento de compostos nitrogenados, bem como a necessidade de exploração dos efeitos gerados pelos suportes de óxido de cério e óxido de titânio, este trabalho teve como objetivos a preparação e a caracterização dos sistemas catalíticos CuO e Co3 O4 suportados em TiO2 , CeO2 e CeO2 -TiO3 (1%, 10%, 20% e 50% de CeO2 ), para aplicação no processo de redução de NO com CO na presença e ausência de O2 . Os catalisadores foram obtidos a partir do método de impregnação. Na caracterização das amostras foram utilizadas as técnicas de difração de raios X (DRX), redução à temperatura programada com H2 (RTP-H2 ), espectroscopia Raman, espectroscopia por energia dispersiva de raios X (EDX), fisissorção de nitrogênio e espectroscopia UV-visível próxima a região do infra-vermelho (UV-VIS-NIR). Os resultados da caracterização mostraram que os catalisadores apresentam fases de CuO altamente dispersas, bem como formando cristalitos com os suportes. Mostraram, também, que o cobalto está sobre a forma oxida Co3 O4 . As reações de redução de NO com CO mostraram que os catalisadores de cobre são mais ativos para estas reações e a adição do suporte CeO2 em TiO2 aumenta significativamente esta atividade. A adição de O2 na reação diminuiu a atividade frente à reação de redução de NO, isso porque o oxigênio é adsorvido sobre a superfície do catalisador, diminuindo sua atividade. / The reduction of the nitrogen composites emissions has been one of the great challenges of the ambient protection area and the catalytic treatment can reduce significantly such emissions. In this way, it has been tested some categories of catalysts. Considering the potential of use of copper and cobalt catalysts in the processes of nitrogen composites discouragement, as well as the necessity of exploration of the effect generated for CeO2 and TiO2 supported , this work had as objective the preparation and the characterization of the catalytic systems supported CuO and Co3O4 in TiO2, CeO2 and CeO2-TiO2 (1%, 10%, 20% and 50% of CeO2), for application in the reduction process of NO with CO in presence and absence of O2. The catalysts had been gotten from the impregnation method. In the characterization of the samples the techniques that had been used was: X-ray diffraction had been used, temperature programmed reduction, Raman spectroscopy, energy dispersive X-ray spectroscopy, nitrogen physsisorption and UV-visible spectroscopy next the region to the infra-red ray (UV-VIS-NIR). The results of the characterization had shown that the catalysts present highly dispersed phases of CuO, as well as cristalitts. And, that cobalto meets under the form Co3O4. The reactions of reduction of NO with CO had shown that the copper catalysts are more active than the cobalto and the addition of the CeO2 support in TiO2 increases significantly this activity. The addition of O2 in the reaction diminished the activity front to the reaction of reduction of NO, just because the oxygen is adsorbed on the surface of the catalysts, diminishing its activity

TiO2 nanoparticles are one of the most suitable materials for photocatalysis, specifically for water and air treatment and removal of a wide variety of organic pollutants such as dyes, aromatic compounds, and chlorinated aromatic compounds. Methods of synthesis of TiO2 are generally categorized in two main classes of wet chemical, and dry methods. Wet chemical methods generally provide a better control over size, size distribution, and shape; all of which significantly affect photocatalytic performance of the produced nanoparticles. Despite its advantages over other semiconductor photocatalysts, wide band-gap of titania restrains its photocatalytic activity to only UV light, which only makes up to 5% of the light reaching surface of the earth. To induce visible-light activity, titania has been doped by different dopants, including transition metal-dopants such as Fe, and Co and non-metal dopants such as N, and C. Nitrogen has been shown to be a better dopant, providing a suitably placed energy state within the band-gap of TiO2, and not suffering from issues related to transition-metal dopants such as low thermal and physical stability and high electron-hole recombination rates. To dope titania with nitrogen, one could add the nitrogen source together with other precursors during synthesis, referred to as wet chemical doping methods, or anneal the synthesized titania nanoparticles under a flow of ammonia at high temperatures, referred to as dry doping methods. While different doping methods have been studied individually, the author maintains that there has been an absence of research comparing the effectiveness of these methods, on photocatalytic performance of N-doped TiO2 within a consistent experiment. In this research TiO2 nanoparticles were synthesized by a facile, inexpensive sol-gel method, and doping was done by wet chemical methods, dry methods, and a combination of both these methods. Visible-light photocatalytic activity of these nanoparticles was evaluated by their efficiency in degradation of methyl orange. The results show wet doping methods increase the efficiency of titania nanoparticles more than dry doping, or combination of both. Further investigation showed that the main reason for higher activity of wet chemically doped nanoparticles is due to their higher available surface area of 131.7 m2.g-1. After normalizing the available surface area, measured by the BET method, it was shown that a combination of wet chemical doping, and dry doping at 600 °C result in the most active nanoparticles, but high temperature dry doping severely decreases the surface area, lowering the overall efficiency of the product. Additionally, N-doped TiO2 nanoparticles were synthesized using a simple hydrothermal method, in which the nitrogen source was used not only to dope, but also to control shape, size, size distribution, and morphology of the titania nanoparticles, and to induce aqueous colloidal stability. It was shown that addition of triethylamine during the synthesis, results in ultra-small, colloidally stable, cubic TiO2 nanoparticles, while using triethanolamine results in formation of TiO2 pallets, assembled into spherical, rose-like structures. The synthesized nanoparticles show impressive efficiency in visible-light removal of phenol, 4-chlorophenol, and pentachlorophenol, achieving 100% degradation of a 100-ppm phenol solution in 90 min, more than 98% degradation of a 20-ppm 4-chlorophenol solution in 90 min, and 97% degradation of a 10-ppm pentachlorophenol in 180 min with 500 ppm loading of the catalyst in all cases. Moreover, synthesized nanoparticles showed no sign of deactivation after 5 consecutive runs, removing 4-chlorophenol, showing their reusability. / Graduate

A atrazina (ATZ) é um herbicida utilizado em larga escala no Brasil de forma intensiva em culturas de cana-de-açúcar, milho e sorgo. A ATZ possui caráter persistente e recalcitrante, de forma que os tratamentos convencionais de efluentes não são capazes de removê-lo. Nesse contexto, os processos oxidativos avançados, como a fotocatálise heterogênea, têm se mostrado eficientes para remoção deste poluente. Este trabalho tem por objetivo avaliar o desempenho dos fotocatalisadores TiO2 P25 e C-TiO2 Kronos vlp 7000 modificado com carbono para a degradação do pesticida atrazina em solução aquosa, utilizando um reator fotoquímico com coletor parabólico composto irradiado por um simulador solar. Os catalisadores TiO2 P25 e C-TiO2 Kronos foram caracterizados por meio de difração de raios-X, espectroscopia de infravermelho, área superficial específica BET e análise de reflectância difusa. As concentrações de TiO2 P25 e C-TiO2 Kronos empregadas foram 500 e 100 mg L&-1, respectivamente. Os resultados obtidos mostraram significativa remoção de ATZ ao final de 120 minutos (100; 98; 98; 93; 86% para concentrações iniciais de ATZ de 1; 5; 10; 20 e 30 mg L-1, respectivamente) com emprego do catalisador TiO2 P25. No entanto, as análises de carbono orgânico total (COT) indicaram que não houve mineralização significativa da ATZ, com valores inferiores a 20% com o uso do TiO2 P25. Para o catalisador C-TiO2 Kronos não se obteve remoção importante da ATZ ao final de 120 minutos de experimento, quando comparado com o TiO2 P25. Neste caso, o catalisador C-TiO2 Kronos permitiu obter remoções do pesticida de 37; 35; 38; 39 e 45%, aproximadamente, para as concentrações iniciais de ATZ de 1; 5; 10; 20 e 30 mg L-1, respectivamente. Apesar disso, o catalisador C-TiO2 Kronos apresentou melhor desempenho em mineralizar a ATZ a CO2 e H2O em relação ao proporcionado pelo TiO2 P25, com aproximadamente 38% de mineralização. O modelo de Langmuir-Hinshelwood (LH) constitui uma aproximação adequada para a cinética de degradação da atrazina para ambos os catalisadores estudados, com valores de Kr e Kads iguais a 1,54 mg L-1 min-1 e 15,47 L mg-1, respectivamente, para o catalisador TiO2 P25 e de 1,34 mg L-1 min-1 e 132,95 L mg-1, respectivamente para o catalisador C-TiO2 Kronos vlp 7000. / Atrazine (ATZ) is a widely used herbicide in Brazil, where it is intensively applied in sugarcane, corn and sorghum cultivations. However, conventional wastewater treatments are not able to remove ATZ due to its persistent and recalcitrant properties. Advanced oxidation processes, such as heterogeneous photocatalysis, have been proved effective for the removal of this pollutant. This study aims to evaluate the performance of TiO2 P25 and carbon-modified TiO2 Kronos vlp 7000 photocatalysts in the degradation of ATZ in aqueous systems using a tubular photochemical reactor equipped with a compound parabolic collector (CPC) irradiated by simulated solar light. Catalysts TiO2 P25 and C-TiO2 Kronos were characterized by X-ray diffraction, infrared spectroscopy, BET analysis and diffuse reflectance analysis. The concentrations of TiO2 P25 and C-TiO2 Kronos were 500 and 100 mg L-1, respectively. For TiO2 P25, the results showed significant ATZ removals after 120 minutes of irradiation (100; 98; 98; 93; 86% for initial ATZ concentrations of 1; 5; 10; 20, and 30 mg L-1, respectively). In contrast, the total organic carbon (TOC) analyses indicated that no significant ATZ mineralization occurred, with values lower than 20% for TiO2 P25. In comparison with TiO2 P25, C-TiO2 was not able to completely remove ATZ at the end of 120 minutes of irradition. In this case, pesticide removals of about 37; 35; 38; 39 and 45% were obtained for initial ATZ concentrations of 1; 5; 10; 20, and 30 mg L-1, respectively. Nevertheless, C-TiO2 Kronos showed better performance for ATZ mineralization to CO2 and H2O in comparison with TiO2 P25, with approximately 38% total carbon organic removal. The Langmuir-Hinshelwood (LH) model was shown to be an appropriate approximation for the degradation kinetics of atrazine for both catalysts, with values of Kr and Kads equal to 1.54 mg L-1 min-1 and 15.47 mg L-1, respectively, for the P25 TiO2 and 1.34 mg L-1 min-1 and 132.95 mg L-1, respectively, for C-TiO2 Kronos vlp 7000.

A redução da emissão de compostos nitrogenados tem sido um dos grandes desafios da área de proteção ambiental e o tratamento catalítico pode reduzir significativamente tal emissão. Neste caminho, têm sido testadas várias categorias de catalisadores. Considerando-se o potencial de utilização de catalisadores de cobre e de cobalto nos processos de abatimento de compostos nitrogenados, bem como a necessidade de exploração dos efeitos gerados pelos suportes de óxido de cério e óxido de titânio, este trabalho teve como objetivos a preparação e a caracterização dos sistemas catalíticos CuO e Co3 O4 suportados em TiO2 , CeO2 e CeO2 -TiO3 (1%, 10%, 20% e 50% de CeO2 ), para aplicação no processo de redução de NO com CO na presença e ausência de O2 . Os catalisadores foram obtidos a partir do método de impregnação. Na caracterização das amostras foram utilizadas as técnicas de difração de raios X (DRX), redução à temperatura programada com H2 (RTP-H2 ), espectroscopia Raman, espectroscopia por energia dispersiva de raios X (EDX), fisissorção de nitrogênio e espectroscopia UV-visível próxima a região do infra-vermelho (UV-VIS-NIR). Os resultados da caracterização mostraram que os catalisadores apresentam fases de CuO altamente dispersas, bem como formando cristalitos com os suportes. Mostraram, também, que o cobalto está sobre a forma oxida Co3 O4 . As reações de redução de NO com CO mostraram que os catalisadores de cobre são mais ativos para estas reações e a adição do suporte CeO2 em TiO2 aumenta significativamente esta atividade. A adição de O2 na reação diminuiu a atividade frente à reação de redução de NO, isso porque o oxigênio é adsorvido sobre a superfície do catalisador, diminuindo sua atividade. / The reduction of the nitrogen composites emissions has been one of the great challenges of the ambient protection area and the catalytic treatment can reduce significantly such emissions. In this way, it has been tested some categories of catalysts. Considering the potential of use of copper and cobalt catalysts in the processes of nitrogen composites discouragement, as well as the necessity of exploration of the effect generated for CeO2 and TiO2 supported , this work had as objective the preparation and the characterization of the catalytic systems supported CuO and Co3O4 in TiO2, CeO2 and CeO2-TiO2 (1%, 10%, 20% and 50% of CeO2), for application in the reduction process of NO with CO in presence and absence of O2. The catalysts had been gotten from the impregnation method. In the characterization of the samples the techniques that had been used was: X-ray diffraction had been used, temperature programmed reduction, Raman spectroscopy, energy dispersive X-ray spectroscopy, nitrogen physsisorption and UV-visible spectroscopy next the region to the infra-red ray (UV-VIS-NIR). The results of the characterization had shown that the catalysts present highly dispersed phases of CuO, as well as cristalitts. And, that cobalto meets under the form Co3O4. The reactions of reduction of NO with CO had shown that the copper catalysts are more active than the cobalto and the addition of the CeO2 support in TiO2 increases significantly this activity. The addition of O2 in the reaction diminished the activity front to the reaction of reduction of NO, just because the oxygen is adsorbed on the surface of the catalysts, diminishing its activity

Les matériaux à base de TiO2 ont déjà été très étudiés. En particulier, les films minces mésoporeux cristallins de TiO2 montrent une activité photo-catalytique élevée due à leur surface spécifique incomparable. Cependant, l'étude et l'optimisation de la photocatalyse dans un tel milieu poreux n'est pas si simple car le processus catalytique dépend de plusieurs paramètres environnementaux et structuraux. Les activités de recherche se sont essentiellement focalisées sur (i) la conception de couches mésoporeuses à base de TiO2 avec une composition et une nanostructure variée et (ii) leur mise en œuvre comme plateforme pour une étude fondamentale par ellipsométrie concernant le processus photocatalytique. Des films mésoporeux ont été produits en couplant la chimie sol-gel, et des procédés de dépôt. Parmi des outils de caractérisation analytiques, 2D-GISAXS, ellipsométrie, SEM-FEG, HR-TEM et WAXS sont notamment les techniques qui ont été utilisées pour obtenir des informations. Premièrement, un film mésoporeux de TiO2 a été analysé par ellipsométrie in-situ pour des investigations fondamentales sur les cinétiques de son processus photocatalytique dans l'air en fonction de la composition environnementale et du polluant organique. La grosse quantité d'information obtenue a d'ailleurs permis la proposition de mécanismes de photo-dégradation dans les conditions étudiées. Dans la seconde partie, des films minces mésoporeux mixtes TiO2/SiO2 avec des propriétés optiques ajustables ont été préparées. Une étude structurale a été conduite sur le réseau et la composition des films poreux. L'ellipsométrie a été également mis en œuvre pour étudier leur le activité photocatalytique. / TiO2-based materials have been extensively studied as potential material to be used in photocatalysis. In particular crystalline mesoporous thin films exhibit increased photocatalytic activities due to their exceptionally high surface area. However the study and the optimization of the photocatalysis in such porous media is not easy to be done due to the fact that the catalytic process is highly dependent from several environmental and structural parameters. The research activities of this thesis were essentially focused on (i) the fabrication of mesoporous TiO2-based photoactive thin films with tunable composition and nanostructure and (ii) their utilization as platform for fundamental study of the photocatalytic process by ellipsometry. The mesoporous films with tunable nanostructure will be fabricated by coupling sol-gel chemistry and highly controlled liquid deposition techniques. Among modern analytical tools, 2D-GISAXS, ellipsometry and ellipso-porosimetry, SEM-FEG, HR-TEM and WAXS, were used to obtain a large set of relevant information. In the first part, a model TiO2 mesoporous film was analysed by ellipsometry for fundamental investigations of the photocatalytic process kinetics in air as function of the environmental and the organic pollutant. The information obtain by ellipsometry has allowed the proposition of photodegradation mechanisms in the studied conditions. In the second part, composite mesoporous TiO2/SiO2 films with tunable optical properties were fabricated by sol-gel chemistry. A structural study on the films porous network and composition was conducted. In-situ ellispometry was also used to study the photocatalytic activity.

Inorganic UV-filters in use today often occur as nanoparticles and have a photocatalytic effect, which can be a problem since they can cause negative health effects. This is why Upsalite®, a mesoporous magnesium carbonate recently has been investigated as a UV-filter. Upsalite® itself is however not suitable as a UV-filter since it mainly protects in the UVC range and hence it needs to be complemented by other substances. The substance studied to functionalize Upsalite® in this thesis is titanium dioxide which is an inorganic UV-filter commonly used in sunscreens. In this work two different sol-gel synthesis routes of titanium dioxide have been investigated as well as a co-synthesis of Upsalite® and titanium dioxide. In the first synthesis route already synthesized Upsalite® was mixed with titanium tetra-isopropoxide and 1-propanol. The second synthesis route was a modified version of synthesis routes described in literature where methanol solvent was used and the pressure was altered by CO2. This route was explored due to its resemblance with the Upsalite® synthesis. Pressure, temperature and amount of water were varied to optimize incorporation of Upsalite® and investigate possibilities for a co-synthesis. Subsequently a co-synthesis of Upsalite® and titanium dioxide was performed that resulted in two amorphous composite materials depending on if water was added in the drying procedure or not. When mixing Upsalite® in the synthesis liquid of titanium dioxide, titanium dioxide seems to be deposited on Upsalite®. It is however difficult to determine whether the pores of Upsalite® have been completely filled or if they have collapsed. The acid catalyst HCl promotes formation to crystalline titanium dioxide but Upsalite® instead prevents it. The limited crystallization of titanium dioxide when synthesized with Upsalite® may be due to confinement in the Upsalite® pores. The UV-blocking properties of the TiO2-Upsalite® without HCl are good with an sun protection factor (SPF) of 27 for a 10 wt% blend in a lotion and an SPF of 7 for the sample with HCl. The modified synthesis route of TiO2 showed that it is possible to perform a sol-gel synthesis with a considerably lower amount of water than found in literature and that alteration of temperature and pressure during the synthesis does not affect the crystallization temperature noteworthy. The materials obtained from the co-synthesis are slightly porous, probably consisting of one or several magnesium titanium oxides and a carbonate phase and showed a transmission cutoff in between Upsalite® and titanium dioxide corresponding to an SPF of 5.

Στην παρούσα ερευνητική εργασία μελετάται η φωτοηλεκτροχημική διάσπαση δύο οργανικών ενώσεων: της χρωστικής Methylene Blue (MB), και της γλυκόζης. Η φωτοκαταλυτική διεργασία πραγματοποιήθηκε με φωτοβόληση υπεριώδους ακτινοβολίας UV (λάμπα Hg, 125 W). Για το σκοπό αυτό χρησιμοποιήθηκαν δύο φωτοκαταλύτες: η νανοκρυσταλλική τιτάνια (TiO2) και το οξείδιο του βολφραμίου (WO3). Η φωτοδιάσπαση των οργανικών ρύπων πραγματοποιήθηκε σε μία φωτοηλεκτροχημική κυψελίδα, η οποία αποτελείται από τα εξής μέρη: 1)Το ηλεκτρόδιο της ανόδου το οποίο φέρει το φωτοκαταλύτη. Στη φωτοάνοδο παράγονται τα ηλεκτρόνια και πραγματοποιόυνται οι αντιδράσεις οξείδωσης. 2)Το ηλεκτρόδιο της καθόδου, το οποίο φέρει τον ηλεκτροκαταλύτη, ο οποίος διευκολύνει τη μεταφορά των ηλεκτρονίων από το ηλεκτρόδιο στο διάλυμα. Στη φωτοκάθοδο πραγματοποιούνται αντιδράσεις αναγωγής. Ως ηλεκτροκαταλύτης χρησιμοποιήθηκε ο λευκόχρυσος ο οποίος είναι ευγενές μέταλλο. 3)Τον ηλεκτρολύτη, ο οποίος ρυθμίζει το pH του διαλύματος και αυξάνει την ιοντική αγωγιμότητα. Ο ηλεκτρολύτης που χρησιμοποιήθηκε είναι το καυστικό νάτριο (NaOH). Όταν ο φωτοκαταλύτης διεγείρεται με ακτινοβολία ενέργειας ίσης ή μεγαλύτερης του ενεργειακού του χάσματος, δημιουργούνται ζεύγη οπών-ηλεκτρονίων. Ένα μέρος των δημιουργούμενων ζευγών φορτίου επανασυνδέονται χάνοντας τη φωτεινή ενέργεια σε θερμότητα. Οι οπές οξειδώνουν το ρύπο απελευθερώνοντας ιόντα υδρογόνου. Τα ηλεκτρόνια ρέουν μέσω του εξωτερικού κυκλώματος στην κάθοδο, όπου αντιδρούν με τα ιόντα υδρογόνου, σχηματίζοντας είτε μοριακό υδρογόνο (υπό αναερόβιες συνθήκες), είτε νερό (υπό αερόβιες συνθήκες). Το πρώτο και σημαντικότερο στάδιο της φωτοκαταλυτικής διεργασίας είναι η προσρόφηση του ρύπου στην επιφάνεια του φωτοκαταλύτη. Ο μηχανισμός προσρόφησης γίνεται σύμφωνα με το κινητικό μοντέλο Langmuir-Hinshelwood. To TiO2 αποτελεί έναν από τους πιο διαδεδομένους και αποδοτικούς φωτοκαταλύτες. Τα υμένια TiO2 εναποτέθηκαν σε υπόστρωμα γυαλιού με τη μέδοδο Doctor Blade. Το WO3 είναι ένας εξίσου αποδοτικός φωτοκαταλύτης με το TiO2, αλλά λιγότερο δημοφιλής. Η εναπόθεση των υμενίων WO3 σε γυάλινα υποστρώματα έγινε με τη μέθοδο του ψεκασμού. Η παρασκευή του αντιηλεκτροδίου, δηλαδή του ηλεκτροδίου της καθόδου, έγινε με τη μέθοδο της ηλεκτροαπόθεσης. Το υψηλό pH του ηλεκτρολύτη (NaOH) είναι απαραίτητο για τη φωτοδιάσπαση οργανικών ενώσεων. Εκτός από την ιοντική αγωγιμότητα που προσφέρει στο φωτοηλεκτροχημικό κελί, επηρεάζει και την επιφανειακή φόρτιση του φωτοκαταλύτη. Η αύξηση της συγκέντρωσης του NaOH, δηλαδή η αύξηση των ιόντων ΟΗ-, είχε σαν αποτέλεσμα την αύξηση της σταθεράς ταχύτητας της φωτοκαταλυτικής αντίδρασης kapp και επομένως ταχύτερη φωτοδιάσπαση του ρύπου. Στα διαλύματα με τις μεγαλύτερες συγκεντρώσεις ηλεκτρολύτη ο χρόνος ημιζωής του ρύπου είναι πολύ μικρότερος συγκριτικά με τα διαλύματα χαμηλής συγκέντρωσης NaOH. Η μέτρηση της συγκέντρωσης των οργανικών ενώσεων στα υδατικά διαλύματα έγινε με φασματοφωτομετρία απορρόφησης ορατού-υπεριώδους (UV/vis). Οι φωτοαποικοδομούμενες ουσίες, λειτουργούν ως «θυσιαστήριες ενώσεις», αφού μειώνουν το ρυθμό επανασύνδεσης ηλεκτρονίων-οπών και επομένως συμβάλλουν στην αύξηση της απόδοσης του συστήματος, ενώ παράλληλα η διάσπασή τους προσφέρει τεράστιο περιβαλλοντικό όφελος. Από τις δύο οργανικές ενωσεις που μελετήθηκαν, μόνο η χρωστική Methylene Blue λειτούργησε αποτελεσματικά ως θυσιαστήρια ένωση. Αντιθέτως η γλυκόζη, που είναι πολύπλοκο μόριο, δεν κατάφερε να διασπαστεί. Τέλος έγινε σύγκριση της δραστικότητας των δύο φωτοκαταλυτών, κατά τη φωτοαποικοδόμηση των οργανικών ρύπων που μελετήθηκαν. Παρατηρήθηκε ότι και το TiO2 και το WO3 είναι εξίσου αποδοτικοί φωτοκαταλύτες. Σε αντίθεση με το TiO2, το WO3 δεν είναι ανθεκτικό στη φωτοδιάβρωση, καθιστώντας αδύνατη την επαναχρησιμοποίησή του σε περισσότερες από δύο φωτοκαταλυτικές διεργασίες. / The present study deals with the photo electrochemical degradation of two organic compounds, namely Methylene Blue and glucose. The photocatalytic process was carried out using UV radiation (Hg lamp, 125 W). The employed photo catalysts were titanium dioxide (TiO2) and tungsten oxide (WO3) deposited in the form of thin films on SnO2:F-coated glass. The photodecomposition of organic wastes was carried out in a photo electrochemical (PEC) cell with the following components: 1) The anode electrode which carries the photo catalyst. The photo anode produces electrodes and oxidation reactions take place there. 2) The cathode electrode, which carries the electro catalyst and facilitates the transfer of electrons from the cathode to the liquid phase. Reduction reactions take place at the cathode. In this study, a noble metal, Pt was used as electro catalyst. Thin films of Pt were obtained by electrodeposition on SnO2:F-coated glass slides. 3) The electrolyte which is added to adjust the Ph in order to increase the ionic conductivity. In this study, an aqueous solution of NaOH has been used as electrolyte. The operation of such a PEC cell is as follows: The absorption of photons by the photocatalyst leads to the creation of electron-hole pairs. The photodegradable substance is oxidized by the holes, liberating hydrogen ions in the aqueous solution. Electrons are transferred through the external circuit towards the cathode, where they reduce hydrogen ions producing hydrogen molecules (in the absence of oxygen). The initial step of the photoelectrocatalytic decomposition is the adsorption of the organic waste on the surface of the photocatalyst according to the Langmuir-Hinshelwood mechanism. TiO2 is among the most successful photo catalysts for heterogeneous photo catalytic degradation of organic wastes. Thin films of nano crystalline titania were deposited on glass substrates using the Doctor Blade method. Another wide band gap semiconductor with that can be used in heterogeneous photo catalysis is WO3. It was also tested and compared with TiO2. The pH value of the electrolyte (NaOH) was found to affect strongly the process. High pH values were required to obtain high OH- concentration because efficient hole scavenging and production of hydrogen radicals is ensured, especially when an organic sacrificial agent is added. As a consequence, the apparent rate constant kapp was increased with increasing NaOH concentrations. The photodegradable substances act like “sacrificial agents” preventing the recombination of electron-hole pairs, which is the main cause for low efficiencies. Of the two organic wastes that have been studied, only MB could be successfully degraded. Finally, the photo catalytic activity of TiO2 and WO3 was compared. Although both catalysts were equally efficient, WO3 is characterized by low stability. .

The use of nanoscale materials is growing exponentially, but there are also concerns about the environmental hazard to aquatic biota. Metal-containing engineered nanoparticles (NPs) are an important group of these new materials, and whilst there are undoubtedly a plethora of beneficial uses for these NPs, it is essential that an appropriate risk assessment is carried out in order to protect the environment and human health, with the consumption of contaminated fish a distinct possibility. The current study aimed to assess the bioavailability, uptake and toxicological effects of two metal-NPs (TiO2 NPs and Cu-NPs) to fish from both dietary and waterborne exposure routes and where appropriate compare them to their bulk counterpart. Whole body system effects were assessed along with the influences of the life stage of exposed fish and abiotic factors on toxicity. A technique to improve the quantification of Ti from TiO2 NPs in fish tissue was also developed. Effects from exposure to dietary TiO2 NPs manifested similarly to traditional dietary metal exposure, with no reduction in growth, but some sublethal affects. Exposure to waterborne Cu-NPs showed that rainbow trout were more acutely sensitive to CuSO4 than the NPs, but that despite limited uptake several body systems were affected (most notably ionoregulation). Larvae were more sensitive to CuSO4 than Cu-NPs, but no differences were seen with embryos, whilst larvae were more sensitive than embryos. Abiotic factors did have an effect on acute Cu-NP toxicity, though not always in a predictable manner, with some effects more pronounced than with CuSO4. Overall, it appears that metal-NPs are not as acutely toxic as their bulk counterparts, but sublethal effects, were routinely observed. As TiO2 NPs appear more toxic than its bulk counterpart, current legislation governing safe environmental limits may have to be adjusted, though the situation with Cu-NPs isn’t as clear and further investigation is required. However, the risk of human exposure via the consumption of NP contaminated fish fillets is extremely low.

The temperature and field dependence of the magnetization of epitaxial, undoped anatase TiO2 thin films on SrTiO3 substrates was investigated. Low-energy ion irradiation was used to modify the surface of the films within a few nanometers, yet with high enough energy to produce oxygen and titanium vacancies. The as-prepared thin film shows ferromagnetism which increases after irradiation with low-energy ions. An optimal and clear magnetic anisotropy was observed after the first irradiation, opposite to the expected form anisotropy. Taking into account the experimental parameters, titanium vacancies as di-Frenkel pairs appear to be responsible for the enhanced ferromagnetism and the strong anisotropy observed in our films. The magnetic impurities concentrations was measured by particle-induced X-ray emission with ppm resolution. They are ruled out as a source of the observed ferromagnetism before and after irradiation.