Photocatalytic activity of nanotubular TiO2films obtained by anodic oxidation: A comparison in gas and liquid phase

The availability of immobilized nanostructured photocatalysts is of great importance in the purification of both polluted air and liquids (e.g., industrial wastewaters). Metal-supported titanium dioxide films with nanotubular morphology and good photocatalytic efficiency in both environments can be produced by anodic oxidation, which avoids release of nanoscale materials in the environment. Here we evaluate the effect of different anodizing procedures on the photocatalytic activity of TiO2nanostructures in gas and liquid phases, in order to identify the most efficient and robust technique for the production of TiO2layers with different morphologies and high photocatalytic activity in both phases. Rhodamine B and toluene were used as model pollutants in the two media, respectively. It was found that the role of the anodizing electrolyte is particularly crucial, as it provides substantial differences in the oxide specific surface area: nanotubular structures show remarkably different activities, especially in gas phase degradation reactions, and within nanotubular structures, those produced by organic electrolytes lead to better photocatalytic activity in both conditions tested

Intrinsic AuPt-alloy particles decorated on TiO2 nanotubes provide enhanced photocatalytic degradation

In this study we investigate the performance of noble metal co-catalysts on anodic TiO2 nanotubes for the photocatalytic degradation of a model pollutant. We create the noble metal decoration (nanoparticles of Au, Pt and mixed AuPt) intrinsically and extrinsically. Intrinsic decoration is achieved using a noble metal containing titanium alloy for anodic tube growth. Extrinsic decoration is carried out by physical vapor deposition (PVD) of the same noble elements on pure titania tubes. We find the AuPt intrinsic decoration to provide a significant enhancement for the photocatalytic decomposition of the model pollutant acid orange 7 (AO7) due to a synergistic effect in the formed AuPt alloy. The AuPt alloy provides a photocatalytic activity that is higher than comparable extrinsic decoration or single element (Pt or Au) intrinsic decoration

Intrinsic AuPt-alloy particles decorated on TiO2 nanotubes provide enhanced photocatalytic degradation

In this study we investigate the performance of noble metal co-catalysts on anodic TiO2 nanotubes for the photocatalytic degradation of a model pollutant. We create the noble metal decoration (nanoparticles of Au, Pt and mixed AuPt) intrinsically and extrinsically. Intrinsic decoration is achieved using a noble metal containing titanium alloy for anodic tube growth. Extrinsic decoration is carried out by physical vapor deposition (PVD) of the same noble elements on pure titania tubes. We find AuPt intrinsic decoration to provide a significant enhancement for the photocatalytic decomposition of the model pollutant acid orange 7 (AO7) due to a synergistic effect in the formed AuPt alloy. The AuPt alloy provides a photocatalytic activity that is higher than comparable extrinsic decoration or single element (Pt or Au) intrinsic decoration

Evaluation of biodiesel corrosiveness for diferent metals using classic microelectrodes and arrangements of microelectrodes

Um dos principais problemas no emprego do biodiesel como combustível de automóveis é a corrosão que ele pode provocar nos motores, devido à facilidade com que pode degradar. A natureza corrosiva do biodiesel é relacionada com a presença de água, ácidos graxos livres, ions metálicos, impurezas, a incidência da luz, a temperatura e a presença de insaturações na cadeia de alquil ésteres. Na atualidade existem poucos trabalhos na literatura sobre a corrosão dos metais em contato com biodiesel e a maioria deles têm um enfoque mais qualitativo que quantitativo. O maior desafio para avaliar a corrosividade do biodiesel mediante técnicas eletroquímicas é sua baixa condutividade. A espectroscopia de impedância eletroquímica (EIE) é uma técnica sensível que tem sido empregada para estudar meios resistivos como o etanol, por muitos anos. No entanto, os experimentos são difíceis assim como a análise dos resultados, principalmente pelo desenvolvimento da queda ôhmica no meio, devido à alta resistividade do meio ao fluxo da corrente elétrica. Os microeletrodos têm sido empregados em várias pesquisas em eletroquímica e têm apresentado algumas vantagens com respeito aos eletrodos de tamanhos convencionais. O principal benefício é a redução da queda ôhmica em meios resistivos, devido às baixas correntes registradas. No presente trabalho foi avaliada a corrosão do cobre e do aço inoxidável, os quais se encontram presentes no circuito de combustível dos motores, quando entram em contato com o biodiesel obtido a partir do óleo de soja (B100) e etanol. A avaliação foi feita mediante técnicas eletroquímicas com auxilio dos microeletrodos clássicos e na forma de arranjos (de 25 m de diâmetro), sem adição de eletrólito suporte. Adicionalmente, os resultados foram correlacionados com as mudanças nas propriedades fisicoquímicas do biodiesel (viscosidade, teor de água, teor de acidez e estabilidade oxidativa) e com ensaios gravimétricos segundo a norma ASTM G31. Os ensaios de impedância eletroquímica com os microeletrodos clássicos e os arranjos de microeletrodos mostraram duas constantes de tempo e foi possível demostrar que a constante em altas frequências está relacionada com a qualidade do biodiesel, enquanto que a constante nas baixas frequências é uma resposta da interface metal-biodiesel. A viscosidade e o teor de umidade aumentaram com a degradação do biodiesel e a estabilidade oxidativa diminuiu na mesma proporção independentemente do metal que estava em contato com o biocombustível. A presença de defeitos nos arranjos de microeletrodos obtidos por fotolitografia é um problema importante e é preciso estar sempre atento para evitar resultados equivocados. A voltametria cíclica se mostrou como técnica quantitativa para caracterizar e controlar a área exposta dos microeletrodos simples e em arranjos. Finalmente se corroborou com os ensaios eletroquímicos, a maior velocidade de corrosão para o cobre obtida nos ensaios gravimétricos, comparada à do aço inoxidável.One of the most relevant aspects related with the use of biodiesel in automobile motors is its corrosivity, due to its susceptibility to oxidation reactions. The corrosive nature of biodiesel is related with the presence of water, free fatty acids, metallic ions, impurities, incidence of light, temperature, as well as the insaturation degree of the main chain of the alkyl esters. Currently there are few works in literature about corrosion of metals in contact with biodiesel, and most of them have more a qualitative than a quantitative focus. The main issue for electrochemical studies in biodiesel is its low conductivity. Electrochemistry impedance spectroscopy (EIS) is a sensitive technique that has been used for studying resistive media like ethanol for many years. However the experiments are difficult and the results are complex to understand, mainly because of the ohmic drop developed in this media due to the inherent solution resistance to the flow of electrical current. Microelectrodes have been used in many researches in electrochemistry showing some advantages with respect to conventional electrodes. The principal benefit is the reduction of the ohmic drop in resistive media, due to its negligible value when small currents are registered. In this work corrosiveness of copper and stainless steel which are present in fuel circuit of an automobile motor was evaluated when they come in contact with biodiesel, obtained from soybean oil and ethanol (B100). The evaluation was made using classic microelectrodes and arrays of microelectrodes (25m diameter) without addition of supporting electrolyte. Aditionally the results were correlated with the changes in biodiesel physicochemical properties (viscosity, water content, acid number and oxidation stability) and weight loss tests according to ASTM G31. The electrochemical results with classic microeletrodes and arrays of microelectrodes showed two time constants and it was demonstrated that the time constant at high frequencies is related with biodiesel quality, while the time constant at low frequencies is due to the response of metal-biodiesel interface. The viscosity and water content increased with biodiesel degradation and oxidation stability decrease in the same proportion independently of the metal in contact with biofuel. The presence of defects in the microelectrodes arrays obtained by photolitography is an important issue and the researcher must be atempt to them to avoid equivocated results. Cyclic voltammetry has shown to be a useful technique to characterize and control the exposed are in microlectrodes and their arrays. Finally, the electrochemical measurements corroborate the higher corrosion rate for copper obtained from weight loss tests compaired to corrosion rate for stainless steel