OLANDIR VERCINO CORREA
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Artigo IPEN-doc 30376 VIS-active TiO2 films decorated by expanded graphite2024 - BENTO, RODRIGO T.; CORREA, OLANDIR V.; GASTELOIS, PEDRO L.; PILLIS, MARINA F.TiO2/C nanocomposite films were applied on water treatment. Expanded graphite nanosheets (EG) were obtained by UVC-assisted liquid-phase exfoliation technique, without the addition of acids, surfactants, or aggressive oxidizing agents, which characterizes the process as an eco-friendly method. The carbon nanosheets were synthesized directly from graphite bulk at different times and deposited on TiO2 films surface by airbrush spray coating method, forming a TiO2/C heterojunction. The increase in the exfoliation time promoted a more efficient photocatalytic dye removal under visible light. Morphological modifications, changes in the electronic structure, and wide range of light absorption were observed from the TiO2/C heterojunction formation. The results showed that hybrid TiO2/C supported photocatalyst is a promise alternative for practical photocatalytic applications under sunlight.Resumo IPEN-doc 30159 Raman spectroscopy applied on the structural characterization of TiO2/expanded graphite films2023 - BENTO, RODRIGO T.; ABE, IGOR Y.; CORREA, OLANDIR V.; PILLIS, MARINA F.Photocatalytic heterojunctions obtained from the use of titanium dioxide (TiO2) and carbon based materials are a promising way for the efficient water treatment [1]. The structural properties of the composite photocatalysts are an important characteristic that can influence their photocatalytic behavior [2]. Here, TiO2/expanded graphite (TiO2-EG) films were synthetized by sol-gel and deposited on borosilicate glass substrates by airbrush spray coating method at room temperature. Then, the hybrid films were heat treated at 350, 450 and 550 °C. Raman spectroscopy technique was applied to evaluate the effect of carbon amount and temperature on the structural properties of the films. The films heat treated at 350 °C exhibited a characteristic profile of amorphous material. Raman spectra of composite films heat treated at 450 and 550 °C showed well-defined peaks that can be attributed to anatase-TiO2phase. No peaks related to the rutile or other phases were observed. The investigation revealed that the G and 2D bands present a slight shift, as well as asymmetry, as the carbon content and heat treatment temperature increase – behavior that may be associated with the formation of the semiconductor-C heterojunction. Peaks deconvolution process demonstrated the presence of a second signal not found in the pure films. This effect may indicate a reduction of sp2 domains after the formation of semiconductor-C heterojunction, mainly due to the removal of oxygenated groups during heat treatment, and consequent Ti-C / Ti-O-C bonds formation [3]. The results suggested that the carbon amount and the temperature of heat treatment have great influence on the TiO2 -EG structural properties, which may contribute to the improvement of the photocatalytic activity of the composite films under visible light.Resumo IPEN-doc 29392 Síntese e caracterização de filmes nanocompósitos de TiO2/C depositados sobre o aço inoxidável AISI 3042022 - SANTOS, T.F. dos; BENTO, R.T.; CORREA, O.V.; PILLIS, M.F.Filmes de TiO2 e TiO2/C foram preparados pelo método sol-gel e aplicados sobre a superfície do aço inoxidável AISI 304 por spray a frio. Inicialmente, grafite natural foi submetido ao processo de esfoliação em fase líquida, onde se obteve grafite expandido. Para tanto, uma suspensão de grafite em solução aquosa contendo isopropanol e acetona foi irradiada por 2h em luz UVC. Foi preparada uma solução de isopropóxido de titânio e isopropanol para a obtenção do sol. O grafite esfoliado, após secagem, foi então adicionado à solução em concentrações entre 2,5 e 10%, razão massa/volume. Os filmes foram secos em estufa a 100ºC e tratados termicamente a temperaturas entre 400 e 500 ºC em forno tubular, sob atmosfera de argônio. Técnicas de difração de raios X, espectroscopia Raman, espectroscopia UV-visível (UV-vis), microscopia de força atômica e microscopia eletrônica de varredura foram utilizadas na caracterização. Os resultados obtidos confirmam a esfoliação do carbono e a formação da fase anatase em todos os filmes. Resultados de AFM sugerem que a formação da heterojunção semicondutor-carbono, confirmada por espectroscopia Raman, promoveu modificações morfológicas nos filmes, e influenciam o comportamento frente à corrosão do aço revestido, o qual foi avaliado por técnicas de impedância eletroquímica e polarização linear em uma solução aquosa 3,5% NaCl à temperatura ambiente.Resumo IPEN-doc 29385 Influência da concentração de carbono na morfologia e propriedades fotocatalíticas dos filmes de TiO2/C obtidos via sol-gel2022 - BENTO, R.T.; CORREA, O.V.; PILLIS, M.F.A disponibilidade de água potável e a poluição das reservas de água devido a compostos orgânicos descartados de maneira inadequada continua a ser um grave problema ambiental e público. O processo de fotocatálise heterogênea é uma tecnologia verde promissora para a remoção de muitos poluentes da água e do ar. Dentre os materiais semicondutores mais empregados em processos fotocatalíticos, o dióxido de titânio (TiO2) tem sido amplamente investigado como um fotocatalisador promissor na remoção e tratamento de contaminantes orgânicos da água e do ar. No entanto, a atividade fotocatalítica do TiO2 é limitada à radiação ultravioleta, em virtude da elevada energia de band gap necessária para ativar o semicondutor. Dessa forma, sua modificação estrutural e morfológica apresenta-se como um método favorável para aumentar a sua eficiência e permitir o seu emprego sob a luz visível. Pesquisas têm mostrado que catalisadores híbridos de TiO2/C são amplamente estudados devido a sua elevada eficiência fotocatalítica sob luz visível na remoção de corantes e degradação de outros poluentes da água. A presente pesquisa destinou-se a síntese e caracterização de filmes compósitos heteroestruturados de TiO2/C, de modo a obter um material fotocatalisador ativo sob luz visível para degradação de compostos orgânicos. Os filmes foram obtidos pelo método sol-gel utilizando isopropóxido de titânio como fonte de TiO2, e grafite exfoliada como fonte de C, adicionado ao sol nas concentrações de 1, 2,5, 5, 7,5 e 10% (m/v). Após a deposição via spray coating, os filmes foram tratados termicamente a diferentes temperaturas a fim de verificar sua influência no comportamento fotocatalítico dos filmes híbridos. A eficiência fotocatalítica dos filmes foi avaliada na remoção do corante alaranjado de metila da água, sob luz visível. Os resultados obtidos sugerem a formação de heterojunções TiO2/C, que promoveram evidentes modificações morfológicas e estruturais nos filmes, além de provocar um deslocamento da borda de absorção dos filmes para a região visível do espectro eletromagnético. Tal efeito, consequentemente, contribuiu para a elevada melhora na atividade fotocatalítica dos filmes nanocompósitos sob luz visível. A concentração de C e a temperatura de tratamento térmico têm importante efeito nas propriedades de superfície (rugosidade e molhabilidade), bem como na eficiência dos filmes, com destaque para o filme contendo 10% de C, tratado a 450°C, com uma eficiência de 79,5%.Resumo IPEN-doc 29191 Tribological evaluation of anodized aluminum applied to biomaterials2022 - PIERETTI, EURICO F.; CORREA, OLANDIR V.; BENTO, RODRIGO T.; NEVES, MAURICIO M. das; ANTUNES, RENATO A.; PILLIS, MARINA F.Biomaterials surfaces need to be adequate to the function they perform; for this reason, the importance of studying surface finish increases as design requirements grow, regarding geometry and precision requirements in biomedical devices. These biomaterials are subject to several types of premature failure, such as wear, fatigue, micro movements, particle detachment and degradation, which may generate the need for new interventions. Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. Due to good biocompatibility, regular arrangement of nanopores, ease of control of nanopore diameter, large specific surface area, low cost, good thermal stability and, absence of toxicity, anodic aluminum oxide has been studied. The geometric arrangement of nanopores makes it possible to use alumina as a mold for the synthesis of several nanostructures that have many advantages in advanced application areas due to their unique chemical, physical, mechanical and optical properties. In the present work, the tribological behavior of samples of aluminum alloy AA6061 anodized in oxalic acid solution (C2H2O4) and sulfuric acid (H2SO4) was evaluated. Prior to the anodization stage, the samples were electrolytically polished in a solution of perchloric acid and ethanol. For comparison reasons, pristine surfaces were also evaluated. The sample's surfaces finishing was analyzed by laser confocal microscopy. Atomic force microscopy was also used to evaluate samples roughness and topography. The wear tests were carried out during 10 min, solid spheres of 52-100 chrome steel, with 2 mm in diameter, were used as counter-bodies. The results indicated that the tribological behavior is influenced by the anodized layer process parameters, and the wear rate is dependent of the normal force and the roughness of each sample.Artigo IPEN-doc 28127 Surface properties enhancement by sulfur-doping TiO2 films2021 - BENTO, RODRIGO T.; CORREA, OLANDIR V.; ANTUNES, RENATO A.; PILLIS, MARINA F.TiO2 films were sulfur-doped through an alternative route based on the decomposition of H2S at low temperatures. MOCVD technique was used to grown the films on borosilicate glass substrates at 400 °C. The doping was carried out at 50, 100 and 150 °C under a mixture of H2-2%v.H2S. SO42− groups were observed in the surface revealing the substitution of Ti4+ by S6+. Superficial roughness and wettability were also modified by the formation of these sulfate groups on the surface. Photocatalytic experiments of methyl-orange dye decolorization under visible light indicated that the 8 at.% S-TiO2 film exhibited the highest photocatalytic activity, with 72.1% of dye decolorization. The results suggest that the exposition of TiO2 films to the mixture H2-H2S at low temperatures is an efficient method of doping. These films allow the decolorization of the dye under visible light irradiation, which enable its practical use under sunlight or even indoor.Artigo IPEN-doc 27737 On the surface chemistry and the reuse of sulfur-doped TiO2 films as photocatalysts2021 - BENTO, RODRIGO T.; CORREA, OLANDIR V.; PILLIS, MARINA F.The surface chemistry and recyclability of sulfur-doped titanium dioxide (TiO2) films was evaluated. The photocatalysts were grown by metalorganic chemical vapor deposition (MOCVD) at 400 ◦C. The films were sulfur-doped at 50 ◦C by using hydrogen sulfide (H2S) as sulfur source. The photocatalytic behavior of the films was measure by monitoring the methyl orange dye decolorization under visible light for several cycles. The films are formed only for the anatase crystalline phase. The results demonstrated that no structural modifications or significant differences in the morphology of the films occurred after their use. The sulfur-doped TiO2 films presented good photocatalytic activity, with an efficiency of 72.1% under visible light in its first use. The durability experiments suggest that even with the dye impregnation on the catalyst surface, the photocatalytic activity of the S-doped TiO2 films remained around 70% in the first 3 cycles, which allows their practical application for water treatment and purification under sunlight.Artigo IPEN-doc 27557 Visible-light photocatalytic activity and recyclability of N-doped TiO2 films grown by MOCVD2020 - OLIVEIRA, E.C. de; BENTO, R.T.; CORREA, O.V.; PILLIS, M.F.Nitrogen-doped TiO2 films were grown on borosilicate glass substrates at 400 °C by the metallorganic chemical vapor deposition (MOCVD) for removing dye from water under visible light. The effect of N-doping on the structural, surface, and photocatalytic properties of films was evaluated. X-ray photoelectron spectroscopy (XPS) analyses revealed that 1.56 and 2.44 at% of nitrogen were incorporated into the films by varying the NH3 flux during the growth. Methyl orange dye degradation experiments showed that the N-doped films presented photoactivity under visible light. The film containing 2.44 at% of nitrogen exhibited the best photocatalytic behavior, with 55% of efficiency. Recyclability tests under visible light showed that the film efficiency dropped gradually after each test. N-TiO2 films grown by MOCVD have the potential to be used in environmental applications by removing pollutants using a green method under sunlight or even under internal illumination, although its reuse is limited.Artigo IPEN-doc 27162 Effect of growth parameters on the photocatalytic performance of TiO2 films prepared by MOCVD2020 - MARCELLO, BIANCA A.; CORREA, OLANDIR V.; BENTO, RODRIGO T.; PILLIS, MARINA F.The present study evaluated the main factors that influence the photocatalytic activity of titanium dioxide (TiO2) films grown by metalorganic chemical vapor deposition (MOCVD) at 400 and 500 °C, in different growth times. The photocatalytic behavior was analyzed by measuring the methyl orange dye degradation at different pH values. Structural and morphological characteristics, and the recyclability of the catalysts for several cycles were also investigated. Anatase phase was identified in all films. The higher photodegradation performances were obtained at acidic pH. The results demonstrated that the photocatalyst thickness is an important parameter in heterogenous photocatalysis. The best photocatalytic result occurred for the 395 nm-thick TiO2 film grown at 400 °C, which presented 65.3% of the dye degradation under UV light. The recyclability experiments demonstrated that the TiO2 films grown by MOCVD present a great stability after several photocatalytic cycles, which allows their practical application for water treatment with high efficiency.Resumo IPEN-doc 26533 Influence of the heat treatment on the photodegradation efficiency of the supported TiO2 catalysts obtained by a facile airbrush spray-coating2019 - BORAZANIAN, TATYANA C.F.; CORREA, OLANDIR V.; BENTO, RODRIGO T.; PILLIS, MARINA F.One of the main topics of thin films processing routes based on sol-gel is the need for low-cost and simple techniques [1]. Airbrush spray-coating method has been applied to coat materials, due to its cost-effective, large area and versatile characteristics [2]. However, this technique is not yet sufficiently explored for supported catalysts employed on the water treatment. In this work, titanium dioxide (TiO2) films were successfully deposited on borosilicate substrates by a facile airbrush spray-coating technique, at room temperature, from a solution of titanium (IV) isopropoxide diluted in isopropanol. The angle of the cold spray was fixed in 45°, and the feed rate was 17 mm.s-1. The coated specimens were dried at 100 °C for 60 min, and then heat treated at 300, 450 and 500 °C for 30 min to evaluate the influence of the temperature process on the methyl orange dye degradation under UV light. The catalysts obtained showed a great surface covering, highly porous surface, and good adherence to substrate. The films presented the formation of TiO2-anatase phase. Methyl orange dye degradation experimental results indicated that the TiO2 film heat treated at 500 °C presented a higher photocatalytic behavior, that exhibited 68.3 % of the dye degradation for 300 minutes under UV radiation – around 18.5 % more efficient than the supported catalysts prepared at 300 and 450 °C, with a photocatalytic efficiency of 31.6 % and 57.7 %, respectively. The study of the influence of heat treatment on the photocatalytic activity suggests the existence of an ideal temperature in which the photocatalyst exhibits the better photodegradation performance. The results suggest that the supported TiO2 catalysts deposited by the airbrush spraycoating method have a promising practical application for the green treatment of organic pollutants.
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