RODRIGO TEIXEIRA BENTO

RODRIGO TEIXEIRA BENTO

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Raman spectroscopy applied on the structural characterization of TiO2/expanded graphite films
2023 - 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.
Síntese e caracterização de filmes nanocompósitos de TiO2/C depositados sobre o aço inoxidável AISI 304
2022 - 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.
Influência da concentração de carbono na morfologia e propriedades fotocatalíticas dos filmes de TiO2/C obtidos via sol-gel
2022 - 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%.
Tribological evaluation of anodized aluminum applied to biomaterials
2022 - 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.
Influence of the heat treatment on the photodegradation efficiency of the supported TiO2 catalysts obtained by a facile airbrush spray-coating
2019 - 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.
Effect of the thickness of TiO2 films on the photodegration of methyl orange dye
2019 - MARCELLO, BIANCA A.; CORREA, OLANDIR V.; BENTO, RODRIGO T.; PILLIS, MARINA F.
The increase of the disposed of azo dyes such as methyl orange (MO) by textile and allied industries in the wastewater results in a significant increase of pollutants, which requires the development of new degradation materials and techniques to purify the effluents [1]. Heterogeneous photocatalysis using titanium dioxide (TiO2) films is a highly efficient oxidative process for water treatment [2]. The TiO2 films were grown on borosilicate substrates by metalorganic chemical vapor deposition (MOCVD) at 500°C, and the growth time was controlled in order to obtain films with the thickness of 400, 600 1100 and 2100 nm. MO dye degradation was evaluated by using anatase-TiO2 as photocatalyst under UV light. The pH of the solutions was set on 2. The TiO2 films presented uniform thickness and well-defined columnar structure that grow perpendicular to the substrate surface. The increasing of the growth time increases both the thickness and the mean grain size of the films. All the films presented the formation of anatase-TiO2 crystalline phase grown preferentially oriented at (112). The results showed that the photocatalytic behavior of the films decreased with increasing the film thickness. The photocatalytic efficiency for the 400, 600, 1100 and 2100 nm films tested at pH 2 are respectively 39.2%, 30.2 %, 24.4 % and 12.2 %. When the thickness of the films augments, the mobility of the electrons is impaired due to the increase of the film opacity, which limits the light penetration through the catalyst, and difficults the diffusion of charge carriers required to activate the semiconductor surface. TiO2 catalysts grown by MOCVD technique is a practical promising application for the water treatment.
Synthesis and characterization of reduced graphene oxide-modified anatase TiO2 photocatalysts grown by MOCVD
2019 - BENTO, RODRIGO T.; SILVA FILHO, JORGE C.; CORREA, OLANDIR V.; TAKIISHI, HIDETOSHI; PILLIS, MARINA F.
Inadequate disposal of industrial waste, such as textile dyes and emerging contaminants, have been caused several environmental hazards. Titanium dioxide (TiO2) photocatalysis is an efficient green method for water treatment by solar energy. However, due to its large band gap of 3.2 eV, TiO2 absorbs mostly the UV radiation, which represents only 5-8% of the sunlight spectrum. Recent studies indicate that the surface modification of TiO2 results in an increase in photocatalytic efficiency. In this way, the present paper aims to evaluate the effects of TiO2 surface modification by reduced graphene oxide (rGO). The 470 nm thick anatase-TiO2 films were grown by MOCVD process in a conventional horizontal homemade reactor, on borosilicate substrates at 400 °C. The TiO2 films obtained were dipped into an alkoxide solution including 0.5, 1.5 and 3.0 mg of rGO and 30 mL isopropanol, ultrasonic-treated at room temperature for 40 min, and then dried in an oven at 100 and 150 °C for 24 h. The photocatalytic activity of rGO-TiO2 composites were evaluated by the methylene blue degradation under UV and visible light. The chemical, structural and morphological properties were also characterized. It was observed the presence of rGO agglomerates completely adhered to TiO2 surface. The diffraction peaks identified correspond to anatase phase. Peaks of graphene were also found. The results suggest that the rGO-TiO2 composites have a great potential to be used in water treatment under sunlight.
Performance of nitrogen-doped TiO2 films grown by MOCVD for water treatment under visible light
2019 - OLIVEIRA, EDUARDO C. de; BENTO, RODRIGO T.; CORREA, OLANDIR V.; PILLIS, MARINA F.
Titanium dioxide is a semiconductor employed as catalyst in the photodegradation of organic pollutants and bacteria. However, due to its large band gap TiO2 only can be excited by UV light. Recently, TiO2 doping with metals or nonmetals elements has been extensively exploited to allow its use under visible light. In the present work, nitrogen-doped and undoped TiO2 films were grown on borosilicate substrates at 400 ° C for 60 minutes by metallorganic chemical vapor deposition (MOCVD). Titanium isopropoxide IV was used as precursor of titanium and oxygen, and ammonia as nitrogen source. Ammonia was incorporated into the films in three different quantities during the growth. The effect of nitrogen contents on the structural and surface properties of TiO2 catalysts was evaluated. Both doped and undoped films presented rounded well-defined anatase grains. XPS analyses revealed that values of 1.6; 2.4 and 7.3 at% of nitrogen were incorporated into the films by varying the ammonia flux during the growth. Degradation assays have shown that nitrogen-doped TiO2 films exhibited high photocatalytic activity under visible light irradiation. Undoped films did not present activity in this condition. The better catalytic performance under visible light, 55% of dye degradation, was attributed to the film containing 2.4 at% of nitrogen. The results suggest that nitrogen-doped TiO2 catalysts grown by MOCVD have great potential to be used in the treatment of water under sunlight.
UV–Vis photocatalytic performance of the S-doped TiO2 and TiO2 thin films for water treatment
2018 - BENTO, R.T.; SZURKALO, M.; OLIVEIRA, E.C.; CORREA, O.V.; PILLIS, M.F.
TiO2 films have been widely used as catalysts in oxidative processes in order to degrade organic contaminant. However, without the presence of a dopant material, its photocatalytic activity is limited only in the region of ultraviolet radiation (UV), due to its high-energy band gap. In this present research, anatase TiO2 thin films were grown on borosilicate substrates by metalorganic chemical vapor deposition (MOCVD) at 400ºC. To make the semiconductor active in the visible light region, sulfur doped TiO2 films were prepared by means of a thermochemical treatment carried out in a tubular oven, under atmosphere of H2S at 50ºC for 60 minutes. The films were characterized by XRD, AFM, FE-SEM and XPS technique. The photocatalytic behavior of the films was evaluated by methyl orange dye degradation under UV-Vis irradiation for 300 minutes. The photocatalytic tests were realized in a reactor illuminated by two tubular UV lamps (352 nm), and in a reactor illuminated by visible light (400-700 nm) on different intensities, both containing 40 mL of the dye solution. The results showed that the S-TiO2 films present promising photocatalytic efficiency. Without the presence of the catalyst, there was no degradation of the methyl orange dye under UV-Vis irradiation. Non-doped TiO2 films do not exhibited photocatalytic activity under visible light. It was possible to observe that the visible light intensity influences the doped films photocatalytic performance.
S-doped TiO2 films applied to UV-Vis heterogeneous photocatalysis
2018 - BENTO, RODRIGO T.; CORREA, OLANDIR V.; PILLIS, MARINA F.
Semiconductors materials such as titanium dioxide (TiO2) have been applied successfully on photocatalytic process for water treatment [1]. Sulfur doping allows the reduction of the TiO2 band gap energy, and changes the absorption edge from the UV to the visible light region, thus obtaining a higher photocatalytic activity [2]. The aim of this research was to study the photocatalytic behavior of sulfur-doped and undoped TiO2 films in the methyl orange dye degradation under UV and visible radiation. The titanium dioxide films were grown on borosilicate substrates, by metalorganic chemical vapor deposition (MOCVD) technique at 400 °C. The doping step was done in a tubular furnace under H2/2 wt.% H2S atmosphere at 50 °C, 100 °C and 150 °C for 60 minutes. All the films presented on their surfaces the formation of well-defined rounded grains. X-ray diffraction analyses shown that S-TiO2 and TiO2 films exhibited the formation of anatase phase, which suggests that the doping process do not causes meaningful changes in the structure of TiO2 films. MO dye degradation tests indicated that the S-TiO2 films present photocatalytic activity both under UV radiation and visible light. S-TiO2 film doped at 50 °C presented the higher photocatalytic performance, and exhibited 72.1 % of MO dye degradation for a total test time of 300 minutes under visible light. Undoped TiO2 film demonstrated photoactivity only under UV light, with an efficiency of 63.5 %. The photolysis curve showed that without the presence of the catalyst there was no degradation of the dye under both UV radiation and visible light. The results suggest that the sulfur doping caused a shift of the TiO2 absorption edge to the visible region, which allows their practical application under sunlight or visible light bulbs.