RODRIGO TEIXEIRA BENTO

RODRIGO TEIXEIRA BENTO

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Physical-chemical characterization of Si3N4-TiO2 ceramic nanocomposites obtained to biomedical applications
2019 - SONA FILHO, CELSO R.; BENTO, RODRIGO T.; SILVA, CECILIA C.G. e; PILLIS, MARINA F.
Silicon nitride based ceramics (Si3N4) are very important materials in the engineering and medical fields because of their physical, chemical, tribological and mechanical properties. However, some researchs have been carried out in order to obtain silicon nitride ceramics with improved biological behavior, including studies about the effect of nanoparticles on their bioactivity. In this work, Si3N4-TiO2 nanocomposites were synthesized and characterized by their physical, chemical and bioactive properties. Initially, Si3N4, MgO, SiO2 and CaO powders were mixed in a ball mill for 24 h The mixture was then dried at 100 ºC for 1 h under the nitrogen atmosphere. Subsequently, the samples were coated with TiO2 from the sol-gel process. The precursor solution of titanium dioxide (TiO2 ) was prepared from the mixture of titanium (IV) isopropoxide and isopropanol at a ration of 1:10. The pH of the solution was adjusted to 3 by the addition of sulfuric acid. The precursor solution was dispersed by constant stirring at 50 ºC for 1 h. The samples were immersed for 10 minutes in this solution at room temperature and then dried for 24h under UV light. The samples were calcined at 400 and 500 ºC for 60 min to obtain Si3N4-TiO2 nanocomposites. The microstructure of the materials were anayzed by scanning electron microscopy, atomic force microscopy, and X-ray diffraction. The samples bioactivity was evaluated by in vitro tests using SBF (Simulated Body Fluid) solution at 37 ºC for 9 days of immersion. The nanocomposites showed good quality, high uniformit of coating and greater adhesion to TiO2 to the substrate of Si3N4. The formation of CaP deposits with globular structure on the samples surface during the SBF experiment is a strong indication of the bioactivity of the nanocomposites. The results suggest that Si3N4-TiO2 ceramic nanocomposites have great potential to be used in biomedical applications.
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.
Structural characterization of aramid fibers
2018 - BENTO, R.T.; FERRUS FILHO, A.; CORREA, O.V.; PILLIS, M.F.
Fibers are polymer matrix composite materials that present one dimensional structure, stiffness, low density, and high structural and thermal properties. They can be used in activities under high temperature, being in the form of fabric and yarn. Aramid yarns are high performance textile fibers with excellent physicochemical properties that favor their use in applications where there is the requirement for advanced technology. The present research proposed the structural characterization of two different types of aramid yarn – 1100 dTex and 3300 dTex. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), atomic force microscopy, thermogravimetric analysis (TGA), and difference thermogravimetry (DTG) were used for structural characterization, morphology analysis, chemical composition, and thermal degradation of samples. The results obtained demonstrated that the aramid fibers exhibit a crystalline structure, presenting a homogeneous surface morphology and low roughness. It was verified that the fibers in study have good thermal stability. The thermal decomposition of the 1100 dTex aramid occurs in the range of 493 °C – 629 °C, while the thermal degradation of the 3300 dTex aramid is initiated at approximately 504 °C and is completed around 644ºC, which allows to conclude that the 3300 dTex aramid is endowed with excellent thermal resistance when compared to other textile materials.
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.
Estudo quantitativo do processo de degradação térmica de fibras de aramida
2017 - BENTO, R.T.; CORREA, O.V.; FERRUS FILHO, A.; PILLIS, M.F.
Fios de aramida são fibras têxteis de alto desempenho, apresentando excelentes propriedades físico-químicas que favorecem a sua utilização em aplicações onde há a necessidade de tecnologia avançada. O presente trabalho tem como objetivo principal o estudo e análise quantitativa do comportamento de dois tipos diferentes de fio de aramida – 1100 dTex e 3300 dTex – durante o processo de degradação térmica, por meio da técnica de análise termogravimétrica (TGA). Para caracterização estrutural, morfológica e composição química das amostras foram realizados ensaios de microscopia eletrônica de varredura (MEV), espectroscopia de energia dispersiva (EDS) e difração de raios-X (DRX). Os resultados obtidos demonstraram que as fibras de aramida apresentam estrutura cristalina, exibindo uma morfologia superficial homogênea e de baixa rugosidade. Verificou-se que as fibras em estudo possuem boa estabilidade térmica. A decomposição térmica dos fios de aramida 1100 dTex ocorre no intervalo de 493ºC – 629 ºC, enquanto que a degradação térmica da aramida 3300 dTex se inicia a aproximadamente 504ºC e se completa em torno de 644ºC, o que permite concluir que a aramida 3300 dTex é dotada de excelente resistência térmica, quando comparada a outros materiais têxteis.
Morphological characterization of S-doped TiO2 thin films
2017 - BENTO, RODRIGO T.; SZURKALO, MARGARIDA; CORREA, OLANDIR V.; PILLIS, MARINA F.