OLANDIR VERCINO CORREA

OLANDIR VERCINO CORREA

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VIS-active TiO2 films decorated by expanded graphite
2024 - 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.
Avaliação eletroquímica de alumina anódica nanoporosa aplicada a revestimentos biomédicos
2023 - PIERETTI, E.F.; CORREA, O.V.; NEVES, M.D.M.; OLIVEIRA, M.C.L.; ANTUNES, R.A.
Óxido de alumínio anódico tem atraído interesse devido ao arranjo regular denanoporos, grande área de superfície específica, boa estabilidade térmica,ausência de toxicidade e biocompatibilidade. As estruturas OAA têm sidoaplicadas em filtros, biossenssores, sensores de oxigênio, catálise efotocatálise. O arranjo geométrico dos nanoporos torna possível utilizar aalumina como molde para a síntese de várias nanoestruturas, como nanoporos,nanotubos, nanobastões e nanofios que apresentam muitas vantagens em áreas deaplicação avançadas devido a suas propriedades químicas, físicas, mecânicas eópticas únicas. Dentre os materiais de aplicação biomédica destacam-se algumasligas de alumínio, pois apresentam resistência mecânica satisfatória,resistência à corrosão e baixo custo.
Surface properties enhancement by sulfur-doping TiO2 films
2021 - 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.
Structural characterization, global and local electrochemical activity of electroless Ni–P-multiwalled carbon nanotube composite coatings on pipeline steel
2021 - OLIVEIRA, MARA C.L. de; CORREA, OLANDIR V.; SILVA, REJANE M.P. da; LIMA, NELSON B. de; OLIVEIRA, JEFFERSON T.D. de; OLIVEIRA, LEANDRO A. de; ANTUNES, RENATO A.
In this work, composite Ni–P-multiwalled carbon nanotube films were produced by electroless deposition. The main goal was to investigate the influence of multiwalled carbon nanotube loading on the local electrochemical behavior of the composite films, as probed by scanning electrochemical microscopy (SECM). The coatings were also characterized with respect to their crystalline structure, surface, and cross-section morphologies. Adhesion strength was examined by scratch tests. The global electrochemical behavior was evaluated by potentiodynamic polarization. The local electrochemical activity was investigated by probing the Fe2+ oxidation in the surface generation/tip collection mode of the SECM. The results revealed that multiwalled carbon nanotubes increased the adhesion strength and reduced the electrochemical activity on the surface of the coated samples.
On the surface chemistry and the reuse of sulfur-doped TiO2 films as photocatalysts
2021 - 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.
Visible-light photocatalytic activity and recyclability of N-doped TiO2 films grown by MOCVD
2020 - 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.
Effect of growth parameters on the photocatalytic performance of TiO2 films prepared by MOCVD
2020 - 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.
Caracterização morfológica de filmes de TiO2 dopados com nitrogênio crescidos por MOCVD
2019 - OLIVEIRA, E.C. de; CORREA, O.V.; BENTO, R.T.; COTINHO, S.P.; SANTOS, T.F. dos; PILLIS, M.F.
O método de deposição química de organometálicos em fase vapor (MOCVD) foi utilizado para o crescimento de filmes de dióxido de titânio (TiO2) e TiO2 dopado com nitrogênio. Os filmes foram crescidos a 400 °C sobre substratos de vidro borossilicato. Isopropóxido de titânio IV foi utilizado como precursor de titânio e de oxigênio, e amônia (NH3) como fonte de nitrogênio. Análises por microscopia de força atômica (AFM) mostraram que ambos os filmes apresentaram grãos bem definidos e arredondados. Todos os filmes são formados apenas pela fase cristalina anatase. Os resultados mostraram que a dopagem com nitrogênio resultou em uma diminuição no tamanho médio de grão e na rugosidade superficial.
Reativação e reutilização de fotocatalisadores de TiO2 dopados com enxofre em baixa temperatura
2019 - BENTO, RODRIGO T.; CORREA, OLANDIR V.; PILLIS, MARINA F.
O presente estudo avaliou a possibilidade de reutilização fotocatalítica dos filmes de dióxido de titânio (TiO2) dopados com enxofre em baixa temperatura. Os filmes foram crescidos por deposição química de organometálicos em fase vapor (MOCVD) a 400°C. A dopagem com enxofre foi realizada a 50°C por um processo semelhante ao utilizado na dessulfuração do sulfeto de hidrogênio (H2S). O comportamento fotocatalítico e a durabilidade dos filmes foram medidos a partir da degradação do corante alaranjado de metila sob luz visível por vários ciclos. Os filmes são formados apenas pela fase cristalina anatase. Os resultados demonstraram que não houve modificações estruturais ou diferenças significativas na morfologia dos filmes após a sua utilização. Os filmes de TiO2 dopados com enxofre apresentaram uma excelente atividade fotocatalítica, com uma eficiência de 72,1% sob luz visível. Os experimentos de durabilidade sugerem que, mesmo com a impregnação de corante na superfície do catalisador, os filmes de TiO2 dopados apresentaram boa estabilidade fotocatalítica após diversas horas de uso, o que permite sua aplicação prática no tratamento e purificação da água sob luz solar com elevada eficiência.
Structural, adhesion and electrochemical characterization of electroless plated Ni-P-carbon black composite films on API 5L X80 steel
2019 - OLIVEIRA, MARA C.L. de; CORREA, OLANDIR V.; SILVA, REJANE M.P. da; LIMA, NELSON B. de; OLIVEIRA, JEFFERSON T.D. de; OLIVEIRA, LEANDRO A. de; ANTUNES, RENATO A.
In this work, composite Ni-P-carbon black coatings were obtained by electroless deposition on API 5L X80 substrates. The effect of carbon black on structural, adhesion and electrochemical properties of the plated samples was evaluated. Scanning electron microscopy analyses were carried out to examine the top surface and cross section of the films. Scratch tests were employed to evaluate coating adhesion properties. Potentiodynamic polarization tests were carried out to investigate the global electrochemical behavior of the deposited layers. Scanning electrochemical microscopy (SECM) was employed to measure local electrochemical activity over the coated surfaces. The carbon black concentration markedly affects the morphology, adhesion and electrochemical properties of the Ni-P-carbon black layers. The results point to an optimum carbon black content to achieve the best performance against corrosion. The coatings obtained at a carbon black concentration of 0.25 g L21 provided the best protection ability. The results are discussed with respect to coating morphology, adhesion and electrochemical activity.