Navegando por Autor "Oliveira, Henrique dos Santos"
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Item A bifunctional catalyst based on Nb and V oxides over alumina : oxidative cleavage of crude glycerol to green formic acid.(2020) Oliveira, Henrique dos Santos; Oliveira, Luiz Carlos Alves de; Chagas, Poliane; Sangiorge, Daniel Lara; Portilho, Marcio de Figueiredo; Siqueira, Kisla Prislen Félix; Hensen, Emiel J. M.A bimetallic vanadium and niobium oxide catalyst using alumina as support was developed for the conversion of crude glycerol from biodiesel production into formic acid. The high dispersion of the active oxide phase combined with the presence of acid and redox active centers resulted in a high glycerol conversion (490% for 25 h) with a good selectivity for formic acid (B55%). This process is the first example of a heterogeneous liquid-phase process for the conversion of crude glycerol to formic acid, which is an important chemical intermediate currently derived from petroleum feedstock.Item Enhanced photocatalytic hydrogen generation from water by Ni(OH)2 loaded on Ni-doped d-FeOOH nanoparticles obtained by one-step synthesis.(2013) Rocha, Thomás da Silva; Nascimento, Eliandro Silva; Silva, Adilson Cândido da; Oliveira, Henrique dos Santos; Garcia, Eric Marsalha; Oliveira, Luiz Carlos Alves de; Monteiro, Douglas Santos; Rodriguez, Mariandry del Valle Rodriguez; Pereira, Márcio CésarNi(OH)2 loaded on Ni-doped d-FeOOH photocatalysts were prepared by a simple and low-cost one-step precipitation method. The effect of Ni(OH)2 nanoparticles and Ni2+ doping on the photocatalytic hydrogen production rates by d-FeOOH in aqueous suspension was investigated. The results showed that the photocatalytic H2-production activity of d-FeOOH was significantly enhanced by doping with Ni2+ ions and by loading Ni(OH)2 on its surface. The maximum H2-production was obtained for the sample with 20 wt% Ni, which provided 5746 mmol h 1 g 1. This high photocatalytic H2-production is due to the combined effects of Ni2+ doping and Ni(OH)2 loaded on the d-FeOOH surface. The Ni2+ doping increased the conductivity and charge transfer in d-FeOOH, whereas the Ni(OH)2 improved the charge separation in the d-FeOOH and, consequently, the photocatalytic H2-production activity.Item High water oxidation performance of W-Doped BiVO4 photoanodes coupled to V2O5 rods as a photoabsorber and hole carrier.(2018) Oliveira, Andreia Teixeira de; Rodriguez, Mariandry del Valle Rodriguez; Andrade, Tatiana Santos; Souza, Helen E. A. de; Ardisson, José Domingos; Oliveira, Henrique dos Santos; Oliveira, Luiz Carlos Alves de; Lorençon, Eudes; Silva, Adilson Cândido da; Nascimento, Lucas Leão; Patrocinio, Antonio Otavio de Toledo; Pereira, Márcio CésarMonoclinic BiVO4 is recognized as a promising photoanode for water oxidation, but its relatively wide bandgap energy (Eg ≈2.5 eV) and poor charge transport limit the light absorption (ηabs) and charge separation (ηsep) efficiencies, thus resulting in low photocurrents. To solve these drawbacks, here the ηabs × ηsep product has been decoupled by combining W‐doped BiVO4 and V2O5 rods (Eg ≈2.1 eV) for simultaneously increasing the light harvesting and the charge separation in photoanodes under back‐side illumination. In this strategy, V2O5 rods maximize the light absorption and hole transport throughout the W‐BiVO4 film, making more holes to achieve the V2O5/W‐BiVO4/H2O interface to trigger the water oxidation reaction with photocurrents as high as 6.6 mA cm−2 at 1.23 VRHE after 2 h reaction. Notably, under back‐side illumination, the W‐BiVO4/V2O5 photoanode exhibited ηabs × ηsep of 74.5 and 93.0% at 0.5 and 1.23 VRHE, respectively, the highest values reported up to date for BiVO4‐based photoelectrodes. This simple strategy brings us closer to develop efficient photoanodes for photoelectrochemical water splitting devices.Item Influence of temperature on the structural and color properties of nickel molybdates.(2020) Silva, Maíra Vieira da; Oliveira, Daynara Faustina Moreira de; Oliveira, Henrique dos Santos; Siqueira, Kisla Prislen FélixIn this work, nickel molybdates were synthesized by co-precipitation method, at 70 °C, and were thermally treated at temperatures ranging from 300 to 1000 °C. Firstly, the hydrated precursor (NiMoO4.0.65H2O) was obtained, followed by calcination at 300–600 °C to produce a mixture of β- and α-NiMoO4 phases. The pure α phase could only be obtained above 700 °C. The relationships among the crystal structure, colorimetric parameters, and spectroscopic properties (Raman and UV–vis diffuse reflectance) of the NiMoO4 were in vestigated. Although the thermochromic β phase was not obtained in the pure form, the heat treatments enabled tuning of the band gaps of the materials, with the color changing from yellow to greenish-yellow and the band gap changing from 3.23 to 2.33 eV. The colorimetric parameters (L*a*b*) were determined and the coloring performances of the NiMoO4 materials were evaluated by incorporating them into a clear polymer substrate material.Item A novel floating photocatalyst device based on cloth canvas impregnated with iron oxide.(2013) Oliveira, Henrique dos Santos; Silva, Adilson Cândido da; Mesquita, João Paulo de; Pereira, Fabiano Vargas; Lima, Diana Quintão; Fabris, José Domingos; Moura, Flávia Cristina Camilo; Oliveira, Luiz Carlos Alves deIn this paper an innovative and versatile design for a catalytic photoreactor is presented. The photoreactor is based on a floating Polypropylene non-woven fabric canvas (NWF) impregnated with particles of a mixture of iron oxides and oxyhydroxides adhered to the surface of microfibers. The canvas was characterized with different techniques including Mo¨ssbauer spectroscopy, Raman scattering, FTIR, and SEM. UV-Vis spectroscopy showed that the impregnated particles presented an average gap of 2.2 eV. The activity and efficiency of the photocatalyst was tested by photodegradation of rhodamine-B (Rh-B) and the results showed that the floating photocatalyst has a high catalytic activity and maintains its efficiency even after five reuse tests at intervals of 90 min with a small average residual concentration of 6.2% Rhodamine-B in each reuse cycle.Item Production of reduced graphene oxide platelets from graphite flakes using the Fenton reaction as an alternative to harmful oxidizing agents.(2019) Velásquez Piñas, Jean Agustin; Andrade, Tatiana Santos; Oliveira, Andreia Teixeira de; Salomão, Pedro Emílio Amador; Rodriguez, Mariandry del Valle Rodriguez; Silva, Adilson Cândido da; Oliveira, Henrique dos Santos; Monteiro, Douglas Santos; Pereira, Márcio CésarThe conventional chemical methods to produce graphene using strong oxidizing agents produce toxic gases during synthesis; therefore, these methods do not meet the principles of green chemistry. In this work, an alternative top-down method for the synthesis of a few layers of graphene sheets has been produced by a Fenton reaction- (a mixture of Fe2+/H2O2) assisted exfoliation process in water using graphite flakes as a starting material. Based on X-ray diffraction data and Fourier transform infrared (FTIR), Raman spectroscopy, and transmission electron microscopy measurements, it is proposed that the oxidation of graphite by Fenton chemistry facilitates the exfoliation of graphene sheets under mild sonication. Subsequent chemical reduction with ascorbic acid produced a few layers of reduced graphene oxide. Compared to Hummers’ method, the Fenton reagent has similar exfoliation efficiency, but due to the Fenton reagent’s preference to react with the edges of graphite, the chemical reduction can lead to the formation of less defective reduced graphene oxides. Moreover, since Fe and H2O2 are cheap and environmentally innocuous, their use in large-scale graphene production is environmentally friendlier than conventional methods that use toxic oxidizing agents.Item Síntese e caracterização do NiMoO4 através dos métodos sol-gel proteico e coprecipitação e estudo de suas aplicações.(2019) Silva, Maíra Vieira da; Siqueira, Kisla Prislen Félix; Siqueira, Kisla Prislen Félix; Oliveira, Henrique dos Santos; Fajardo, Humberto VieiraEste trabalho apresenta a síntese do molibdato de níquel (NiMoO4), composto pertencente a uma importante classe dos materiais cerâmicos, os quais apresentam aplicações nas mais diversas áreas. Os métodos de síntese utilizados foram de coprecipitação (CP) e solgel proteico (SG), sendo este último ainda não reportado para a produção desse material, o que torna este trabalho inédito. Neste trabalho utilizou-se a gelatina comercial como precursor proteico, tornando o método mais barato e ambientalmente correto quando comparado ao método convencional. Além disso, a gelatina apresenta baixo custo e é atóxica. Os produtos obtidos após as sínteses foram tratados termicamente em mufla de 300 a 1000 °C durante 2h (método CP) e 4h (método SG). O comportamento termocrômico e a energia do band gap (Egap) dos pós obtidos foram investigados através de medidas de espectroscopia de reflectância difusa (DRS-UV-vis) e através dos parâmetros colorimétricos do sistema CIE-Lab. Observou-se a transição dos precursores no polimorfo α (alfa) para as amostras calcinadas em temperaturas superiores a 700 °C e em uma mistura de fases α e β (beta) para as amostras obtidas em temperaturas entre 300 e 600 °C, confirmadas através das técnicas de difração de raios X (DRX) e espectroscopia vibracional Raman. O composto NiMoO4 em sua forma hidratada apresentou estrutura cristalina do tipo triclínica ( P1 ) enquanto o composto em sua forma anidra exibiu estrutura monoclínica (C2/m) confirmadas através das análises de DRX. Medida de espectroscopia Raman polarizado foi realizada para a amostra calcinada a 1000 °C obtida via CP a fim de identificar e atribuir seus modos de vibração ativos em Raman com o auxílio da teoria de grupos. Através das análises térmicas (TGA e DTA) foi possível investigar o processo de desidratação das amostras precursoras e no caso da amostra hidratada obtida por CP calcular a quantidade de moléculas de água de hidratação. A morfologia dos compostos estudados e suas propriedades estruturais foram analisadas através das medidas de microscopias eletrônicas de varredura (MEV) e transmissão (MET), onde evidenciou-se o processo de aglutinação das partículas à medida que a temperatura de calcinação aumentou. As amostras obtidas na síntese de coprecipitação foram incorporadas em uma matriz polimérica a fim de avaliar sua potencial aplicação como pigmento cerâmico como alternativa aos pigmentos inorgânicos existentes. Para as amostras calcinadas nas temperaturas de 300, 500 e 700 °C obtidas através da metodologia SG foi testado o potencial uso das mesmas como catalisadores na reação de reforma a vapor do etanol para produção de hidrogênio.