Navegando por Autor "Rodriguez, Mariandry del Valle Rodriguez"
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Item Bismuth vanadate photoelectrodes with high photovoltage behave as photoanode and photocathode in photoelectrochemical cells for water splitting.(2018) Santos, Wayler Silva dos; Rodriguez, Mariandry del Valle Rodriguez; Khoury, Julia M. O.; Nascimento, Luiza A.; Mesquita, João Paulo de; Silva, Adilson Cândido da; Nogueira, Francisco Guilherme Esteves; Pereira, Márcio CésarUsing dual-photoelectrode photoelectrochemical (PEC) devices based on earth-abundant metal oxides for unbiased water splitting is an attractive means of producing green H2 fuel, but is challenging, owing to low photovoltages generated by PEC cells. This problem can be solved by coupling n-type BiVO4 with n-type Bi4V2O11 to create a virtual p/n junction due to the formation of a hole-inversion layer at the semiconductor interface. Thus, photoelectrodes with high photovoltage outputs were synthesized. The photoelectrodes exhibited features of pand n-type semiconductors when illuminated under an applied bias, suggesting their use as photoanode and photocathode in a dual-photoelectrode PEC cell. This concept was proved by connecting a 1 mol% W-doped BiVO4/Bi4V2O11 photoanode with an undoped BiVO4/Bi4V2O11 photocathode, which produced a high photovoltage of 1.54 V, sufficient to drive standalone water splitting with 0.95% efficiency.Item Cobalt as a sacrificial metal to increase the photoelectrochemical stability of CuBi2O4 films for water splitting.(2023) Bruziquesi, Carlos Giovani Oliveira; Stolzemburg, Matheus Cata Preta; Souza, Rafael R. de; Rodriguez, Mariandry del Valle Rodriguez; Pereira, Maria Luiza Rocco Duarte; Salomão, Pedro Emílio Amador; Nogueira, André Esteves; Lopez Cabaña, Zoraya Elena; Pereira, Márcio César; Silva, Adilson Cândido daCuBi2O4 is an excellent photocathode candidate in water-splitting photoelectrochemical cells. However, its poor photoelectrochemical stability caused by the reduction of Cu2þ to Cu metal limits its use. Here, we show a strategy to decrease the reduction of Cu2þ to Cu using cobalt as a sacrificial metal. Co-doped CuBi2O4 films were prepared by spray pyrolysis using Co2þ salt as the precursor. Co2þ ions replace Cu2þ in the CuBi2O4 structure, and subsequent heat treatment at 500 C leads to partial oxidation of Co2þ to Co3þ. As the reduction potential of Co3þ/Co2þ is higher than that of Cu2þ/Cu, Cu2þ reduction can be minimized. Comparatively, about 72% of the photocurrent produced by the CuBi2O4 film is lost in the first few minutes of illumination. In the Co-doped CuBi2O4 film, the photocurrent drops by less than 7%. Thus, the Co-doping can increase the CuBi2O4 photostability and be helpful for the fabrication of more stable photocathodes.Item Electrocatalytic performance of different cobalt molybdate structures for water oxidation in alkaline media.(2018) Rodriguez, Mariandry del Valle Rodriguez; Stolzemburg, Matheus Cata Preta; Bruziquesi, Carlos Giovani Oliveira; Silva, Adilson Cândido da; Abreu, Cíntia Grossi de; Siqueira, Kisla Prislen Félix; Oliveira, Luiz Carlos Alves de; Pires, Maíra dos Santos; Lacerda, Lívia Clara Tavares; Ramalho, Teodorico de Castro; Dias, Anderson; Pereira, Márcio CésarCobalt molybdates with different crystalline structures, i.e., α, β, and hydrated (H)-CoMoO4, were synthesized, and their electrocatalytic activities were thoroughly examined for catalyzing the oxygen evolution reaction (OER) in alkaline media. The material characteristics were associated with the electrocatalytic properties by evaluating the CoMoO4 crystal structures (XRD and Raman), morphologies (TEM), and electrochemical features (electrochemically active surface area, roughness factor, electrochemical impedance, Tafel analysis, and controlled-current electrolysis). These combined findings revealed that the electrocatalytic performance is greatly influenced by the crystalline structures of CoMoO4, following the order α-CoMoO4 > H-CoMoO4 > β-CoMoO4. The H-CoMoO4 catalysts crystallized in the triclinic space group, P[1 with combining macron] (#2), with Z = 4. On the other hand, the α- and β-CoMoO4 catalysts exhibited a monoclinic structure, C2/m (#12), with Z = 8. In the OER experiments, α-CoMoO4 showed an overpotential of 0.43 ± 0.05 V compared to the 0.51 ± 0.05 V and 0.56 ± 0.04 V exhibited by the H-CoMoO4 and β-CoMoO4 catalysts, respectively, to achieve 10 mA cm−2. All CoMoO4 structures displayed stability for at least 6 h at a controlled current density of 10 mA cm−2. Finally, computational simulations indicate that the coexistence of Co and Mo ions in edge-shared octahedral sites of α-CoMoO4 may favor the interaction between the O atom of the water molecule and the metal adsorption sites due to its surface being electronically less dense than β- and H-CoMoO4 surfaces, thus resulting in its higher performance for OER.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 Improved photocatalytic activity of d-FeOOH by using H2O2 as an electron acceptor.(2017) Silva, Adilson Cândido da; Almeida, Monique Rocha; Rodriguez, Mariandry del Valle Rodriguez; Machado, Alan Rodrigues Teixeira; Oliveira, Luiz Carlos Alves de; Pereira, Márcio CésarIn this work, d-FeOOH nanoparticles were synthesized by a simple co-precipitation method and used as a photocatalyst in the presence of H2O2 for the oxidation of Rhodamine B (RhB) dye under artificial light. The d-FeOOH was characterized by powder X-ray diffraction, 57Fe Mössbauer spectroscopy, N2 adsorption/desorption and UV–vis diffuse reflectance measurements. The d-FeOOH nanoparticles have high specific surface area (101 m2 g 1) and optical bandgap energy of 2.02 eV. Under artificial light, only 59% of RhB (100 mL; 20 mg L 1) was photocatalytically degraded by d-FeOOH in 60 min reaction. However, after adding H2O2, the photocatalytic activity of d-FeOOH was significantly improved, reaching 87% of dye removal. Tests using scavengers of reactive species and EPR analysis revealed that h+ and OH are the main species in this system. Based on the experimental results, the mechanism of RhB photodegradation in the presence of d-FeOOH and H2O2 was proposed. By this mechanism, the OH can be formed by direct water oxidation or by H2O2 reduction, as the electron transfer from the conduction band of d-FeOOH to H2O2 is thermodynamically favorable. Moreover, the H2O2 retards the electron-hole recombination in d-FeOOH, thus increasing its photocatalytic activity. Given its high efficiency for degrading RhB in water, d-FeOOH revealed to be a promising photocatalyst to be tested in the oxidation of emerging pollutants for the environmental decontamination.Item Photoassisted chemical energy conversion into electricity using a sulfite-iron photocatalytic fuel cell.(2021) Sena, Izabela Campos; Sales, Davi de Oliveira; Andrade, Tatiana Santos; Rodriguez, Mariandry del Valle Rodriguez; Silva, Adilson Cândido da; Nogueira, Francisco Guilherme Esteves; Rodrigues, Jairo Lisboa; Mesquita, João Paulo de; Pereira, Márcio CésarPhotocatalytic fuel cells (PFC) are light-assisted devices that convert chemical energy into electricity. However, con ventional PFC produces extremely low photocurrents due to the slow kinetics of the photoanodes to oxidized organic fuels, thus limiting the power generation. Here, an all-inorganic PFC manufactured with heterostructured W-BiVO4/ V2O5 photoanode separated from a platinum cathode by a porous membrane is described. Sulfite ions are used as a fuel anolyte and Fe3+ is the catholyte. Under lighting, the W-BiVO4/V2O5 photoanode is exceptionally efficient for oxidizing sulfite to sulfate, which results in a high photocurrent output. Under optimized conditions, the W-BiVO4/V2O5-Pt cell produces a high short-circuit current of 8.79 mA cm−2 , an open-circuit potential 0.85 V, and a power density of 1.89 mW cm−2 at 4.30 mA cm−2 . The excellent PFC performance is attributed to the photovoltage generated by W-BiVO4/sulfite-sulfate liquid-junctions and efficient charge separation and hole transport in the photoanode bulk promoted by the W-BiVO4/V2O5 junctions. Also, the kinetics of redox reactions are fast, eliminating the use of cocatalysts. Thus, this simple PFC concept can be a viable alternative for electricity generation.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.