Navegando por Autor "Oliveira, Marisa Carvalho de"

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Connecting the surface structure, morphology and photocatalytic activity of Ag2O: An in depth and unified theoretical investigation
(Elsevier, 2020-04-15) Ribeiro, Renan Augusto Pontes; Oliveira, Marisa Carvalho de; Delmonte, Maurício Roberto Bomio; Lazaro, Sérgio Ricardo de; Andrés, Juan; Silva, Elson Longo da
The surface morphology of the materials is known to have significant influence on the overall photocatalytic performance. Therefore, identifying the corresponding electronic structures associated with the surface redox centers is essential for the rational design of Ag2O-based photocatalysts. In this study, comprehensive and sys- tematic theoretical calculations revealed the connection between electronic structure and morphology responsible for the photo-induced mechanism. First-principles calculations showed that the activity of Ag+ cations on the exposed surfaces is dependent of their local coordination and electronic configuration. Electrons were found to migrate to the energetically favorable (1 1 1) surface, while holes are concentrated in the more unstable (1 0 0) and (1 1 0) surfaces. The complete set of available morphologies was obtained, enabling us to rationalize the photocatalytic activity in terms of composition, geometry, and electronic structure of the exposed surfaces. Moreover, the localization and characterization of excited electronic states of both bulk material and exposed surfaces allow us to discuss the fundamental reactions involved in the photocatalytic mechanism underlying the morphological evolution and would promote significantly the development and application of singlet-triplet mechanism. The detailed insights provided by our work could benefit the design and preparation of new efficient photocatalysts based on Ag2O
Connecting theory with experiment to understand the photocatalytic activity of CuO–ZnO heterostructure
(Elsevier, 2020-05) Oliveira, Marisa Carvalho de; Fonseca, V. S.; Andrade Neto, Nivaldo Ferreira da; Ribeiro, Renan Augusto Pontes; Silva, Elson Longo da; Lazaro, Sérgio Ricardo de; Motta, Fabiana Villela da; Delmonte, Maurício Roberto Bomio
Semiconductor based photocatalysis attracts wide attention because of its ability to directly utilize solar energy to degrade pollutants and convert energy, with heterojunction photocatalysts being good candidates for superior activity due to the spatial separation of photogenerated electron–hole pairs. Herein, CuO/ZnO heterostructures were successfully synthesized by a microwave-assisted hydrothermal method, with the structure, electronic and photocatalytic properties analyzed by means of experimental and theoretical methods. The X-ray diffraction patterns revealed that a CuO/ZnO heterostructure was formed, while FE-SEM analysis indicates the role of different morphologies for CuO, ZnO and CuO/ZnO heterostructures. The solar-driven photocatalytic mea-surements combined with DFT calculations indicate that CuO, as a p-type and narrow band-gap sensitizer, can make the n-type ZnO respond to visible light and promote the separation of photogenerated charge carriers by building a p-n heterogeneous structure. As a result, the CuO/ZnO heterostructure shows good promise for solar-driven photodegradation
Disclosing the structural, electronic, magnetic, and morphological properties of CuMnO2: a unified experimental and theoretical approach
(American Chemical Society, 2020-02-14) Santiago, Anderson de Azevedo Gomes; Tranquilin, Ricardo Luis; Oliveira, Marisa Carvalho de; Ribeiro, Renan Augusto Pontes; Lazaro, Sérgio Ricardo de; Corrêa, Marcio Assolin; Bohn, Felipe; Silva, Elson Longo da; Motta, Fabiana Villela da; Delmonte, Maurício Roberto Bomio
Precise control of the overall performance for solid-state materials is associated with morphological modulations which provide an alternative way to the rational design based on understanding the corresponding electronic structures of the exposed surfaces. Experimental and theoretical efforts were combined herein to elucidate the structural−property relationship of CuMnO2 nanoparticles from different morphologies. The microwave-assisted hydrothermal method was employed to synthesize these crystals with different morphologies, while first-principle quantum mechanical calculations were performed at the DFT level to obtain the structural, electronic, and magnetic properties of CuMnO2 surfaces. Our structural results have confirmed a monoclinic structure for crednerite-type CuMnO2 nanoparticles described by the Jahn−Teller-distorted octahedral [MnO6] clusters, which are connected by linear 2-fold [CuO2]. FE-SEM images combined with Wulff construction analyses indicated that CuMnO2 nanoparticles adopt a hexagonal nanoplate-like morphology which can enclose a major extent of the (100) surface with contributions from (101), (110), and (111) surfaces. Electronic structure and magnetic characterizations were discussed by the role of the corresponding electronic states of exposed surfaces which control the energy-level band diagram and spin density distribution. These results extend our fundamental understanding of the atomic processes which underpin the morphological modulations of the CuMnO2 material, thus creating a new path to obtain selected nanoparticles with desirable properties which optimize their applications
Estudo das propriedades fotocatalíticas do compósito AgCl/xGO
(Universidade Federal do Rio Grande do Norte, 2020-11-09) Oliveira, Yasmim Gomes de; Motta, Fabiana Villela da; Delmonte, Maurício Roberto Bomio; Oliveira, Marisa Carvalho de
Neste trabalho foram obtidos os pós de cloreto de prata (AgCl), óxido de grafeno (GO) e dos compósitos de AgCl/xGO, com variações de concentração de GO em 1, 2, 4 e 8% em massa. Os pós foram caracterizados por Difração de Raios-X (DRX), Espectroscopia de Infravermelho por Transformada de Fourier (FTIR), Microscopia Eletrônica de Varredura por Emissão de Campo (MEV-FEG), Absorbância na região do ultravioleta visível e Espectroscopia de reflectância difusa, Espectroscopia na Região do UV-Visivel (UV-Vis). As propriedades fotocatalíticas dos compósitos foram avaliadas pela variação de concentração do corante azul de metileno, iluminado por lâmpadas de UV. Os padrões de DRX expressam que a modificação no método de Hummer’s e utilização da ponteira sonoquímica são eficientes na obtenção do pós de GO e AgCl. As imagens de MEV-FEG indicam a formação de nanopartículas de prata na superfície das partículas de AgCl e a existência de interface entre as partículas de AgCl/GO. O acréscimo de GO provocou uma potencialização nas propriedades ópticas do AgCl, aumentando sua absorção para comprimento de ondas maiores e reduzindo a sua Egap. A interface obtida pelo AgCl/GO provoca melhoramento na eficiência fotocatalítica do compósito, devido o impedimento da recombinação dos pares elétron/buraco (e-/h+). Depois de 3 minutos de exposição à radiação UV, o compósito com 8% de GO causou degradação completa no corante e o pó de AgCl puro degradou 75,3%.
Experimental and theoretical study to explain the morphology of CaMoO4 crystals
(Elsevier, 2018-03) Paskocimas, Carlos Alberto; Silva, Elson Longo da; Oliveira, Fernanda Karine Fonseca de; Oliveira, Marisa Carvalho de; Gracia, Lourdes; Tranquilin, Ricardo Luis; Motta, Fabiana Villela da; Andrés, Juan; Delmonte, Maurício Roberto Bomio
CaMoO4 crystals were prepared by a controlled co-precipitation method and processed in a domestic microwave-assisted hydrothermal system with two different surfactants (ethyl 4-dimethylaminobenzoate and 1,2,4,5-benzenetetracarboxylic dianhydride). The corresponding structures were characterized by X-ray diffraction and Rietveld refinement techniques, Fourier transform infrared spectroscopy, ultraviolet–visible absorption spectroscopy, and photoluminescence measurements. Field emission scanning electron microscopy was used to investigate the morphology of the as-synthesized aggregates. The structure, the surface stability of the (001), (112), (100), (110), (101), and (111) surfaces of CaMoO4, and their morphological transformations were investigated through systematic first-principles calculations within the density functional theory method at the B3LYP level. Analysis of the surface structures showed that the electronic properties were associated with the presence of undercoordinated [CaOx] (x 1⁄4 5 and 6) and [MoOy] (y 1⁄4 4 and 3) clusters. The relative surfaces energies were tuned to predict a complete map of the morphologies available through a Wulff construction approach. The results reveal that the experimental and theoretical morphologies obtained coincide when the surface energies of the (001) and (101) surfaces increase, while the surface energy of the (100) facet decreases simultaneously. The results provide a comprehensive catalog of the morphologies most likely to be present under realistic conditions, and will serve as a starting point for future studies on the surface chemistry of CaMoO4 crystals
Presence of excited electronic states on terbium incorporation in CaMoO4: Insights from experimental synthesis and first-principles calculations
(Elsevier, 2021-02) Tranquilin, Ricardo Luis; Oliveira, Marisa Carvalho de; Santiago, Anderson de Azevedo Gomes; Lovisa, Laura Ximena; Ribeiro, Renan Augusto Pontes; Silva, Elson Longo da; Lazaro, Sergio R. de; Almeida, Cláudio Romero Rodrigues de; Paskocimas, Carlos Alberto; Motta, Fabiana Villela da; Delmonte, Maurício Roberto Bomio
We present a combined experimental and theoretical study to understand the structure and electronic and optical properties of CaMoO4:xTb3+ (x = 1 mol%, 2 mol%, and 4 mol%) microspheres. The microspheres were prepared by ultrasonic spray pyrolysis and characterized by X-ray diffraction (XRD), field-emission gun scanning electron microscopy (FEG-SEM), micro Raman spectroscopy, and photoluminescence (PL) spectroscopy. First-principles quantum mechanical calculations were performed at the density functional theory level to obtain the geometry and electronic properties of CaMoO4:xTb3+ microspheres in the ground electronic state and excited electronic states (singlet and triplet). These results, combined with XRD patterns, indicate that these crystals have a scheelite-type tetragonal structure. The morphology of the CaMoO4:xTb3+(x = 1 mol%, 2 mol%, and 4 mol%) samples was investigated by FEG-SEM, and a spherical shape was found. The optical properties were investigated by UV–vis spectroscopy and PL spectroscopy, and the chromaticity coordinates of these compounds were obtained. The relationships between the PL properties and the Raman spectra indicate that Tb3+-doped CaMoO4 microspheres constitute promising photoluminescent materials for use in new lighting devices. This also allowed us to understand the charge transfer process that happens in the singlet (s) ground state and the singlet (s*) and triplet (t*) excited states, which generates the photoluminescent emissions of the Tb3+-doped CaMoO4 microspheres
Quantum mechanical modeling of Zn-based spinel oxides: Assessing the structural, vibrational, and electronic properties
(Wiley, 2020-07-06) Oliveira, Marisa Carvalho de; Ribeiro, Renan Augusto Pontes; Silva, Elson Longo da; Delmonte, Maurício Roberto Bomio; Lazaro, Sérgio Ricardo de
The structural, electronic, and vibrational properties of two leading representatives of the Zn-based spinel oxides class, normal ZnX2O4 (X = Al, Ga, In) and inverse Zn2MO4 (M = Si, Ge, Sn) crystals, were investigated. In particular, density functional theory (DFT) was combined with different exchange-correlation functionals: B3LYP, HSE06, PBE0, and PBESol. Our calculations showed good agreement with the avail- able experimental data, showing a mean percentage error close to 3% for structural parameters. For the electronic structure, the obtained HSE06 band-gap values overcome previous theoretical results, exhibiting a mean percentage error smaller than 10.0%. In particular, the vibrational properties identify the significant differences between normal and inverse spinel configurations, offering compelling evidence of a structure-property relationship for the investigated materials. Therefore, the combined results confirm that the range-separated HSE06 hybrid functional performs the best in spinel oxides. Despite some points that cannot be directly compared to experimental results, we expect that future experimental work can confirm our predictions, thus opening a new avenue for understanding the structural, electronic, and vibrational properties in spinel oxides
Structural, electronic, vibrational and magnetic properties of Zn2+ substituted MnCr2O4 nanoparticles
(Elsevier, 2020-05-15) Manjunatha, K.; Angadi, V. Jagadeesha; Ribeiro, Renan Augusto Pontes; Silva, Elson Longo da; Oliveira, Marisa Carvalho de; Delmonte, Maurício Roberto Bomio; Lázaro, Sérgio Ricardo de; Matteppanavar, Shidaling; Rayaprol, Sudhindra; Babu, Peram Delli; Pasha, Mahaboob
In the present investigation, we report the structural, vibrational, electronic and magnetic properties of Mn0.5Zn0.5Cr2O4 nanoparticles fabricated by the solution combustion method and complemented by Density Functional theory (DFT) calculations. X-ray diffraction (XRD), Neutron diffraction, X-ray photoelectron spec- troscopy and Raman analysis confirms the formation of single-phase with spinel cubic structure. The average crystallite size was found to be 8 nm. The theoretical calculations suggest that Zn-doping on the MnCr2O4 matrix induces a unit cell contraction associated with structural distortions along both [AO4] (A = Mn, Zn) and [CrO6] clusters, in agreement with the experimental evidence. These structural distortions contribute to narrowing the band-gap of Mn0.5Zn0.5Cr2O4 from disturbed energy levels in the vicinity of Fermi level. Field dependent magnetization confirms that the samples exhibit paramagnetic nature at 300 K and antiferromagnetic nature at 3 K. In the theoretical context, the exchange coupling constant for pure and Zn2+ substituted MnCr2O4 materials were calculated confirming the dominant antiferromagnetic character of Cr-Cr interactions. The temperature dependent susceptibility reveals that the magnetic transition from paramagnetic phase to antiferromagnetic phase occurs at 19 K (TN). The spin frustration factor of Mn0.5Zn0.5Cr2O4 is found to be 22 K. Hence, our experimental and theoretical result suggests that synthesized materials are useful for low and high frequency applications
Structure, morphology and photoluminescence emissions of ZnMoO4: RE 3+=Tb3+ - Tm3+ - X Eu3+ (x = 1, 1.5, 2, 2.5 and 3 mol%) particles obtained by the sonochemical method
(Elsevier, 2018-06-25) Paskocimas, Carlos Alberto; Lovisa, Laura Ximena; Oliveira, Marisa Carvalho de; Andres, Juan; Gracia, Lourdes; Li, Maximo Siu; Silva, Elson Longo da; Tranquilin, Ricardo Luis; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
ZnMoO4 and ZnMoO4: RE3+ = 1% Tb3+, 1% Tm3+, x Eu3+ (x = 1, 1.5, 2, 2.5 and 3 mol%) particles were prepared by a sonochemical method. The influence of the dopant content on photoluminescent behavior was investigated. The X-ray diffraction results confirmed the formation of the α-ZnMoO4 phase with a triclinic crystalline structure. The influence of the chemical compositions on photoluminescence emissions has been studied and the results clearly show the specific emissions of Tb3+ and Eu3+, simultaneously, with a strong contribution of the matrix. Band gap values are in the range of 3.55–4.25 eV. From the values calculated for the CIE coordinates, it was observed that this material develops an emission tendency in the orange-red region. It has been demonstrated for the first time that the sample ZnMoO4: 1% Tb3+, 1% Tm3+, 2% molEu3+, presented higher photoluminescence intensity. At higher concentrations of RE3+, the quenching effect was observed. The morphology of samples are interpreted based on a comparative analysis of the calculated and experimental field emission scanning electron microscopy (FE-SEM) images. First-principle calculations at a density functional theory level were performed to obtain the values of surface energies and relative stability of the (120), (001), (011), (201), and (100) surfaces by employing the Wulff construction. A complete map of the available morphologies of ZnMoO4 and ZnMoO4:12.5%molEu3+ is obtained and a possible explanation for the transformation processes is provided in which the experimental and theoretical morphologies can match. The present study offers a fundamental knowledge that is expected to enable the fabrication of ZnMoO4-based phosphor materials with a controllable emission peak shift and intensity
Structure, morphology and photoluminescence emissions of ZnMoO4: RE 3+=Tb3+ -Tm3+ - x Eu3+ (x = 1, 1.5, 2, 2.5 and 3 mol%) particles obtained by the sonochemical method
(Elsevier, 2018-06-25) Lovisa, Laura Ximena; Oliveira, Marisa Carvalho de; Andrés, Juan; Gracia, Lourdes; Li, Maximo Siu; Silva, Elson Longo da; Tranquilin, Ricardo Luis; Paskocimas, Carlos Alberto; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
ZnMoO4 and ZnMoO4: RE3+= 1% Tb3+, 1% Tm3+, x Eu3+ (x = 1, 1.5, 2, 2.5 and 3 mol%) particles were prepared by a sonochemical method. The influence of the dopant content on photoluminescent behavior was investigated. The X-ray diffraction results confirmed the formation of the α-ZnMoO4 phase with a triclinic crystalline structure. The influence of the chemical compositions on photoluminescence emissions has been studied and the results clearly show the specific emissions of Tb3+ and Eu3+, simultaneously, with a strong contribution of the matrix. Band gap values are in the range of 3.55 to 4.25 eV. From the values calculated for the CIE coordinates, it was observed that this material develops an emission tendency in the orange-red region. It has been demonstrated for the first time that the sample ZnMoO4: 1% Tb3+, 1% Tm3+, 2% molEu3+, presented higher photoluminescence intensity. At higher concentrations of RE3+, the quenching effect was observed. The morphology of samples are interpreted based on a comparative analysis of the calculated and experimental field emission scanning electron microscopy (FE-SEM) images. First-principle calculations at a density functional theory level were performed to obtain the values of surface energies and relative stability of the (120), (001), (011), (201), and (100) surfaces by employing the Wulff construction.A complete map of the available morphologies of ZnMoO4 and ZnMoO4:12.5%molEu3+ is obtained and a possible explanation for the transformation processes is provided in which the experimental and theoretical morphologies can match. The present study offers a fundamental knowledge that is expected to enable the fabrication of ZnMoO4-based phosphor materials with a controllable emission peak shift and intensity
Temperature dependence on phase evolution in the BaTiO3 polytypes studied using ab initio calculations
(Wiley, 2019-10) Oliveira, Marisa Carvalho de; Ribeiro, Renan Augusto Pontes; Silva, Elson Longo da; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da; Lazaro, Sérgio Ricardo de
Identifying the forces that drive a temperature-induced phase transition is always challenging in the prospect of the first-principles methods. Herein, we perform a first-principles study of the temperature effects on structural, energetic, electronic, and vibrational properties of four BaTiO3 polymorphs using quasi-harmonic approxi- mations. Study of the stability between these four phases, which we break into contributions arising from the vibration of the lattice, electronic structure, and volume expansion/contraction, is helpful to confirm the sequence of phase transitions as cubic ! tetragonal ! orthorhombic ! rhombohedral, as well as its transition tem- peratures. A general mechanism was proposed based on the combination between structural distortions at [TiO6] clusters, vibrational characteristics, and electronic structure. These findings confirm the power of quasi-harmonic approximations to disclose the main fingerprints associated with both thermic and mechanical phase transitions, serving as a guide for further theoretical studies
Understanding the white-emitting CaMoO4 Co-Doped Eu3+, Tb3+, and Tm3+ phosphor through experiment and computation
(American Chemical Society, 2019-07-09) Paskocimas, Carlos Alberto; Tranquilin, Ricardo Luis; Lovisa, Laura Ximena; Almeida, Cláudio Romero Rodrigues de; Li, Maximo Siu; Oliveira, Marisa Carvalho de; Gracia, Lourdes; Andres, Juan; Silva, Elson Longo da; Motta, Fabiana Villela da; Delmonte, Maurício Roberto Bomio
In this article, the synthesis by means of the spray pyrolysis method, of the CaMoO4 and rare-earth cation (RE3+)-doped CaMoO4:xRE3+ (RE3+ = Eu3+, Tb3+, and Tm3+; and x = 1, 2, and 4% mol) compounds, is presented. The as-synthesized samples were characterized using X-ray diffraction, Rietveld refinement, field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, and photoluminescence (PL) spectroscopy. To complement and rationalize the experimental results, first-principles calculations, at the density functional theory level, have been performed to analyze the band structure and density of states. In addition, a theoretical method based on the calculations of surface energies and Wulff construction was applied to obtain the morphology transformation of the CaMoO4 and CaMoO4:RE3+ microstructures. The experimental morphologies can be observed in the FE-SEM images. The PL behavior of the Co-doped samples exhibited well-defined bands in the visible region. The samples with 2 and 4% of RE3+ released white emission according to the chromaticity coordinates (0.34, 0.34) and (0.34, 0.33), respectively. The present results provide not only a deep understanding of the structure−property relationships of CaMoO4-based phosphor but also can be employed as a guideline for the design of the electronic structure of the materials and the fabrication of photofunctional materials with optimal properties, which allows for the modeling of new phosphors for applications in solid-state lighting

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Navegando por Autor "Oliveira, Marisa Carvalho de"