Navegando por Autor "Ribeiro, Renan Augusto Pontes"

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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
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
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

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Navegando por Autor "Ribeiro, Renan Augusto Pontes"