Toward Understanding the Photocatalytic Activity of PbMoO4 Powders with Predominant (111), (100), (011), and (110) Facets. A Combined Experimental and Theoretical Study

A complementary combination of experimental work and first-principle calculations, based on the density functional theory (DFT) method, has been used to increase our limited understanding of the enhanced photocatalytic activity of PbMoO4 powders with predominant (111), (100), (011), and (110) facets. In this work, PbMoO4 powders were prepared by the coprecipitation method and processed on a hydrothermal reactor at 100 °C/10 min. The variation of different types of modifiers such as acetylacetone (acac) or polyvinylpyrrolidone (PVP) is found to play a crucial role in controlling the particle size and morphology of products and their photocatalytic properties. The structure and morphology of these crystals were characterized by X-ray diffraction (XRD), micro-Raman (MR) spectroscopy, field-emission gun scanning electron microscopy (FEG-SEM), and ultraviolet visible (UV-vis) absorption spectroscopy. Furthermore, the as-synthesized PbMoO4 micro-octahedrons without the presence of the (001) surface exhibit enhanced activity for the photodegradation of rhodamine B (RhB) under ultraviolet-visible light irradiation. On the basis of the theoretical and experimental results, we provide a complete assignment of the micro-Raman spectra of PbMoO4, while a growth mechanism for the formation of PbMoO4 micro-octahedrons was systematically discussed. A schematic illustration of the probable formation of morphologies in the whole of the synthetic process was also proposed, which reveals that the high photocatalytic activity is attributed to the absence of the (001) facet.The authors thank the financial support from the following Brazilian research financing institutions: CNPq, FAPESP, CAPES, RECAM (Rede de Pesquisa em Catalisadores Ambientais) processo no 564913/2010-3; MCT/CNPq no 74/2010 and Universal 14/2011 processo no 481288/2011-2, and no 150753/2013-6 National Council for Scientific and Technological Development (CNPq), Prometeo/2009/053 (Generalitat Valenciana) and Ministerio de Economiá y Competitividad (Spain), CTQ2012-36253-C03-02, and the Spanish−Brazilian program (PHB2009-0065-PC) for their financial support

Structure, electronic properties, morphology evolution, and photocatalytic activity in PbMoO4 and Pb12xCaxSrxMoO4 (x = 0.1, 0.2, 0.3, 0.4 and 0.5) solid solutions

In this work PbMoO4 and Pb12xCaxSrxMoO4 (x = 0.1, 0.2, 0.3, 0.4 and 0.5) solid solutions have been successfully prepared, for the first time, by a simple co-precipitation method and the as-synthesized samples were subjected to a water-based reflux treatment. Structural characterization of these samples was performed using X-ray diffraction with Rietveld refinement analysis and Raman spectroscopy. Their optical properties were investigated by UV-Vis absorption spectroscopy and PL emissions, and the photocatalytic activity of the as-synthesized samples for the degradation process of Rhodamine B has been demonstrated. The surface structure and morphologies were characterized by field emission scanning electron microscopy. To complement and rationalize the experimental results, the geometry, electronic structures, and morphologies of as-synthesized samples were characterized by first-principles quantum-mechanical calculations at the density functional theory level. By using Wulff construction, based on the values of the surface energies for the (001), (100), (110), (111), (011) and (112) surfaces, a complete map of the available morphologies for PbMoO4 was obtained and a good agreement between the experimental and theoretical predicted morphologies was found. The structural and electronic changes induced by the substitution of Pb by Ca and Sr allow us to find a relationship among morphology, the electron-transfer process at the exposed surfaces, optical properties, and photocatalytic activity. We believe that our results offer new insights regarding the local coordination of superficial Pb/Ca/Sr and Mo cations (i.e., clusters) on each exposed surface of the corresponding morphology, which dictate the photocatalytic activities of the as-synthesized samples, a field that has so far remained unexplored. The present study, which combines multiple experimental methods and first-principles calculations, provides a deep understanding of the local structures, bonding, morphologies, band gaps, and electronic and optical properties, and opens the door to exploit the electrical, optical and photocatalytic activity of this very promising family of materials

Understanding the White-Emitting CaMoO4 Co-Doped Eu3+, Tb3+, and Tm3+ Phosphor through Experiment and Computation

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

MIOPLASTIA EXPERIMENTAL DO ESFÍNCTER ANAL EXTERNO COM Fascia lata AUTÓLOGA, EM CÃES

A incontinência fecal em cães e gatos é uma situação na qual o proprietário tem dificuldades para resolver as conseqüências advindas desta lesão, e geralmente os pacientes são submetidos à eutanásia. Algumas técnicas cirúrgicas empregadas na esfincteroplastia são passíveis de complicações como estenose anal ou incontinência fecal. Este experimento teve como objetivo reconstituir o músculo esfíncter anal externo em cães, após iatrogenização da incontinência fecal. Foram utilizados 10 cães hígidos, machos, sem raça definida, com peso variando entre 9 a14 kg. Após incisão de pele circundando a abertura anal, procedeu-se a miectomia bilateral de esfíncter anal externo, iatrogenizando-se a incontinência fecal, a qual foi diagnosticada por meio de avaliação física diária. Trinta dias após, os pacientes foram novamente preparados para cirurgia asséptica e submetidos à esfincteroplastia anal externa com o uso de Fascia lata autológa medindo 8 cm de comprimento e 0,5 cm de largura, em média. Os dez cães incontinentes, em decorrência da miectomia do esfíncter anal externo, apresentaram controle da emissão de fezes em 10 dias após a realização da esfincteroplastia e mantiveram-se assim durante os dois meses de observação póscirúrgica. Dessa maneira concluiu-se que a mioplastia do esfíncter anal externo com Fascia lata autóloga, representa um procedimento eficaz de simples e rápida aplicação, podendo ser utilizado rotineiramente para restabelecer a continência fecal em cães. Experimental myoplasty of the external anal sphincter with autologous Fascia lata in dogs Abstract Fecal incontinence in dogs and cats is a hard condition for owners to solve the consequences of this lesion, being patients usually subjected to euthanasia. Some surgical techniques used in sphincteroplasty are prone to complications such as anal stenosis or fecal incontinence. This experiment objectified to reconstruct the external anal sphincter in dogs after iatrogeny of the fecal incontinence. Ten healthy male dogs of undefined breed, weight ranging from 9 to 14 kg, were used. After dermal incision surrounding the anal opening, bilateral myectomy of the external anal sphincter was performer, with iatrogeny of fecal incontinence, diagnosed by daily physical evaluation. Thirty days later, patients were again prepared for aseptic surgery and went under external anal sphincteroplasty using autologous Fascia lata averaging 8 cm long and 0,5 cm wide. Ten incontinent dogs, due to external anal sphincter myectomy, presented fecal control in ten days after surgery and for the two subsequent months of follow-up. In conclusion, myoplasty of external anal sphincter using autologous Fascia lata is a simple and effective treatment that can be used in fecal incontinence in dogs

A Combined Experimental and Theoretical Study on the Formation of Ag Filaments on β-Ag 2 MoO 4 Induced by Electron Irradiation

A combined experimental and theoretical study is presented to understand the novel observed nucleation and early evolution of Ag fi laments on β-Ag 2 MoO 4 crystals, driven by an accelerated electron beam from an electronic micro-scope under high vacuum. The growth process, chemical composition, and the element distribution in these fi laments are analyzed in depth at the nanoscale level using fi eld-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) with energy-dispersive spectros-copy (EDS) characterization. To complement experimental results, chemical stability, structural and electronic aspects have been studied systematically using fi rst-principles electronic structure theory within a quantum theory of atoms in molecules (QTAIM) framework. The Ag nucleation and formation on β-Ag 2 MoO 4 are a result of structural and electronic changes of the AgO 4 tetrahedral cluster as a constituent building block of β-Ag 2 MoO 4 , consistent with Ag metallic formation. The formation of Ag fi lament transforms the β-Ag 2 MoO 4 semiconductor from n- to p- type concomitant with the appearance of Ag defects

Effect of polyvinyl alcohol on the shape, photoluminescence and photocatalytic properties of PbMoO4 microcrystals

For this study, lead molybdate (PbMoO4) microcrystals were prepared by theco-precipitation method and processed using a conventional hydrothermal method at 100 °C for 10 min with polyvinyl alcohol (PVA) as the capping agent. These microcrystals were structurally characterized by X-ray diffraction (XRD) and micro-Raman spectroscopy, and their morphology was investigated by field-emission gun scanning electron microscopy (FEG-SEM). The optical properties were analyzed by ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD pattern sand MR spectrum indicate that the PbMoO4 microcrystals have as cheelite-type tetragonal structure. FE-SEM images reveal that the PVA promotes the aggregation of several octahedrons and the formation of large porous stake-like PbMoO4 microcrystals which are related to the oriented attachment growth process. Moreover, the effect of the capping agent hinders the growth of a large amount of micro-octahedrons which can be verified with by several nanocrystals on large crystals. Intense green PL emission was observed at room temperature for PbMoO4 microcrystals which are related to structural defects at medium range and intermediary energy levels between the valence band (VB) and the conduction band (CB). Photocatalytic activity was observed for PbMoO4 as a catalyst in the degradation of the rhodamine B (RhB) dye, achieving total degradation after 90 min under UV-light.CNPqFAPESP - Centro de Desenvolvimento de Materiais Funcionais (CDMF) (13/07296-2)CAPES (AUX PE-PNPD-2280/2011)Rede de Pesquisa em Catalisadores Ambientais (RECAM) (564913/2010-3)MCTI/CNPq (74/2010)Generalitat Valenciana (Prometeo 2009/053)Ministerio de Economía y Competitividad (CTQ2012-36253-C03-02)Spanish-Brazilian Program (PHB2009-0065-PC

Experimental and theoretical study to explain the morphology of CaMoO4 crystals

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 = 5 and 6) and [MoOy] (y = 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

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

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

Experimental and theoretical study to explain the morphology of CaMoO4 crystals

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 = 5 and 6) and [MoOy] (y = 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