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

Photoluminescent properties of ZrO2: Tm3+, Tb3+, Eu3+ powdersd-A combined experimental and theoretical study

Rare-earth (RE) element-based materials for optical applications have received increasing attention owing to the emission properties of RE ions, which render these materials suitable for use in color displays, lasers, and solid-state lighting. In the present work, ZrO2:RE (RE = Tm3+, Tb3+, and Eu3+) powders were obtained via complex polymerization, and characterized by means of X-ray diffraction (XRD), Raman spectroscopy, UV–visible absorption spectroscopy, and photoluminescence measurements. The XRD patterns and Raman spectra revealed the tetragonal phase of ZrO2 co-doped with up to 4 mol.% RE3+ and stabilization of the cubic phase, for up to 8 mol.% RE3+. In addition, the photoluminescence measurements revealed simultaneous emissions in the blue (477 nm), green (496.02 nm and 548.32 nm), and red-orange (597.16 nm and 617.54 nm) regions. These emissions result from the Tm3+, Tb 3+, and Eu3+ ions, respectively. Energy transfers, such as 1G4 levels (Tm3+) → 5D4 (Tb3+) and 5D4 levels (Tb3+) → 5D0 (Eu3+), occurred during the emission process. Calculations based on density functional theory (DFT) were performed, to complement the experimental data. The results revealed that structural order/disorder effects were generated in the cubic and tetragonal ZrO2 phases in the ZrO2:Eu3+ powders, and changes in the electronic structure were manifested as a decrease in the band gap values. The chromaticity coordinates of all the samples were determined from the PL spectrum. The coordinates, x = 0.34 and y = 0.34, of the ZrO2:8%RE sample corresponded to a point located in the white region of the CIE diagram and color correlated temperature (CCT) was found to be 5181 K. More importantly, the present results indicate that ZrO2:RE powders constitute promising photoluminescent materials for use in new lighting devices.The authors gratefully acknowledge the financial support of the Brazilian governmental research funding agencies CAPES, CNPq 402127/2013-7, FAPESP2013/07296-2 and INCTMN2008/57872-1

Functional results after hiatal repair and gastropexy without fundoplication in patients with paraoesophageal hernia.

Paraoesophageal hernias (PEH) are associated with a high complication rate and often occur in elderly and fragile patients. Surgical gastropexy without fundoplication is an accepted alternative procedure; however, outcomes and functional results are rarely described. Our study aims to evaluate short-term outcomes and the long-term quality of life after gastropexy as treatment for PEH. Single center cohort analysis of all consecutive patients who underwent gastropexy for PEH without fundoplication. Postoperative outcomes and functional results were retrospectively collected. Reflux symptoms developed postoperatively were reported using the validated quality of life questionnaire: GERD-Health Related Quality of Life Qestionnaire (GERD-HRQL). Thirty patients (median age: 72 years (65-80)) were included, 40% classified as ASA III. Main PEH symptoms were reflux (63%), abdominal/thoracic pain (47%), pyrosis (33%), anorexia (30%), and food blockage (26%). Twenty-six laparoscopies were performed (86%). Major complications (III-IVb) occurred in 9 patients (30%). Seven patients (23%) had PEH recurrence, all re-operated, performing a new gastropexy. Median follow-up was 38 (17-50) months. Twenty-two patients (75%) reported symptoms resolution with median GERD-HRQL scale of 4 (1-6). 72% (n = 21) reported operation satisfaction. GERD-HRQL was comparable between patients who were re-operated for recurrence and others: 5 (2-19) versus 3 (0-6), p = 0.100. Gastropexy without fundoplication was performed by laparoscopy in most cases with acceptable complications rates. Two-thirds of patients reported symptoms resolution, and long-term quality-of-live associated to reflux symptoms is good. Although the rate of PEH recurrence requiring a new re-intervention remained increased (23%), it does not seem to affect long-term functional results

Computational procedure to an accurate DFT simulation to solid state systems

The density functional theory has become increasingly common as a methodology to explain the properties of crystalline materials because of the improvement in computational infrastructure and software development to perform such computational simulations. Although several studies have shown that the characteristics of certain classes of materials can be represented with great precision, it is still necessary to improve the methods and strategies in order to achieve more realistic computational modeling. In the present work, strategies are reported in a systematic way for the accurate representation of crystalline systems. The crystalline compound chosen for the study as a case test was BaMoO4, both because of its potential technological application and because of the low accuracy of the simulations previously reported in the literature. The computational models were carried out with the B3LYP and WC1LYP functionals selected from an initial set containing eight hybrid functionals in conjunction with an all-electron basis set. Two different strategies were applied for improving the description of the initial models, both involving atomic basis set optimization and Hartree-Fock exchange percentage adjustment. The results obtained with the two strategies show a precision of structural parameters, band gap energy, and vibrational properties never before presented in theoretical studies of BaMoO4. Finally, a flowchart of good calculation practices is elaborated. This can be of great value for the organization and conduction of calculations in new research

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

Influence of reaction temperature, proportions of iron, cobalt and KOH on the CoFe2O4 synthesis by hydrothermal method assisted by microwave heating

In this study, several factors such as reaction temperature, proportions of iron, cobalt and KOH were considered in the synthesis of cobalt ferrite nanoparticles by hydrothermal method assisted by microwave radiation. These parameters were studied using the full factorial experiment design. The effect of these factors on crystallite size was investigated using surface response methodology. The structure, crystallite size, magnetic properties, degree of inversion, as well as the chemical occupation of Fe ions were investigated in this study. The results indicated that all factors were statistically significant by analysis of variance (F-test), with a confidence level of 95%. The factors that influenced the growth of the crystallite were: KOH and iron concentration, precursors of cobalt salts and the effect of the interaction between the concentration of KOH and the concentration of precursors. The analysis of variance at a significance level of 95% indicates that the model adjusted to the experimental points is significan

Regulamento da Millenium - Journal of Education, Technologies, and Health

PbMoO(4) micro-octahedrons were prepared by the coprecipitation method at room temperature without the presence of surfactants and processed in a conventional hydrothermal at different temperatures (from 60 to 120 degrees C) for 10 min. These micro-octahedrons were structurally characterized by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy, and its 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 patterns and MR spectra confirmed that the PbMoO(4) micro-octahedrons are characterized by a scheelite-type tetragonal structure. FEG-SEM micrographs points, out that these structures present a polydisperse particle size distribution in consequence of a predominant growth mechanism via aggregation of particles. In addition, it was observed that the hydrothermal conditions favored a spontaneous formation of micro-octahedrons interconnected along a common crystallographic orientation (oriented-attachment), resulting in self-organized structures. An intense blue PL emission at room temperature was observed in these micro-octahedrons when they were excited with a 350 nm wavelength. The origin of the PL emissions as well as its intensity variations are explained by means of a model based on both distorted [MoO(4)] and [PbO(8)] clusters into the lattice.CAPESCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPqFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPES

Removal study of the hormone17 alpha‐ethynylestradiol and methylene blue dye from water using TiO2, Mn2O3 and TiO2/Mn2O3 thin flms

The disposal of pollutants in the surface, underground, and public water supply is an important problem, which is why it is necessary to study more efcient photocatalysts in the treatment of wastewater. In this context, thin flms of TiO2, Mn2O3 and TiO2/Mn2O3 were prepared by the hydrolysis of precursors in the presence of citric acid and ethylene glycol, to evaluate the photocatalytic performance in the degradation of methylene blue dye and the hormone 17a-ethinylestradiol (EE2), the measurements were repeated 10 times in a period of 300 min. Thin flms were deposited by spin-coating on Si (100) substrates and calcined at 500 °C and 600 °C for 2 h. Nanocomposites were characterized by X-ray difraction, atomic force microscopy, scanning electron microscopy, UV–visible spectroscopy, photocatalytic activity, and photoluminescence. X-ray difraction results revealed that no other phase was formed besides anatase and bixbite, indicating that there was no chemical interaction between the TiO2 and Mn2O3 layers. The results show the degradation values of methylene blue in approximately 57% and for the 17a-ethinylestradiol a degradation around 82%, showing that the studied photocatalysts are promising, mainly for the degradation of 17a-ethinylestradio

Influence of the number of layers and crystallization temperature on the photocatalytic activity of Tio2 / In2 o3 thin films

The TiO2/In2 O3 thin films were prepared by the spin coating method, varying their number of layers (4, 8 and 16 layers). The Method of polymerization of complex (CPM) was used to synthesize the precursor resins in order to produce thin films. The TiO2/In2 O3 films were heat–treated at 300°C, 500°C and 700°C and characterized by X–ray diffraction, scanning electron microscopy (FEG–SEM), atomic force microscopy (AFM), UV–vis spectrophotometer and photoluminescence (PL). It was found that the band gap energy of the as–prepared TiO2/In2 O3 composite thin films decrease as temperature increases. According to the UV–vis diffuse reflectance spectra, the TiO2/In2 O3 composite shows good visible–light absorption ability. The photoluminescent properties of the films were studied at room temperature using a wavelength of 350nm excitation. High photoluminescent intensity was observed for the films treated at 300°C heat, studied in different films. The photocatalytic activity of the composite TiO2/In2 O3 was evaluated by the hotodecomposition of methylene blue dye in aqueous solution and showed that all the composite samples presented excellent photocatalytic performance even when recycled. This study shows that the coupling of TiO2 with In2O3 is an effective way to increase the TiO2 absorption in the visible region for catalytic applications and that the temperature has a greater influence on the results than the number of layer