TiO2/PDMS nanocomposites for use on self-cleaning surfaces

AbstractIn this study, polydimethylsiloxane (PDMS)/TiO2 nanocomposite was processed by the spray method. TiO2 nanoparticles were synthesized by microwave-assisted hydrothermal method. Varying the proportion of nanoparticles in 0%, 0.5% and 1% by weight, commercial TiO2 (P25) was used for comparison purposes. The photocatalytic activity of nanocomposites impregnated with methylene blue was assessed by means of UV–visible spectroscopy. Changes in contact angle were analyzed before and after UV degradation tests. The effect of ultraviolet radiation on the chemical structure of the PDMS matrix was evaluated by Fourier transform infrared spectroscopy (FTIR). The results indicated that the addition of TiO2 nanoparticles in PDMS provides good photocatalytic properties in the decomposition of methylene blue, which is an important characteristic for the development of coatings for self-cleaning. For comparison purposes, commercial P25 was also used to investigate the photocatalytic activity

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

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

Antibody-Mediated Neutralization of the Exotoxin Mycolactone, the Main Virulence Factor Produced by Mycobacterium ulcerans

Mycolactone, the macrolide exotoxin produced by Mycobacterium ulcerans, causes extensive tissue destruction by inducing apoptosis of host cells. In this study, we aimed at the production of antibodies that could neutralize the cytotoxic activities of mycolactone.; Using the B cell hybridoma technology, we generated a series of monoclonal antibodies with specificity for mycolactone from spleen cells of mice immunized with the protein conjugate of a truncated synthetic mycolactone derivative. L929 fibroblasts were used as a model system to investigate whether these antibodies can inhibit the biological effects of mycolactone. By measuring the metabolic activity of the fibroblasts, we found that anti-mycolactone mAbs can completely neutralize the cytotoxic activity of mycolactone.; The toxin neutralizing capacity of anti-mycolactone mAbs supports the concept of evaluating the macrolide toxin as vaccine target

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

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

First principle investigation of the exposed surfaces and morphology of β-ZnMoO4

Crystal shape is a critical determinant of the physical and chemical properties of crystalline materials; hence, it is the challenge of controlling the crystal morphology in a wide range of scientific and technological applications. The morphology is related to the geometry of their exposed surfaces, which can be described by their surface energies. The surface properties of β-ZnMoO4 have not yet been well explored, either experimentally or theoretically. Thus, the first-principle calculation at the density functional theory level was carried out for different low-index surfaces of β-ZnMoO4, specifically (001), (010), (110), (011), (101), and (111), and the surface energy values (Esurf) were reported. The surface stability was found to be controlled by the undercoordinated [MoOn…yVxO] and [ZnOn…yVxO] (n = 4 and 5; y = 1 and 2) clusters, i.e., their local coordination of Mo and Zn cations at the exposed surfaces, respectively, with the (111) surface being the most stable. A complete map of investigated β-ZnMoO4 morphologies was obtained using the Wulff construction and changing the values of the calculated energy surfaces. The final geometries from this map were compared with field emission-scanning electron microscopy images showing excellent agreement, prevising rectangular and hexagonal plates. Our findings will promote the use of facet engineering and might provide strategies to produce β-ZnMoO4-based materials for achieving morphology-dependent technological applications

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

Optical characterization of europium-doped indium hydroxide nanocubes obtained by Microwave-Assisted Hydrothermal method

Crystalline europium-doped indium hydroxide (In(OH)3:Eu) nanostructures were prepared by rapid and efficient Microwave-Assisted Hydrothermal (MAH) method. Nanostructures were obtained at low temperature. FE-SEM images confirm that these samples are composed of 3D nanostructures. XRD, optical diffuse reflectance and photoluminescence (PL) measurements were used to characterize the products. Emission spectra of europium-doped indium hydroxide (IH:xEu) samples under excitation (350.7 nm) presented broad band emission regarding the indium hydroxide (IH) matrix and 5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3 and 5D0 → 7F4 europium transitions at 582, 596, 618, 653 and 701 nm, respectively. Relative intensities of Eu3+ emissions increased as the concentration of this ion increased from 0, 1, 2, 4 and 8 mol %, of Eu3+, but the luminescence is drastically quenched for the IH matrix.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Universidade Federal do Rio Grande do Norte Centro de Tecnologia Departamento de Engenharia de MateriaisUniversidade Federal de São Paulo (UNIFESP)Universidade de São Paulo Instituto de Física de São CarlosUniversidade Estadual Paulista Instituto de Química Laboratório Interdisciplinar de Eletroquímica e CerâmicaUNIFESPFAPESP: 2013/07296-2SciEL