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Strategies for improving the performance of solar cells have been the focus of several researchers. The evaluation of the effects resulting from the variation in assembly parameters was the approach adopted in this study. Three construction parameters of a dye-sensitized solar cell were varied, and an experimental factorial design method was used to analyze these modifications simultaneously, verifying the photovoltaic results. The modifications were conducted for the semiconductor area (Factor A), substrate area (Factor B), and semiconductor composition (Nb2O5 with/without TiO2) (Factor C). The curves of the current density versus voltage (J–V) were analyzed to evaluate the effects of the variations of each parameter and their combined interactions. The change related to the semiconductor composition (Factor C) was statistically significant, being relevant to improve the photovoltaic parameters evaluated. The current density, on average, increased 93.12% in the cells with the change in the semiconductor composition. Similarly, the average increase in open-circuit voltage in the respective cells was 28.71%. The reason that Factor C was predominant was attributed to the uniformity of the semiconductor layer observed by results of scanning electron microscopy (SEM).

Niobium pentoxide (Nb2O5) was synthesized by the microwave-assisted hydrothermal method using two different niobium precursors: niobium ammoniacal oxalate (P1) and niobium chloride (P2). The XRD result confirms the presence of Nb2O5 with low crystallinity for both precursor samples. The SEM images show differences between the material morphologies but with the same aggregation particle characteristics. Photocatalytic degradation of the rhodamine B (RhB) dye was performed using both samples of Nb2O5 as a photocatalyst under UVC illumination using a 24 factorial design experimental method. The studied variables were the type of precursor (P1 and P2), the RhB concentration (1 × 10−5 and 3 × 10−5 M), the Nb2O5 photocatalyst dosage (25 and 50 mg), and the time of the photocatalysis analysis (30 and 60 min), verifying the influence on the RhB dye removal efficiency. The factorial design showed that all variables had a significant effect on the process, but the variables with the most influence were RhB concentration and photocatalysis time. For both precursors, the samples that showed greater removal efficiency were those under conditions 1 × 10−5 M, 50 mg, and 60 min, obtaining 92.87% and 98.99%, respectively. The high rate of RhB removal suggests that the Nb2O5 obtained by microwave-assisted hydrothermal synthesis has the potential to be used in photocatalytic processes to remove organic pollutants from effluents.

In the present work, we present a method of obtaining sodium niobate nanowires, in less time, using the microwave-assisted hydrothermal method followed by a calcination step.The photocatalytic activity of the samples was investigated through the photodegradation of Rhodamine B. The Perovskite obtained has an orthorhombic structure, space group Pbma and it was demonstrated that the heat treatment applied increased the crystallinity and band gap of the samples, reflecting in a better photocatalytic performance, resulting in high degradation rate of RhB, reaching a percentage of degradation ~ 99.21%.

The performance of niobium pentoxide (Nb2O5) as photoanodes in dye-sensitized solar cells (DSSCs) and as catalysts in the photocatalytic degradation of Rhodamine B (RhB) was investigated. Four samples of Nb2O5 (Nb2O5_SG, Nb2O5_CR, Nb2O5_PP, and Nb2O5_MA) were synthesized by four different methods, respectively, entailing the sol-gel, combustion, polymeric precursors, and a microwave-assisted hydrothermal reaction. In all these samples, the orthorhombic phase of Nb2O5 was obtained, which resulted in different shapes and assemblies, which is very relevant because the surface area, shape, and size distribution of the nanoparticles significantly contribute to the optical process. The bandgap remained constant at 3.0 eV for all the samples, even for the sample prepared by the combustion method. An additional phase, which is related to local distortions, was revealed by Raman spectroscopy within the vibration range of 688–260 cm−1. DSSCs using photoanodes with smaller and more dispersed Nb2O5 particles showed better results than those with inhomogeneities. For comparison, DSSCs were assembled using two different counter electrodes, platinum and graphite. The DSSC with platinum showed better photovoltaic results, mainly with photocurrents from 1.17 mA.cm−2 for Nb2O5_CR to 1.64 mA.cm−2 for Nb2O5_SG. The same trend was observed for the photocatalytic degradation of RhB, where the smaller and dispersed particles of Nb2O5_CR and Nb2O5_SG exhibited the best performance and, respectively, degraded approximately 75% and 61% of the RhB dye over 180 min. Therefore, the results of this study established a correlation between the synthesis methods and photonic behavior.

High electrocatalytic activity and conductivity are two unshakable objectives for the counter electrode used in dye-sensitized solar cells (DSSCs). Cobalt sulfide (CoS) has been deposited on the fluorine-doped tin oxide (FTO) substrate using the microwave-assisted chemical bath with very low thermal treatment, in the range of 100–120 °C. This deposition method improves the electrocatalytic properties of Pt-free materials and offers to reduce numerous film-making steps by direct synthesis-deposition onto the FTO. The counter electrodes were evaluated in symmetrical dummy cells and tested in solar cells. Results achieved with low-temperature exhibit a power conversion efficiency of 8.39% against 7.88% of the commercial Pt, which demonstrates that it can be used as a Pt-free counter electrode for high-performance DSSCs.

In this work, we explored the properties of Barium Titanate (BaTiO3) for application in photoanodes. Unlike other works that used heterojunction, we developed a solar cell by combining Titanium Dioxide (TiO2) and BaTiO3 without sensitization. The increase of Voc in the cell with heterojunction may be explained with TiO2 acted as a blocking layer and as a charge acceptor from BaTiO3, improving the photovoltaic response of the cells, even without dye. For comparison, we developed a Dye-Sensitized Solar Cell (DSSC) by using Barium Titanate (BaTiO3) photoanodes with dye (N-3). The compounds used in the cells has been synthesized with: the microwave-assisted hydrothermal method for BaTiO3 and the Pechini method for TiO2. We use the techniques spin coating for TiO2 layer deposition and doctor blade for BaTiO3 layer. Typical features of a tetragonal structure were revealed by Raman and XAS spectroscopy, suggesting a non-centrosymmetric Ti atom in the TiO₆ octahedron. This result may generate localized states into the band gap. UV–vis absorption and photoluminescence indicate low recombination of the electron-hole pair. That may contribute to the photovoltaic behavior if associated with heterojunctions.

In the present work, a relationship between the pencil-like growth of wurtzite zinc oxide (ZnO) with specific surfaces to support zinc sulfide (ZnS) deposition and its photovoltaic behavior is proposed. The wurtzite ZnO and zinc blende ZnS were explored in the context of the ZnO/ZnS interfaces obtained from zinc acetate (ZA) and zinc nitrate (ZN). A more effective ZnS coating was obtained on polar (101) ZnO surfaces, using ZN precursors, since the growth of planes is electronically and sterically favored because of the accentuated charge polarization. The hexagonal rod shaped ZnO with pencil-like end was examined by scanning electron microscopy, its surface stability was confirmed by density functional theory, and the shape change diagram obtained from the classic Wulff construction demonstrated that the (100) and (101) ZnO planes have increased energetic stability. From photovoltaic measurements we observed improvements in the ZnO/ZnS (ZN) (i) photocurrent density, from 0.88 to 1.03 mA cm−2, corresponding to an increment of 17%; (ii) open-circuit photovoltage, from 0.62 to 0.67 V, equivalent to an increment of 8%; and (iii) photoconversion efficiency, from 0.40 to 0.42%, representing an improvement of 4.7% in the case of the predominant (101) plane growth. On the other hand all ZnO/ZnS systems have the same main absorption bandgap of 3.1 eV. Significantly, this data set demonstrates that better photovoltaic behavior can be achieved in ZnO/ZnS (ZN) through covering and surface growth control, resulting in adequate band alignment.

Rapid pyrolysis at high temperatures is a promising process to obtain black SiO2 nanoparticles, which can be applied, for their characteristic color, in different areas, such as cosmetics, graphite, paints, ceramics and polymer industry (thermoplastics, rubber and tires). In this work, the physico-chemical and toxicological characteristics of rice husk (RH) and rice husk ash (RHA) pyrolysis were investigated. The main characteristic of the method is the production of black nanoparticles in a short time of synthesis and with a high thermal stability. The ash and organic matter contents obtained were 15.7 and 84.3% respectively, showing that the method is efficient to obtain black particles and with a high yield. The chemical elements determination of the black nanoparticles was confirmed with predominance of Si and K. Optical properties were extremely important to demonstrate that the black pigmentation was maintained, as low reflectance indices were detected for all the samples, even for the sample obtained at the temperature of 1200 °C. The pyrolysis of RHA was characterized by thermogravimetric analysis and 38% loss of carbon mass was identified. The X-ray diffraction (XRD) denoted a greater presence of amorphous SiO2, so that the SiO2 nanoparticles are a mixture of amorphous and crystalline particles. The transmission electron microscopy (TEM) results show the formation of nanoparticles having a particle size of about 10–20 nm through scanning electron microscopy (SEM) images, the cellular porous structure, known as the silica skeleton, was noted, and BET surface area of about 114 m2/g. In the biocompatibility test, it was possible to observe that the RHA presented values below 70%, showing that there was no cell growth and, therefore, the product did not showed toxicity; for this reason, the product does not need to undergo purification steps when used in more noble areas such as cosmetics. Thus, it was concluded that the pyrolysis method was efficient and that, even after a second heat treatment at 1200 °C, the SiO2 nanoparticles remained black and not presented the typical white color reported in several studies in the literature.

Zinc titanates are compounds that have shown great application versatility, including in the field of semiconductors. Solid state reactions, the polymeric precursor method and the hydrothermal method are the most mentioned synthesis of these compounds in the literature. In the present work, we use microwave assisted hydrothermal method (MAH) to synthesize zinc titanate and evaluate its potential for solar cell applications through structural and optical characterization techniques. The synthesized samples were also subjected to a variable temperature heat treatment in the range of 500 °C–800 °C. The analysis showed that the crystallization of the material starts at 500 °C and that samples submitted to temperatures of 600 °C–800 °C showed the formation of two phases of zinc titanates, being a cubic phase of ZnTiO3, considered rare in the literature, predominant up to a temperature of 800 °C. The optical characterization, based on the techniques of photoluminescence spectroscopy and UV-Visible spectroscopy, showed that the photoluminescent activity and the energy of the band gap increased with the increase of the temperature of the heat treatment, having the highest response in 700 °C, facts that can be linked to the predominant formation of the cubic phase of ZnTiO3 and simultaneous of the cubic and rhombohedral phases of ZnTiO3 at 700 and 800 °C. Finally, we highlight as the most important results, the fact that it was possible to obtain these titanates at a temperature lower than that reported in the literature, and that the heat-treated sample at 500 °C is the one with the lowest energy expenditure to be synthesized and the one with the greatest potential for application in dye-sensitized solar cells (DSSC's)., Zinc titanates; Spinel; Microwave assisted hydrothermal

Titanium dioxide–cellulose nanocomposites were nucleated and grown by decomposition of titanium isopropoxide in ethanol media together with wood cellulose fibers into the microwave-assisted solvothermal (MAS) system; the low temperature and fast formation time of the nanocomposites stand out in this methodology. The MAS method was successfully applied in the synthesis of TiO2 with anatase structure in wood cellulose fibers to produce TiO2–cellulose nanocomposites based on hydrolysis, condensation and subsequent polymerization of titanium nanoparticles on cellulose fibers. Through scanning electron microscope it was possible to confirm nanocomposite formation by impregnation/nucleation/growth of titanium dioxide (TiO2) nanoparticles on the fiber walls. The nanocomposites X-ray powder diffraction showed peaks of crystalline titanium dioxide anatase phase associated to additional cellulose diffraction remarks, as well as the absence of the CaCO3 phase, proving the nanocomposite design concept. This means that the inclusion of TiO2 nanoparticles on fibers does not alter the crystalline structure of cellulose, also confirmed by Fourier-transform mid-infrared spectroscopy. Based on the thermogravimetric analysis, nanocomposites are thermally more stable than pure cellulose, reaching a 19% difference of mass loss reduction.

This work demonstrates the application of crystalline Nb2O5 powders with different phases as photocatalysts in the degradation of Rhodamine B (RhB). The crystalline structure and the corresponding surface area of Nb2O5 changed with an increase in the heat-treatment temperature, leading to different photocatalytic activities. Thus, for Nb2O5 with low crystallinity, the total degradation of RhB on pseudohexagonal Nb2O5 is 97%, whereas that on orthorhombic Nb2O5 is 57%. The degradation products of RhB were identified from the results of high-performance liquid chromatography, mass spectrometry, and total organic content analysis, and the possible photocatalytic degradation pathways are proposed.

The improvement on the development of porous ceramic materials has leaded to new technologies in thermal insulation, for example, composite materials for better performance of pressure vessels in rocket engines. Within this context, the present work aims to evaluate the ability of a refractory ceramic base alumina/zirconia through the processes of co-precipitation and replica method in an organic fiber template. The green body was burnt-out and sintered at 1200-1600°C to obtain the continuous porous ceramic fibers. In the FEG-SEM analysis, an interconnected porous structure with small grains was observed. The crystalline phases were determined by X-ray diffraction and compared to micro-Raman results regarding the crystalline structure confirms that there present in the material zirconia is composed of more than one phase. Porosity was calculated through a mercury porosimeter as 77.9%, and the Laser Flash method gave a thermal conductivity value of 1.61 K W.m−1.K−1 for the Al2O3-ZrO2 fibers.

A shift of the photoluminescence (PL) emission was observed in ZnS prepared by microwave assisted solvothermal method with the increase of the time in microwave. In this work we reported a study of the optical behavior linking with the structural disorder according to XRD and FEG-TEM results. The reduction of intrinsic defects in the lattice is responsible for the decrease of electronic levels in the band gap changing the PL profile. This effect was confirmed by electronic structure calculations.

Wurtzite-structured ZnS nanostructures have been synthesized by means of a microwave-solvothermal method at 140°C using three precursors (chloride, nitrate and acetate). Different techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements have been employed to characterize this material. The structure, surface morphology, chemical composition and optical properties were investigated as function of precursor. In order to complement experimental results, first principles calculations at DFT level were carried out in order to obtain the relative stability of the proposed intermediates along the formation mechanism.

In this research report, a sintering process of porous ceramic materials based on Al 2 O 3 was employed using a method where a cation precursor solution is embedded in an organic fibrous cotton matrix. For porous green bodies, the precursor solution and cotton were annealed at temperatures in the range of 100–1600 °C using scanning electron microscopy (SEM) and thermogravimetric (TG) analysis to obtain a porous body formation and disposal process containing organic fibers and precursor solution. In a structure consisting of open pores and interconnected nanometric grains, despite the low porosity of around 40% (calculated geometrically), nitrogen physisorption determined a specific surface area of 14 m 2 /g, which shows much sintering of porous bodies. Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analytical methods revealed a predominant amount of α-Al 2 O 3 in the sintered samples. Thermal properties of the sintered Al 2 O 3 fibers were obtained by using the Laser Flash which resulted in the lower thermal conductivity obtained by α-Al 2 O 3 and therefore improved its potential use as an insulating material.

Submitted by Fabiano Malheiro (fabianomalheiro22@hotmail.com) on 2013-11-11T15:25:39Z No. of bitstreams: 1 Evandro Piva_22.pdf: 659899 bytes, checksum: 956a06b6c50ade0b7b48d2692e50a3db (MD5) Approved for entry into archive by Fabiano Malheiro(fabianomalheiro22@hotmail.com) on 2013-11-11T15:26:04Z (GMT) No. of bitstreams: 1 Evandro Piva_22.pdf: 659899 bytes, checksum: 956a06b6c50ade0b7b48d2692e50a3db (MD5) Made available in DSpace on 2013-11-11T15:26:04Z (GMT). No. of bitstreams: 1 Evandro Piva_22.pdf: 659899 bytes, checksum: 956a06b6c50ade0b7b48d2692e50a3db (MD5) Previous issue date: 2012-09 The objective of this study was to evaluate the effect of functionalizing a dental adhesive resin with YbF3/SiO2 fillers for use as radiopacifiers. Particles of YbF3/SiO2 were obtained with the high-energy mechanical milling method and characterized by both physical and chemical methods. After characterization, the particles were sieved and silanized prior to being incorporated into an adhesive resin. The stability of the particle suspension was then evaluated. After light activation, the radiopacity, degree of conversion, flexural strength and elastic modulus were determined. The dental adhesive resins with 10 and 15 wt% of filler provided satisfactory radiopacity, while flexural strength and elastic modulus were not affected. The degree of conversion was statistically lower than that of the control (p

An intense red-green photoluminescence (PL) emission was observed, at room temperature, in a CdS@ZnS core–shell system. The PL intensity emission of CdS@ZnS core–shell was strongly superior from that observed in individual CdS and ZnS nanoparticles. In this sense, we reported a comprehensive experimental and theoretical study of the optical behavior of CdS and ZnS nanoparticles (NPs), and CdS@ZnS core–shell system in the light the structural order–disorder conception. We also propose a model were the core and shell interface leads to favorable condition that triggers PL emission in CdS@ZnS core–shell.

This research investigated the synthesis of the Al2O3/ZrO2 core-shell system using a polymeric precursor method. The interfacial features emission show the possibility for control of the luminescence behaviour. X-ray diffraction (XRD) patterns are well defined for α-Al2O3 and for γ-Al2O3, core structures and a zirconia shell phase for high concentrations. Photoluminescence (PL) spectra (λexc = 350.7 nm) reveal that the effect of the zirconia coating on the alumina was more effective for α-Al2O3 than for γ-Al2O3 which may be related to the zirconia coating process on alumina. The image transmission electron microscopy (TEM) shows an amorphous region of 10 nm which is attributed to a ZrO2 shell layer.

O desenvolvimento de nanocompósitos para recobrimento de superfícies de partículas tem sido alvo de inúmeras pesquisas, devido ao fato de que novas e incomuns propriedades físicas e químicas, ausentes em tamanho macro e microscópico, são observadas nesses novos nanomateriais. Este trabalho apresenta o procedimento de preparação de nanocompósitos à base de nanoargila de haloisita nanorecoberta com TiO2 e Ni, usando o método dos precursores poliméricos. Através dessa síntese foram obtidas partículas de tamanho médio variando entre 7 e 35 nm. Os produtos obtidos foram caracterizados por fisissorção de N2 a 77 K, difração de raios X, microscopia eletrônica de varredura e microscopia eletrônica de transmissão de alta ressolução. Os resultados mostram que a obtenção do nanorecobrimento é uma estratégia altamente promissora para a fabricação de novos compósitos, baseados em TiO2/Ni na superfície da argila, com aplicações tecnológicas.

The gadolinium-doped ceria nanorods (Gd0.2Ce0.8O2−x) were synthesized by hydrothermal treatment. It was shown that the use of microwave heating during hydrothermal treatment decreases the treatment time required to obtain gadolinium-doped ceria nanorods and that oriented attachment is the dominant mechanism responsible for anisotropic growth. It was clear that Gd0.2Ce0.8O2−x nanorods were more catalytically active than commercial CeO2 in the ethanol reforming reaction.

article i nfo Two different routes to obtain SnO2 nanoparticles, undoped and doped with rare earth metals (Eu or Pr), are described herein. The first route was based on the polymeric precursor method that led to the obtainment of SnO2 nanoparticles dispersed in amorphous silica. The second route was simply the impregnation with SnCl4 aqueous solution of SiO2-CaO glass microparticles functionalized with hydroxyl ( � OH) groups. The materials were characterized by N2 physisorption, XRD, EDS and TEM analyses. We also present the results of catalytic experiments involving the nanocrystalline composites in ethanol steam reforming. The catalytic properties of the undoped composites with SnO2 supported on SiO2-CaO glass differ from their doped analogues, however, they were both selective towards ethylene formation, in contrast to the doped composite obtained by the polymeric precursor method.

For the first time, the calcium sulfide (CaS) photoluminescent (PL) emission blue shift synthesized by the microwave-assisted solvothermal (MAS) method was examined to understand its key role in the PL activity. PL emission in the visible region showed a blue shift with synthesis time variations. In addition, we also investigated the electronic structure using first-principles calculations based on density functional theory (DFT) which was applied to periodic models at the B3LYP level. Two models were selected to simulate the effects of structural deformation on the electronic structure: (1) the ordered model (o-CaS) and (2) the disordered model (d-CaS). This PL emission shift is linked to distortions and defects which generate modifications in the electronic states and facilitate the possibility of numerous decay transactions to the valence band (VB).

In this article, we report the development of an efficient and rapid microwave assisted solvothermal (MAS) method to prepare wurtzite ZnS nanoparticles at 413 K using different precursors. The materials obtained were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (MET) ultraviolet–visible (UV–vis) and photoluminescence (PL) measurements. The structure, surface chemical composition and optical properties were investigated as a function of the precursor. In addition, effects as well as merits of microwave heating on the processing and characteristics of ZnS nanoparticles obtained are reported. The possible formation mechanism and optical properties of these nanoparticles were also reported.

Carbon nanocomposites have received more attention in the last years in view of their special properties such as low density, high specific surface area, and thermal and mechanical stability. Taking into account the importance of these materials, many studies aimed at improving the synthesis process have been conducted. However, the presence of impurities could affect significantly the properties of these materials, and the characterisation of these compounds is an important challenge to assure the quality of the new carbon nanocomposites. Thus, in this work are presented the characteristics of carbon nanocomposites, the improvements and developments in the synthesis process, as well as the most used characterisation techniques of these compounds.

A novel and simple method to prepare nickel-based catalysts for ethanol steam reforming is proposed. The present method was developed using castor oil as a precursor. The results clarify that the nickel–carbon (Ni/C) catalyst has a high activity for ethanol steam reforming. It was observed that the catalytic behavior could be modified according to the experimental conditions employed. Moreover, it is interesting to note that the increase in the catalytic activity of the Ni/C nanocomposite over time, at 500 and 600 °C of reaction temperature, may be associated with the formation of filamentous carbon. The preliminary results indicate that the novel methodology used, led to the obtainment of materials with important properties that can be extended to applications in different catalytic process.

Herein, we report a theoretical and experimental study on the photocatalytic activity of CeO2 ZnS, and ZnS decorated CeO2 nanoparticles prepared by a microwave-assisted solvothermal method. Theoretical models were established to analyze electron transitions primarily at the interface between CeO2 and ZnS. As observed, the particle morphology strongly influenced the photocatalytic degradation of organic dye Rhodamine B. A model was proposed to rationalize the photocatalytic behavior of the prepared decorated systems taking into account different extrinsic and intrinsic defect distributions, including order-disorder effects at interfacial and intra-facial regions, and vacancy concentration.

The photoluminescence (PL) emission from zinc sulfide (ZnS) synthesized by the microwave-assisted solvothermal method in the presence/absence of a capping agent was examined to understand the key role of its PL activity. In addition, we also investigated the electronic structure using a first-principle calculation based on density functional theory (DFT) applied to periodic models at B·LYP level. Two models were selected to simulate the effects of structural deformation on the electronic structure; the ordered o-ZnS model and the disordered d-ZnS model, dislocating the Zn atom, 0.1 A, in the z-direction. The PLemission in the visible region showed different peak positions and intensities in capped and uncapped ZnS. The PL emission was linked to distinct distortions in lattices and the emission of two colors, green in the capped and blue in the uncapped, was also examined in the light of favorable structural and electronic conditions. The computational simulations indicate that the electronic behavior can ...