Navegando por Autor "Garcia, Laurênia Martins Pereira"

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Citrate–hydrothermal synthesis, structure and electrochemical performance of La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes for IT-SOFCs
(Elsevier, 2013) Garcia, Laurênia Martins Pereira; Macedo, Daniel Araújo de; Souza, Graziele L.; Motta, Fabiana Villela da; Paskocimas, Carlos Alberto; Nascimento, Rubens Maribondo do
La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) powders were synthesized by a combination of citrate and hydrothermal methods. The thermal decomposition behavior of the as-prepared powder was carried out by simultaneous thermogravimetry–differential thermal analysis. The calcined powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and particle size distribution (PSD). Screen-printed LSCF/CGO/LSCF symmetrical cells were sintered between 1150 and 1200 °C and studied by impedance spectroscopy in order to assess the cathode kinetics for the oxygen reduction reaction. Rietveld refinement of XRD data showed the formation of a single perovskite LSCF phase with crystallite size of 53 nm at 900 °C. The best area specific resistance (ASR) value, measured in static air, was found to be 0.34 Ω cm2 at 750 °C, demonstrating that the novel citrate–hydrothermal method is an effective way to prepare cathode materials for SOFC. Cathode performance can be further enhanced by additional surface modification through impregnation with Pr-containing solution, reaching 0.17 Ω cm2 at 750 °C. Furthermore, the activation energy of the PrOx-impregnated cathode is 83.4 kJ/mol, i.e., much lower than 123.8 kJ/mol, the best value determined for PrOx-free cathodes
Effect of temperature on the photocatalytic properties of TiO2 -CeO2 multilayer thin films obtained by spin coating method
(ABCERAM, 2020) Nunes, T. B. O.; Andrade Neto, Nivaldo Freire de; Garcia, Laurênia Martins Pereira; Nascimento, Rubens Maribondo do; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
TiO2-CeO2 multilayer thin films were deposited by the spin coating method and calcined at 500 and 700 °C. Thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and diffuse reflectance spectroscopy. Photocatalytic properties were estimated by varying the concentration of the methylene blue dye (MB) when illuminated by UV radiation. The XRD patterns showed that the temperatures of 500 and 700 °C were effective to obtain TiO2 and CeO2 phases. The difference in the homogeneity of TiO2 and CeO2 films was evident in the AFM images, where the films showed an average roughness of 2.0 and 5.3 nm, respectively. The CeO2 -TiO2 thin film obtained at 700 °C showed the best photocatalytic activity, reducing the concentration of MB by approximately 80%, while the CeO2 and TiO2 films obtained at 700°C reduced only 20% and 29%, respectively. The reuse test showed that the thin films maintained their photocatalytic activity after 4 cycles, and there was no need for thermal treatment, indicating that it is an immobilized photocatalyst with high efficiency in the degradation of organic dyes
Effect of the Eu3+ (x = 0, 1, 2 and 3 mol%) doped Zn2−xTiO4 and Zn2Ti1−xO4 obtained by complex polymerization method: photoluminescent and photocatalytic properties
(Springer, 2019-11-08) Paskocimas, Carlos Alberto; Nascimento, G. G.; Andrade Neto, Nivaldo Freire de; Garcia, Laurênia Martins Pereira; Li, Maximo Siu; Silva, Elson Longo da; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In this work, Zn2EuxTi1−xO4 and Zn2−xEuxTiO4 (x=0, 1, 2 and 3 mol%) powders were synthesized by complex polymerization method (CPM) and calcined at 1000 °C for 4 h. The powders were characterized by X-ray difraction (XRD), scanning electron microscopy (SEM), UV–Vis spectroscopy in the visible region and photoluminescence properties (PL). The photocatalytic properties were estimated by degradation of methylene blue (MB) dye when irradiated by UV lamps. X-ray difraction results demonstrated the existence of Zn2TiO4 as primary phase and ZnO with secondary phase. According to difractograms, the crystallite size varied between 49 and 67 nm. The Eu3+ ions introduction provides increased absorption in visible region, but the band-gap remains practically constant. In samples were observed an increased in photocatalysis with the increase in europium concentration, while in the Zn2EuxTi1−xO4 samples, photocatalysis was reduced to europium concentrations greater than 1%. Eu3+ doped Zn2TiO4 provided a photoluminescent intensity increasing. CIE chromaticity coordinates confrm emission in the red region of the phosphor
Effects of MnO2/In2O3 thin films on photocatalytic degradation 17 alpha-ethynylestradiol and methylene blue in water
(Springer, 2018-05-23) Ferreira, T. L. B.; Garcia, Laurênia Martins Pereira; Gurgel, G. H. M.; Nascimento, Rubens Maribondo do; Godinho Junior, Mario; Rodrigues, Murillo Henrique de Matos; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In recent years, there has been a growing concern about some substances in the aquatic environment such as methylene blue dye (MB) and 17α-ethynylestradiol (EE2) hormone, mainly from waste textile and pharmaceutical industries, respectively. This waste, which is not effectively treated, generates large amounts of contaminated effluents. Textile industries, which use dyes mainly in their dyeing and finishing processes, generate a lot of effluent contamination by dyes. The 17α-ethynylestradiol hormone which is used in different contraceptive pills and in hormone replacement therapy, is the main substance found in the aquatic environment because of its high resistance to biodegradation. It is known that conventional water treatment processes, which involve the steps of coagulation, flocculation and sedimentation among others, have been reported to be ineffective in the removal of dyes and hormones. The heterogeneous photocatalysis has attracted great interest from many research groups around the world due to its potential application as a pollutant degradation method. For this purpose, the present work evaluated the performance of MnO2/In2O3 thin films in the degradation process of the blue methylene and 17α-ethynylestradiol in aqueous solutions. The degradation processes were monitored by UV–Vis spectroscopy and HPLC chromatography. From these analyzes, the concentration of the solutions was evaluated and it was possible to infer that the MnO2/ In2O3 thin films significantly promoted a degradation of 89% of 17α-ethynylestradiol, however, the degradation of the methylene blue was not efficient
Increased degradation capacity of methylene blue dye using Mg-doped ZnO nanoparticles decorated by Ag0 nanoparticles
(Springer, 2019-02-23) Paskocimas, Carlos Alberto; Paula, Celmo Hudson Reis de; Andrade Neto, Nivaldo Freire de; Garcia, Laurênia Martins Pereira; Nascimento, Rubens Maribondo do; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
Photocatalytic activity has been widely used for the treatment of organic effluents, mainly those generated by textile industries. Zinc oxide is widely investigated for this application due to its low cost, non-toxicity and high efficiency. In this work, the photocatalytic properties of ZnO:xMg (x = 1 mol.%, 2 mol.%, 4 mol.% and 8 mol.%) decorated with Ag0 were investigated against methylene blue dye (MB). Initially, the nanostructures of ZnO:xMg were produced by the microwave-assisted hydrothermal method, and the nanoparticles of Ag0 were deposited by ultraviolet (UV) photoreduction. The structural characteristics of the powders were determined by x-ray diffraction, the morphologies were investigated by field emission scanning electron microscopy (FE-SEM) and the optical absorbance of the photocatalysts was characterized by the diffuse reflectance spectra [UV–visible light (UV–Vis)]. The photocatalytic properties were estimated by degradation of MB, and the capacity for reuse of the powders was estimated by application in three consecutive cycles. Undoped ZnO powders reduced 84% of MB concentration, while the ZnO:8%Mg sample reduced 97% of it, indicating that doping with Mg2+ is efficient in increasing the degradation capacity of ZnO against MB degradation. The deposition of metallic silver nanoparticles on the ZnO surface considerably increases the photocatalytic efficiency, in which after 18 min, the 8%Mg sample completely degraded the MB. The reuse tests showed that the powders maintain their photocatalytic activity after three cycles and can be used for such application without generating secondary residues
Influence of doping with Sm3+ on photocatalytic reuse of ZnO thin films obtained by spin coating
(Rede Latino-Americana de Materiais, 2019-11) Paskocimas, Carlos Alberto; Andrade Neto, Nivaldo Freire de; Carvalho, Raquel Guilherme de; Garcia, Laurênia Martins Pereira; Nascimento, Rubens Maribondo; Silva, Elson Longo da; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
The difficulty in the powder reuse favors the study of materials in the form of thin films. ZnO based films have high photocatalytic potential. In this work, ZnO:xSm3+ (x = 0, 1, 2 and 4 %mol) thin films were prepared by spin coating method. The resins obtained to manufacture the thin films were prepared by complex polymerization method. The samples were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and spectroscopy UV-Vis. XRD patterns indicate that doping with 4%Sm forms Sm2O3 as the secondary phase. FE-SEM images of the cross section of thin films indicated a uniform thickness ranging from 354 to 367 nm between samples. The incorporation of Sm3+ ions in the ZnO lattice increases the Egap of the films. The photocatalytic performance of the films was tested with the photodegradation of methylene blue dye. Pure ZnO and ZnO:1%Sm3+ exhibited the best activity in the photodegradation. Thin films of pure ZnO exhibit the best photocatalytic results for the first cycle, but considerably reduce their efficiency with reuse. Sm3+ incorporation, without secondary phase formation, was efficient for the maintenance of the photocatalytic property after 3 cycles
Influence of reaction temperature, proportions of iron, cobalt and KOH on the CoFe2O4 synthesis by hydrothermal method assisted by microwave heating
(Springer, 2017-06-19) Paskocimas, Carlos Alberto; Conceição, Ozivam Lopes de Aquino; Garcia, Laurênia Martins Pereira; Lovisa, Laura Ximena; Torres, M. M.; Soares, J. M.; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
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 significant
Influence of the number of layers and crystallization temperature on the photocatalytic activity of Tio2 / In2 o3 thin films
(MedCrave Group, 2017-07-20) Paskocimas, Carlos Alberto; Garcia, Laurênia Martins Pereira; Gurgel, G. H. M.; Lovisa, Laura Ximena; Nascimento, Rubens Maribondo do; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
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 layers
Photocatalytic activity and photoluminescence properties of TiO2, In2O3, TiO2/In2O3 thin films multilayer
(Springer, 2018-01-20) Paskocimas, Carlos Alberto; Garcia, Laurênia Martins Pereira; Tavares, Mara Tatiane de Souza; Andrade Neto, Nivaldo Freire de; Nascimento, Rubens Maribondo do; Silva, Elson Longo da; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
This study evaluated the effect of crystallization temperature (300, 500 and 700 °C) on the photocatalytic and photoluminescent properties of the multilayer thin films of TiO2, In2O3 and TiO2/In2O3 which were prepared by the Complex Polymerization Method (CPM) and deposited on substrates of Si (100) by the spin coating method. The results of X-ray diffraction (XRD) revealed that there was no chemical interaction between the oxides (TiO2/In2O3) in crystalline films. The morphology was observed by atomic force microscopy (AFM) with a mean grain size of 15–35 nm. The result showed that the photocatalytic property is significantly increased by increasing the crystallization temperature. This is due to the agitation of the molecules which facilitates the transfer of charge between the electron and the catalyst bore. UV–vis light absorption spectra indicated that the addition of In2O3 in TiO2 films is an effective way of increasing the uptake of TiO2 in the visible region up to ~600 nm for photocatalytic applications, it was also possible to observe that these films could be easily Recycled for reuse. The samples were also characterized by photoluminescence, where it was possible to observe that the reduction of the PL intensity increased the photocatalytic activity of the thin films, with the increase of the crystallization temperature. In addition, the method used in this study is simple and economical compared to other methods
Photoluminescence and photocatalytic properties of Ag/AgCl synthesized by sonochemistry: statistical experimental design
(Springer, 2017-05-03) Paskocimas, Carlos Alberto; Andrade Neto, Nivaldo Freire de; Garcia, Laurênia Martins Pereira; Silva, Elson Longo da; Li, Maximo Siu; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
Silver chloride (AgCl) particles were produced by sonochemistry synthesis. The effect of the variables such as the time of synthesis, amount of surfactant and reagent in the photocatalytic property of AgCl have were all investigated. AgCl particles became well known for their high photocatalytic activity and their plasmonic properties because of the metallic silver on their surface. In this study, AgCl particles were prepared with sodium chloride (NaCl), polyvinylpyrrolidone and silver nitrate (AgNO3), using a full 23 factorial design and three central points, resulting in 11 experiments. The synthesis was carried out using ultrasonic tip at time intervals of 5, 20 and 35 min. It was used X-ray diffraction, scanning electron microscopy with field emission (SEM-FEG), UV–Vis degradation test and photoluminescence to characterize the particles. The experimental design not only used variables present in the photocatalytic ability of the particles, but also provided a mathematical model. The (ANOVA) analysis of variance was used to confirm this model. Thus the values predicted could be observed. It is provided a response surface that characterizes the optimization zone of the photocatalytic activity of the AgCl particles to better visualize the information about its effects
Study of obtaining thin films of CeO2 doped with 2 and 4 mol% of europium, terbium and thulium by spin coating: photocatalytic properties
(Scielo, 2019-12) Dias, Beatriz Pinheiro; Andrade Neto, Nivaldo Freire de; Garcia, Laurênia Martins Pereira; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In this study, thin films of Eu3+, Tb3+ and Tm3+ doped CeO2 in the proportions of 2 and 4 mol% were obtained by spin coating and calcined at 700 °C. The films were characterized by XRD, SEM, AFM and UV-vis techniques. The photocatalytic activity of the thin films was measured by the degradation of the methylene blue (MB) dye. The thin films were submitted to 4 photocatalytic cycles to analyze the capacity to be reused. XRD patterns showed no secondary phase formation, where all characteristic peaks were related to CeO2. SEM micrographs indicated that doping at 4 mol% promoted the reduction in the thickness and surface porosity of the thin films. AFM images indicated the increase in surface roughness with rare earths doping. Doping with Eu3+, Tb3+ and Tm3+ increased the degradation of the methylene blue dye by at least 15% for thin films doped at 4 mol%. The reuse tests indicated that the photocatalytic activity remained practically constant even with the application of four consecutive cycles
Tb3+/Pr3+ co-doped ZnMoO4 phosphor with tunable photoluminescence and energy transfer processes
(Elsevier, 2019-10) Paskocimas, Carlos Alberto; Delmonte, Maurício Roberto Bomio; Lovisa, Laura Ximena; Fernandes, Y.L.R.L.; Garcia, Laurênia Martins Pereira; Barros, Bráulio S.; Silva, Elson Longo da; Motta, Fabiana Villela da
ZnMoO4:Tb3+, Pr3+ particles in different Tb:Pr ratios (2:0, 1.5:0.5, 1:1, 0.5:1.5 and 0:2) were synthesized by the sonochemical method. These materials were characterized structurally, morphologically and optically by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Ultraviolet–visible absorption spectroscopy and Photoluminescence (PL). From studying the photoluminescent properties, the PL spectra presented 5 D4 → 7 Fj (j = 6, 5, 4 and 3) transitions bands of Tb3+, along with the transitions 3 P0 → 3 H5, 1 D2 → 3 H4, 3 P0 → 3 H6 and 3 P0 → 3 F3 of Pr3+. Time resolved photoluminescence was investigated and an energy transfer (n) mechanism between the matrix and the Tb3+ and Pr3+ ions is simultaneously proposed for better understanding the process efficiency. Parallel to this perspective, the photocatalytic behavior of ZnMoO4:Tb3+, Pr3+ was evaluated. The degradation of methylene blue dye was favored by the effect of increasing the Pr3+concentration. This work deals with the development of inorganic phosphor materials capable of converting UV radiation into light-emitting diode, which can be suitably combined to produce white light

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Navegando por Autor "Garcia, Laurênia Martins Pereira"