Navegando por Autor "Andrade Neto, Nivaldo Freire de"

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Characterization and photocatalytic application of Ce4+, Co2+, Mn2+ and Ni2+ doped Fe3O4 magnetic nanoparticles obtained by the co-precipitation method
(Elsevier, 2020-02-15) Andrade Neto, Nivaldo Freire de; Nascimento, Leulomar Enedino do; Corrêa, Marcio Assolin; Bohn, Felipe; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In this work, Ce4+, Co2+, Mn2+ and Ni2+ doped Fe3O4 nanoparticles were obtained by the co-precipitation method at 70 °C. The effects of the metal cations in the Fe3O4 lattice were investigated by X-ray diffraction (XRD), X-ray fluorescence (XRF), field emission scanning electron microscopy (SEM), nitrogen adsorption by the Brunauer-Emmett-Teller (BET) and UV–Visible (UV–Vis) spectroscopy. Magnetic properties were estimated by vibrating sample magnetometer (VSM) at room temperature and the electrical properties are studied through I–V curves. The photocatalytic properties were studied by the discoloration of the methylene blue (MB) dye. The reduction in the intensity of the diffraction peaks, followed by their enlargement, indicate that doping reduces the crystallite size of Fe3O4. Doping provided the reduction of the remaining magnetization, as the saturation magnetization increases, not being reached with 17 kOe. The electrical results indicate that only cobalt reduces the resistivity of Fe3O4, as manganese is the most increasing doping. Photocatalytic tests indicate that the defects generated by doping increase the photocatalytic activity of Fe3O4, being more expressive through doping with cerium
Characterization and photoluminescent, photocatalytic and antimicrobial properties of Boron-Doped TiO2 Nanoparticles Obtained by Microwave-Assisted Solvothermic Method
(Springer, 2019-02-27) Andrade Neto, Nivaldo Freire de; Zanatta, Paolo; Nascimento, Leulomar Enedino do; Nascimento, Rubens Maribondo do; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
Boron doped TiO2:xB (x = 0 mol.%, 1 mol.%, 2 mol.%, 4 mol.% and 8 mol.%) was quickly synthesized by a microwave-assisted solvothermic method at 140C for 10 min. The nanoparticles obtained were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy, Raman spectroscopy, photoluminescence, field emission scanning electron microscopy, electron microscopy and diffuse optical reflectance. The photocatalytic properties were estimated against methylene blue dye. The antimicrobial activity was measured by the disc diffusion technique against S. aureus and E. coli bacteria. The XRD patterns show that there was no formation of secondary phases and that all the peaks correspond to the anatase phase of TiO2. Rietveld’s refinement showed that the addition of B3+ in the TiO2 lattice promotes a reduction in the size of the crystallites and this reduction it effectively increases the degradation capacity of the methylene blue dye, which after 50 min the 8%B sample degraded completely, while the pure TiO2 sample reduced its concentration by 95%. Boron-doped TiO2 was effective when reused and after the third cycle the photocatalytic activity of the powders was maintained. In addition, the incorporation of 8%B in the TiO2 lattice resulted in an increase from 8.66 mm to 15.61 mm and 9.04 mm to 13.65 mm in the inhibition halos of the S. aureus and E. coli bacteria, respectively
Effect of temperature on the morphology and optical properties of Ag2WO4 obtained by the co-precipitation method: Photocatalytic activity
(Elsevier, 2019-08-15) Andrade Neto, Nivaldo Freire de; Oliveira, P. M.; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In this work, Ag2WO4 was obtained at different co-precipitation temperatures (10, 30, 50, 70 e 90 °C). X-ray diffraction (XRD), X-ray fluorescence (XRF), field emission electron microscopy (SEM), chemical mapping, X- ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller method (BET) and spectroscopy in the ultraviolet region (UV–Vis) were used to characterize the Ag2WO4 particles. The photocatalytic and adsorbent activities were estimated by contact with methylene blue (MB) and methyl orange (MO) dyes. The Ag2WO4 obtained by the co-precipitation method presented monoclinic crystalline phase with nanorod morphology. The increase of the temperature favored the elongation and reduction of the thickness of the nanorods, which increased the surface area of the powders, favoring the photocatalytic and adsorptive activities. The high adsorption of the cationic molecules (MB dye), accompanied by the low anionic adsorption (MO dye), indicate the anionic character of the Ag2WO4 nanorods. In addition, the AW90 sample showed the best result in the reuse tests, where it lost only 5% of its efficiency in the fourth cycle
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
Enhanced photocatalytic properties of Zinc-Doped CuO decorated with silver obtained by Microwave-Assisted Hydrothermal method: statistical factorial design
(Springer, 2019-05-16) Paskocimas, Carlos Alberto; Oliveira, P. M.; Andrade Neto, Nivaldo Freire de; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
Zinc-doped CuO powders were obtained by microwave-assisted hydrothermal processing at 140C for 30 min then decorated with silver by photodeposition and characterized by x-ray diffraction (XRD) analysis, field-scanning electron microscopy (SEM), and ultraviolet–visible (UV–Vis) spectroscopy region for Egap estimation. The photocatalytic activity of the powders was measured using methylene blue dye. To provide further information on the influence of the process variables on the photocatalytic activity, a 23 factorial design was carried out with three central points, using the amounts of zinc and silver and the stirring time under UV radiation as variables. The XRD patterns indicated ZnO precipitation when 8% Zn was added. SEM micrographs showed that the CuO had predominantly nanoplate morphology, with loss of the regular aspect of the ends and increased thickness on addition of zinc atoms. The photocatalytic activity results showed that addition of zinc and silver increased the photocatalytic activity of pure CuO. According to the factorial design, the stirring time of the CuO powder in contact with AgNO3 solution was the most significant variable affecting the photocatalytic properties, with longer time being detrimental due to an increase in the size of the silver nanoparticles
Estudo das atividades fotocatalítica e antimicrobiana de partículas de AgCl impregnadas com CuO obtidas via síntese sonoquímica
(2017-06-16) Andrade Neto, Nivaldo Freire de; Motta, Fabiana Villela da; ; ; Delmonte, Mauricio Roberto Bomio; ; Matsui, Katia Nicolau; ; Barros, Braulio Silva;
O crescimento das atividades industriais vem proporcionando um aumento na geração de efluentes, que fez com que órgãos governamentais relacionados ao meio ambiente propusessem a criação de marcos regulatórios para limitar a geração de efluentes. Os efluentes gerados pelas indústrias têxteis são de difícil degradação por métodos tradicionais de tratamento. Os processos oxidativos avançados (POAs) são uma alternativa eficiente para a degradação de poluentes orgânicos, como corantes (azul de metileno). Neste trabalho, partículas de cloreto de prata (AgCl) impregnadas com óxido de cobre (CuO) foram sintetizadas via método sonoquímico. Foram preparadas composições molares de 1:1 e 2:1 de AgCl/CuO, respectivamente. Tais composições passaram por três rotas de obtenção distintas. Para a caracterização das partículas, utilizou-se as técnicas de difração de raios-X (DRX), microscopia eletrônica de varredura com emissão de campo (MEV-FEG), e espectroscopia UV-visível (UV-vis). Para verificar a aplicabilidade do composto foram realizados nas amostras de AgCl/CuO testes fotocatalíticos para degradação do corante azul de metileno e a atividade antimicrobiana frente às bactérias Escherichia coli e Staphylococcus aureus. Os resultados da difração de raios-X confirmaram a formação de AgCl e CuO em todas as amostras, não havendo indícios de dopagem para nenhuma rota utilizada. Os resultados da atividade fotocatalítica indicam que o aumento da proporção molar de AgCl (1:1 para 2:1) acelera a degradação do azul de metileno em média em 25%.
Fast and continuous obtaining of Eu3+ doped CeO2 microspheres by ultrasonic spray pyrolysis: characterization and photocatalytic activity
(Springer, 2019-05-17) Paskocimas, Carlos Alberto; Santiago, Anderson de Azevedo Gomes; Andrade Neto, Nivaldo Freire de; Silva, Elson Longo da; Motta, Fabiana Villela da; Delmonte, Maurício Roberto Bomio
In this work, CeO2:xEu3+ (x=0, 0.01, 0.02, 0.04 and 0.08 mol%) microspheres were obtained by the fast and continuous ultrasonic spray pyrolysis method. Powders were characterized by X-ray difraction (XRD), X-ray fuorescence analysis (XRF), scanning electronic microscopy (FESEM), Raman spectra, UV–Visible spectroscopy (UV–Vis) and photocatalytic activity. All XRD patterns were indexed by the cubic structure of the fuorite type, without the presence of secondary phases, indicating success in the Eu3+ doping in the CeO2 structure. In addition, The XRF analysis confrmed the presence of Eu in the CeO2 powders. In the Raman spectra of the samples occurs the vibrational mode F2g, which is a characteristic band of materials with the fuorite type structure. Moreover, as the Eu3+ ion increased, it was noticed the appearance of additional bands referring to oxygen vacancies. FESEM showed that the CeO2:xEu3+ particles have a spherical morphology with homogeneous chemical composition and particle size between 73 and 1560 nm. It can be seen a slight increase of defects in their morphology as the Eu3+ ion increases. The band gap varies between 3.22 and 3.28 eV, being infuenced by defects in oxygen vacancies and the concentration of Ce3+ ion. The addition of Eu3+ generates the introduction of intermediary levels in the conduction band of CeO2, besides increasing the reactive species efects, favoring the photocatalysis of Rhodamine B dye
Fast and facile sonochemical synthesis of Mg‐ and Zn‐doped PbS nanospheres: optical properties and photocatalytic activity
(Springer, 2020-07-14) Andrade Neto, Nivaldo Freire de; Ramalho, Onécima Biatriz de Medeiros; Fantucci, Hugo; Santos, Rafael Mattos dos; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In this work, Mg2+- and Zn2+-doped PbS nanopowders were synthesized simply and quickly by a sonochemical method. The nanopowders were characterized by X-ray difraction, wavelength dispersive X-ray fuorescence, scanning electron microscopy, and ultraviolet–visible spectroscopy. The photocatalytic activity was estimated by methylene blue dye degradation. The sonochemical method produces crystalline PbS particles with cubic structure and free of secondary phases. The use of polyvinylpyrrolidone as a surfactant, and reaction medium at pH 13, results in the formation of nanospheres with diameter ranging from 31.4 to 114.5 nm. Doping favors the absorption of radiation in the visible region, and consequently, reduces the optical bandgap of the PbS. Photocatalytic assays show that magnesium and zinc codoping results in 80% reduction of methylene blue concentration after 180 min, while undoped PbS achieves only 42%. Tests with charge scavengers indicate that holes (h+) act as the main mechanism in the photocatalytic process
Increase of antimicrobial and photocatalytic properties of silver- doped PbS obtained by sonochemical method
(Springer, 2018-09-08) Paskocimas, Carlos Alberto; Andrade Neto, Nivaldo Freire de; Oliveira, Y. G.; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In this work, pure PbS powders doped with silver were obtained in the proportions of 1, 2, 4 and 8 mol% by sonochemical method. Powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV–Vis spectroscopy (UV–Vis) and EPR analysis. The photocatalytic properties were estimated by degradation of methylene blue dye. The antimicrobial properties were studied by the formation of inhibition halos against Escherichia coli and Staphylococcus aureus bacteria and Candida albicans yeast. XRD patterns show that PbS, with a cubic structure, was obtained without the formation of secondary phases. FE-SEM analysis indicates loss of the cubic aspect of PbS samples as the Ag+ concentration increases and particle size reduces. The defects generated by the substitution of Pb2+ by Ag+ increase the photocatalytic activity, where PbS and P8A samples reduced by 25% and 68%, respectively, the MB concentration and significantly increased the antimicrobial activity against E. coli and S. aureus bacteria and C. albicans yeast
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 pH on the morphology and photocatalytic activity of CuO obtained by the sonochemical method using different surfactants
(Elsevier, 2019-01-01) Paskocimas, Carlos Alberto; Andrade Neto, Nivaldo Freire de; Oliveira, P. M.; Nascimento, Rubens Maribondo do; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In this work, copper oxide II (CuO) was obtained using different surfactants (PVP, PEG and EDA), as well as without surfactant (WS), varying synthesis pH (8, 11 and 13). The powders were characterized by X-ray diffraction (XRD), field scanning electron microscopy (SEM), Brunauer-Emmett-Teller method (BET), UV-Visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), photoluminescent properties and their photocatalytic properties were measured against the methylene blue dye under UV radiation. XRD patterns showed that a pH increase from 8 to 13 favors CuO single phase formation, whereas Cu2(OH)3(NO3) secondary peaks appear at lower values. FTIR spectra confirmed the appearance of Cu2(OH)3(NO3) through the vibrations related to the hydroxide nitrate. The SEM images showed the variations in morphology obtained through the different surfactants and the medium pH, in which, the morphology presents a leaf appearance with a lower value (pH = 8), while increasing the pH to 13, changed the morphology into agglomerate flower-like nanoparticles. The BET results showed that the samples obtained without surfactant and with PEG at pH = 8 had the highest and lowest surface area, being 18.935 and 4.531 m2-1, respectively. The photocatalytic activity shows that the CuO powders that have a small amount of Cu2(OH)3(NO3) present better methylene blue dye degradability when illuminated by UV-Vis radiation
Influence of pH variation on CuWO4, CuWO4/WO3 and CuWO4/CuO structures stabilization: study of the photocatalytic properties under sunlight
(Springer Science and Business Media LLC, 2020-09-08) Andrade Neto, Nivaldo Freire de; Oliveira, Yasmim Gomes de; Nascimento, José Heriberto Oliveira do; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In this work, the reaction pH range (from 2 to 10) was used to study the stabilization of the CuWO4 phase in the presence of polyvinylpyrrolidone surfactant synthesized by the sonochemical method. The powders were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy (FE-SEM), nitrogen adsorption and desorption using the Brunauer–Emmett–Teller methodology and ultraviolet–visible spectroscopy (UV–Vis). The photocatalytic activity was studied against MB dye under sunlight and CuWO4 powders were tested at 5 reuse cycles. Diffractograms indicated that syntheses at pH 2 and 4 generate WO3/CuWO4 heterostructures, while reaction pH at 8 and 10 generate CuO/CuWO4 heterostructures and at pH 6 generates pure CuWO4. FE-SEM images indicated semispherical morphology for CuWO4, nanoplate morphology for CuO, and large particles without definite form for WO3 powders. The scavenger’s methodology indicates that hydroxyl radicals are the main responsible for the photodegradation of methylene blue in all samples. Also, it indicates that the formation of the WO3/CuWO4 and CuO/CuWO4 heterostructures increase the e-/h? pair recombination rate, reducing the photocatalytic activity in sunlight
Influence of solution pH on forming silver molybdates obtained by sonochemical method and its application for methylene blue degradation
(Elsevier, 2019-06-15) Ferreira, Erik Alexander Cunha; Andrade Neto, Nivaldo Freire de; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
Catalytic processes such as heterogenous photocatalysis or adsorptions have been extensively studied due to the difficulty in treating organic effluents, mainly textiles. The catalysts stability is essential to enable their ap- plicability, so that the catalytic converter does not turn into secondary residues after the catalytic cycle, enabling its re-employment in the catalytic process. In this work was studied the photocatalytic activity of different phases of silver molybdates obtained by the sonochemical method at different pH in the medium reaction. The powders were characterized by X-ray diffraction (XRD) field emission scanning electron microscopy (FE-SEM), and diffuse reflectance spectroscopy was used to estimate the Egap of the powders. The photocatalytic activity of the powders was measured by varying the degradation of the methylene blue dye (MB). According to the XRD patterns, the crystalline structure of the obtained silver molybdates changes from Ag2Mo3O10. 2H2O at very acidic pH 1 and 2, to pure Ag2Mo2O7 with the values of pH 3 and 4 it is then converted into Ag2Mo2O7 and Ag2MoO4 phases in pH 5, and shifts to pure Ag2MoO4 phase when the pH is increased up to 6. The results indicate that the microstructures of Ag2Mo3O10. 2H2O and Ag2Mo2O7 phases have high adsorbent properties, with the powders obtained at pH 1 and 2 being able to completely remove the MB from the solution in 5 min and the powders of Ag2Mo2O7 phases removing up to 90% of MB after 5 min of exposure without UV irradiation. In contrast, the powders with Ag2MoO4 phase showed high photocatalytic properties, being able to removing up to 90% of MB in less than 20 min and 40 min of ultraviolet exposure to powders obtained at pH 5 and 6, respectively. All presented catalysts maintained their stability and performance after 3 test cycles
Microwave-assisted hydrothermal synthesis of Ag2Mo1-xWxO4 (x = 0, 0.25, 0.50, 0.75 and 1 mol%) heterostructures for enhanced photocatalytic degradation of organic dyes
(Elsevier, 2020-12-05) Andrade Neto, Nivaldo Freire de; Lima, A.B.; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In this work, Ag2Mo1-xWxO4 (x = 0, 0.25, 0.50, 0.75 and 1 mol%) heterostructures were synthesized by a microwave-assisted hydrothermal (MAH) method under 140 °C. The powders are characterized by X-ray diffractogram (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, and spectroscopy in the ultraviolet-visible region (UV-Vis). The photocatalytic degradations are investigated by methylene blue (cationic) and methyl orange (anionic) dyes and the mechanisms acting in the photocatalysis are estimated by a scavenger’s methodology. The diffractograms indicate that the MAH method provides powders with high crystallinity and without secondary phases. SEM micrographs indicate that the Ag2MoO4 phase is formed by micrometric particles with a coarse aspect and the Ag2WO4 phase is formed by micrometric rods with a square cross-section. The direct Egap varied from 3.46 to 3.23 eV for the Ag2MoO4 and Ag2WO4 phases, respectively. The adsorptive and photocatalytic tests showed that the Ag2WO4 phase has a better performance against both dyes than the Ag2MoO4 phase, being the best performance against the MB dye (complete discoloration after 20 min). The scavenger’s tests showed that the positive charges (h+) are the main mechanism acting in the photocatalysis for the Ag2MoO4 phase, while the h+ and hydroxyl radicals (∙OH) have a similar influence in the Ag2WO4 phase. Photocatalytic tests of reuse indicated that the samples have a good photocatalytic capacity even in the third consecutive cycle
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
Photocatalytic properties of the CeO2-xTiO2 and TiO2-xCeO2 (x = 10, 30 and 50 mol%) heterostructures obtained by a MAH
(Wiley, 2020-06-18) Nascimento, Leulomar Enedino do; Andrade Neto, Nivaldo Freire de; Ramalho, Onécima Biatriz de Medeiros; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In this work, CeO2-TiO2 heterostructures were submitted to the microwave-assisted hydrothermal (MAH) method at 140 °C for 30 min, and varying the CeO2 and TiO2 percentages like 10, 30 and 50 mol%. The heterostructures were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer-Emmett-Teller methodology (BET), and UV-Vis diffuse reflectance spectroscopy (UV-Vis). The photocatalytic were estimated varying the concentration of methylene blue dye (MB). The diffractograms indicate the formation of TiO2 anatase and CeO2 phases, without the formation of secondary phases. TEM images indicate the formation of nanocubes and nanospheres for CeO2 and TiO2, respectively. BET analysis indicates that CeO2 has the largest surface area (62.80 m2.g-1), and TiO2-10%CeO2 heterostructure has a low surface area (26.13 m2.g-1). The addition of TiO2 to CeO2 increases photocatalytic activity from 32 to 80 % for CeO2 and CeO2-50%TiO2, respectively. In contrast, the addition of CeO2 significantly decreases the photocatalytic activity of TiO2 from 98.9 to 50 % for TiO2 and TiO2-50%CeO2, respectively. Reuse tests showed that the TiO2-xCeO2 samples maintaining the photocatalytic response in subsequent cycles while the CeO2-xTiO2 samples have an increase in the response
Photocatalytic properties under sunlight of heterostructures AgCl/CuO obtained by sonochemical method
(Springer, 2018-06-13) Paskocimas, Carlos Alberto; Andrade Neto, Nivaldo Freire de; Silva, Elson Longo da; Matsui, Katia Nicolau; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
AgCl/CuO heterostructures were synthesized via a sonochemical method. AgCl/CuO molar compositions of 1:1 and 2:1 were prepared, respectively. Such compositions were prepared using three distinct routes. The particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM-FEG) and UV-Vis spectroscopy (UV-Vis). In order to analyze the applicability of the heterostructure, photocatalytic tests were performed under sunlight and UV-Vis radiation for the degradation of the methylene blue dye. The results of the X-ray diffraction confirmed the formation of the AgCl/CuO heterostructure in all samples, with no evidence of doping or formation of deleterious phases. SEM images indicate a cubic-like morphology for the AgCl particles, forming Ag0 on its surface, the CuO particles have a leaf appearance. The results of the photocatalytic activity indicate that the increase of the AgCl molar ratio from 1:1 to 2:1 accelerates the degradation of methylene blue for both the radiations and shows that sunlight decreases by at least 55% for the degradation of the methylene blue, depending on the composition, to the heterostructure
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

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