Síntese e caracterização de heteroestrutura à base de α-Ag2WO4 e ZnO
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Data
2019-08-27
Autores
Jacomaci, Natalia
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Universidade Estadual Paulista (Unesp)
Resumo
Esta pesquisa desenvolveu a síntese e caracterização de heteroestrutura a base de alfa tungstato de prata, α-Ag2WO4 , e oxido de zinco ZnO. Os compostos individuais e a heteroestrutura foram obtidas por síntese hidrotérmica em forno micro-ondas em duas etapas: na 1° etapa foram obtidasnanocristais anisotrópicos de α-Ag2WO4 e de ZnO; na 2°etapa foi obtida a Heteroestrutura α-Ag2WO4/Ag/ZnO. As amostras puras e a heteroestrutura foram analisadas por difração de Raios X (DRX) e os dados foram tratados por método de refinamento de Rietveld. A avaliação do modelo estrutural, parametros de rede, volume de cela únitária, angulos e distâncias de ligação, quantidade de fases foram obtidas através de refinamento refinamento. A morfologia das amostras puras foram analisadas por microscopia eletrônica de varredura de alta resolução e a heteroestrutura bem como as regiões interfaciais foram analisadas por microscopia eletronica de varredura com elétrons retroespalhado e microscopia eletrônica de transmissão de alta magnificação, em que obteve-se a formação de 3 regiões interfaciais formando heteroestrutra tipo II o α-Ag2WO4/ZnO e heteroestrutura decorada com nanopartículas de prata o Ag/ α-Ag2WO4 e Ag/ZnO. As medidas de espectroscopia de refletância difusa permitiram determinar a energia de band gap óptico cujos valores encontrados foram 3,11 eV para o α-Ag2WO4, 3,28 eV para o ZnO e 3,21 eV para a heteroestrutura α-Ag2WO4/Ag/ZnO que permitiu estimar as posições relativas da (BV) e (BC). Os resultados observados para as medidas de espectroscopia de fotoluminescência possibilitaram observar menor intensidade de emissão da heteroestrutura, devido a recombinação eletrônica entre os clusters [AgOy] e [WO6] com [ZnO4]. A fotodescoloração da Rodamina B, aumentou significativamente para a heteroestrutura obtendo 93% de fotodescoloração em 90 minutos.
This research developed of the synthesis and characterization of heterostructure alpha-silver tungstate-based heterostructure, α-Ag2WO4 and ZnO zinc oxide. The pure and heterostructured samples were obtained by hydrothermal in the microwave oven in two stages: in the first stage were obtained anisotropic nanocrystals of α-Ag2WO4 and ZnO were destroyed; In the second stage, the α- α-Ag2WO4/Ag/ZnO heterostructure was used. The pure and heterostructure sample were analyzed by X-ray diffraction (XRD) and the data were analyzed by Rietveld refinement method. Structural model evaluation, lattice parameters, single cell volume, angles and bonding distances, number of phases were obtained by refinement. The morphology of the pure samples was analyzed by high resolution scanning electron microscopy and the heterostructure was analyzed by backscattered electron scanning electron microscopy and high magnification transmission electron microscopy, which obtained the formation of 3 interfacial regions: α -Ag2WO4/ZnO and Ag/α-Ag2WO4 and Ag/ZnO decorated with silver nanoparticles. The diffuse reflectance spectroscopy measurements allowed the determination of the optical band gap energy whose values were 3.11 eV for α-Ag2WO4, 3.28 eV for ZnO and 3.21 eV for α-Ag2WO4/Ag/ ZnO heterostructure which allowed estimating the relative positions of (VB) and (CB). The results observed for the photoluminescence spectroscopy measurements made it possible to observe lower intensity of the heterostructure emission, due to the electronic recombination between the clusters [AgOy] and [WO6] with [ZnO4]. A photodiscoloration of Rhodamine B, increased to a heterostructure obtaining 93% photodiscoloration in 90 minutes.
This research developed of the synthesis and characterization of heterostructure alpha-silver tungstate-based heterostructure, α-Ag2WO4 and ZnO zinc oxide. The pure and heterostructured samples were obtained by hydrothermal in the microwave oven in two stages: in the first stage were obtained anisotropic nanocrystals of α-Ag2WO4 and ZnO were destroyed; In the second stage, the α- α-Ag2WO4/Ag/ZnO heterostructure was used. The pure and heterostructure sample were analyzed by X-ray diffraction (XRD) and the data were analyzed by Rietveld refinement method. Structural model evaluation, lattice parameters, single cell volume, angles and bonding distances, number of phases were obtained by refinement. The morphology of the pure samples was analyzed by high resolution scanning electron microscopy and the heterostructure was analyzed by backscattered electron scanning electron microscopy and high magnification transmission electron microscopy, which obtained the formation of 3 interfacial regions: α -Ag2WO4/ZnO and Ag/α-Ag2WO4 and Ag/ZnO decorated with silver nanoparticles. The diffuse reflectance spectroscopy measurements allowed the determination of the optical band gap energy whose values were 3.11 eV for α-Ag2WO4, 3.28 eV for ZnO and 3.21 eV for α-Ag2WO4/Ag/ ZnO heterostructure which allowed estimating the relative positions of (VB) and (CB). The results observed for the photoluminescence spectroscopy measurements made it possible to observe lower intensity of the heterostructure emission, due to the electronic recombination between the clusters [AgOy] and [WO6] with [ZnO4]. A photodiscoloration of Rhodamine B, increased to a heterostructure obtaining 93% photodiscoloration in 90 minutes.
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Palavras-chave
Heteroestruturas, Prata, Óxido de zinco, Fotoluminescência, Fotocatálise