Hidrotermalização assistida por micro-ondas seguida de tratamento térmico: uma nova rota para obtenção do CaZrO3
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Data
2020-05-04
Autores
Macêdo Junior, Wagner Costa [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Cerâmica com estrutura do tipo perovskita e minério recentemente descoberto, o CaZrO3 se aplica, com destaque, em componentes de circuito para sensores de oxigênio, hidrogênio e umidade, além de poder ser utilizado na adsorção de corantes, como material abrasivo, refratário e como matriz em sólidos fósforos dopados com Eu3+. Devido a este leque de aplicações, torna-se imprescindível o estudo de novos métodos de síntese visando a obtenção deste material, principalmente em escala nanométrica. O método Hidrotermal Assistido por Micro-ondas (HAM) é um excelente candidato para tal, já que é empregado na obtenção de cerâmicas avançadas, utilizando menores tempos e temperaturas durante o processo de síntese. Este trabalho apresenta os primeiros resultados da obtenção do CaZrO3 pelo método HAM, no qual diversos parâmetros de síntese foram variados para uma melhor avaliação de suas características estruturais, morfológicas e ópticas. Partículas CaZrO3 foram nucleados pelo método HAM em 140 ºC durante 1, 10, 40 e 180 min e cristalizados via tratamento térmico de 600 até 1200 ºC. Duas fases principais foram obtidas, uma estequiométrica e outra não estequiométrica, as quais podem ter suas porcentagens modificadas de acordo com os precursores, tempo de síntese e temperatura de tratamento térmico. Três propriedades distintas foram analisadas: (1) sensibilidade à umidade; (2) capacidade de adsorção dos corantes rodamina B, vermelho congo, azul de metileno e alaranjado de metila e; (3) viabilidade deste material como matriz do íon Eu3+ (1, 3 e 5%). Todas estas propriedades foram observadas, das quais foi concluído que: (1) amostras sintetizadas com menores tempos apresentam maior variação de resistência em relação à mudança da umidade relativa, principalmente em umidades superiores à 50%; (2) as melhores adsorções ocorrem para os corantes rodamina B e vermelho congo (até 100% de adsorção), o que potencializa o material para ser utilizado, por exemplo, como membrana porosa, em dispositivos voltados para a área ambiental e; (3) por meio dos espectros de emissão fotoluminescente em temperatura ambiente e em 14 K, foi concluído que os íons de Eu3+ substituem tanto os átomos de Ca como de Zr, em ambas as fases, com limite de substituição de 3%, amostra que apresenta maior rendimento quântico (0,29) quando utilizado o laser 395 nm no processo de excitação, o que qualifica as amostras aqui sintetizadas para aplicações em recobrimentos de LED’s que trabalham com radiações de excitação localizadas no UV-próximo.
Ceramic with a perovskite type structure and recently discovered mineral, CaZrO3 is especially used in circuit components for oxygen, hydrogen and humidity sensors, in addition to being able to be used in the adsorption of dyes, as an abrasive, refractory material and as a matrix in solid phosphors doped with Eu3+. Due to this range of applications, it is essential to study new methods of synthesis in order to obtain this material, mainly on a nanometric scale. The Microwave-Assisted Hydrothermal (MAH) method is an excellent candidate for this, since it is usually used to obtain advanced ceramics, using shorter times and temperatures during the synthesis process. This work presents the first results for obtaining CaZrO3 by the MAH method, in which several parameters of synthesis were varied for a better evaluation of its structural, morphological and optical characteristics. CaZrO3 particles were nucleated by the MAH method at 140 ºC for 1, 10, 40 and 180 min and crystallized via heat treatment from 600 to 1200 ºC. Two main phases were obtained, one stoichiometric and the other non-stoichiometric, which can have their percentages modified according to the precursors, synthesis time and heat treatment temperature. Three distinct properties were analyzed: (1) sensitivity to humidity; (2) adsorption capacity of rhodamine B, congo red, methylene blue and methyl orange dyes; (3) viability of this material as an Eu3+ ion matrix (1, 3 and 5%). All these properties were observed, where it was concluded that: (1) samples synthesized with shorter times show greater resistance variation in relation to the change in relative humidity, mainly in humidity above 50%; (2) the best adsorption occurs for rhodamine B and congo red dyes (up to 100% adsorption), which enhances the material to be used, for example, as a porous membrane, in devices aimed at the environmental area and; (3) through high resolution photoluminescent emission spectra (14 K), it was concluded that Eu3+ ions replace both Ca and Zr atoms, in both phases, with a luminescent quenching at 3%, a sample that has a higher quantum yield (0.29) when using the 395 nm laser (excitation), which qualifies the samples synthesized here for applications in LED coatings that work with excitation radiation located in the near UV.
Ceramic with a perovskite type structure and recently discovered mineral, CaZrO3 is especially used in circuit components for oxygen, hydrogen and humidity sensors, in addition to being able to be used in the adsorption of dyes, as an abrasive, refractory material and as a matrix in solid phosphors doped with Eu3+. Due to this range of applications, it is essential to study new methods of synthesis in order to obtain this material, mainly on a nanometric scale. The Microwave-Assisted Hydrothermal (MAH) method is an excellent candidate for this, since it is usually used to obtain advanced ceramics, using shorter times and temperatures during the synthesis process. This work presents the first results for obtaining CaZrO3 by the MAH method, in which several parameters of synthesis were varied for a better evaluation of its structural, morphological and optical characteristics. CaZrO3 particles were nucleated by the MAH method at 140 ºC for 1, 10, 40 and 180 min and crystallized via heat treatment from 600 to 1200 ºC. Two main phases were obtained, one stoichiometric and the other non-stoichiometric, which can have their percentages modified according to the precursors, synthesis time and heat treatment temperature. Three distinct properties were analyzed: (1) sensitivity to humidity; (2) adsorption capacity of rhodamine B, congo red, methylene blue and methyl orange dyes; (3) viability of this material as an Eu3+ ion matrix (1, 3 and 5%). All these properties were observed, where it was concluded that: (1) samples synthesized with shorter times show greater resistance variation in relation to the change in relative humidity, mainly in humidity above 50%; (2) the best adsorption occurs for rhodamine B and congo red dyes (up to 100% adsorption), which enhances the material to be used, for example, as a porous membrane, in devices aimed at the environmental area and; (3) through high resolution photoluminescent emission spectra (14 K), it was concluded that Eu3+ ions replace both Ca and Zr atoms, in both phases, with a luminescent quenching at 3%, a sample that has a higher quantum yield (0.29) when using the 395 nm laser (excitation), which qualifies the samples synthesized here for applications in LED coatings that work with excitation radiation located in the near UV.
Descrição
Palavras-chave
Perovskita, Sensores, Adsorção, Fotoluminescência, Hidrotermalização assistida por micro-ondas, Microwave-assisted hydrothermal, Perovskite, Sensors, Adsorption, Photoluminescence