Síntese, caracterização e avaliação das propriedades fotocatalíticas do WO3, obtido pelo método Poliol
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Data
2018-10-11
Autores
Carvalho Neto, Alberto Gonçalves Vieira de
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Universidade Estadual Paulista (Unesp)
Resumo
Este trabalho teve por objetivo preparar o trióxido de tungstênio nano-estruturado com atividade catalítica para a reação de fotodegradação da Rodamina B e do Índigo Blue. Sua síntese foi a partir do ácido túngstico mediada por tetra-etilenoglicol (poliol), a 327 °C, variando-se o tempo de reação de 15 min a 24h. A formação de uma suspensão de cor azulada foi observada no decorrer da reação em poliol. Após separação e lavagem do material precipitado, as amostras foram tratadas termicamente (a 150 oC, 350 oC, 500 oC e 800 oC), para obtê-las sob diferentes fases e graus de cristalinidades. Os materiais tratados termicamente até 150 °C foram encontrados sob fases ortorrômbica, triclínica, tetragonal e cúbica, do trióxido. Entretanto, quando submetidos ao tratamento acima de 350 °C, os materiais se mostraram totalmente convertidos para a fase monoclínica. Para tratamentos abaixo de 500 °C as amostras eram constituídas de partículas porosas esferoidais ou em bastonetes, cujas dimensões dependeram do tempo de reação em poliol. A atividade catalítica do WO3 foi avaliada para reações de degradação da Rodamina B (RhB) e do Indigo Blue (IB) sob irradiação de luz UV-Vis e em diferentes pH da solução de corantes. A maior atividade foi observada para a amostra obtida por 15 min de reação em poliol e submetida a tratamento térmico de 500 °C. Para esta amostra, o grau de mineralização (degradação à CO2) da Rodamina B alcançado foi de 95% em 180 min enquanto que em ensaio com WO3 obtido apenas pela calcinação do ácido precursor a mineralização foi de apenas 2%. O mesmo material catalisador promoveu a degradação de 56,5% (em 300 min) do corante Índigo Blue, contra 3% do WO3 proveniente da calcinação direta do ácido túngstico. Quanto ao pH do meio reacional, observou-se grande influência desta variável na eficácia da mineralização, sendo que os melhores resultados foram encontrados em pHs ácidos.
This work aimed to prepare the nanostructured tungsten trioxide with catalytic activity for the photodegradation reaction of Rhodamine B and Indigo Blue. Itwas synthetized from the tungstic acid mediated by polyol (tetra-ethylene glycol) at 327 °C, varying the reaction time from 15 min to 24h. The formation of a blue colored suspension was observed during the reaction in polyol. The suspension was separated, washed and heat treated (at 150 °C, 350 °C, 500 °C and 800 °C) to obtain it under different phases and crystallinities. The orthorhombic, triclinic, tetragonal e cubic phases were found for tungsten trioxides when treated up to 150 °C. When subjected to the heat treatment above 350 °C it showed the material was completely converted to the monoclinic phase. For treatments below 500 °C the samples consisted of porous spherical or rod shape particles, whose sizes depended on the polyol reaction time. The catalytic activity of prepared WO3 was evaluated for the degradation reaction of Rhodamine B (RhB) and Indigo Blue (IB) under irradiation of UV-Vis light and different pH conditions. The highest activity was observed for the sample obtained under reaction in polyol of 15 min and subjected to heat treatment at 500 °C. For this sample, the achieved degree of mineralization (degradation to CO2) of Rhodamine B was 95% in 180 min, while in the assay for WO3 obtained by calcining the precursor acid the mineralization was only 2%. The same catalyst material promoted the degradation of 56.5% (in 300 min) of Indigo Blue dye against 3% for WO3 directly obtained from tungstic acid. Regarding to the pH of the reaction medium, there was a great influence of this variable on the mineralization effectiveness, with the best results being found in acidic pHs.
This work aimed to prepare the nanostructured tungsten trioxide with catalytic activity for the photodegradation reaction of Rhodamine B and Indigo Blue. Itwas synthetized from the tungstic acid mediated by polyol (tetra-ethylene glycol) at 327 °C, varying the reaction time from 15 min to 24h. The formation of a blue colored suspension was observed during the reaction in polyol. The suspension was separated, washed and heat treated (at 150 °C, 350 °C, 500 °C and 800 °C) to obtain it under different phases and crystallinities. The orthorhombic, triclinic, tetragonal e cubic phases were found for tungsten trioxides when treated up to 150 °C. When subjected to the heat treatment above 350 °C it showed the material was completely converted to the monoclinic phase. For treatments below 500 °C the samples consisted of porous spherical or rod shape particles, whose sizes depended on the polyol reaction time. The catalytic activity of prepared WO3 was evaluated for the degradation reaction of Rhodamine B (RhB) and Indigo Blue (IB) under irradiation of UV-Vis light and different pH conditions. The highest activity was observed for the sample obtained under reaction in polyol of 15 min and subjected to heat treatment at 500 °C. For this sample, the achieved degree of mineralization (degradation to CO2) of Rhodamine B was 95% in 180 min, while in the assay for WO3 obtained by calcining the precursor acid the mineralization was only 2%. The same catalyst material promoted the degradation of 56.5% (in 300 min) of Indigo Blue dye against 3% for WO3 directly obtained from tungstic acid. Regarding to the pH of the reaction medium, there was a great influence of this variable on the mineralization effectiveness, with the best results being found in acidic pHs.
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Palavras-chave
Trióxido de tungstênio, Método poliol, Fotocatálise heterogênea, Rodamina B, Indigo blue, Síntese, Synthesis, Tungsten trioxide, Polyol method, Heterogeneous photocatalysis, Rhodamine B, Blue indigo