Preparação, caracterização e estudo da eficiência na fotodegradação e adsorção de Rodamina B de heteroestruturas de TiO2/α-Fe2O3
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Data
2016-04-18
Autores
Maluf, Nágila El Chamy [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A fotocatálise heterogênea, utilizando dióxido de titânio com estrutura do tipo anatase, tem se mostrado uma alternativa promissora para a remediação de sistemas aquáticos contaminados. Com o intuito de aumentar a eficiência do fotocatalisador, estudos científicos têm reportado a heterojunção deste óxido com estruturas do tipo hematita do óxido de ferro, α-Fe2O3. Neste estudo, foi investigada a síntese de nanoestruturas de TiO2 puro, α-Fe2O3 pura e heteroestruturas de TiO2/α-Fe2O3 em diferentes proporções dos óxidos a fim de testá-los como fotocatalisadores na degradação de um corante com elevada toxicidade, a Rodamina B. Os materiais foram sintetizados por rotas híbridas, utilizando o Metódo do Peróxido Oxidante com posterior tratamento hidrotérmico, totalizando a produção de 8 amostras. Foram empregadas três rotas de síntese: a rota (a) foi responsável pela síntese de TiO2 puro variando-se o pH do meio reacional na etapa de tratamento hidrotérmico, a rota (b) foi utilizada para a preparação de α-Fe2O3 pura e a rota (c) foi empregada na produção das heteroestruturas de TiO2/α-Fe2O3 nas concentrações de 0,1, 0,5, 1,0 e 5,0% p/p de hematita. As amostras foram caracterizadas quanto a sua estrutura, microestrutura e propriedades superficiais com o auxílio das técnicas de DRX, FT-Raman, método de BET, MEV/FEG, MET, TG e FT-IR. A análise dos resultados de caracterização estrutural mostrou que a rota (a) é eficiente para a síntese de TiO2 anatase quando realizada em meio básico, produzindo uma mistura de fases anatase/rutilo quando procedida em meio ácido. Sendo assim, na rota (c) foi utilizado o meio sintético básico para a síntese de TiO2 anatase e hematita. Em resumo, foi produzida pela rota (a) em meio básico a amostra HTTI1, que degradou a molécula de RhB em 95,0% e os materiais HTTI2 e HTTI3, produzidos em meio ácido, os quais degradaram a solução do corante em 70,9 e 24,4%, respectivamente, em 90 minutos de ensaio fotocatalítico, o que evidencia a importância em se obter nanomateriais com estrutura anatase do TiO2. Com o estudo da atividade fotocatalítica dos materiais produzidos, notou-se que alguns dos semicondutores apresentavam elevada taxa de adsorção no decorrer do processo. Devido a isso, a cinética de adsorção de RhB pelos materiais produzidos foi também estudada no período de 14 horas, cujos resultados mostraram que o óxido de ferro com estrutura hematita é um excelente adsorvente para o corante. Os resultados dos ensaios fotocatalíticos e de adsorção de RhB evidenciaram, principalmente, a elevada eficiência do TiO2 anatase como fotocatalisador e, em contrapartida, a elevada capacidade da hematita em adsorver as moléculas do corante. As heteroestruturas produzidas apresentaram o efeito de reduzir a eficiência na fotodegradação da RhB em relação a amostra HTTI1 com o aumento da concentração do óxido de ferro, porém as mesmas heterojunções se mostraram favoráveis para as propriedades adsortivas dos compostos quanto maior a concentração de α-Fe2O3.
The heterogeneous photocatalysis using titanium dioxide with anatase type structure, has proved to be a promising alternative for the remediation of contaminated aquatic systems. In order to increase the efficiency of this photocatalyst, scientific studies have reported the heterojunction of this oxide with hematite structures of iron oxide, α-Fe2O3. In this study, it was investigated the synthesis of pure TiO2 nanostructures, pure α-Fe2O3 and TiO2/α-Fe2O3 heterostructures in different proportions in order to test them as photocatalysts in the degradation of a dye having high toxicity, the Rhodamine B. The materials were synthesized by hybrid routes, using the Oxidant Peroxo Method with subsequent hydrothermal treatment, producing a total of 8 samples. Three synthesis routes were employed: the route (a) was responsible for the pure TiO2 synthesis by varying the pH of the reaction medium in the hydrothermal treatment step, route (b) was used for the preparation of pure α-Fe2O3 and route (c) was employed in the production of TiO2/α-Fe2O3 heterostructures in concentrations of 0.1, 0.5, 1.0 and 5.0% w/w of hematite. The samples were characterized as their structure, microstructure and surface properties with XRD, FT-Raman, BET method, SEM/FEG, TEM, TG and FT-IR techniques. The results of the structural characterization showed that route (a) is effective for the synthesis of anatase TiO2 when carried out in basic medium, producing a mixture of phases anatase/rutile when performed in an acid medium. Thus, in route (c) it was used the basic synthetic medium for the synthesis of anatase TiO2 and hematite. In summary, it was produced by route (a) in a basic medium the HTTI1 sample, that degraded RhB molecule in 95.0%, HTTI2 and HTTI3 materials, produced in acid medium, which degraded dye solution in 70.9 and 24.4%, respectively, in 90 minutes of the photocatalytic test, which highlights the importance of obtaining nanomaterials with anatase TiO2 structure. With the study of the photocatalytic activity of the materials, it was noted that some of the semiconductor had high adsorption rate during the process. Because of this, the RhB adsorption kinetics by the materials produced was also studied within 14 hours. The results showed that the iron oxide with hematite structure is an excellent adsorbent for the dye. Especially, the results of the photocatalytic tests and RhB adsorption showed high efficiency of anatase TiO2 as a photocatalyst and, conversely, high capacity of hematite to adsorb dye molecules. The heterostructures produced had the effect of reducing the efficiency in photodegradation of RhB comparing with HTTI1 sample with increasing concentration of iron oxide, however the same heterojunctions demonstrated favorable for adsorptive properties of the compounds the greater the concentration of α-Fe2O3.
The heterogeneous photocatalysis using titanium dioxide with anatase type structure, has proved to be a promising alternative for the remediation of contaminated aquatic systems. In order to increase the efficiency of this photocatalyst, scientific studies have reported the heterojunction of this oxide with hematite structures of iron oxide, α-Fe2O3. In this study, it was investigated the synthesis of pure TiO2 nanostructures, pure α-Fe2O3 and TiO2/α-Fe2O3 heterostructures in different proportions in order to test them as photocatalysts in the degradation of a dye having high toxicity, the Rhodamine B. The materials were synthesized by hybrid routes, using the Oxidant Peroxo Method with subsequent hydrothermal treatment, producing a total of 8 samples. Three synthesis routes were employed: the route (a) was responsible for the pure TiO2 synthesis by varying the pH of the reaction medium in the hydrothermal treatment step, route (b) was used for the preparation of pure α-Fe2O3 and route (c) was employed in the production of TiO2/α-Fe2O3 heterostructures in concentrations of 0.1, 0.5, 1.0 and 5.0% w/w of hematite. The samples were characterized as their structure, microstructure and surface properties with XRD, FT-Raman, BET method, SEM/FEG, TEM, TG and FT-IR techniques. The results of the structural characterization showed that route (a) is effective for the synthesis of anatase TiO2 when carried out in basic medium, producing a mixture of phases anatase/rutile when performed in an acid medium. Thus, in route (c) it was used the basic synthetic medium for the synthesis of anatase TiO2 and hematite. In summary, it was produced by route (a) in a basic medium the HTTI1 sample, that degraded RhB molecule in 95.0%, HTTI2 and HTTI3 materials, produced in acid medium, which degraded dye solution in 70.9 and 24.4%, respectively, in 90 minutes of the photocatalytic test, which highlights the importance of obtaining nanomaterials with anatase TiO2 structure. With the study of the photocatalytic activity of the materials, it was noted that some of the semiconductor had high adsorption rate during the process. Because of this, the RhB adsorption kinetics by the materials produced was also studied within 14 hours. The results showed that the iron oxide with hematite structure is an excellent adsorbent for the dye. Especially, the results of the photocatalytic tests and RhB adsorption showed high efficiency of anatase TiO2 as a photocatalyst and, conversely, high capacity of hematite to adsorb dye molecules. The heterostructures produced had the effect of reducing the efficiency in photodegradation of RhB comparing with HTTI1 sample with increasing concentration of iron oxide, however the same heterojunctions demonstrated favorable for adsorptive properties of the compounds the greater the concentration of α-Fe2O3.
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Palavras-chave
Síntese hidrotérmica, Dióxido de titânio, Óxido de ferro, Fotocatálise, Adsorção, Hydrothermal synthesis, Titanium dioxide, Iron oxide, Photocatalysis, Adsorption