Síntese de óxidos de ferro modificados com cério para a degradação da cefalexina por processos Fenton heterogêneo
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Data
2019-08-07
Autores
Lima, Amanda Santos de
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Universidade Estadual Paulista (Unesp)
Resumo
Este trabalho teve como objetivo avaliar a atividade catalítica de óxidos de ferro modificados com diferentes quantidades de cério (0, 0,55, 1,1 e 2,2% m/m) e submetidos a tratamento térmico em duas diferentes temperaturas (70 e 140 °C) na degradação da cefalexina (CFX) por processos Fenton e foto-Fenton, utilizando como fonte de irradiação os dispositivos LED na faixa do visível (λ = 460 nm), visto que pouco foi explorado na literatura sobre a variação dessas modificações. Os materiais sintetizados foram caracterizados pelas técnicas de Difração de Raios- X, Espectroscopia de Reflectância Difusa, Microscopia Eletrônica de Varredura de Alta Resolução, área superficial específica, Magnetometria de Amostra Vibrante e Potencial Zeta. Foi observado que com o tratamento térmico a 140 °C ocorreu a conversão da fase cristalina magnetita (MGT) para a fase cristalina maghemita (MAG) verificada pela mudança de coloração dos materiais e um deslocamento no pico do difratograma, o que não foi observado a 70 °C. Todos os materiais apresentaram absorção na faixa UVA, UVB e visível, no entanto os materiais submetidos a tratamento térmico a 70 °C apresentam maior absorção nos comprimento de onda >500 nm. A microscopia eletrônica de varredura mostrou que a inserção de cério nos óxidos de ferro proporciona uma perda da forma esférica uniforme das partículas, apresentando esferas irregulares. A área superficial específica foi influenciada tanto pela modificação com cério quanto pelo tratamento térmico. Foi observado que com a menor quantidade de cério (0,55% m/m) há um aumento na área superficial específica de 91,2 a 171,6 m² g-¹ em relação ao óxido de ferro puro que diminui com a inserção de maiores quantidade de cério (99,2 m² g-¹ para 2,2% m/m). O mesmo comportamento foi observado para as amostras tratadas a 140 °C, no entanto, com menores áreas. A magnetometria de amostra vibrante confirmou que houve a mudança de fase nos materiais submetidos a 140 °C com a diminuição da curva de histerese do material puro e que a inserção de cério também conferiu um perda da propriedade magnética do material. A atividade catalítica dos materiais foi avaliada frente à degradação da CFX inicialmente a pH = 6,0, avaliando diferentes concentrações de peróxido de hidrogênio (1,0 3,0 e 5,0 mmol L-¹), diferentes concentrações de catalisador (0,125, 0,250 e 0,500 g L-¹) sob irradiação de dispositivos LED visível. Foi observado que o material apresentava baixa atividade e um alto consumo de peróxido de hidrogênio em pH 6,0, pois estava decompondo o peróxido de hidrogênio em água e oxigênio. Porém em pH 3,5 foi verificada uma alta produção de radicais hidroxilas e este pH foi então escolhido como pH de trabalho. O aumento na quantidade de cério e a temperatura foram fatores importantes na eficiência catalítica da degradação da CFX pelo processo Fenton, que teve como destaque o material C140-11, que degradou 0,05 mg de CFX por m² de catalisador com uma dosagem de catalisador de 0,125 g L-¹ e 1,0 mmol L-¹ de H2O2 após 150 min. Todos os materiais se mostraram estáveis e não apresentaram lixiviação de ferro, indicando que todas as degradações ocorriam somente no meio heterogêneo. A identificação de intermediários de degradação da CFX indicaram a hidroxilação como principal rota de degradação.
The objective of this work was to evaluate the catalytic activity of iron oxides modified with different amounts of cerium (0, 0.55, 1.1 and 2.2% w/w) and submitted to different heat treatment temperatures (70 and 140 °C) for the degradation of cephalexin (CFX) by Fenton and photo-Fenton processes, using LED devices in the visible range (λ = 460 nm) as irradiation source, a little has been explored in the literature about the variation of these modifications. The materials were characterized by the techniques of X-ray diffraction, diffuse reflectance spectroscopy, high resolution scanning electron microscopy, specific surface area, vibrating sample magnetometry and zeta potential. It was observed that with the thermal treatment at 140 °C the conversion of the magnetite crystalline phase (MGT) to the maghemite crystalline phase (MAG), verified by the color change of the materials and a displacement at the peak of the diffractogram occurred, which was not observed at 70 °C. All materials presented absorption in the UVA, UVB and visible range, however the materials submitted to thermal treatment at 70 °C presented a higher absorption in the wavelength >500 nm. Scanning electron microscopy showed that the insertion of cerium in the iron oxides resulted in a loss of the uniform spherical shape of the particles, presenting irregular spheres. The specific surface area was influenced by both the cerium modification and heat treatment. It was observed that with the lowest amount of cerium (0.55% w/w) there is an increase in the specific surface area from 91.2 to 171.6 m² g-¹ relative to the pure iron oxide that decreases with the insertion of greater amount of cerium (99.2 m² g-¹ for 2.2% w/w). The same behavior was observed for samples treated at 140 °C, however, with smaller areas. Vibrating sample magnetometry confirmed that there was a phase change in the materials subjected to 140 °C with the decrease in the hysteresis curve of the pure material and that the insertion of cerium also conferred a loss of the magnetic property of the material. The catalytic activity of the materials was evaluated against the CFX degradation initially at pH 6.0, evaluating different concentrations of hydrogen peroxide (1.0, 3.0 and 5.0 mmol L-¹), different concentrations of catalyst (0.125 , 0.250 and 0.500 g L-¹) under irradiation of visible LED devices. It was observed that the material presented low activity and a high consumption of hydrogen peroxide at pH 6.0, because it was decomposing the hydrogen peroxide into water and oxygen. However at pH 3.5 a high production of hydroxyl radicals was observed and this was chosen as working pH. The increase in the amount of cerium and the temperature were important factors in the catalytic efficiency of CFX degradation by the Fenton process, in whichthe material C140-11 was highlighted, which degraded 0.05 mg of CFX per m² of catalyst with a catalyst dosage of 0.125 g L-¹ and 1.0 mmol L-¹ of H2O2 after 150 min. All materials were stable and showed no iron leaching, indicating that all degradations occurred only in the heterogeneous medium. Identification of CFX degradation intermediates indicated hydroxylation as the major route of degradation.
The objective of this work was to evaluate the catalytic activity of iron oxides modified with different amounts of cerium (0, 0.55, 1.1 and 2.2% w/w) and submitted to different heat treatment temperatures (70 and 140 °C) for the degradation of cephalexin (CFX) by Fenton and photo-Fenton processes, using LED devices in the visible range (λ = 460 nm) as irradiation source, a little has been explored in the literature about the variation of these modifications. The materials were characterized by the techniques of X-ray diffraction, diffuse reflectance spectroscopy, high resolution scanning electron microscopy, specific surface area, vibrating sample magnetometry and zeta potential. It was observed that with the thermal treatment at 140 °C the conversion of the magnetite crystalline phase (MGT) to the maghemite crystalline phase (MAG), verified by the color change of the materials and a displacement at the peak of the diffractogram occurred, which was not observed at 70 °C. All materials presented absorption in the UVA, UVB and visible range, however the materials submitted to thermal treatment at 70 °C presented a higher absorption in the wavelength >500 nm. Scanning electron microscopy showed that the insertion of cerium in the iron oxides resulted in a loss of the uniform spherical shape of the particles, presenting irregular spheres. The specific surface area was influenced by both the cerium modification and heat treatment. It was observed that with the lowest amount of cerium (0.55% w/w) there is an increase in the specific surface area from 91.2 to 171.6 m² g-¹ relative to the pure iron oxide that decreases with the insertion of greater amount of cerium (99.2 m² g-¹ for 2.2% w/w). The same behavior was observed for samples treated at 140 °C, however, with smaller areas. Vibrating sample magnetometry confirmed that there was a phase change in the materials subjected to 140 °C with the decrease in the hysteresis curve of the pure material and that the insertion of cerium also conferred a loss of the magnetic property of the material. The catalytic activity of the materials was evaluated against the CFX degradation initially at pH 6.0, evaluating different concentrations of hydrogen peroxide (1.0, 3.0 and 5.0 mmol L-¹), different concentrations of catalyst (0.125 , 0.250 and 0.500 g L-¹) under irradiation of visible LED devices. It was observed that the material presented low activity and a high consumption of hydrogen peroxide at pH 6.0, because it was decomposing the hydrogen peroxide into water and oxygen. However at pH 3.5 a high production of hydroxyl radicals was observed and this was chosen as working pH. The increase in the amount of cerium and the temperature were important factors in the catalytic efficiency of CFX degradation by the Fenton process, in whichthe material C140-11 was highlighted, which degraded 0.05 mg of CFX per m² of catalyst with a catalyst dosage of 0.125 g L-¹ and 1.0 mmol L-¹ of H2O2 after 150 min. All materials were stable and showed no iron leaching, indicating that all degradations occurred only in the heterogeneous medium. Identification of CFX degradation intermediates indicated hydroxylation as the major route of degradation.
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Palavras-chave
Cefalosporinas, Magnetita, Maghemita, Cephalosporins, Magnetite, Maghemite, Processos oxidativos avançados, Advanced oxidative processes