| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 16.34 MB | Adobe PDF |
Abstract(s)
O presente trabalho teve como objetivos a síntese e caracterização de óxidos metálicos mistos do tipo perovesquite, das famílias (Sr,La,Bi)(Ti,Fe)O3, e o estudo da sua aplicação na degradação foto-, eletro- e fotoeletrocatalítica, e por reação tipo-Fenton heterogéneo, de três poluentes orgânicos.
Os óxidos foram sintetizados pelo método cerâmico, através da substituição parcial de um, ou dois, elementos na estrutura de perovesquites “mãe”, nomeadamente, SrTiO3, SrFeO3, LaTiO3, LaFeO3, BiTiO3 e BiFeO3. Para as quatro séries Sr1-xLaxFeO3, Sr1-xBixFeO3, SrTi1-yFeyO3 e Sr1-xBixTi1-yFeyO3 todos os compostos sintetizados apresentaram uma fase única, pertencente à simetria cúbica da perovesquite “mãe” correspondente (SrTiO3 ou SrFeO3), indicando uma boa solubilidade dos catiões parcialmente substituídos na estrutura cristalina. Com as séries La1-xBixFeO3 e LaTi1-yFeyO3 observou-se uma mudança de fase predominante com o aumento de x ou y, correspondendo à fase de um extremo da série (x ou y = 0) a outro (x ou y = 1). Relativamente à série La1-xBixFeO3, a síntese não foi considerada completa para três óxidos, x = 0,05, 0,1 e 0,3, devido à identificação nas amostras finais de picos correspondentes às fases dos reagentes usados. Nas séries Sr1-xLaxTiO3 e Sr1-xBixTiO3, identificou-se a presença de fases secundárias para todas as amostras parcialmente substituídas, indicando que tinham sido excedidos os limites de solubilidade.
Numa primeira fase, testaram-se dois métodos de imobilização dos pós dos óxidos de perovesquite, antes do estudo da sua aplicação na degradação fotoeletrocatalítica do corante Acid Orange 7: como filmes de Sr1-xBixTiO3 depositados sobre um substrato de espuma de níquel e como elétrodos de pastilha de SrTi1-yFeyO3. Os filmes Ni/Sr1-xBixTiO3, preparados com os óxidos parcialmente substituídos, apresentaram uma atividade fotocatalítica muito superior à obtida com o filme da perovesquite não substituída, Ni/SrTiO3, com reduções de Abs484nm de 4,4% e 82,6% para os respetivos filmes de Ni/SrTiO3 e Ni/Sr0,9Bi0,1TiO3, após 7 horas de irradiação visível. Esta atividade fotocatalítica foi relacionada com a presença da fase secundária Bi4Ti3O12, em todos os óxidos parcialmente substituídos. Os elétrodos de pastilha, preparados com a série SrTi1-yFeyO3, foram aplicados na degradação eletrocatalítica (j = 1 mA cm-2) do mesmo corante (25 mg L-1), atingindo decaimentos de Abs484nm entre 55,4% e 71,0%, após 8 horas. A aplicação fotoeletrocatalítica do elétrodo SrFeO3 resultou num aumento da percentagem de decaimento da Abs484nm de 6% quando comparado com o processo eletrocatalítico, indicando um efeito sinergético entre o processo foto e eletrocatalítico. No entanto, estes dois métodos de imobilização apresentaram algumas limitações experimentais, tais como a perda de massa de pós depositados nos filmes de Ni/Sr1-xBixTiO3, durante a sua aplicação, ou a pequena área superficial dos elétrodos de pastilha.
Todos os óxidos sintetizados foram testados como fotocatalisadores em suspensão (0,2 e 0,5 g L-1), na degradação do corante Acid Orange 7, sob luz visível. Dentro das famílias (Sr,La,Bi)(Ti,Fe)O3, as séries Sr1-xLaxTiO3, Sr1-xBixTiO3 e Sr1-xBixTi1-yFeyO3 apresentaram atividade fotocatalítica, demonstrando que a substituição parcial, dos elementos em questão, na estrutura da perovesquite “mãe” SrTiO3, melhorou significativamente a atividade fotocatalítica dos materiais. Das três séries, a Sr1-xBixTiO3 apresentou os melhores resultados, com uma degradação completa do corante (10 mg L-1), para alguns dos óxidos, após 1 hora de irradiação. Sob condições experimentais diferentes, o óxido Sr0,95Bi0,05TiO3 exibiu a melhor atividade fotocatalítica de todos os óxidos da série, atingindo degradação completa do corante (C0 = 10 e 25 mg L-1). Através da análise dos resultados, obtidos durante a monitorização dos diferentes produtos de degradação, foi proposto um mecanismo de degradação para o corante Acid Orange 7. Suspensões do mesmo óxido foram aplicadas na degradação de oxitetraciclina, imidaclopride e misturas dos dois compostos em água destilada e numa matriz real. Em todas as condições experimentais estudadas, a velocidade de degradação da oxitetraciclina apresentou-se superior à do imidaclopride, o que foi relacionado com a estrutura das moléculas dos dois poluentes, e as suas afinidades com alguns constituintes da matriz ou superfície do fotocatalisador. O óxido de Sr0,95Bi0,05TiO3 foi aplicado em vários ciclos consecutivos de utilização, para as degradações fotocatalíticas de todos os poluentes mencionados, e em todas as instâncias não se verificou alteração na sua atividade fotocatalítica, nem perda de estabilidade estrutural, morfológica e ótica.
Óxidos do tipo perovesquite contendo ferro, pertencentes à série SrTi1-yFeyO3 (y = 0,5, 0,7, 0,9 e 1), foram aplicados na degradação de soluções de oxitetraciclina através de reações do tipo-Fenton heterogéneo, atingindo degradações superiores a 70%, após 3 horas. Os melhores resultados foram obtidos com a perovesquite que continha maior teor em ferro, SrFeO3, com uma degradação do antibiótico de 99,7%, após 3 horas. A reutilização da perovesquite por três ciclos consecutivos não resultou numa perda de atividade nem estabilidade estrutural ou morfológica.
The main objective of this work was to synthesize and characterize perovskite-like metal oxides, belonging to the (Sr,La,Bi)(Ti,Fe)O3 families, and study their applications in the degradation of three organic pollutants by photo-, electro- and photoelectrocatalysis and by heterogeneous Fenton-like reaction. The oxide samples were synthesized by solid-state method, through partial substitution of one, or two, elements in the structure of each “mother” perovskite, such as, SrTiO3, SrFeO3, LaTiO3, LaFeO3, BiTiO3 and BiFeO3. For the series of general formula Sr1-xLaxFeO3, Sr1-xBixFeO3, SrTi1-yFeyO3 and Sr1-xBixTi1-yFeyO3, all synthesized samples exhibited one phase, belonging to the cubic perovskite symmetry of the corresponding “mother” oxide (SrTiO3 or SrFeO3), indicating that all the partially substituted cations were soluble in the perovskite structure. With the La1-xBixFeO3 and LaTi1-yFeyO3 series a change of the predominant phase was observed, with the increase of x or y, corresponding to the phases exhibited at x or y = 0 and x or y = 1. Regarding the series of general formula La1-xBixFeO3, the synthesis of three oxides, x = 0,05, 0,1 e 0,3, was considered incomplete, due to the detection and identification of diffraction peaks, in the final sample, belonging to the reagents. In both Sr1-xLaxTiO3 e Sr1-xBixTiO3 series, secondary phases were identified, for all partially substituted samples, indicating that the solubility limits, of the corresponding cations, were exceeded. In an initial approach, two powder immobilization methods were tested, before studying the perovskite oxides application on the photoelectrocatalytic degradation of Acid Orange 7 dye: as Sr1-xBixTiO3 deposited films over a nickel foam substrate and as SrTi1-yFeyO3 pellet electrodes. The Ni/Sr1-xBixTiO3 films prepared with the partially substituted oxides exhibited higher photocatalytic activity than the film prepared with the non-substituted sample, Ni/SrTiO3, with Abs484nm reductions of 4,4% and 82,6% for the Ni/SrTiO3 and Ni/Sr0,9Bi0,1TiO3 films, respectively, after 7 hours under visible light. This photocatalytic activity was associated with the presence of the secondary phase Bi4Ti3O12 in all partially substituted oxides. The pellet electrodes, prepared with the SrTi1-yFeyO3 perovskites, were tested on the electrocatalytic degradation (j = 1 mA cm-2) of the same dye (25 mg L-1), achieving Abs484nm decays between 55,4% and 71,0%, after 8 hours. The photoelectrocatalytic application of the SrFeO3 pellet electrode increased the Abs484nm decay by 6%, when compared with the electrocatalytic process, indicating a synergistic effect between the photo and electrocatalytic process. However, both immobilization methods presented some experimental limitations, such as the loss of mass deposited in the Ni/Sr1-xBixTiO3 films during their application, or the small surface area of the pellet electrodes. Suspensions (0,2 e 0,5 g L-1) of all synthesized oxides were tested as photocatalysts on the degradation of Acid Orange 7 dye, under visible light. Amongst all tested perovskites, belonging to the (Sr,La,Bi)(Ti,Fe)O3 families, the Sr1-xLaxTiO3, Sr1-xBixTiO3 and Sr1-xBixTi1-yFeyO3 series exhibited photocatalytic activity, indicating that the partial substitution, of said elements, in the “mother” oxide SrTiO3, improved the photocatalytic activity significantly. Among the three series, Sr1-xBixTiO3 showed the best results, achieving complete degradation of the dye (10 mg L-1), for some of the oxides, after 1 hour of irradiation. Under different experimental conditions, the Sr0,95Bi0,05TiO3 oxide exhibited the best photocatalytic activity, from all other oxides belonging to the Sr1-xBixTiO3 series, achieving complete dye removal (C0 = 10 e 25 mg L-1). Through the monitorization of the different degradation products, a degradation mechanism for the dye was proposed. Suspensions of the Sr0,95Bi0,05TiO3 oxide were applied on the degradation of oxytetracycline, imidacloprid and mixtures of both compounds in distilled water and in a real matrix. For all experimental conditions tested, the degradation rate of oxytetracycline was always higher than the observed for imidacloprid. This behavior was associated with both molecules’ structure, and their affinity with some constituents of the real matrix or the photocatalysts’ surface. The Sr0,95Bi0,05TiO3 oxide was applied during several consecutive cycles of photocatalytic degradation, of all mentioned pollutants, and in all experiments no change to the oxide’s photocatalytic activity was observed. Also, no loss in structural, morphological, and optic stability was observed. Some perovskite-like oxides containing iron, belonging to the SrTi1-yFeyO3 (y = 0,5, 0,7, 0,9 e 1) series, were applied as catalysts in the heterogeneous Fenton-like degradation of oxytetracycline solutions, achieving degradations above 70%, after 3 hours. The best results were obtained with the perovskite with higher iron content, SrFeO3, with a degradation of 99,7%, after 3 hours. The reuse of the perovskite oxide, during three consecutive cycles, resulted in no loss in catalytic activity nor structural and morphologically stability.
The main objective of this work was to synthesize and characterize perovskite-like metal oxides, belonging to the (Sr,La,Bi)(Ti,Fe)O3 families, and study their applications in the degradation of three organic pollutants by photo-, electro- and photoelectrocatalysis and by heterogeneous Fenton-like reaction. The oxide samples were synthesized by solid-state method, through partial substitution of one, or two, elements in the structure of each “mother” perovskite, such as, SrTiO3, SrFeO3, LaTiO3, LaFeO3, BiTiO3 and BiFeO3. For the series of general formula Sr1-xLaxFeO3, Sr1-xBixFeO3, SrTi1-yFeyO3 and Sr1-xBixTi1-yFeyO3, all synthesized samples exhibited one phase, belonging to the cubic perovskite symmetry of the corresponding “mother” oxide (SrTiO3 or SrFeO3), indicating that all the partially substituted cations were soluble in the perovskite structure. With the La1-xBixFeO3 and LaTi1-yFeyO3 series a change of the predominant phase was observed, with the increase of x or y, corresponding to the phases exhibited at x or y = 0 and x or y = 1. Regarding the series of general formula La1-xBixFeO3, the synthesis of three oxides, x = 0,05, 0,1 e 0,3, was considered incomplete, due to the detection and identification of diffraction peaks, in the final sample, belonging to the reagents. In both Sr1-xLaxTiO3 e Sr1-xBixTiO3 series, secondary phases were identified, for all partially substituted samples, indicating that the solubility limits, of the corresponding cations, were exceeded. In an initial approach, two powder immobilization methods were tested, before studying the perovskite oxides application on the photoelectrocatalytic degradation of Acid Orange 7 dye: as Sr1-xBixTiO3 deposited films over a nickel foam substrate and as SrTi1-yFeyO3 pellet electrodes. The Ni/Sr1-xBixTiO3 films prepared with the partially substituted oxides exhibited higher photocatalytic activity than the film prepared with the non-substituted sample, Ni/SrTiO3, with Abs484nm reductions of 4,4% and 82,6% for the Ni/SrTiO3 and Ni/Sr0,9Bi0,1TiO3 films, respectively, after 7 hours under visible light. This photocatalytic activity was associated with the presence of the secondary phase Bi4Ti3O12 in all partially substituted oxides. The pellet electrodes, prepared with the SrTi1-yFeyO3 perovskites, were tested on the electrocatalytic degradation (j = 1 mA cm-2) of the same dye (25 mg L-1), achieving Abs484nm decays between 55,4% and 71,0%, after 8 hours. The photoelectrocatalytic application of the SrFeO3 pellet electrode increased the Abs484nm decay by 6%, when compared with the electrocatalytic process, indicating a synergistic effect between the photo and electrocatalytic process. However, both immobilization methods presented some experimental limitations, such as the loss of mass deposited in the Ni/Sr1-xBixTiO3 films during their application, or the small surface area of the pellet electrodes. Suspensions (0,2 e 0,5 g L-1) of all synthesized oxides were tested as photocatalysts on the degradation of Acid Orange 7 dye, under visible light. Amongst all tested perovskites, belonging to the (Sr,La,Bi)(Ti,Fe)O3 families, the Sr1-xLaxTiO3, Sr1-xBixTiO3 and Sr1-xBixTi1-yFeyO3 series exhibited photocatalytic activity, indicating that the partial substitution, of said elements, in the “mother” oxide SrTiO3, improved the photocatalytic activity significantly. Among the three series, Sr1-xBixTiO3 showed the best results, achieving complete degradation of the dye (10 mg L-1), for some of the oxides, after 1 hour of irradiation. Under different experimental conditions, the Sr0,95Bi0,05TiO3 oxide exhibited the best photocatalytic activity, from all other oxides belonging to the Sr1-xBixTiO3 series, achieving complete dye removal (C0 = 10 e 25 mg L-1). Through the monitorization of the different degradation products, a degradation mechanism for the dye was proposed. Suspensions of the Sr0,95Bi0,05TiO3 oxide were applied on the degradation of oxytetracycline, imidacloprid and mixtures of both compounds in distilled water and in a real matrix. For all experimental conditions tested, the degradation rate of oxytetracycline was always higher than the observed for imidacloprid. This behavior was associated with both molecules’ structure, and their affinity with some constituents of the real matrix or the photocatalysts’ surface. The Sr0,95Bi0,05TiO3 oxide was applied during several consecutive cycles of photocatalytic degradation, of all mentioned pollutants, and in all experiments no change to the oxide’s photocatalytic activity was observed. Also, no loss in structural, morphological, and optic stability was observed. Some perovskite-like oxides containing iron, belonging to the SrTi1-yFeyO3 (y = 0,5, 0,7, 0,9 e 1) series, were applied as catalysts in the heterogeneous Fenton-like degradation of oxytetracycline solutions, achieving degradations above 70%, after 3 hours. The best results were obtained with the perovskite with higher iron content, SrFeO3, with a degradation of 99,7%, after 3 hours. The reuse of the perovskite oxide, during three consecutive cycles, resulted in no loss in catalytic activity nor structural and morphologically stability.
Description
Keywords
Perovesquite (Sr,La,Bi)(Ti,Fe)O3 Fotocatálise heterogénea Eletrocatálise Fotoeletrocatálise Reação tipo-Fenton heterogénea Acid Orange 7 Oxitetraciclina Imidaclopride