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Abstract(s)
O principal objetivo deste trabalho consistiu em preparar óxidos metálicos de
perovesquites do tipo (La,Ba)(Fe,Ti)O3, caracterizá-los e utilizá-los como fotoânodos em
aplicações ambientais, nomeadamente fotocatálise, eletrocatálise e/ou
fotoeletrocatálise, na degradação dos poluentes modelo AO7 e Diclofenac.
Foram preparados 44 pós perovesquíticos da família LaxBa1-xFeyTi1-yO3, com 0≤x,y≤1,
utilizando dois métodos de preparação, o cerâmico e o de polimerização de complexos,
e diferentes condições de calcinação. Estes pós foram caracterizados estrutural e
morfologicamente e foram determinadas algumas outras propriedades, como
composição química e energia de Band Gap. Foi dada especial ênfase às perovesquites
com índices (0,0), (0,1), (1,0) e (1,1), tendo-se verificado que BaTiO3 cristaliza no
sistema cúbico, BaFeO3 exibe diferentes estruturas, predominantes consoante o método
de síntese, sendo hexagonal quando sintetizada pelo método cerâmico e cúbica quando
o método de preparação é o de polimerização de complexos, LaFeO3 cristaliza no
sistema ortorrômbico e La2Ti2O7 no sistema monoclínico .
Em relação às outras amostras preparadas, verificou-se que grande parte das amostras
não corresponde a fases puras. Pode, ainda, concluir-se que a introdução de elementos
na estrutura perovesquítica e/ou a substituição de elementos leva a modificações
estruturais na perovesquite, sendo que as estruturas predominantes nos diferentes
elementos preparados mostram uma relação com (x,y) que é a seguinte: (x≤0.6, y≤0.3)
cúbica; (x≥0.8, y=0) monoclínica; (x≥0.6, y≥0.8 e x≥0.8, y≥0.6) ortorrômbica; (x≤0.1,
y≥0.4) hexagonal; para y=1 e 0.2≤x≤0.6, tetragonal. Em relação à caracterização
morfológica, embora haja algumas diferenças na morfologia das amostras preparadas,
não foram identificados padrões de relevo.
A maior parte dos pós preparados apresenta energias de Band Gap na zona do
ultravioleta, com valores superiores 3.2 eV. De um modo geral, verifica-se que diminui
com a introdução simultânea de La e Fe. Contudo, a perovesquite que apresenta menor
energia de Band Gap é a BaFeO3.
A maioria das perovesquites testadas em fotocatálise com luz UV conduziram a
remoções superiores às obtidas na fotólise. Contudo, em relação às perovesquites
testadas em fotocatálise com luz visível, apenas a perovesquite La0.1Ba0.9Fe0.2Ti0.8O3 mostrou atividade catalítica com luz visível superior à apresentada na presença de
radiação UV. Nos ensaios com perovesquite imobilizada sobre substrato de TiO2NTs,
os melhores resultados também foram obtidos na presença de radiação UV.
Algumas perovesquites também foram testadas num Reactor LED, com radiação UV de
365 nm para a fotodegradação de diclofenac em soluções aquosas e numa amostra de
água engarrafada. Os melhores resultados foram obtidos com a perovesquite BaTiO3,
preparada pelo método cerâmico, que é, de entre as perovesquites testadas, a que
apresenta uma energia de Band Gap mais próxima da energia da radiação utilizada.
Alguns destes ensaios foram também realizados com adição de persulfato, o que
conduziu a um aumento da velocidade de degradação do diclofenac.
Nos ensaios de fotocatálise realizados com luz solar foi possível perceber que, em
condições idênticas de luminosidade e temperatura, as perovesquites BaTiO3,
preparada pelo método de polimerização de complexos, e BaFeO3, preparada pelo
método cerâmico, degradaram com eficácia soluções aquosas de AO7 e também dos
seus metabolitos, aminonaftol e ácido sulfanílico. Contudo, as perovesquites com
substituições nas posições A e/ou B que foram testadas em fotocatálise com luz solar
manifestaram resultados inferiores à fotólise, possivelmente porque a introdução dos
pós em suspensão levou, nesses casos, a uma absorção dos fotões pelos pós, sem que
ocorresse ativação das suas propriedades catalíticas.
Em suma, o principal objetivo deste trabalho foi alcançado, pois foi possível o
desenvolvimento de materiais foto-ativos não-poluentes e de baixo custo, apropriados
para a degradação de compostos orgânicos em processos amigos do ambiente.
The main objective of this work was to prepare metal oxides of perovskites of the type (La,Ba)(Fe,Ti)O3, characterize them and use them as photo-anodes in environmental applications, namely photocatalysis, electrocatalysis and/or photoelectrocatalysis, for the degradation of the model pollutants AO7 and Diclofenac. In this work, 44 perovskitic powders of the LaxBa1-xFeyTi1-yO3 family were prepared, with 0≤x, y≤1, using two preparation methods, the ceramic and the complex polymerization, and different calcination conditions. These powders were characterized structurally and morphologically, and some other properties were determined, such as chemical composition and band-gap energy. Special emphasis was given to perovskites with indices (0.0), (0.1), (1.0) and (1.1), with BaTiO3 crystallizing in the cubic system, BaFeO3 exhibiting different structures, depending on the synthesis method, being hexagonal predominant when synthesized by the ceramic method and cubic when the method of preparation is the complex polymerization, LaFeO3 crystallizes in the orthorhombic system and La2Ti2O7 in the monoclinic system. Regarding the other samples, it was found that most of the samples do not correspond to pure phases. It can also be concluded that the introduction of elements in the perovskitic structure and/or the substitution of elements leads to structural changes in perovskite, with the predominant structures in the different prepared elements showing a relationship with (x, y) which is the following: (x≤0.6, y≤0.3) cubic; (x≥0.8, y = 0) monoclinic; (x≥0.6, y≥0.8 and x≥0.8, y≥0.6) orthorhombic; (x≤0.1, y≥0.4) hexagonal; for y = 1 and 0.2≤x≤0.6, tetragonal. Regarding the morphological characterization, although there are some differences in the morphology of the prepared samples, no relevant patterns were identified. Most of the prepared powders present band-gap energies in the ultraviolet zone, with values above 3.2 eV. In general, there is a decrease with the simultaneous introduction of La and Fe. However, the perovskite that presents lower band-gap energy is BaFeO3. Most of the perovskites tested in photocatalysis with UV light LED to removals higher than those obtained in photolysis. However, for the perovskites tested in photocatalysis with visible light, only the perovskite La0.1Ba0.9Fe0.2Ti0.8O3 showed catalytic activity with visible light superior to that presented in the presence of UV radiation. In tests with the perovskites immobilized on a TiO2NTs substrate, the best results were also obtained in the presence of UV radiation. Some perovskites were also tested in a LED Reactor, with 365 nm UV radiation, for the photodegradation of diclofenac in aqueous solutions and in bottled water. The best results were obtained with the BaTiO3 perovskite, prepared by the ceramic method, which is, among the tested perovskites, the one presenting the band-gap energy closest to the energy of the radiation utilized. Some of these tests were also carried out with the addition of persulfate, which led to an increase in the rate of diclofenac degradation. In the photocatalysis tests carried out with sunlight it was possible to observe that, under identical conditions of luminosity and temperature, the perovskites BaTiO3, prepared by the complex polymerization method, and BaFeO3, prepared by the ceramic method, effectively degraded aqueous solutions of AO7 and also its metabolites, aminonaftol and sulfanilic acid. However, perovskites A and or B substituted that were tested in photocatalysis with sunlight showed inferior results to photolysis, possibly because the introduction of suspended powders, in these cases, led to an absorption of the photons by the powders, without activation of its catalytic properties. Thus, the main objective of this work was achieved, as it was possible to develop nonpolluting and low-cost photo-active materials, suitable for the degradation of organic compounds in environmentally friendly processes.
The main objective of this work was to prepare metal oxides of perovskites of the type (La,Ba)(Fe,Ti)O3, characterize them and use them as photo-anodes in environmental applications, namely photocatalysis, electrocatalysis and/or photoelectrocatalysis, for the degradation of the model pollutants AO7 and Diclofenac. In this work, 44 perovskitic powders of the LaxBa1-xFeyTi1-yO3 family were prepared, with 0≤x, y≤1, using two preparation methods, the ceramic and the complex polymerization, and different calcination conditions. These powders were characterized structurally and morphologically, and some other properties were determined, such as chemical composition and band-gap energy. Special emphasis was given to perovskites with indices (0.0), (0.1), (1.0) and (1.1), with BaTiO3 crystallizing in the cubic system, BaFeO3 exhibiting different structures, depending on the synthesis method, being hexagonal predominant when synthesized by the ceramic method and cubic when the method of preparation is the complex polymerization, LaFeO3 crystallizes in the orthorhombic system and La2Ti2O7 in the monoclinic system. Regarding the other samples, it was found that most of the samples do not correspond to pure phases. It can also be concluded that the introduction of elements in the perovskitic structure and/or the substitution of elements leads to structural changes in perovskite, with the predominant structures in the different prepared elements showing a relationship with (x, y) which is the following: (x≤0.6, y≤0.3) cubic; (x≥0.8, y = 0) monoclinic; (x≥0.6, y≥0.8 and x≥0.8, y≥0.6) orthorhombic; (x≤0.1, y≥0.4) hexagonal; for y = 1 and 0.2≤x≤0.6, tetragonal. Regarding the morphological characterization, although there are some differences in the morphology of the prepared samples, no relevant patterns were identified. Most of the prepared powders present band-gap energies in the ultraviolet zone, with values above 3.2 eV. In general, there is a decrease with the simultaneous introduction of La and Fe. However, the perovskite that presents lower band-gap energy is BaFeO3. Most of the perovskites tested in photocatalysis with UV light LED to removals higher than those obtained in photolysis. However, for the perovskites tested in photocatalysis with visible light, only the perovskite La0.1Ba0.9Fe0.2Ti0.8O3 showed catalytic activity with visible light superior to that presented in the presence of UV radiation. In tests with the perovskites immobilized on a TiO2NTs substrate, the best results were also obtained in the presence of UV radiation. Some perovskites were also tested in a LED Reactor, with 365 nm UV radiation, for the photodegradation of diclofenac in aqueous solutions and in bottled water. The best results were obtained with the BaTiO3 perovskite, prepared by the ceramic method, which is, among the tested perovskites, the one presenting the band-gap energy closest to the energy of the radiation utilized. Some of these tests were also carried out with the addition of persulfate, which led to an increase in the rate of diclofenac degradation. In the photocatalysis tests carried out with sunlight it was possible to observe that, under identical conditions of luminosity and temperature, the perovskites BaTiO3, prepared by the complex polymerization method, and BaFeO3, prepared by the ceramic method, effectively degraded aqueous solutions of AO7 and also its metabolites, aminonaftol and sulfanilic acid. However, perovskites A and or B substituted that were tested in photocatalysis with sunlight showed inferior results to photolysis, possibly because the introduction of suspended powders, in these cases, led to an absorption of the photons by the powders, without activation of its catalytic properties. Thus, the main objective of this work was achieved, as it was possible to develop nonpolluting and low-cost photo-active materials, suitable for the degradation of organic compounds in environmentally friendly processes.
Description
Keywords
Perovesquites - (La,Ba)(Fe,Ti)O3 Nanotubos Slurry_Paint Caracterização Aplicação Ambiente Diclofenac Fotocatálise Fotoeletrocatálise Radiação Visível Luz Solar