Estudo da conversão fotoeletrocatalítica de biometano e CO2 em biohidrogênio e outros produtos combustíveis
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2018-10
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Stülp, Simone
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A produção de energia tornou-se uma grande preocupação mundial devido ao esgotamento dos combustíveis fósseis e aos problemas ambientais relacionados com as emissões antropogênicas de gases de efeito estufa, que estão alterando o equilíbrio natural do meio ambiente e causando diversas mudanças ambientais globais, cuja extensão ainda é incerta. Nesse contexto, a conversão de biometano e CO2 em hidrogênio e outros produtos combustíveis através da fotoeletrocatálise tornou-se uma estratégia altamente promissora na busca por opções energéticas renováveis. Com isso, este trabalho descreve a síntese e caracterização de materiais
semicondutores para aplicação na conversão eletrocatalítica, fotocatalítica e fotoeletrocatalítica de biometano e CO2 em hidrogênio e outros produtos combustíveis. Na primeira parte do trabalho, investigou-se a conversão eletrocatalítica, fotocatalítica e fotoeletrocatalítica de biometano em hidrogênio sobre um semicondutor nanoestruturado de Ti/TiO2. A caracterização morfológica do semicondutor demonstrou que, após a síntese houve a formação de nanotubos de TiO2 na superfície do Ti, com diâmetro interno médio de 90,3 nm. A composição do semicondutor foi confirmada através da análise de espectroscopia de energia dispersiva, sendo que o peso por porcentagem de cada elemento foi de 58,8% de Ti e 41,2% de O2. A
adsorção do metano na superfície do Ti/TiO2 foi confirmada através da análise de FTIR e esse resultado é de extrema relevância, uma vez que, após a excitação, os elétrons e lacunas da superfície do semicondutor podem interagir com as moléculas adsorvidas, resultando na sua redução e/ou oxidação. A fotoatividade do
semicondutor para reações fotoeletrocatalíticas foi analisada através de ensaios de fotocorrente, cronoamperometria e espectroscopia de impedância eletroquímica. Através das análises eletroquímicas, pode-se observar que sob irradiação ultravioleta há uma maior separação dos pares e-/h+ fotogerados, o que comprova a fotoatividade dos nanotubos de Ti/TiO2 enquanto catalisador para as reações fotoeletrocatalíticas.
Após a caracterização, a atividade fotoeletrocatalítica do semicondutor de Ti/TiO2 nanoestruturado foi avaliada através de experimentos de conversão de biometano em hidrogênio, onde obteve-se uma produção de 4,42±0,079 mmol h-1 de H2 com o uso da fotoeletrocatálise. Na segunda parte do trabalho, realizou-se a modificação superficial do eletrodo de Ti/TiO2 por deposição eletroquímica de óxido de cobre, em diferentes temperaturas (25oC e 65oC), e sua aplicação na conversão fotoeletrocatalítica de CO2 e biogás em produtos de interesse energético. As diferentes temperaturas de deposição de óxido de cobre resultaram na formação de diferentes formas geométricas na superfície dos nanotubos de Ti/TiO2 e em diferentes atividades fotoeletrocatalíticas. A conversão fotoeletrocatalítica em Na2SO4 0,1 M com aplicação de -0,1V e irradiação UV resultou na formação de acetona, metanol e metano a partir de CO2 e acetona, etanol e hidrogênio a partir de biogás, sendo que a produção de acetona foi maior para o semicondutor sintetizado a 65oC, enquanto que
a produção de metanol e de etanol foi maior para o semicondutor a 25oC. Esses resultados indicam a maior atividade fotoeletrocatalítica para o semicondutor de Ti/TiO2/óxido de cobre sintetizado a 65oC, pois sua utilização levou a formação de produtos que exigem um maior número de elétrons na reação. Esses resultados são extremamente relevantes, uma vez que contribuem na busca por opções energéticas viáveis, de baixo impacto ambiental e que garantam o fornecimento de energia.
Energy production has become a major concern worldwide due to the depletion of fossil fuels and the environmental problems related to anthropogenic greenhouse gas emissions, which are altering the natural balance of the environment and causing several global environmental changes, the extent of which it is still uncertain. In this context, the conversion of biomethane and CO2 into hydrogen and other fuel products through photoelectrocatalysis has become a highly promising strategy in the search for renewable energy options. Thus, this work describes the synthesis and characterization of semiconductor materials for application in electrocatalytic, photocatalytic and photoelectrocatalytic conversion of biomethane and CO2 to hydrogen and other combustible products. In the first part of the work, we investigated the electrocatalytic, photocatalytic and photoelectrocatalytic conversion of biomethane to hydrogen on a nanostructured Ti/TiO2 semiconductor. The morphological characterization of the semiconductor showed that, after synthesis, TiO2 nanotubes were formed on the Ti surface, with an average internal diameter of 90.3 nm. The composition of the semiconductor was confirmed by dispersive energy spectroscopy analysis, and the weight by percentage of each element was 58.8% Ti and 41.2% O2. Methane adsorption on the Ti/TiO2 surface was confirmed by FTIR analysis and this result is extremely relevant since, after excitation, semiconductor surface electrons and gaps can interact with the adsorbed molecules, resulting in its reduction and / or oxidation. Semiconductor photoactivity for photoelectrocatalytic reactions was analyzed by photocurrent, chronoamperometry and electrochemical impedance spectroscopy assays. Through the electrochemical analysis, it can be observed that under ultraviolet irradiation there is a greater separation of the photogenerated e-/h+ pairs, which proves the photoactivity of Ti/TiO2 nanotubes as a catalyst for photoelectrocatalytic reactions. After characterization, the photoelectrocatalytic activity of the nanostructured Ti/TiO2 semiconductor was evaluated through experiments of conversion of biomethane to hydrogen, which yielded 4.42 ± 0.079 mmol h-1 H2 using photoelectrocatalysis. In the second part of the work, the surface modification of the Ti/TiO2 electrode was performed by electrochemical deposition of copper oxide at different temperatures (25oC and 65oC), and its application in the photoelectrocatalytic conversion of CO2 and biogas into products of energy interest. The different deposition temperatures of copper oxide resulted in the formation of different geometric forms on the surface of Ti/TiO2 nanotubes and different photoelectrocatalytic activities. The photoelectrocatalytic conversion to 0.1 M Na2SO4 with application of -0.1V and UV irradiation resulted in the formation of acetone, methanol and methane from CO2 and acetone, ethanol and hydrogen from biogas, being that acetone production was higher for semiconductor synthesized at 65oC, while methanol and ethanol production was higher for semiconductor at 25oC. These results indicate the greater photoelectrocatalytic activity for the Ti/TiO2/copper oxide semiconductor synthesized at 65oC, as their use led to the formation of products that require a higher number of electrons in the reaction. These results are extremely relevant as they contribute to the search for viable energy options with low environmental impact and that guarantee the supply of energy.
Energy production has become a major concern worldwide due to the depletion of fossil fuels and the environmental problems related to anthropogenic greenhouse gas emissions, which are altering the natural balance of the environment and causing several global environmental changes, the extent of which it is still uncertain. In this context, the conversion of biomethane and CO2 into hydrogen and other fuel products through photoelectrocatalysis has become a highly promising strategy in the search for renewable energy options. Thus, this work describes the synthesis and characterization of semiconductor materials for application in electrocatalytic, photocatalytic and photoelectrocatalytic conversion of biomethane and CO2 to hydrogen and other combustible products. In the first part of the work, we investigated the electrocatalytic, photocatalytic and photoelectrocatalytic conversion of biomethane to hydrogen on a nanostructured Ti/TiO2 semiconductor. The morphological characterization of the semiconductor showed that, after synthesis, TiO2 nanotubes were formed on the Ti surface, with an average internal diameter of 90.3 nm. The composition of the semiconductor was confirmed by dispersive energy spectroscopy analysis, and the weight by percentage of each element was 58.8% Ti and 41.2% O2. Methane adsorption on the Ti/TiO2 surface was confirmed by FTIR analysis and this result is extremely relevant since, after excitation, semiconductor surface electrons and gaps can interact with the adsorbed molecules, resulting in its reduction and / or oxidation. Semiconductor photoactivity for photoelectrocatalytic reactions was analyzed by photocurrent, chronoamperometry and electrochemical impedance spectroscopy assays. Through the electrochemical analysis, it can be observed that under ultraviolet irradiation there is a greater separation of the photogenerated e-/h+ pairs, which proves the photoactivity of Ti/TiO2 nanotubes as a catalyst for photoelectrocatalytic reactions. After characterization, the photoelectrocatalytic activity of the nanostructured Ti/TiO2 semiconductor was evaluated through experiments of conversion of biomethane to hydrogen, which yielded 4.42 ± 0.079 mmol h-1 H2 using photoelectrocatalysis. In the second part of the work, the surface modification of the Ti/TiO2 electrode was performed by electrochemical deposition of copper oxide at different temperatures (25oC and 65oC), and its application in the photoelectrocatalytic conversion of CO2 and biogas into products of energy interest. The different deposition temperatures of copper oxide resulted in the formation of different geometric forms on the surface of Ti/TiO2 nanotubes and different photoelectrocatalytic activities. The photoelectrocatalytic conversion to 0.1 M Na2SO4 with application of -0.1V and UV irradiation resulted in the formation of acetone, methanol and methane from CO2 and acetone, ethanol and hydrogen from biogas, being that acetone production was higher for semiconductor synthesized at 65oC, while methanol and ethanol production was higher for semiconductor at 25oC. These results indicate the greater photoelectrocatalytic activity for the Ti/TiO2/copper oxide semiconductor synthesized at 65oC, as their use led to the formation of products that require a higher number of electrons in the reaction. These results are extremely relevant as they contribute to the search for viable energy options with low environmental impact and that guarantee the supply of energy.
Descrição
Palavras-chave
Materiais semicondutores; Fotoeletrocatálise; Hidrogênio; Produtos combustíveis; Semiconductor materials; Photoelectrocatalysis; Hydrogen; Combustible products
Citação
BRESCIANI, Laís. Estudo da conversão fotoeletrocatalítica de biometano e CO2 em biohidrogênio e outros produtos combustíveis. 2019. Dissertação (Mestrado) – Curso de Ambiente e Desenvolvimento, Universidade do Vale do Taquari - Univates, Lajeado, nov. 2019. Disponível em: http://hdl.handle.net/10737/2764.