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Abstract(s)
Foram preparados nanomateriais com propriedades óticas e fotocatalíticas melhoradas para a degradação de poluentes orgânicos, em particular de produtos farmacêuticos e de higiene pessoal (PPCPs), através de uma síntese rápida e de baixo custo.
Os nanomateriais foram sintetizados através de um processo hidrotérmico integrado que gera simultaneamente nanotubos de titanato (TNTs) e pontos de carbono (C-dots) através de uma fonte amorfa de titânio, águas de cozedura da cortiça como fonte de carbono e etilenodiamina como aditivo. As propriedades estruturais, microestruturais, morfológicas e óticas dos novos nanocompósitos TNT/C-dots foram estudados por DRX, STEM, espectroscopia de refletância difusa UV-Vis e espectroscopia de fluorescência, sendo a sua área superficial específica determinada pelo método B.E.T.
Como pretendido, os TNT/C-dots apresentam hiatos óticos desviados para o vermelho em comparação com as amostras de TNTs simples, permitindo aos nanocompósitos um uso mais eficiente da radiação visível. Em particular, o nanocompósito TNT/C-dots(12.4%) apresenta um hiato ótico Eg = 2.96±0.03 eV, dentro da região do visível próximo. A diminuição de Eg com o aumento do conteúdo de C-dots da amostra poderá ter origem na criação de estados intermédios de energia na banda proibida dos TNTs resultantes de ligações Ti-O-C estabelecidas entre os TNTs e os C-dots.
Foram testadas amostras de TNT/C-dots com diferentes teores de C-dots na fotodegradação da cafeína, usada como modelo poluente para PPCPs. De entre os nanomateriais sintetizados, o nanocompósito TNT/C-dots (12.4%) apresentou o melhor desempenho fotocatalítico.
Realizaram-se ensaios fotocatalíticos na presença de captadores para avaliar quais as espécies mais relevantes no processo de oxidação da cafeína. Verificou-se que, entre outros mecanismos possíveis, as lacunas e os radicais hidroxilo gerados desempenham um papel determinante na fotodegradação da cafeína na presença dos nanocompósitos TNT/C-dots. Com base nestes resultados foi proposto um modelo para os mecanismos de fotoativação dos TNT/C-dots no processo de degradação
Advanced nanomaterials with enhanced optical and photocatalytic properties for the photodegradation of organic pollutants, in particular pharmaceuticals and personal care products (PPCPs), were successfully prepared by a swift and low cost one-pot synthesis. The nanostructured materials were synthesized through an integrated hydrothermal procedure which generates simultaneously titanate nanotubes (TNTs) with carbon dots (C-dots) embedded onto them, from an amorphous Ti source, cork industry wastewaters as the carbon source, and ethylenediamine as additive. The structural, microstructural, morphological, and optical properties of the new TNT/C-dots nanocomposites were studied by XRD, TEM, UV-Vis diffuse reflectance spectroscopy and fluorescence spectroscopy, being their specific surface areas measured by the B.E.T. method. As aimed, the new materials present optical bandgap energies red shifted in comparison to pristine TNTs, prompting the nanocomposites for a more efficient use of visible light irradiation in photocatalysis. In particular, sample TNT/C-dots(12.4%) shows Eg = 2.96±0.03 eV, within the near-visible region. The decrease of Eg values with increasing sample’s C-dots content may be originated from energy intermediate states formed within the TNTs’ forbidden band resulting from Ti-O-C bonds established between the TNTs and the C-dots. A series of as-synthesized TNT/C-dots nanocomposites varying their content of C-dots were tested in the degradation of caffeine as a pollutant model for PPCPs. Among the nanomaterials synthesized, the TNT/C-dots(12.4%) nanocomposite showed the best photocatalytic performance. Photocatalysis was also performed in the presence of scavengers in order to study the most reactive species during the caffeine oxidation process. The results show that holes and hydroxyl radicals play a key role in the caffeine photodegradation process in the presence of TNT/C-dots nanocomposites. A model for the mechanisms underpinning the photoactivation of the TNT/C-dots nanocomposites is proposed.
Advanced nanomaterials with enhanced optical and photocatalytic properties for the photodegradation of organic pollutants, in particular pharmaceuticals and personal care products (PPCPs), were successfully prepared by a swift and low cost one-pot synthesis. The nanostructured materials were synthesized through an integrated hydrothermal procedure which generates simultaneously titanate nanotubes (TNTs) with carbon dots (C-dots) embedded onto them, from an amorphous Ti source, cork industry wastewaters as the carbon source, and ethylenediamine as additive. The structural, microstructural, morphological, and optical properties of the new TNT/C-dots nanocomposites were studied by XRD, TEM, UV-Vis diffuse reflectance spectroscopy and fluorescence spectroscopy, being their specific surface areas measured by the B.E.T. method. As aimed, the new materials present optical bandgap energies red shifted in comparison to pristine TNTs, prompting the nanocomposites for a more efficient use of visible light irradiation in photocatalysis. In particular, sample TNT/C-dots(12.4%) shows Eg = 2.96±0.03 eV, within the near-visible region. The decrease of Eg values with increasing sample’s C-dots content may be originated from energy intermediate states formed within the TNTs’ forbidden band resulting from Ti-O-C bonds established between the TNTs and the C-dots. A series of as-synthesized TNT/C-dots nanocomposites varying their content of C-dots were tested in the degradation of caffeine as a pollutant model for PPCPs. Among the nanomaterials synthesized, the TNT/C-dots(12.4%) nanocomposite showed the best photocatalytic performance. Photocatalysis was also performed in the presence of scavengers in order to study the most reactive species during the caffeine oxidation process. The results show that holes and hydroxyl radicals play a key role in the caffeine photodegradation process in the presence of TNT/C-dots nanocomposites. A model for the mechanisms underpinning the photoactivation of the TNT/C-dots nanocomposites is proposed.
Description
Trabalho final de mestrado para obtenção do grau de mestre em Engenharia Química e Biológica
Keywords
Nanotubos de titanatos (TNTs) Titanate nanotubes (TNTs) Nanocompósitos TNT/C-dots TNT/C-dots nanocomposites Energia do hiato ótico Optical bandgap energy Fotocatálise Photocatalysis Poluentes orgânicos Organic pollutants C-dots PPCPs
Citation
ALVES, Diogo Manuel Pereira - Síntese da nanocompósitos de TNT/C-dots e o seu potencial uso na degradação fotocatalítica de poluentes orgânicos. Lisboa: Instituto Superior de Engenharia de Lisboa, 2018. Dissertação de mestrado.
Publisher
Instituto Superior de Engenharia de Lisboa