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Doctoral Thesis
DOI
10.11606/T.75.2009.tde-26082009-103253
Document
Author
Full name
Lisbeth Zelayarán Melgar
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 2009
Supervisor
Committee
Gessner, Fergus (President)
Pezza, Leonardo
Rezende, Maria Olimpia de Oliveira
Venâncio, Tiago
Cavalheiro, Carla Cristina Schmitt
Title in Portuguese
Estudo das interações entre os fungicidas (carbendazim e fuberidazole) e as partículas de argila em suspensão aquosa. Adsorção, fotofísica e fotoquímica
Keywords in Portuguese
adsorção
argilas
fotodegradação
fotofísica
montmorilonitas
pesticidas
Abstract in Portuguese
Neste trabalho foi realizado um estudo das interações entre os fungicidas (carbendazim e fuberidazole) e as partículas de argilas SWy-1, SHCa-1 e SYn-1 em suspensão aquosa. Foram determinados através de isotermas de adsorção, espectrofometria de absorção no UV, de emissão de fluorescência e difratometria de raios -X. Os resultados experimentais envolvendo a adsorção foram bem ajustados pelas isotermas de Langmuir, Freundlich e Dubinin-Radushkevich os quais indicam haver alta afinidade entre os fungicidas e as argilas. A capacidade de adsorção foi maior na argila SWy-1 comparada às argilas SHCa-1 e SYn-1, sendo estas ultimas com capacidade de adsorção similares. Foi observada a adsorção dos fungicidas carbendazim e fuberidazole à região interlamelar das partículas de argila, onde ocorre a protonação da molécula dos fungicidas, tornando-a mais estável. Medidas espectrofotométricas, na região do UV, foram efetuadas em função do tempo durante 24 horas. Pela análise dos resultados obtidos, foi possível propor um mecanismo geral para explicar as mudanças espectrais que ocorrem durante a adsorção dos fungicidas nas partículas das argilas em suspensão aquosa. Os resultados de espectrofotometria de absorção no UV do fuberidazole adsorvido nas partículas das argilas e as isotermas de adsorção indicaram que existe uma correlação entre a saturação das argilas e a saturação dos sítios ácidos no processo de adsorção. A intensidade de emissão aumentou significativamente quando o carbendazim foi adsorvido nas argilas SHCa-1 e SYn-1. No entanto, com o fuberidazole observou-se uma diminuição da fluorescência. Nenhuma emissão da fluorescência dos fungicidas carbendazim e fuberidazole adsorvidos nas partículas da argila SWy-1 foi observada devido ao alto teor de ferro. A fotodegradação do carbendazim foi significativamente acelerada quando foi adsorvido nas partículas das argilas. Foi possível observar o aparecimento de novas bandas nos espectros de absorção e de emissão dos fotoprodutos formados na argila que não foram reportados na literatura.
Title in English
Study of the interaction between fungicides (carbendazim and fuberidazole) and the clay particles in suspension aqueous. Adsorption, photophysical, photochemical
Keywords in English
adsorption
clay
montmorillonite
pesticide
photodegradation
photophysical
Abstract in English
In the present work, studies on the interaction between the fungicides (carbendazim and fuberidazole) and clay particles in aqueous suspension. It has been studied by isotherm adsorption, UV spectroscopy, emission of fluorescence and X-Ray. The results were fitted according the Langmuir, Freundlich and Dubinin- Radushkevich isotherms indicating a high affinity between the fungicide and the clay surfaces. The adsorption capacity in the SWy-1 clay was higher than the SHCa-1 and SYn-1 clays, being these last clays with same adsorption capacity between them. The fungicides can be adsorbed as neutral molecules in the external surfaces as well can be protonated in the interlamellar region of the clay particles. Spectrofothometric measurements in the UV region were taken after different time intervals. A mechanism for the adsorption of fungicides molecules on the clay particles was perceived, leading to a better understanding of the adsorption of this compound on clays. The data obtained by the absorption spectrophotometry in the UV region of the fuberidazole adsorbed in the particle clays and its adsorption isotherms indicated the correlation between the saturation of the clays and the saturation of the acid sites in the adsorption process. When carbendazim was adsorbed on the SHCa-1 and SYn-1 clay particles, the emission intensity increased significantly. However with the fuberidazole was decreased. The emission spectra showed bands attributed to both neutral adsorbed and protonated forms of the fungicides. The emission of the fungicides molecules adsorbed on the particles of SWy-1 clays was almost totally quenched due to the high load of iron. The carbendazim photodegradation process was significantly accelerated when carbendazim was adsorbed on the clay particles compared to the aqueous phase. It was possible to determine the absorption and emission spectra of photoproducts formed on the clay particles, which were not detected in other studies reported in the literature.
 
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Publishing Date
2009-08-27
 
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