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Fotodegradação de pesticidas: caso do fenarimol
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Orientador(es)
Resumo(s)
este trabalho estudou-se o comportamento fotoquímico do pesticida
fenarimol, em solução aquosa. O estudo foi desenvolvido no sentido da
caracterização molecular do pesticida sob o ponto de vista espectroscopico e
fotofísico, cinética de fotodegradação e caracterização dos fotoprodutos
resultantes do processo de fotodegradação.
Assim, foram registados os espectros de absorção e emissão
(fluorescência e fosforescência) do fenarimol em diversos solventes e
determinados os rendimentos quânticos de fluorescência e respectivos tempos de
vida. No sentido de caracterizar o estado excitado responsável pelo processo de
fotodegradação do pesticida foram desenvolvidos estudos de efeito de solvente
utilizando como referência o parâmetro de polaridade E^SO). Com o mesmo
objectivo, foram também realizados estudos de supressão de fluorescência do
pesticida por acção de diversos sais, halogenados e não halogenados, tendo-se
também procurado caracterizar os respectivos mecanismos de acção.
Para estudar o comportamento cinético do pesticida em solução aquosa,
foi desenvolvida metodologia para a exposição e análise das soluções irradiadas
ao Sol e em fotoreactor (com irradiação centrada a 313 nm). Determinaram-se as
constantes de velocidade de fotodegradação, em água destilada e em soluções
aquosas com diversos aditivos potencialmente existentes nos sistemas aquáticos
naturais e susceptíveis de interferirem no processo de fotodegradação do
fenarimol. Foi também determinado o rendimento quântico de fotodegradação do
pesticida em água destilada ao Sol e em fotoreactor utilizando dois métodos
diferentes. Os resultados foram discutidos e relacionados com os resultados
espectroscópicos e fotofísicos.
Finalmente procurou-se caracterizar os fotoprodutos formados durante o
processo de degradação fotoquímica do fenarimol. Os fotoprodutos obtidos por
irradiação de soluções aquosas do pesticida ao Sol, com tempos de exposição
diferentes, foram extraídos e separados por técnicas cromatográficas. A
caracterização da molécula de fenarimol e dos compostos existentes nas
II
diferentes fracções recolhidas foi feita com base em metodologias instrumentais
designadamente, Cromatografia Liquida de Alta Pressão com detector de
multicanais (HPLC-PDA), Cromatografia Gasosa associada à Espectometria de
Massa (GC-MS) e Espectroscopia de Infravermelho com transformada de Fourier
(FR-IR). Os resultados foram discutidos, tendo-se avançado com propostas para
as estruturas moleculares dos fotoprodutos obtidos. Foram também feitos estudos
comparativos em função do solvente.
A relação dos resultados alcançados, através das três vertentes do
trabalho desenvolvido, conduziu-nos a apresentar algumas sugestões mecanísticas para a fotodecomposição do fenarimol.
The photophysics and photochemistry of the pesticide fenarimol were studied in aqueous solution. The kinetics of photodegradation and the spectroscopic characterization of the pesticide molecule and its photoproducts were performed. The phosphorescence emission spectra were also registered The absorption and emission spectra of fenarimol (fluorescence and phosphorescence), in different solvents were registered and their fluorescence quantum yields and life times were determined. To characterize the excited state responsible by the photodegradation process of the pesticide, two kinds of studies were performed: solvent polarity effects using as reference the empirical solvent parameter E-^SO); fluorescence quenching using different salts (halogenated and not halogenated) being the respective mechanism of action investigated. A methodology was developed to irradiate (by sunlight and photoreactor at 313 nm) and analyze the solutions in order to study the kinetic behavior of the pesticide. The photodegradation rate constants were determined in distilled water and aqueous solutions with different additives potentially present in natural waters which could interfere with the photodegradation process. The quantum yield of photodegradation under sunlight and photoreactor was also determined in distilled water by two different methods. The results were discussed and related with the spectroscopic and photophysical data. The photoproducts of the fenarimol obtained during the photochemical degradation under sunlight were characterized. The photoproducts resulting from samples with different exposure times were extracted and separated using chromatographic techniques. The characterization of the fenarimol molecule and the compounds collected in the different fractions was performed using different instrumental methods, namely, High Pressure Liquid Chromatography with a phodiode array detector (HPLC-PDA), Gas Chromatography with Mass Spectrometry detector (GC-MS) and Fourier Transform Infrared Spectroscopy (FRIVIR).The results were discussed and suggestions for the molecular structures of the photoproducts were presented. Comparative studies with different solvents were also made. The correlation between the results obtained from the three parts of this work suggests some mechanistic processes for the photodegradation of the fenarimol.
The photophysics and photochemistry of the pesticide fenarimol were studied in aqueous solution. The kinetics of photodegradation and the spectroscopic characterization of the pesticide molecule and its photoproducts were performed. The phosphorescence emission spectra were also registered The absorption and emission spectra of fenarimol (fluorescence and phosphorescence), in different solvents were registered and their fluorescence quantum yields and life times were determined. To characterize the excited state responsible by the photodegradation process of the pesticide, two kinds of studies were performed: solvent polarity effects using as reference the empirical solvent parameter E-^SO); fluorescence quenching using different salts (halogenated and not halogenated) being the respective mechanism of action investigated. A methodology was developed to irradiate (by sunlight and photoreactor at 313 nm) and analyze the solutions in order to study the kinetic behavior of the pesticide. The photodegradation rate constants were determined in distilled water and aqueous solutions with different additives potentially present in natural waters which could interfere with the photodegradation process. The quantum yield of photodegradation under sunlight and photoreactor was also determined in distilled water by two different methods. The results were discussed and related with the spectroscopic and photophysical data. The photoproducts of the fenarimol obtained during the photochemical degradation under sunlight were characterized. The photoproducts resulting from samples with different exposure times were extracted and separated using chromatographic techniques. The characterization of the fenarimol molecule and the compounds collected in the different fractions was performed using different instrumental methods, namely, High Pressure Liquid Chromatography with a phodiode array detector (HPLC-PDA), Gas Chromatography with Mass Spectrometry detector (GC-MS) and Fourier Transform Infrared Spectroscopy (FRIVIR).The results were discussed and suggestions for the molecular structures of the photoproducts were presented. Comparative studies with different solvents were also made. The correlation between the results obtained from the three parts of this work suggests some mechanistic processes for the photodegradation of the fenarimol.
Descrição
Tese dout. em Química, Unidade de Ciências Exactas e Humanas, Univ. do Algarve, 1997
Palavras-chave
Fotoquímica Pesticidas Fenarimol Solução aguosa Fotodegradação