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FotodegradaĆ§Ć£o de pesticidas: caso do fenarimol
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Advisor(s)
Abstract(s)
este trabalho estudou-se o comportamento fotoquĆmico do pesticida
fenarimol, em soluĆ§Ć£o aquosa. O estudo foi desenvolvido no sentido da
caracterizaĆ§Ć£o molecular do pesticida sob o ponto de vista espectroscopico e
fotofĆsico, cinĆ©tica de fotodegradaĆ§Ć£o e caracterizaĆ§Ć£o dos fotoprodutos
resultantes do processo de fotodegradaĆ§Ć£o.
Assim, foram registados os espectros de absorĆ§Ć£o e emissĆ£o
(fluorescĆŖncia e fosforescĆŖncia) do fenarimol em diversos solventes e
determinados os rendimentos quĆ¢nticos de fluorescĆŖncia e respectivos tempos de
vida. No sentido de caracterizar o estado excitado responsƔvel pelo processo de
fotodegradaĆ§Ć£o do pesticida foram desenvolvidos estudos de efeito de solvente
utilizando como referĆŖncia o parĆ¢metro de polaridade E^SO). Com o mesmo
objectivo, foram tambĆ©m realizados estudos de supressĆ£o de fluorescĆŖncia do
pesticida por acĆ§Ć£o de diversos sais, halogenados e nĆ£o halogenados, tendo-se
tambĆ©m procurado caracterizar os respectivos mecanismos de acĆ§Ć£o.
Para estudar o comportamento cinĆ©tico do pesticida em soluĆ§Ć£o aquosa,
foi desenvolvida metodologia para a exposiĆ§Ć£o e anĆ”lise das soluƧƵes irradiadas
ao Sol e em fotoreactor (com irradiaĆ§Ć£o centrada a 313 nm). Determinaram-se as
constantes de velocidade de fotodegradaĆ§Ć£o, em Ć”gua destilada e em soluƧƵes
aquosas com diversos aditivos potencialmente existentes nos sistemas aquƔticos
naturais e susceptĆveis de interferirem no processo de fotodegradaĆ§Ć£o do
fenarimol. Foi tambĆ©m determinado o rendimento quĆ¢ntico de fotodegradaĆ§Ć£o do
pesticida em Ɣgua destilada ao Sol e em fotoreactor utilizando dois mƩtodos
diferentes. Os resultados foram discutidos e relacionados com os resultados
espectroscĆ³picos e fotofĆsicos.
Finalmente procurou-se caracterizar os fotoprodutos formados durante o
processo de degradaĆ§Ć£o fotoquĆmica do fenarimol. Os fotoprodutos obtidos por
irradiaĆ§Ć£o de soluƧƵes aquosas do pesticida ao Sol, com tempos de exposiĆ§Ć£o
diferentes, foram extraĆdos e separados por tĆ©cnicas cromatogrĆ”ficas. A
caracterizaĆ§Ć£o da molĆ©cula de fenarimol e dos compostos existentes nas
II
diferentes fracƧƵes recolhidas foi feita com base em metodologias instrumentais
designadamente, Cromatografia Liquida de Alta PressĆ£o com detector de
multicanais (HPLC-PDA), Cromatografia Gasosa associada Ć Espectometria de
Massa (GC-MS) e Espectroscopia de Infravermelho com transformada de Fourier
(FR-IR). Os resultados foram discutidos, tendo-se avanƧado com propostas para
as estruturas moleculares dos fotoprodutos obtidos. Foram tambƩm feitos estudos
comparativos em funĆ§Ć£o do solvente.
A relaĆ§Ć£o dos resultados alcanƧados, atravĆ©s das trĆŖs vertentes do
trabalho desenvolvido, conduziu-nos a apresentar algumas sugestƵes mecanĆsticas para a fotodecomposiĆ§Ć£o 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.
Description
Tese dout. em QuĆmica, Unidade de CiĆŖncias Exactas e Humanas, Univ. do Algarve, 1997
Keywords
FotoquĆmica Pesticidas Fenarimol SoluĆ§Ć£o aguosa FotodegradaĆ§Ć£o