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- A comparative study of the photophysics and photochemistry of 4-chlorophenol adsorbed on silicalite and beta-cyclodextrinPublication . Da Silva, José Paulo; Ferreira, Luís F. Vieira; Silva, Abílio M. da; Oliveira, A. S.The photochemistry and photophysics of 4-chlorophenol (4-CP) were studied onto two model solid supports, silicalite and beta-cyclodextrin (beta-Cl)), using time resolved diffuse reflectance techniques and product degradation analysis. The results have shown that the photochemistry and photophysics of 4-CP are different from solution and depend on the solid. Ground state diffuse reflectance and time resolved luminescence demonstrated the inclusion of the probe in both substrates. 4-CP exhibits room temperature luminescence in both hosts, being structured and much more intense in beta-CD. The emission was assigned to phosphorescence of the inclusion complex. Transient absorption demonstrated the formation of the unsubstituted phenoxyl radical and of 4-chlorophenoxyl radical in beta-CD. In silicalite only the later was detected. The studies of the photodegradation products indicate that phenol is the main photoproduct in beta-CD. In silicalite the chromatographic analysis indicates the presence of products that involve the ring cleavage. (C) 2002 Elsevier Science B.V. All rights reserved.
- Aqueous photochemistry of pesticides triadimefon and triadimenolPublication . Silva, José P. da; Ferreira, Luís F. Vieira; Silva, Abílio M. daThe photochemistry of pesticides triadimefon and triadimenol was studied in aqueous solution and in methanol/water mixtures, in controlled and natural conditions. The photodegradation kinetics and product distribution are strongly dependent on the solvent and on the irradiation wavelength. The degradation rates are faster at 254 nm than at 313 nm. The kinetics is faster in water than methanol. Direct photoreaction is an important dissipation pathway of triadimefon in natural water systems while triadimenol is stable in these conditions. 1,2,4-Triazole and 4-chlorophenol are two of the major photodegradation products. The formation of the 4-chlorophenoxyl radical was detected for both pesticides in methanol and methanol/water mixtures. In methanol/water mixtures the reaction of both pesticides also occurs with 4-chlorophenolate formation, which increases with the water content. The photochemical studies of pesticides and other pollutants should be made in conditions as similar as possible to those observed in environmental systems. (C) 2003 Elsevier Science B.V. All rights reserved.
- Solution and surface photochemistry of fenarimol: a comparative studyPublication . Silva, José P. da; Mateus, Maria Da Conceição; Silva, Abílio M. da; Ferreira, Luís F. Vieira; Burrows, Hugh D.The photochemistry of the pesticide fenarimol was studied in methanol and on a cellulose surface. The ground state absorption and fluorescence spectra are similar in solution and at the solid/gas interface. Room temperature phosphorescence emission was observed in cellulose. Transient absorption of fenarimol and of its chromophoric units, chlorobenzene and pyrimidine, showed a common absorption band centered at 320 nm in methanol. An absorption band above 350 nm was observed only for fenarimol and was assigned to a recombination intermediate. On cellulose the transient absorption is broader and extends up to 600 nm. The main photodegradation pathway in methanol involves the homolytic cleavage of the bond to the pyrimidyl ring, followed by a fast in-cage recombination of the initially formed pyrimidine and ketyl radicals. On cellulose surfaces, dechlorination is also one of the important photodegradation pathways. (c) 2006 Elsevier B.V. All rights reserved.