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Mechanisms of direct and TiO2-photocatalysed UV degradation of phenylurea herbicides.
Chemphyschem. 2005 Oct 14; 6(10):2064-74.C

Abstract

Phenylurea herbicides undergo low-yield (phi(PI) <15 %) monophotonic photoionisation upon 193-nm laser flash excitation. The so-formed radical cations (phenylurea.+) are highly acidic (-1.5 < pKa <0.5) and deprotonate readily to yield the corresponding neutral radical (phenylurea.). Pulse radiolysis experiments allowed limitation of the reduction potential of phenylurea.+ within 2.22 V versus the normal hydrogen electrode (NHE) < E degrees (phenylurea.+/phenylurea) < 2.43 V versus NHE. The main photoproducts of UVC (lambda=193 nm) photodegradation of phenylureas correspond to a photo-Fries rearrangement. One-electron reduction with e-(aq) yields the corresponding radical anions (phenylurea.-), for which 4.3< pKa < 5.33. The rate constants for reaction with e-(aq) show that in photocatalysis the generation of phenylurea.- and O2.- on the surface of the photocatalyst may be competitive. High reactivity toward e-(aq) is predicted from linear free-energy relationships (LFER) for phenylureas bearing electron-withdrawing groups. Reaction with HO. takes place mainly via addition to the aromatic ring and/or H. abstraction from a saturated carbon atom (98 %), rather than one-electron oxidation (2 %). High reactivity toward oxidation by HO. is predicted from LFER for phenylureas bearing electron-donating groups. Adsorption studies for TiO2 in its polymorphic forms of rutile and anatase, as well as with the commercial mixture Degussa P-25, show photocatalysis is independent of the specific area of the catalyst. A variety of compounds are generated during the photocatalytic degradation of Diuron, while only two hydroxychloro derivatives are observed upon prolonged direct 365 nm irradiation. The photocatalytic degradation proceeds mainly by oxidation of the Me group of the side chain, hydroxylation of the aromatic ring, and dechlorination. The photoproducts of photocatalytic degradation differ from one polymorphic form of TiO2 to another.

Authors+Show Affiliations

Grupo de Reactividade Química e Fotorreactividade, Departamento de Química Física e Enxeñería Química I, Universidade da Coruña, Rúa Alejandro de la Sota 1, 15008A Coruña, Galicia, Spain. mcanle@udc.essNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

16158459

Citation

Canle López, Moisés, et al. "Mechanisms of Direct and TiO2-photocatalysed UV Degradation of Phenylurea Herbicides." Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry, vol. 6, no. 10, 2005, pp. 2064-74.
Canle López M, Fernández MI, Rodríguez S, et al. Mechanisms of direct and TiO2-photocatalysed UV degradation of phenylurea herbicides. Chemphyschem. 2005;6(10):2064-74.
Canle López, M., Fernández, M. I., Rodríguez, S., Santaballa, J. A., Steenken, S., & Vulliet, E. (2005). Mechanisms of direct and TiO2-photocatalysed UV degradation of phenylurea herbicides. Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry, 6(10), 2064-74.
Canle López M, et al. Mechanisms of Direct and TiO2-photocatalysed UV Degradation of Phenylurea Herbicides. Chemphyschem. 2005 Oct 14;6(10):2064-74. PubMed PMID: 16158459.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Mechanisms of direct and TiO2-photocatalysed UV degradation of phenylurea herbicides. AU - Canle López,Moisés, AU - Fernández,M Isabel, AU - Rodríguez,Santiago, AU - Santaballa,J Arturo, AU - Steenken,Steen, AU - Vulliet,Emmanuelle, PY - 2005/9/15/pubmed PY - 2007/2/13/medline PY - 2005/9/15/entrez SP - 2064 EP - 74 JF - Chemphyschem : a European journal of chemical physics and physical chemistry JO - Chemphyschem VL - 6 IS - 10 N2 - Phenylurea herbicides undergo low-yield (phi(PI) <15 %) monophotonic photoionisation upon 193-nm laser flash excitation. The so-formed radical cations (phenylurea.+) are highly acidic (-1.5 < pKa <0.5) and deprotonate readily to yield the corresponding neutral radical (phenylurea.). Pulse radiolysis experiments allowed limitation of the reduction potential of phenylurea.+ within 2.22 V versus the normal hydrogen electrode (NHE) < E degrees (phenylurea.+/phenylurea) < 2.43 V versus NHE. The main photoproducts of UVC (lambda=193 nm) photodegradation of phenylureas correspond to a photo-Fries rearrangement. One-electron reduction with e-(aq) yields the corresponding radical anions (phenylurea.-), for which 4.3< pKa < 5.33. The rate constants for reaction with e-(aq) show that in photocatalysis the generation of phenylurea.- and O2.- on the surface of the photocatalyst may be competitive. High reactivity toward e-(aq) is predicted from linear free-energy relationships (LFER) for phenylureas bearing electron-withdrawing groups. Reaction with HO. takes place mainly via addition to the aromatic ring and/or H. abstraction from a saturated carbon atom (98 %), rather than one-electron oxidation (2 %). High reactivity toward oxidation by HO. is predicted from LFER for phenylureas bearing electron-donating groups. Adsorption studies for TiO2 in its polymorphic forms of rutile and anatase, as well as with the commercial mixture Degussa P-25, show photocatalysis is independent of the specific area of the catalyst. A variety of compounds are generated during the photocatalytic degradation of Diuron, while only two hydroxychloro derivatives are observed upon prolonged direct 365 nm irradiation. The photocatalytic degradation proceeds mainly by oxidation of the Me group of the side chain, hydroxylation of the aromatic ring, and dechlorination. The photoproducts of photocatalytic degradation differ from one polymorphic form of TiO2 to another. SN - 1439-4235 UR - https://www.unboundmedicine.com/medline/citation/16158459/Mechanisms_of_direct_and_TiO2_photocatalysed_UV_degradation_of_phenylurea_herbicides_ L2 - https://doi.org/10.1002/cphc.200500004 DB - PRIME DP - Unbound Medicine ER -