Abstract
The mechanistic pathway for degradation of cinnamic acids using 2,4,6-triphenylpyrylium as well as 2,4,6-triphenyl(thia)pyrylium salts (1a,b) as solar photocatalysts has been unambiguously established. Results obtained in steady-state experiments have been correlated with time-resolved photophysical studies. High percentages of photodegradation (60–70%) were achieved when aqueous solutions of caffeic and ferulic acids (2a,b) as model pollutants were submitted to irradiation in the presence of 1a,b. Electron-transfer quenching of both the singlet and triplet excited states of 1a,b by 2a,b has been proved, and the quenching rate constants (close to diffusion control) have been determined. However, the percentages of singlet quenching by 2a,b, even at relatively high concentrations of the model pollutants, is lower than 5%. In addition to this, growth of the signal corresponding to the pyranyl radical occurs in the microsecond timescale, incompatible with the singlet state as precursor. Thus, photodegradation of 2a,b mainly involves the triplet state of the photocatalysts.
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L. Martinez, Nieto, A. Ramos Cormenzana, Ma P. García Pareja, S. E. Garrido Hoyos, Phenolic compounds biodegradation of olive mill wastewater with Aspergillus terreus, Grasas y Aceites, 1992, 43, 75–81.
M. Hamdi, Future prospects and constraints of olive mill wastewaters use and treatment: a review, Bioprocess Eng., 1993, 8, 209–214.
R. Andreozzi, G. Longo, M. Majone and G. Modesti, Integrated treatment of olive oil mill efluents (OME): study of ozonation coupled with anaerobic digestion, Water Res., 1998, 32, 2357–2368.
H. Debellefontaine, M. Chakchouk, M. Hamdi and J. N. Foussard, Complete treatment of olive oil mill wastewaters by a wet air oxidation process coupled with a biological step, Environ. Technol., 1994, 15, 323–332.
F. Vigo and M. Cagliari, Photocatalytic oxidation on anaerobic biodegradation of model phenolic compounds, Water Environ. Res., 1992, 64, 268–273.
F. J. Benitez, J. Beltrán-Heredia, J. L. Acero, T. González, Oxidation of vanillic acid as a model of poliphenolic compound present in olive oil wastewaters I. Ozonation process, Toxicol. Environ. Chem., 1994, 46, 37–47.
F. J. Benitez, J. Beltrán-Heredia, J. Torregrosa and J. R. Dominguez, Aerobic treatment of black olive wastewater and the effect of an ozonation stage, Bioprocess Eng., 1999, 20, 355–361.
F. J. Benitez, J. Beltrán-Heredia, J. L. Acero and T. Gonzalez, Degradation of protocatechuic acid by two advanced oxidation processes: ozone/UV radiation and H2O2/UV radiation, Water Res., 1996, 30, 1597–1606.
F. J. Beltrán, J. F. García-Araya, J. Frades, P. Alvarez and O. Gimeno, Effects of single and combined ozonation with hydrogen peroxide or UV radiation on the chemical degradation and biodegradability of debittering table olive industrial wastewaters, Water Res., 1999, 33, 723–732.
R. R. Bacsa and J. Kiwi, Effect of rutile phase on the photocatalytic properties of nanocrystalline titania during the degradation of p-coumaric acid, Appl. Catal., B, 1998, 16, 19–29.
P. A. S. S. Marques, M. F. Rosa, F. Mendes, M. Collares, Pereira, J. Blanco and S. Malato, Wastewater detoxification of organic and inorganic toxic compounds with solar collectors, Desalination, 1996, 108, 213–220.
M. R. Hoffmann, S. C. Martin, W. Choi and D. W. Bahnemann, Environmental applications of semiconductor photocatalysis, Chem. Rev., 1995, 95, 69–96.
M. A. Fox and M. T. Dulay, Heterogeneous photocatalysis, Chem. Rev., 1993, 93, 341–357.
F. Herrera, C. Pulgarin, V. Nadtochenko and J. Kiwi, Accelerated photooxidation of concentrated p-coumaric acid in homogeneous solution. Mechanistic studies, intermediates and precursors formed in the dark, Appl. Catal., B, 1998, 17, 141–156.
J. Gimenez, D. Curco and M. A. Queral, Photocatalytic treatment of phenol and 2,4-dichlorophenol in a solar plant in the way to scaling-up, Catal. Today, 1999, 54, 229–243.
R. Gerdes, D. Wohrle, W. Spiller, G. Schneider, G. Schnurpfeil, G. Schulz-Ekloff, Photo-oxidation of phenol and monochlorophenols in oxygen-saturated aqueous solutions by different photosensitizers, J. Photochem. Photobiol., 1997, 111, 65–74.
A. Corma and H. Garcia, Zeolite-based phtocatalysts, Chem. Commun., 2004 1443–1459.
M. A. Miranda and H. Garcia, 2,4,6-Triphenylpyrylium tetrafluoroborate as an electron-transfer photosensitizer, Chem. Rev., 1994, 94, 1063–1089.
M. A. Miranda, M. A. Izquierdo and F. Galindo, Involvement of triplet excited states and olefin radical cations in electron-transfer cycloreversion of four-membered ring compounds photosensitized by (thia)pyrylium salts, J. Org. Chem., 2002, 67, 4138–4142.
M. Alvaro, E. Carbonell, V. Fornes and H. Garcia, Novel photocatalysts containing 2,4,6-triphenylthiapyrylium encapsulated within zeolites. Enhanced photocatalytic activity as compared to the pyrylium analogues, New J. Chem., 2004, 28, 631–639.
M. Alvaro, E. Carbonell, H. Garcia, C. Lamaza and M. Narayana, Ship-in-a-bottle synthesis of 2,4,6-triphenylthiapyrylium cations encapsulated in zeolites Y and beta: a novel robust photocatalyst, Photochem. Photobiol. Sci., 2004, 3, 189–193.
M. Alvaro, E. Carbonell and H. Garcia, Photocatalytic degradation of sulfur-containing aromatic compounds in the presence of zeolite-bound 2,4,6-triphenylpyrylium and 2,4,6-triphenylthiapyrylium, Appl. Catal., B, 2004, 51, 195–202.
A. M. Amat, A. Arques, S. H. Bossmann, A. M. Braun, S. Gob and M. A. Miranda, A “camel through the eye of a needle”: Direct introduction of the TPP+ ion inside Y-zeolites by formal ion exchange in aqueous medium, Angew. Chem. Int. Ed., 2003, 42, 1653–1655.
M. Alvaro Rodriguez, H. Garcia Gomez, C. Lamaza and M. Narayana Pillai, Thiopyryl cation and derivatives of same trapped in a zeolitic material, PCT Int. Appl. WO 2003011456, 2003.
M. A. Miranda, F. Galindo, A. M. Amat and A. Arques, Pyrylium salt-photosensitized degradation of phenolic pollutants derived from cinnamic acid with solar light. Correlation of the observed reactivities with fluorescence quenching, Appl. Catal., B, 2000, 28, 127–133.
M. A. Miranda, F. Galindo, A. M. Amat and A. Arques, Pyrylium salt-photosensitized degradation of phenolic contaminants present in olive oil wastewaters with solar light. Part II. Benzoic derivatives, Appl. Catal., B, 2001, 30, 437–444.
M. A. Miranda, M. L. Marín, A. M. Amat, A. Arques, S. Seguí, Pyrylium salt-photosensitized degradation of phenolic contaminants present in olive oil wastewaters with solar light. Part III. Tyrosol, and p-hydroxyphenylacetic acid, Appl. Catal., B, 2002, 35, 167–174.
R. Perez-Ruiz, M. A. Izquierdo and M. A. Miranda, Reductive PET Cycloreversion of Oxetanes: Singlet Multiplicity, Regioselectivity, and Detection of Olefin Radical Anion, J. Org. Chem., 2003, 68, 10103–10108.
R. Perez-Ruiz, S. Gil and M. A. Miranda, Stereodifferentiation in the Photochemical Cycloreversion of Diastereomeric Methoxynaphthalene-Oxetane Dyads, J. Org. Chem., 2005, 70, 1376–1381.
J. Mlcoch and E. Steckhan, Photochemically initiated, electron-transfer-catalyzed Diels–Alder reactions of electron-rich dienophiles, Angew. Chem., Int. Ed. Engl., 1985, 24, 412–414.
G. C. Calhoun and G. B. Schuster, The triplex Diels–Alder reaction of indene and cyclic dienes, J. Am. Chem. Soc., 1986, 108, 8021–8027.
J. Kim and G. B. Schuster, Enantioselective catalysis of the triplex Diels–Alder reaction: addition of trans-β-methylstyrene to 1,3-cyclohexadiene photosensitized with (−)-1,1′-bis(2,4-dicyanonaphthalene), J. Am. Chem. Soc., 1990, 112, 9635–9637.
F. Morlet-Savary, S. Parret, J. P. Fouassier, K. Inomata and T. Matsumoto, Excited state interactions of thiopyrylium salts, J. Chem. Soc., Faraday Trans., 1998, 94, 745–752.
M. A. Miranda, M. A. Izquierdo and F. Galindo, Steady-state and time-resolved studies on oxetane cycloreversion using (thia)pyrylium salts as electron-transfer photosensitizers, Organic Letters, 2001, 3, 1965–1967.
M. A. Miranda, M. A. Izquierdo, R. Pérez-Ruiz, Direct photophysical evidence for quenching of the triplet excited state of 2,4,6-triphenyl(thia)pyrylium salts by 2,3-diaryloxetanes, J. Phys. Chem. A, 2003, 107, 2478–2482.
M. Martiny, E. Steckhan and T. Esch, Cycloaddition reactions initiated by photochemically excited pyrylium-salts, Chem. Ber., 1993, 126, 1671–1682.
R. Searle, J. L. Williams, D. Demeyer and J. C. Doty, Sensitization of stilbene isomerization, J. Chem. Soc., Chem. Commun., 1967, 22, 1165.
D. Rehm and A. Weller, Kinetics of fluorescence quenching by electron and h-atom transfer, Isr. J. Chem., 1970, 8, 259–271.
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Marín, M.L., Miguel, A., Santos-Juanes, L. et al. Involvement of triplet excited states in the electron transfer photodegradation of cinnamic acids using pyrylium and thiapyrylium salts as photocatalysts. Photochem Photobiol Sci 6, 848–852 (2007). https://doi.org/10.1039/b702752d
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DOI: https://doi.org/10.1039/b702752d