A mechanistic study on the potential of quinolinium salts as photocatalysts for the abatement of chlorinated pollutants

[EN] Photocatalytic degradation of three highly chlorinated contaminants, namely 2,4,6-trichlorophenol (TCP), 2,4,6-trichloroanisole (TCA) and 5-chloro-2-(2,4-dichlorophenoxy)phenol (triclosan, TCS) has been investigated in the presence of N-methylquinolinium tetrafluoroborate (NMQ(+)), a photocatalyst able to act via Type I or Type II mechanism. Photodegradation of contaminants under aerobic conditions was achieved within hours; and it was accompanied by mineralization, as demonstrated by trapping of the evolved carbon dioxide as barium carbonate. Moreover, a high degree of detoxification, based on % inmobilization of daphnids (Daphnia magna bioassay), was reached after 70 h of irradiation. Quenching of the NMQ(+) fluorescence by the pollutants was evidenced by a decrease in the emission intensity and lifetime. Detection of the reduced NMQ. by laser flash photolysis in the presence of the pollutants provided an unambigous evidence of the electron transfer process. Quenching of singlet oxygen by the contaminants showed the typical singlet oxygen quenching constants (10(5)-10(6) M-1 s(-1)). Evaluation of the relative contribution of both pathways (Type I vs Type II) point to the photodegradation occurring via a Type I mechanism, being the contribution of Type II mechanism negligible at any concentration range.Financial support from Spanish Government (Grant SEV-2016.0683 and CTQ2015-69832-C4) and generous contribution from Generalitat Valenciana (Prometeo Program) are gratefully acknowledged. We also thank support from VLC/Campus. R Martinez-Haya thanks financial support from Spanish Government (Grant SEV-2012-0267).Martínez-Haya, R.; Sabater Marco, C.; Castillo López, M.; Miranda Alonso, MÁ.; Marín García, ML. (2018). A mechanistic study on the potential of quinolinium salts as photocatalysts for the abatement of chlorinated pollutants. Journal of Hazardous Materials. 351:277-284. https://doi.org/10.1016/j.jhazmat.2018.03.010S27728435

Xanthone-photosensitized detoxification of the veterinary anthelmintic fenbendazole

Fenbendazole (1) is a common veterinary anthelmintic, toxic to water living microorganisms. Fluorescence quantum yields of 1 were found to be 0.11 in acetonitrile, 0.068 in methanol, 0.034 in cyclohexane, and 0.013 in water. The singlet excited state energy was ca. 96 kcal mol(-1) in all solvents. The phosphorescence spectrum of 1 in ethanol at 77 K displayed a maximum at 450 nm, leading to a triplet energy of 75 kcal mol(-1). Experimental excited state energies agree well with the results of OFT calculations at the time-dependent B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) level. Laser flash photolysis (LFP) of 1 at 266 nm led to transients absorbing in the 300-700 nm range, ascribed to radical cation 1(.+), which were also observed upon 355 nm LFP of xanthone (XA) in the presence of 1. Solar-simulated photolysis revealed XA-enhanced photodegradation of 1 and led to decreased toxicity, as shown by Daphnia magna assays. (c) 2013 Elsevier B.V. All rights reserved.Financial support from the MICINN (CTQ2010-19909) and the Generalitat Valenciana (Prometeo Program) is gratefully acknowledged.Jornet Olivé, MD.; Castillo López, MÁ.; Sabater Marco, C.; R. Domingo, L.; Tormos Faus, RE.; Miranda Alonso, MÁ. (2013). Xanthone-photosensitized detoxification of the veterinary anthelmintic fenbendazole. Journal of Photochemistry and Photobiology A: Chemistry. 264:34-40. https://doi.org/10.1016/j.jphotochem.2013.05.002S344026

Photodegradation of carbendazim sensitized by aromatic ketones

Carbendazim (1) is a benzimidazole extensively used as post-harvest fungicide on fruits and vegetables. The aim of the present work is to study the photodegradation of I sensitized by aromatic ketones, with special attention to mechanistic aspects and to the possible detoxification associated with photochemical treatment. Laser flash photolysis (LPF) lambda(exc) = 355 nm of xanthone (XA) and anthraquinone (AQ) was performed in MeCN solutions, in the presence of 1. A new transient absorbing at lambda(max) 500 and 320 nm was obtained and assigned to the semioxidized radical cation 1(+center dot). An exergonic thermodynamics for electron transfer quenching was confirmed by means of the Rehm-Weller equation. The same species was observed by direct LFP of 1 at 266 nm in polar solvents. Conversely, when a deoxygenated solution of 1 was submitted to LFP in cyclohexane the transient spectrum presented a band with maximum at 380 nm; it was assigned to the triplet excited state ((3)1*) on the basis of energy transfer to oxygen and beta-carotene. The photodegradation of 1 was achieved using XA and AQ as electron acceptors in a solar-simulator, in aerated aqueous medium; the reaction was faster with XA. Formation of a new photoproduct was initially observed; its structure was assigned as carbendazim N-C5 dimer (2). A balance of the total organic carbon (TOC) after prolonged irradiation indicated that mineralization does not occur to a significant extent, pointing to oxidative fragmentation of 1 and 2 to give a variety of low molecular weight products. To check whether the observed photodegradation of 1 results in a decreased toxicity, biological assays were performed using an established model based on the inhibition of mobility of Daphnia magna. The results demonstrate that photodegradation leads to a diminished toxicity, indicating that the photoproducts are less toxic than the parent compound. (C) 2013 Elsevier B.V. All rights reserved.Financial support from the MICINN (Grant: CTQ2010-19909) and the Generalitat Valenciana (Prometeo Program) is gratefully acknowledged.Jornet Olivé, MD.; Castillo López, MÁ.; Sabater Marco, C.; Tormos Faus, RE.; Miranda Alonso, MÁ. (2013). Photodegradation of carbendazim sensitized by aromatic ketones. Journal of Photochemistry and Photobiology A: Chemistry. 256:36-41. https://doi.org/10.1016/j.jphotochem.2013.02.004S364125

Jornada de Grandes infraestructuras europeas de Ciencias Sociales y Humanidades en el CSIC: DARIAH y CLARÍN en el horizonte (11 de mayo de 2023)

Peer reviewe

Determination of photostability, biocompatibility and efficiency as photo-Fenton auxiliaries of three different types of soluble bio-based substances (SBO)

[EN] The aim of this work is to determine the photostability biocompatibility and efficiency of water soluble bio-based substances (SBO) in photo-oxidative processes for wastewater treatment. Three batches of SBO, isolated from different sources, have been investigated. Differences in the functional groups present in these substances can explain major trends in their physical/chemical properties. Bioassays have proven those materials to be non-toxic but to show poor biodegradability. Their ability to enhance a photo-Fenton process at milder pH (5.2) has been investigated using a mixture of emerging compounds in wastewaters. All the tested SBO were able to remove all pollutants in less than one hour irradiation, and the best results were obtained with those substances showing higher hydrophilic/hydrophobic ratio. Moreover, although SBOs themselves undergo a slight oxidation, no relevant negative effect has been observed for their use in wastewater treatment.The authors want to thank the financial support of the European Union (PIRSES-GA-2010-269128, EnvironBOS) and Spanish Ministerio de Educacion y Ciencia (CTQ2012-38754-C03-02). Juan Gomis would like to thank UPV for his FPI grant (2010-07).Gomis, J.; Gonçalves, MG.; Vercher Aznar, R.; Sabater Marco, C.; Castillo López, MÁ.; Prevot, AB.; Amat Payá, AM.... (2015). Determination of photostability, biocompatibility and efficiency as photo-Fenton auxiliaries of three different types of soluble bio-based substances (SBO). Catalysis Today. 252:177-183. https://doi.org/10.1016/j.cattod.2014.10.015S17718325