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Photodegradation of Pollutants

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Materials Chemistry".

Deadline for manuscript submissions: closed (15 June 2022) | Viewed by 13702

Special Issue Editor

Faculty of Health Sciences, University of Ljubljana, Ljubljana, Slovenia
Interests: photodegradation; organic pollutants; photocatalysis; disinfection; toxicity assessment

Special Issue Information

Dear Colleagues,

Water pollution is a worldwide problem, as various industries discharge their effluents into water resources. The photodegradation of water pollutants has important transformation pathways, and is in line with biodegradation and abiotic processes like hydrolysis. They may occur naturally as a self-cleaning process of some pollutants in sunlit surface waters.

Photoreaction pathways include direct photolysis, where the substrate absorbs sunlight and gets transformed, or indirect photochemistry. In the latter, sunlight is absorbed by naturally occurring molecules—photosensitisers—producing reactive transient species in aqueous solution when irradiated, which are involved in pollutant phototransformation. Photodegradation may be the main degradation pathway for various compounds—so-called contaminants of emerging concern (CECs).

Additionally, the photodegradation of water pollutants examines advanced oxidation processes (AOPs), which include irradiation with UV light and sunlight, and the use of homogenous sensitizers or heterogeneous photocatalysts. Such processes have been successfully applied in the treatment of various contaminants present in industrial and agricultural effluents, in municipal and hospital wastewaters, and for the inactivation of microorganisms including resistant pathogens.

This Special Issue deals with photodegradation as well as photocatalytic degradation of organic pollutants; including pesticides, dyes, phenols, chlorinated compounds, nitrogen containing compounds, surfactants, etc. It includes also photosensitisers, like nitrate, nitrite and dissolved organic matter, photogenerated transients.

This Special Issue of Molecules, “Photodegradation of Pollutants”, welcomes manuscripts covering all aspects of the photochemical reactions of pollutants, including their design and product assessment, as well as all aspects of heterogeneous and homogeneous photocatalytic processes and applications for the degradation of organic pollutants and disinfection in water and wastewater.

Prof. Dr. Polonca Trebse
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • surface-water photochemistry
  • photodegradation
  • indirect photolysis
  • photosensitisers
  • water pollutants
  • photocatalysis (homogeneous and heterogeneous)
  • advanced oxidation processes
  • water disinfection

Published Papers (5 papers)

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Research

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14 pages, 2297 KiB  
Article
Aqueous Chlorination of D-Limonene
by Albert T. Lebedev, Elena A. Detenchuk, Tomas B. Latkin, Mojca Bavcon Kralj and Polonca Trebše
Molecules 2022, 27(9), 2988; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27092988 - 06 May 2022
Cited by 3 | Viewed by 4142
Abstract
Limonene (1-methyl-4-(1-methylethenyl)-cyclohexene) is one of the most widespread monocyclic terpenes, being both a natural and industrial compound. It is widely present in the environment, including in water supplies. Therefore, it may be subjected to aqueous chlorination at water treatment stations during drinking water [...] Read more.
Limonene (1-methyl-4-(1-methylethenyl)-cyclohexene) is one of the most widespread monocyclic terpenes, being both a natural and industrial compound. It is widely present in the environment, including in water supplies. Therefore, it may be subjected to aqueous chlorination at water treatment stations during drinking water preparation. Besides, being a component of numerous body care and cosmetic products, it may present at high levels in swimming pool waters and could also be subjected to aqueous chlorination. Laboratory experiments with aqueous chlorination of D-limonene demonstrated the prevalence of the conjugated electrophilic addition of HOCl molecule to the double bonds of the parent molecule as the primary reaction. The reaction obeys the Markovnikov rule, as the levels of the corresponding products were higher than those of the alternative ones. Fragmentation pattern in conditions of electron ionization enabled the assigning of the structures for four primary products. The major products of the chlorination are formed by the addition of two HOCl molecules to limonene. The reactions of electrophilic addition are usually accompanied by the reactions of elimination. Thus, the loss of water molecules from the products of various generations results in the reproduction of the double bond, which immediately reacts further. Thus, a cascade of addition-elimination reactions brings the most various isomeric polychlorinated species. At a ratio of limonene/active chlorine higher than 1:10, the final products of aqueous chlorination (haloforms) start forming, while brominated haloforms represent a notable portion of these products due to the presence of bromine impurities in the used NaOCl. It is worth mentioning that the bulk products of aqueous chlorination are less toxic in the bioluminescence test on V. fischeri than the parent limonene. Full article
(This article belongs to the Special Issue Photodegradation of Pollutants)
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16 pages, 1008 KiB  
Article
Heterogeneous Photocatalysis of Metronidazole in Aquatic Samples
by Klaudia Stando, Patrycja Kasprzyk, Ewa Felis and Sylwia Bajkacz
Molecules 2021, 26(24), 7612; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26247612 - 15 Dec 2021
Cited by 9 | Viewed by 2235
Abstract
Metronidazole (MET) is a commonly detected contaminant in the environment. The compound is classified as poorly biodegradable and highly soluble in water. Heterogeneous photocatalysis is the most promoted water purification method due to the possibility of using sunlight and small amounts of a [...] Read more.
Metronidazole (MET) is a commonly detected contaminant in the environment. The compound is classified as poorly biodegradable and highly soluble in water. Heterogeneous photocatalysis is the most promoted water purification method due to the possibility of using sunlight and small amounts of a catalyst needed for the process. The aim of this study was to select conditions for photocatalytic removal of metronidazole from aquatic samples. The effect of catalyst type, mass, and irradiance intensity on the efficiency of metronidazole removal was determined. For this purpose, TiO2, ZnO, ZrO2, WO3, PbS, and their mixtures in a mass ratio of 1:1 were used. In this study, the transformation products formed were identified, and the mineralization degree of compound was determined. The efficiency of metronidazole removal depending on the type of catalyst was in the range of 50–95%. The highest MET conversion (95%) combined with a high degree of mineralization (70.3%) was obtained by using a mixture of 12.5 g TiO2–P25 + PbS (1:1; v/v) and running the process for 60 min at an irradiance of 1000 W m−2. Four MET degradation products were identified by untargeted analysis, formed by the rearrangement of the metronidazole and the C-C bond breaking. Full article
(This article belongs to the Special Issue Photodegradation of Pollutants)
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11 pages, 1906 KiB  
Article
Removal of Flotation Collector O-Isopropyl-N-ethylthionocarbamate from Wastewater
by Zhe Wang, Jun Yao, Mojca Bavcon Kralj, Darko Dolenc and Polonca Trebše
Molecules 2021, 26(21), 6676; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26216676 - 04 Nov 2021
Cited by 2 | Viewed by 1383
Abstract
Flotation collector O-isopropyl N-ethylthionocarbamate (IPETC) is widely used for separation of sulfide ores. Its removal from water by several oxidation processes was studied. Photocatalytic oxidation with air in the presence of iron salts, utilizing solar irradiation or artificial UV-A light is [...] Read more.
Flotation collector O-isopropyl N-ethylthionocarbamate (IPETC) is widely used for separation of sulfide ores. Its removal from water by several oxidation processes was studied. Photocatalytic oxidation with air in the presence of iron salts, utilizing solar irradiation or artificial UV-A light is very efficient. Oxidation leads through the formation of O-isopropyl N-ethylcarbamate and several other reaction intermediates to total decomposition of organic compound in the final stage in 1 day. Similar results were obtained with a Fenton type oxidation with hydrogen peroxide and iron salts. Treatment with sodium hypochlorite yields mainly O-isopropyl N-ethylcarbamate. The formation of this compound in wastewaters can be of concern, since simple alkyl carbamates are cancer suspect agents. Full article
(This article belongs to the Special Issue Photodegradation of Pollutants)
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16 pages, 1484 KiB  
Article
Investigation of the Aquatic Photolytic and Photocatalytic Degradation of Citalopram
by Cristina Jiménez-Holgado, Paola Calza, Debora Fabbri, Federica Dal Bello, Claudio Medana and Vasilios Sakkas
Molecules 2021, 26(17), 5331; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26175331 - 02 Sep 2021
Cited by 7 | Viewed by 2016
Abstract
This study investigated the direct and indirect photochemical degradation of citalopram (CIT), a selective serotonin reuptake inhibitor (SSRI), under natural and artificial solar radiation. Experiments were conducted in a variety of different operating conditions including Milli-Q (MQ) water and natural waters (lake water [...] Read more.
This study investigated the direct and indirect photochemical degradation of citalopram (CIT), a selective serotonin reuptake inhibitor (SSRI), under natural and artificial solar radiation. Experiments were conducted in a variety of different operating conditions including Milli-Q (MQ) water and natural waters (lake water and municipal WWT effluent), as well as in the presence of natural water constituents (organic matter, nitrate and bicarbonate). Results showed that indirect photolysis can be an important degradation process in the aquatic environment since citalopram photo-transformation in the natural waters was accelerated in comparison to MQ water both under natural and simulated solar irradiation. In addition, to investigate the decontamination of water from citalopram, TiO2-mediated photocatalytic degradation was carried out and the attention was given to mineralization and toxicity evaluation together with the identification of by-products. The photocatalytic process gave rise to the formation of transformation products, and 11 of them were identified by HPLC-HRMS, whereas the complete mineralization was almost achieved after 5 h of irradiation. The assessment of toxicity of the treated solutions was performed by Microtox bioassay (Vibrio fischeri) and in silico tests showing that citalopram photo-transformation involved the formation of harmful compounds. Full article
(This article belongs to the Special Issue Photodegradation of Pollutants)
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Review

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23 pages, 6046 KiB  
Review
Stability and Removal of Benzophenone-Type UV Filters from Water Matrices by Advanced Oxidation Processes
by Belma Imamović, Polonca Trebše, Elma Omeragić, Ervina Bečić, Andrej Pečet and Mirza Dedić
Molecules 2022, 27(6), 1874; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27061874 - 14 Mar 2022
Cited by 12 | Viewed by 3034
Abstract
Benzophenone (BP) type UV filters are common environmental contaminants that are posing a growing health concern due to their increasing presence in water. Different studies have evidenced the presence of benzophenones (BP, BP-1, BP-2, BP-3, BP-4, BP-9, HPB) in several environmental matrices, indicating [...] Read more.
Benzophenone (BP) type UV filters are common environmental contaminants that are posing a growing health concern due to their increasing presence in water. Different studies have evidenced the presence of benzophenones (BP, BP-1, BP-2, BP-3, BP-4, BP-9, HPB) in several environmental matrices, indicating that conventional technologies of water treatment are not able to remove them. It has also been reported that these compounds could be associated with endocrine-disrupting activities, genotoxicity, and reproductive toxicity. This review focuses on the degradation kinetics and mechanisms of benzophenone-type UV filters and their degradation products (DPs) under UV and solar irradiation and in UV-based advanced oxidation processes (AOPs) such as UV/H2O2, UV/persulfate, and the Fenton process. The effects of various operating parameters, such as UV irradiation including initial concentrations of H2O2, persulfate, and Fe2+, on the degradation of tested benzophenones from aqueous matrices, and conditions that allow higher degradation rates to be achieved are presented. Application of nanoparticles such as TiO2, PbO/TiO2, and Sb2O3/TiO2 for the photocatalytic degradation of benzophenone-type UV filters was included in this review. Full article
(This article belongs to the Special Issue Photodegradation of Pollutants)
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