title: Photobleaching-induced changes in photosensitizing properties of dissolved organic matter.
abstract: Photosensitizing properties of different dissolved organic matter (DOM) were investigated according to their performance in singlet oxygen ((1)O2), triplet state of DOM ((3)DOM*), and hydroxyl radical (·OH) productions. The photobleaching of DOM solutions after irradiation was characterized by fluorescence excitation-emission matrix and UV-Vis spectroscopy. The photosensitizing properties of pre-irradiated DOM solutions were changed in a sunlight simulator. The performance of DOMs in photosensitized degradation of several contaminants was investigated. For a 20 h exposure, the observed degradation rate constant (kobs) of some contaminants decreased as a function of exposure time, and highly depended on the properties of both DOM and contaminant. Degradation of contaminants with lower kobs was more susceptible to DOM photobleaching-induced decrease in kobs. Under the current experimental conditions, the photobleaching-induced decrease of DOM photo-reactivity in contaminant degradation was mainly attributed to indirect phototransformation of DOM caused by the interactions between photo-inductive DOM moieties and photochemically-produced reactive species. Reactive contaminants can inhibit DOM indirect photobleaching by scavenging reactive species, photosensitized degradation of these contaminants exhibited a stable kobs as a result. This is the first study to report DOM photobleaching-induced changes in the simultaneous DOM photosensitized degradation of contaminants and the inhibitory effect of reactive contaminants on DOM photobleaching.
authors.affiliation: Water Desalination and Reuse Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
authors.forename: Xi-Zhi
authors.initials: XZ
authors.lastname: Niu
authors.affiliation: Water Desalination and Reuse Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
authors.forename: Chao
authors.initials: C
authors.lastname: Liu
authors.affiliation: Water Desalination and Reuse Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia; Facultad del Mar y Medio Ambiente, Universidad del Pacifico, Guayaquil, Ecuador.
authors.forename: Leo
authors.initials: L
authors.lastname: Gutierrez
authors.affiliation: Water Desalination and Reuse Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia. Electronic address: jp.croue@kaust.edu.sa.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Croué
mesh_terms: D009930:Organic Chemicals / Q000737:chemistry*; D038761:Photobleaching; D010782:Photolysis; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D009930:Organic Chemicals; D014874:Water Pollutants, Chemical
keywords: Contaminant degradation; DOM characterization; Dissolved organic matter; Photobleaching; Photosensitization