Photosensitizing properties of different dissolved organic matter (DOM) were investigated according to their performance in singlet oxygen (1O2), triplet state of DOM (3DOM*), 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 hob 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.
Copyright © 2014 Published by Elsevier Ltd.