Photoreactivity of humic substances: relationship between fluorescence and singlet oxygen production |
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Authors: | Christian Coelho Ghislain Guyot Alexandra ter Halle Luciano Cavani Claudio Ciavatta Claire Richard |
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Institution: | (1) Laboratoire de Photochimie Mol?culaire et Macromol?culaire (LPMM), Clermont Universit?, Universit? Blaise Pascal, BP 10448, 63000 Clermont-Ferrand, France;(2) UMR 6505, LPMM, CNRS, 63171 Aubi?re, France;(3) Dipartimento di Scienze e Tecnologie Agroambientali, Alma Mater Studiorum-Universit? di Bologna, Viale Fanin 40, 40127 Bologna, Italy; |
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Abstract: | Humic substances are natural compounds abundantly present in the environment. They play a significant role in the natural
attenuation of pollution in surface water due to their capacity to generate reactive species upon solar light excitation.
Finding physico chemical parameters related to this property would be of a great help in the prediction studies of the organic
pollutants fate. In this work, we investigated relationships between the ability of the humic substances to produce singlet
oxygen and their fluorescence properties. For this, a series of sixteen humic acids, fulvic acids, and water-extractable organic
matter from soils were studied. The steady-state singlet oxygen concentrations in the irradiated humic substances solutions
were measured by monitoring the loss of furfuryl alcohol added as a singlet oxygen scavenger. The emission spectra of the
sixteen samples were also recorded. Values of the steady-state singlet oxygen concentrations and the emission intensities
showed significant variations among the humic samples and a parallel increase. Thus, here we demonstrate that the rate of
singlet oxygen production and the emission intensity of the humic samples are correlated, the best correlation being obtained
for emission wavelengths between 500 and 580 nm. This correlation which was never reported until now can be used to estimate
the singlet oxygen-production capacity of the humic substances based on their fluorescent properties. |
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