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Nanosecond transient absorption studies of the pH-dependent hydrated electron quenching by HSO3

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Abstract

The large standard reduction potential of an aqueous solvated electron (eaq, E° = −2.9 V) makes it an attractive candidate for reductive treatment of wastewater contaminants. Using transient absorption spectroscopy, the nanosecond to microsecond dynamics of eaq generated from 10 mM solutions of Na2SO3 at pH 4 to 11 in H2O and D2O are characterized, resulting in the determination that between pH 4 and 9 it is the HSO3, and not H+ as previously postulated by others, that effectively quenches eaq. The observed bimolecular quenching rate constant (k = 1.2 × 108 M−1 s−1) for eaq deactivation by HSO3 is found to be consistent with a Brønsted acid catalysis mechanism resulting in formation of H˙ and SO32–. A large solvent isotope effect is observed from the lifetimes of the eaq in H2O compared to D2O (kH2O/kD2O = 4.4). In addition, the bimolecular rate constant for eaq deactivation by DSO3 (k = 2.7 × 107 M−1 s−1) is found to be an order of magnitude lower than by HSO3. These results highlight the role of acids, such as HSO3, in competition with organic contaminant targets for eaq and, by extension, that knowledge of the pKa of eaq sources can be a predictive measure of the effective pH range for the treatment of wastewater contaminants.

Graphical abstract: Nanosecond transient absorption studies of the pH-dependent hydrated electron quenching by HSO3−

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Publication details

The article was received on 04 Feb 2019, accepted on 27 Feb 2019 and first published on 12 Apr 2019


Article type: Paper
DOI: 10.1039/C9PP00063A
Photochem. Photobiol. Sci., 2019, Advance Article

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    Nanosecond transient absorption studies of the pH-dependent hydrated electron quenching by HSO3

    W. A. Maza, V. M. Breslin, N. T. Plymale, P. A. DeSario, A. Epshteyn, J. C. Owrutsky and B. B. Pate, Photochem. Photobiol. Sci., 2019, Advance Article , DOI: 10.1039/C9PP00063A

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