Nanosecond transient absorption studies of the pH-dependent hydrated electron quenching by HSO3−. Issue 6 (15th April 2019)

• Record Type: Journal Article
• Authors: Maza, William A.; Breslin, Vanessa M.; Plymale, Noah T.; DeSario, Paul A.; Epshteyn, Albert; Owrutsky, Jeffrey C.; Pate, Bradford B.
• Is Part Of: Photochemical & photobiological sciences. Volume 18:Issue 6(2019)
• Page Start: 1526
• Page End: 1532
• Publication Date: 2019-04-15
• Subjects: Photochemistry -- Periodicals; Photobiology -- Periodicals; 541.35
• DOI: 10.1039/c9pp00063a
• Languages: English
• ISSNs: 1474-905X

Abstract

Abstract : Hydrated electron lifetimes in photodetached sulfite solutions at intermediate pH (5–10) are limited by HSO3 – rather than proton (H + ) quenching. 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 Na2 SO3 at pH 4 to 11 in H2 O and D2 O 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 × 10 8 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 SO3 2– . A large solvent isotope effect is observed from the lifetimes of the eaq − in H2 O compared to D2 O ( k H2 O / k D2 O = 4.4). In addition, the bimolecular rate constant for eaq − deactivation by DSO3 − ( k = 2.7 × 10 7 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 p K a of eaq − sources can be a predictive measure of the effective pH range for the treatment of wastewater contaminants.