Advanced water treatment with hydrated electrons is increasingly being considered for hard-to-degrade contaminants, for example, per- and polyfluoroalkyl substances. In addition, hydrated electrons are generated photochemically in natural waters by photolysis of dissolved organic matter. In both natural and engineered systems, scavenging by DOM plays a role in determining the concentration of hydrated electron, yet absolute bimolecular rate constants for the reaction of hydrated electron with DOM remain unknown. Herein, we employed pulse radiolysis and transient absorption spectroscopy to measure absolute hydrated electron bimolecular rate constants for 10 humic substance and natural organic matter isolates from the International Humic Substances Society. Values ranged over almost 200-fold (0.09 to 1.5 x 108 MC-1s-1) at room temperature and low ionic strength. The bimolecular rate constant depended on solution pH, ionic strength, temperature, but to different extents for different isolates. Our results indicate that the range of bimolecular rate constants for DOM is much larger than for scavenging by the hydroxyl radical (~108 MC-1s-1). When pooling the results, a negative correlation exists between absolute the hydrated electron bimolecular rate constant and DOM charge.

Reaction of the hydrated electron with humic substance and natural organic matter isolates

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