Reaction mechanisms
Ultrasound microdroplets make H2O2 from dissolved O2
Open access · cc by · source: Europe PMC
Water-in-hexadecane droplets under 40 kHz ultrasound produce H2O2 at 0.24 mM min−1, almost entirely at the oil–water interface via superoxide from dissolved oxygen.
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Ultrasound microdroplets make H2O2 from dissolved O2
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H2O2 production was 0.24 mM min−1, reaching 14.37 mM after 1 hour.
We demonstrated that under ultrasound irradiation, the H 2 O 2 concentration increases linearly with time, with a production rate of approximately 0.24 mM min −1 , reaching up to 14.37 mM after 1 hour of irradiation.
Bulk water yielded only 0.14 mM after 1 hour—1% of the microdroplet yield.
The concentration of H 2 O 2 in bulk water increased linearly with ultrasound exposure, at a production rate of about 0.0024 mM min −1 , resulting in 0.14 mM H 2 O 2 after 1 hour—only 1% of the yield obtained in microdroplets ().
Key findings
H2O2 reaches 14.37 mM in 1 h (0.24 mM min−1); ~99% forms at the interface. Superoxide is ~10× H2O2 and ~1000× ·OH. 18O shows peroxide oxygen comes from O2, not water.
Methodology
Authors emulsified water in hexadecane with an ultrasonic bath, quantified H2O2 versus time, blocked the interface with surfactant, purged O2, used 18O2/H218O mass spectrometry, and compared NBT superoxide versus TA hydroxyl yields.
Limitations
The mechanism is for ultrasound-driven water-in-oil droplets, not spontaneous H2O2 in sprayed air–water microdroplets without ultrasound.
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