Water can spontaneously form hydrogen peroxide, and we finally understand why

(ORDO NEWS) — After we have plunged into a global pandemic, we are probably much more aware that we are surrounded by microdroplets of water. In humid air or when coughing, sneezing or talking, these droplets can carry tiny particles with them, from pollution to viruses like the flu.

Back in 2019, the underlying chemistry of these environmental water particles came as a surprise: researchers found that normal, harmless water droplets can somehow spontaneously form small but significant amounts of hydrogen peroxide (H 2 O 2 ).

Yes, the same weakly acidic substance that we use to bleach hair or disinfect wounds.

Now a team of researchers has found that a spontaneous reaction occurs on contact with hard surfaces, and this may play a role in flu seasonality.

“We think we know so much about water, one of the most commonly found substances, but then we are humiliated,” says Stanford University chemist Richard Zahr, who was involved in both discoveries.

In a mass, water is fairly stable, but separating it into tiny droplets drastically changes how it behaves in comparison.

As objects decrease in size, their relative volume decreases faster than their surface area. This means that a tiny drop of water will have a much larger proportion of its molecules exposed to the environment than molecules in a glass, bucket, or lake.

It was on this exposed surface that hydrogen peroxide was confirmed by Jianghan University chemists Boley Chen, Zare and their colleagues.

Using a dye that glows in the presence of H 2 O 2 , the team mapped its occurrence in droplets in contact with the glass surface and found that it was most concentrated at the interface between the two types of substance.

The researchers demonstrated that H 2 O 2 sub> was also produced when the droplets touched nine other solids, including soil or finer dust floating in our air.

In a previous study, they also showed that this happened naturally, simply when water condenses from the air onto cold surfaces. . Moreover, the amount of H 2 O 2 increased with humidity.

“It seems that contact electrification with the formation of hydrogen peroxide is a universal phenomenon in water. -hard interfaces,” Zare explains.

To find out where the droplets are stealing the extra oxygen atom from, the researchers treated the surface of the glass with the heavy oxygen isotope 18O .

Sure enough, the droplets formed hydrogen peroxide by accepting 18 O atoms onto the glass surface, confirming that the source was excitable hydrogen and oxygen elements called hydroxyl radicals attached to the surface material. .

As the acid formed, Chen and his team were also able to measure the electrical current flowing from the solid to the ground as the dye intensified.

This confirmed the results of previous studies, which suggested that the exchange of electrons occurs in a process called contact electrification, creating hydroxyl radicals.

This, of course, is not true. This does not rule out that some of the feedstock may come from other sources in the environment, such as ozone (O 3 ), the team writes in their paper. But it confirms that water drops and a hard surface are sufficient.

“Contact electrification provides a chemical basis for partially explaining the seasonality of viral respiratory diseases,” Zare says.

Since the high humidity of warm summer air contains small amounts of hydrogen peroxide, this can be another barrier to circulating pathogens.

On the contrary, cool and dry winter air can simply become a source of viruses. this is a small advantage in jumping from one blowing nose to another.


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