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Chemists discover that water microdroplets spontaneously produce hydrogen peroxide



  Stanford Chemists discover that water microdroplets spontaneously produce hydrogen peroxide
Richard Zare and his lab have shown that water microdroplets spontaneously ̵
1; and unexpectedly – produce hydrogen peroxide. Photo credits: L. A. Cicero / Stanford University

There is water all over the world, but perhaps it gives him more room to hide his secrets. His latest surprise, Stanford researchers report on August 26, in Proceedings of the National Academy of Sciences is that microscopic water droplets spontaneously produce hydrogen peroxide.

The discovery could pave the way for greener production of the molecule, a common bleach and disinfectant, said Richard Zare, Marguerite Blake Wilbur Professor of Natural Sciences and Professor of Chemistry at the Stanford School of Humanities and Sciences.

"Water is one of the most abundant materials, and it has been studied for years, and one would think that there was nothing left to learn about this molecule, but here is another surprise," said Zare, who is a member of Stanford Bio-X.

The discovery was made by chance when Zare and his lab investigated a new, more efficient way to create gold nanostructures in tiny water droplets known as microdroplets. To create these structures, the team added an additional molecule called the reducing agent. As a control test, Zare suggested testing whether gold nanostructures could be generated without the reducing agent. Theoretically that should have been impossible, but it still worked – an indication of a still undiscovered feature of microdroplet chemistry.




In this demonstration, a test strip turns blue when sprayed with water microdroplets, indicating the presence of hydrogen peroxide. Credit: Jae Kyoo Lee and Hyun Soo Han

Finally, the team attributed these results to the existence of a molecule called hydroxyl, a single hydrogen atom that is paired with an oxygen atom and can also act as a reductant. This equally unexpected result prompted Katherine Walker, at the time a graduate student in Zare's lab, to wonder if hydrogen peroxide – a molecule with two hydrogen and two oxygen atoms – was also present.

To Find Out, Zare, Walker, Associate Scientist Jae Kyoo Lee and her colleagues performed a series of tests, the simplest of which was to spray microdroplets of seemingly pure water onto a treated surface to make them in the presence of hydrogen peroxide turns blue – and she did. Additional tests confirmed that water microdroplets spontaneously form hydrogen peroxide, that smaller microdroplets produce higher concentrations of the molecule, and that hydrogen peroxide is not lost when the microdroplets recombine into water.

The researchers precluded a number of possible explanations before they arrived. What they argue is the most likely explanation for the presence of hydrogen peroxide. They suggest that a strong electric field near the surface of water microdroplets in the air causes the binding of hydroxyl molecules to hydrogen peroxide.

Although the results represent a fundamental scientific curiosity, they could have important practical consequences. Hydrogen peroxide is an important commercial and industrial chemical, most commonly produced in an environmentally harmful process. The new discovery could help make these methods more eco-friendly, Zare said, and it could lead to simpler ways of disinfecting surfaces – it might be enough to spray water droplets on a table or floor to clean them.

"I think it could be one of the most important things I've ever done," Zare said.


Scientists produce gold nanoparticles in water


Further information:
Jae Kyoo Lee et al., "Spontaneous Production of Hydrogen Peroxide from Aqueous Microdroplets", PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1911883116

Provided by
Stanford University




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Chemists discover that water microdroplets spontaneously produce hydrogen peroxide (2019, August 26)
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