Research reveals the chemical underpinnings of how benign water can turn into harsh hydrogen peroxide

Research reveals the chemical underpinnings of how benign water can turn into harsh hydrogen peroxide

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A new study has put a remarkable and unexpected chemical genesis on firmer footing.

In 2019, researchers and colleagues at Stanford University revealed the startling discovery that hydrogen peroxide – a caustic substance used to disinfect surfaces and bleach hair – forms spontaneously in microscopic droplets of plain water and benign. Researchers have since sought to flesh out how the new reaction occurs, as well as explore potential applications, such as more environmentally friendly cleaning methods.

The latest study found that when micro-droplets of sprayed water hit a solid surface, a phenomenon known as contact electrification occurs. Electric charge jumps between the two materials, liquid and solid, producing unstable molecular fragments called reactive oxygen species. Pairs of these species known as hydroxyl radicals, and which have the chemical formula OH, can then combine to form hydrogen peroxide, H2O2in minute but detectable quantities.

The new study further demonstrated that this process occurs in humid environments when water hits soil particles as well as fine particles in the atmosphere. These additional findings suggest that water can transform into small amounts of reactive oxygen species, such as hydrogen peroxide, anywhere microdroplets naturally form, including in fogs, mists and drops. of rain, reinforcing the results of a related study from 2020.

“We now have a real understanding that we didn’t have before of what’s causing this formation of hydrogen peroxide,” said study lead author Richard Zare, Marguerite Blake Wilbur Professor of Natural Sciences and Professor of chemistry at Stanford School. humanities and science. “Furthermore, it appears that contact electrification producing hydrogen peroxide is a universal phenomenon at water-solid interfaces.”

Zare led this work, in collaboration with researchers from two Chinese universities, Jianghan University and Wuhan University, as well as the Chinese Academy of Sciences. The study was published on August 1 in the Proceedings of the National Academy of Sciences (PNAS).

The origins of hydrogen peroxide

For the study, the researchers constructed a glass device with microscopic channels where water could be forcibly injected. The channels formed a strong, airtight boundary. The researchers infused the water with a fluorescent dye that glows in the presence of hydrogen peroxide. An experiment showed the presence of the aggressive chemical in the glass microfluidic channel, but not in a bulk water sample that also contained the dye. Additional experiments established that hydrogen peroxide formed rapidly, within seconds, at the water-solid boundary.

To assess whether the extra oxygen atom in hydrogen peroxide (H2O2) came from a reaction with glass or in water (H2O) itself, the researchers processed the glass coating of some microfluidic channels. These processed channels contained a heavier isotope or version of oxygen, called oxygen-18 or 18O. Comparison of the post-reaction mixture of water and hydrogen peroxide fluid of the treated and untreated channels showed the signal of 18O in the first, involving the solid as a source of oxygen in hydroxyl radicals and finally in hydrogen peroxide.

The new findings could help settle some of the debate that has ensued in the scientific community since Stanford researchers first announced their new detection of hydrogen peroxide in water microdroplets three years ago. Other studies have pointed to major contributions of hydrogen peroxide production via chemical interactions with ozone gas, O3, and a process called cavitation, when vapor bubbles appear in low-pressure areas within accelerated liquids. Zare pointed out that both of these processes also clearly produce hydrogen peroxide, and in comparatively larger amounts.

“All of these processes contribute to the production of hydrogen peroxide, but the present work confirms that this production is also intrinsic to how microdroplets are made and interact with solid surfaces through contact electrification,” Zare said.

Turning the tables on seasonal respiratory viruses

Defining how and in what situations water can transform into reactive oxygen species, such as hydrogen peroxide, offers a wealth of information and real-world applications, Zare explained. Among the most compelling is the understanding of hydroxyl radical and hydrogen peroxide formation as an overlooked contributor to the well-known seasonality of many viral respiratory illnesses, including the common cold, flu, and likely COVID-19. 19 once the disease finally becomes fully endemic.

Viral respiratory infections spread through the air as watery droplets when sick people cough, sneeze, sing or even just talk. These infections tend to increase in winter and decline in summer, a trend due in part to people spending more time indoors and in close proximity and transmissible during the cold season. However, between work, school, and nighttime sleep, people end up spending about the same amount of time indoors during the warmer months. Zare said the results of the new study offer a possible explanation for the correlation between winter and more flu cases: the key variable at work is humidity, the amount of water in the air. In summer, higher relative levels of indoor humidity — linked to higher humidity in warm air outside — likely facilitate reactive oxygen species in droplets having enough time to kill viruses. In contrast, in winter, when the air inside buildings is warmed and its humidity lowered, the droplets evaporate before the reactive oxygen species can act as a disinfectant.

“Contact electrification provides a chemical basis to partially explain why there is seasonality in viral respiratory illnesses,” Zare said. As a result, Zare added, future research should investigate any link between indoor humidity levels in buildings and the presence and spread of contagion. If the links are further confirmed, simply adding humidifiers to heating, ventilation and cooling systems could reduce disease transmission.

“Taking a new approach to surface disinfection is just one of the big practical implications of this work involving the fundamental chemistry of water in the environment,” Zare said. “It just goes to show that we think we know so much about water, one of the most commonly encountered substances, but then we’re humbled.”

Zare is also a fellow of Stanford Bio-X, Cardiovascular Institute, Stanford Cancer Institute, Stanford ChEM-H, Stanford Woods Institute for the Environment, and Wu Tsai Neurosciences Institute.

Chemists discover that micro-droplets of water spontaneously produce hydrogen peroxide

More information:
Bolei Chen et al, water-solid contact electrification causes the production of hydrogen peroxide from hydroxyl radical recombination in the sprayed microdroplets, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2209056119

Provided by Stanford University

Quote: Research reveals the chemical underpinnings of how benign water can turn into aggressive hydrogen peroxide (2022, August 2) Retrieved August 3, 2022 from reveals-chemical-underpinnings-benign-harsh.html

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