Nanotechnology

Researchers observe nanoscale water formation in real time

Water bubbles coming out of palladium nanocubes. Observed with a transmission electron microscope. Scale bar corresponds to 50 nanometers. Credit: Vinayak Dravid/Northwestern University

For the first time, researchers have witnessed hydrogen and oxygen atoms combining to form tiny nano-sized water bubbles in real time and on a molecular scale.

The incident occurred as part of a new study at Northwestern University in which scientists seek to understand how palladium, a rare metal element, catalyzes gas reactions to produce water. Ta. By witnessing the reaction at the nanoscale, the Northwestern University team has uncovered how the process occurs and discovered new strategies to accelerate it.

Because the reaction does not require extreme conditions, the researchers say it could be used as a practical solution to quickly produce water in arid environments, including on other planets.

The study is published in the Proceedings of the National Academy of Sciences.

“By directly visualizing nanoscale water production, we were able to identify optimal conditions for rapid water production under ambient conditions,” said senior author of the study, from Northwestern University. Vinayak Dravid said. “These discoveries have important implications for practical applications, such as enabling rapid water production in deep space environments using gas and metal catalysts without the need for extreme reaction conditions.”

“Remember Mark Watney, played by Matt Damon in the movie The Martian? He burned rocket fuel to extract hydrogen and added oxygen from an oxygen supply device. Avoiding fire and other extreme conditions. Our process is similar, except we just mix palladium and gas.”

Dravid is the Abraham Harris Professor of Materials Science and Engineering in Northwestern University’s McCormick School of Engineering and founding director of the Northwestern University Atomic and Nanoscale Characterization Experimental (NUANCE) Center, where the research was conducted. He is also Director of Global Initiatives at the International Nanotechnology Institute.

New technology enables discovery

Since the early 1900s, researchers have known that palladium acts as a catalyst to rapidly produce water. However, exactly how this reaction occurs remains a mystery.

“This is a known phenomenon, but it was not fully understood,” said Yukun Liu, Ph.D., lead author of the study. candidate in Dravid’s lab. “Because to understand what’s happening in the reaction and how to optimize it, we need to be able to combine direct visualization of water production with structural analysis at the atomic scale. .”

But observing processes with atomic-level precision was simply impossible until nine months ago. In January 2024, Dravid’s team announced a new method for analyzing gas molecules in real time. Dravid and his team developed an ultrathin glassy membrane that holds gas molecules inside a honeycomb-shaped nanoreactor. This allows the gas molecules to be observed using a high-vacuum transmission electron microscope.

Using this new technique, which was previously published in Science Advances, researchers were able to perform large scale measurements with a resolution of just 0.102 nanometers, compared to 0.236 nanometers using other state-of-the-art tools. It becomes possible to test samples in atmospheric gas. This technology also allows for the first time the simultaneous analysis of spectral and mutual information.

“By using ultrathin films, we can get more information from the sample itself,” says lead author of the Science Advances paper, a researcher at the NUANCE Center and supervised by research associate professor Xiaobing Hu. Kunmo Koo said. “Otherwise, the information from the thick container will hinder the analysis.”

Smallest bubble ever seen

Using a new technique, Dravid, Liu, and Koo investigated the reaction of palladium. First, they observed hydrogen atoms entering palladium and expanding its square lattice. But the researchers couldn’t believe their eyes when they saw tiny water bubbles forming on the surface of palladium.

“We think this may be the smallest bubble ever formed that has been directly observed,” Liu said. “It wasn’t what we expected. Luckily, we had recorded it so we could prove to others that we weren’t crazy. .”

“We were skeptical,” Koo added. “Further investigation was needed to prove that it was actually water that formed.”

The research team deployed a technique called electron energy loss spectroscopy to analyze the bubbles. By studying the energy loss of scattered electrons, the researchers determined the unique oxygen-binding properties of water and confirmed that the bubbles were indeed water. The researchers then cross-checked this result by heating the foam and assessing its boiling point.

“This is a nanoscale analog of the lunar probe Chandrayaan 1’s experiment, which searched for evidence of the presence of water in lunar soil,” Professor Khoo said. “While exploring the Moon, we used spectroscopy to analyze and identify molecules in the atmosphere and on the surface. We used similar methods to determine whether the products produced were really water. We adopted the spectroscopy method.

Optimization recipe

After confirming that the palladium reaction produced water, the researchers next sought to optimize the process. They added hydrogen and oxygen separately at different times or mixed them together to determine which series of events produced water at the fastest rate.

Dravid, Liu, and Koo found that adding hydrogen first and then oxygen resulted in the fastest reaction rate. The hydrogen atoms are so small that they can squeeze between the palladium atoms, causing the metal to expand. The researchers filled the palladium with hydrogen and then added oxygen gas.

“Oxygen atoms are energetically favorable for adsorption to the palladium surface, but they are too large to enter the lattice,” Liu said. “When oxygen was first poured in, the dissociated atoms covered the entire surface of the palladium, so the hydrogen could not adsorb to the surface and cause a reaction. However, first the palladium stored hydrogen, and then the oxygen When hydrogen was added to the palladium, the reaction began.” Hydrogen comes out of the palladium and reacts with oxygen, causing the palladium to contract and return to its original state. ”

Sustainable systems in deep space

The Northwestern research team imagines that in the future, other researchers might be able to prepare hydrogen-filled palladium before going on a space trip. Travelers can then simply add oxygen to produce water for drinking or watering plants. The research focused on studying bubble formation at the nanoscale, but larger sheets of palladium would produce larger amounts of water.

“Palladium may seem expensive, but it is recyclable,” Liu says. “Our process does not consume palladium; only gas is consumed, and hydrogen is the most abundant gas in the universe. After the reaction, the palladium platform can be reused many times.”

Further information: Yukun Liu et al. “Elucidation of adsorption-limited hydrogen oxidation reactions on palladium surfaces using in-situ electron microscopy,” Proceedings of the National Academy of Sciences of the United States of America (2024). DOI: 10.1073/pnas.2408277121

Provided by Northwestern University

Citation: Researchers witness nanoscale water formation in real time (September 30, 2024) from https://phys.org/news/2024-09-witness-nanoscale-formation-real.html 2024 Retrieved September 30th

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