scientists explore scaling nanocages for practical, nuclear and beyond applications |

In recent years, scientists have demonstrated how porous cage-like structures made of silicon and oxygen measuring only billionths of a meter can trap rare gases like argon, krypton and xenon. However, for these silica nanocages to be useful in practice, for example to improve the efficiency of nuclear power generation, they need to be scaled up compared to their laboratory versions. Scientists have now taken a step forward by bringing this technology out of the lab and into the real world. As they recently reported in Small, commercially available materials can provide a potentially scalable platform for trapping noble gases.

(Left to right) Anibal Boscoboinik, Yixin Xu, Shruti Sharma, Alejandro Boscoboinik and Dario Stacchiola with the AP-XPS instrument at CFN.

Yixin Xu, a graduate student in the Department of Materials Science and Chemical Engineering at Stony Brook University, is the lead author of the research and works with corresponding author Anibal Boscoboinik, a materials scientist in the Interface Science group. and Catalysis at the Center. for Functional Nanomaterials (CFNs) at Brookhaven National Laboratory, and his team.

“Making a square centimeter of our lab-scale nanocages, which can only trap nanograms of gas, takes us a few weeks and requires expensive starting components and equipment,” Boscoboinik said. “There are commercial processes to synthesize tons of these silica nanocages, which are so inexpensive that they are used as additives in concrete. However, these commercial materials do not trap noble gases, so a challenge in advancing our technology was to understand what is special about our nanocages. “

Boscoboinik has led nanocage research at CFN since 2014. He and his colleagues became the first group to trap a noble gas inside a two-dimensional porous structure at room temperature. In 2019, they trapped two other rare gases inside the cages: krypton and xenon. In this second study, they learned that for the trapping to work, two processes had to occur: the gas atoms had to be converted into ions (electrically charged atoms) before entering the cages, and the cages had to be in contact. with a metal support. to neutralize ions once inside the cages – effectively trapping them in place.

With this understanding, in 2020, Boscoboinik and his team filed a patent application, which is currently pending. The same year, the DOE Office of Technology Transitions selected a research proposal submitted by CFN in collaboration with the Brookhaven Nuclear Science and Technology Department and Forge Nano to extend the nanocages developed in the laboratory. The goal of this scaling is to maximize the trapping area for krypton and xenon, both products of the nuclear fission of uranium. Their capture is desirable for improving the efficiency of nuclear reactors, preventing operational failures due to increased gas pressures, reducing radioactive nuclear waste and detecting nuclear weapons tests.

The start of scaling up

A representation of silica nanocages on a thin film of ruthenium trapping xenon atoms (blue).
A representation of silica nanocages on a thin film of ruthenium trapping xenon atoms (blue).

The CFN team began to explore how they could scale nanocages for practical, nuclear and beyond applications. During their explorations, the CFN team found a company that manufactures large volumes of silica nanocages, in powder form. Instead of depositing the nanocages on single crystals of ruthenium, the team deposited them on thin layers of ruthenium, less expensive. Unlike laboratory nanocages, these nanocages have organic components (containing carbon). So, after depositing the cages on the thin films, they heated the material in an oxidizing environment to burn these components. However, the cages would not trap any gas.

“We have found that the metal must be in the metallic state,” Xu said. “By burning the organic compounds, we partially oxidize the ruthenium. We have to reheat the material again in hydrogen or some other reducing environment to bring the metal back to its metallic state. Then the metal can act as a source of electrons to neutralize the gas inside the cages.

Next, CFN scientists and their collaborators at Stony Brook University tested whether the new material would still trap the gases. To do this, they performed ambient pressure X-ray photoelectron spectroscopy (AP-XPS) at the National Synchrotron Light Source II (NSLS-II) at Brookhaven Lab. In AP-XPS, X-rays excite a sample, causing the surface to emit electrons. A detector records the number and kinetic energy of the electrons emitted. By plotting this information, scientists can infer the sample’s chemical composition and chemical bond states. In this study, x-rays were not only important for measurements but also for ionizing gas – in this case, xenon. They started the experiment at room temperature and gradually increased the temperature, finding the optimum range for trapping (350 to 530 degrees Fahrenheit). Outside of this range, the efficiency begins to decrease. At 890 degrees Fahrenheit, the trapped xenon is completely released.

Successive steps for scaling

Now the scientists will fabricate the materials with a large area (a few hundred square meters) and see if they continue to function as desired. They will also study more practical ways to ionize gas.

The team is considering several potential applications for their technology. For example, nanocages may be able to trap noble gases like xenon and krypton from the air in a more energy efficient way. Currently, these gases are separated from the air using an energy-intensive process in which the air must be cooled to extremely low temperatures.

Xenon and Krypton are used to make many products, such as lighting. One of the main uses of xenon is in high intensity discharge lamps, including some bright white car headlights. Likewise, krypton is used for airport runway lights and photographic flashes for high speed photography.

The team believe their process should also be able to trap radioactive noble gases, including radon. Commonly found in basements and lower levels of buildings, radon can damage lung cells, potentially leading to cancer. This ability to trap radioactive noble gases would be relevant for several applications, such as the attenuation of released radioactive gases, the monitoring of nuclear non-proliferation and the production of medically relevant isotopes. The CFN team is exploring the medical application in collaboration with the medical isotope research and production program at Brookhaven.

Read the full Brookhaven National Lab press release

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