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Sci-fi stories are teeming with terraforming schemes and oxygen generators for a very good reason: we humans need molecular oxygen (O2) to breathe, and the space in is essentially lacking. Even on other planets with thick atmosphere, the O2 is hard to find.
So when we explore space, we must bring our own supply of oxygen. This is not ideal because it takes a lot of energy to hoist objects into space at the top of a rocket and, once the supply is exhausted, there is nothing left.
A place where molecular oxygen appears outside the Earth is in the gas lodes that escape comets. The source of this oxygen remained a mystery two years ago when Konstantinos P. Giapis, professor of chemical engineering at Caltech, and his postdoctoral fellow Yunxi Yao, proposed the existence of a new chemical process that can explain its production. Giapis, along with Tom Miller, professor of chemistry, have now demonstrated a new reaction to generate oxygen that, according to Giapis, could help humans explore the universe and perhaps even combat the changes at home. More fundamentally though, he says that the reaction represents a new type of chemistry discovered by studying comets.
Most chemical reactions require energy, which is usually provided in the form of heat. Giapis' research shows that kinetic energy can cause unusual reactions. When water molecules are thrown like extremely tiny bullets on surfaces containing oxygen, such as sand or rust, the water molecule can extract oxygen to produce of molecular oxygen. This reaction occurs on comets when water molecules vaporize from the surface and are then accelerated by the solar wind until they fall back into the comet at high speed.
However, comets also emit carbon dioxide (CO2). Giapis and Yao wanted to check if CO2 could also produce molecular oxygen in collisions with the surface of the comet. When they found O2 in the gas stream coming out of the comet, they wanted to confirm that the reaction was similar to the water reaction. They have developed an experiment to inject CO2 on the inert surface of a gold foil, which can not oxidize and must not produce molecular oxygen. Nevertheless, the O2 continued to be emitted by the surface of the gold. This meant that the two oxygen atoms came from the same molecule of CO2, separating it effectively in an extraordinary way.
"At the time, we thought that it would be impossible to combine the two oxygen atoms of a CO2 molecule because CO2 is a linear molecule, and you had to bend strongly the molecule for it to work, "explains Giapis. "You are doing something really radical to the molecule."
To understand the mechanism of decomposition of CO2 into molecular oxygen, Giapis contacted Miller and his postdoctoral colleague Philip Shushkov, who designed computer simulations of the entire process. Understanding the reaction was a major challenge because of the possible formation of excited molecules. These molecules have so much energy that their constituent atoms vibrate and rotate a lot. All this movement makes it more difficult to simulate the reaction in a computer because the atoms in the molecules move in a complex way.
"In general, excited molecules can lead to unusual chemistry, so we started with that," says Miller. "But, to our surprise, the excited state did not create molecular oxygen. Instead, the molecule was broken down into other products." In the end, we found that a highly curved CO2 can also form without exciting the molecule, which could produce O2. "
The device that Giapis designed to perform the reaction works as a particle accelerator, transforming the CO2 molecules into ions by giving them a charge and then accelerating them with the help of an electric field although at energies well below those found in a particle accelerator. However, he adds that such a device is not necessary for the reaction to occur.
"You can throw a rock with enough speed with CO2 and get the same result," he says. "He would have to travel about as fast as a comet or asteroid in space."
This could explain the presence of small amounts of oxygen observed in the Martian atmosphere. There has been speculation that oxygen would be generated by the ultraviolet rays of the Sun striking CO2, but Giapis believes that oxygen is also generated by high speed colliding dust particles. with CO2 molecules.
He hopes that a variant of his reactor could be used to do the same thing at more useful scales – maybe someday it would serve as a source of breathable air to astronauts on Mars or would it be used to fight against climate change by using CO2, a greenhouse gas, out of the Earth's atmosphere and turning it into oxygen. It recognizes however that these two applications are far away because the current version of the reactor has a low efficiency, creating only one to two molecules of oxygen per 100 molecules of CO2 sent into the accelerator.
"Is it a final device? No. Is it a device that can solve the problem with Mars? No. But it's a device that can do something very difficult," he says. "We are doing crazy things with this reactor."
Reference: "Direct Evolution of Oxygen in Carbon Dioxide Collisions with Surfaces", Yunxi Yao et al., 2019, May 24, 2018, Nature Communications. [https://www.nature.com/articles/s41467-019-10342-6]. Caltech's co-authors include Tom Miller, professor of chemistry; Philip Shushkov, postdoctoral researcher in chemistry; and Yunxi Yao, a postdoctoral researcher, formerly of Caltech. Funding for the research was provided by the National Science Foundation, the Joint Center for Artificial Photosynthesis, and the US Department of Energy.
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