Making nanodiamonds from plastic will allow new recycling methods and have implications for Neptune and Uranus, which rain diamonds, reports Vice.
On the ice giants, under extreme pressure and high temperatures deep below the surface of the planet, hydrocarbons turn into diamonds, which remain there forever. Since the 1970s, scientists have believed that diamonds can indeed form diamond rain.
In 2017, researchers from Germany and California produced nanodiamonds, recreating the conditions in which diamonds form on Neptune and Uranus. For this, they used polystyrene (aka Styrofoam). A study published on Friday in Science Advances suggests that years later, scientists returned to experiments, this time using polyethylene terephthalate (PET). This research has implications not only for our understanding of space, but also paves the way for creating nanodiamonds from plastic waste.
Dominik Kraus, a scientist at Germany’s Helmholtz-Zentrum Dresden-Rossendorf research laboratory and lead author of the study, told Vice in an email that he and his colleagues first experimented with polystyrene, which contains the same carbon and hydrogen elements as Neptune and Uranus. They did this by bombarding the material with the Linac Coherent Light Source, a powerful X-ray laser at the SLAC National Acceleratory Laboratory in California. This process rapidly heated the polystyrene to 5,000 Kelvin and compressed it to 150 gigapascals, nearly replicating the conditions found at about 9,656 km deep on icy planets.
Later, the researchers realized that the experiment lacked oxygen, so they turned to PET, because plastic has a good balance of the necessary elements. This makes it chemically closer to the ice giants than polystyrene.
“TThe chemistry at these conditions is very complex and modeling extremely difficult. ‘Anything can happen’ is a typical phrase when discussing such scenarios with theorists,” Kraus said. “Indeed, there were some predictions showing that the presence of oxygen is helping [carbon separate from hydrogen] and diamond formation, but also ideas that it may be the other way around.”
Kraus and his colleagues took a piece of PET and ran it through the same experimental motions as in 2017, but included so-called small-angle X-ray diffraction. This was done to see how fast and how large diamonds grow.
“We found that the presence of oxygen enhances diamond formation instead of preventing it, making ‘diamond rain’ inside those planets a more likely scenario,” Kraus said. “We [also] see that diamonds grow larger for higher pressures and with progressing time in the experiments.”
Scientists have been able to get a lot of tiny diamonds from just one X-ray, but Kraus said that’s not enough for applications such as diamond quantum sensors used to detect magnetic flux or chemical catalysts, which require a minimum of a couple of milligrams. However, this can later be scaled up to meet the goals and is the first step towards a more luxurious way to recycle plastic.
“If industrial scaling of the formation process indeed works as discussed above, and nanodiamonds will be required in very large quantitates for certain processes, e.g., catalysis for light-induced CO2 reduction reactions helping to reduce global warming, this may indeed become a potential way to recycle large amounts of PET,” Kraus said.
However, it is important not to lose sight of the scientific intent: to better understand how extreme environmental conditions on icy planets lead to diamond showers. Kraus and his team believe they have also found more evidence of a strange type of water, first theorized but then finally discovered in 2019.
In 2018, the New York Times reported that it is called superionic water, and it acts as something between solid and liquid substances. It is believed to fill the mantles of Neptune, Uranus, and potentially countless other ice giants and planets. This substance may not have any application on Earth, but its presence may explain why some celestial bodies have peculiar magnetic fields.
According to Kraus, the discovery that nanodiamonds do form inside ice giants raises the possibility of conditions for superionic water. However, he says that his team’s experiments “did not yet see direct evidence for superionic water forming alongside with diamonds.”
“[But] our experiments show that carbon is separating from hydrogen and oxygen allowing pure water regions to form inside the planets. Thus, by making diamond precipitation a more realistic scenario inside those planets, also the formation of superionic water becomes more likely,” Kraus adds.
Beyond superionic water, Krauss and his colleagues need more time to investigate nanodiamonds. They are looking for ways to produce large quantities of tiny gems in minutes using more affordable but still high-energy laser systems. Scientists can try adding nitrogen to see how it affects the shape of the nanodiamond. Nitrogen itself is quite common in diamonds — about 98 percent of natural diamonds contain tens to several hundred parts per million nitrogen atoms.