Scientists Used Lasers to Transform Plastic Into Tiny Diamonds

Is it a new form of recycling or a pipe dream?

ULTRA.F / Getty Images

They say one person's trash is another person's treasure.

Now, an international team of scientists has managed to make that statement literal by turning cheap polyethylene terephthalate (PET) plastic into nanodiamonds–synthetic, microscopic diamonds.

"Within nanoseconds, [...] 10 percent of all the carbon atoms inside this plastic sample are transformed to very small diamonds," study co-author and professor at the University of Rostock's Institute of Physics Dominik Kraus tells Treehugger. "And those very small nanodiamonds can have–or already have in some form, but maybe even more so in the future–very interesting applications for technology."

The transformation, published in Science Advances in the fall of 2022, was a bit of a surprise, Kraus says. That's because the research team—from the Department of Energy's SLAC National Accelerator Laboratory in California, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the University of Rostock in Germany and France's École Polytechnique—wasn't trying to find earthly uses for plastic, but rather understand the chemistry of other planets.

"Originally, this was motivated to get a better picture of what kind of chemistry is happening inside giant planets like Neptune and Uranus," Kraus says.

This is important for understanding the universe, at large, because scientists think ice giants are the most common type of planet beyond our solar system. On an elemental level, these planets are mostly made up of carbon, hydrogen, and oxygen with a little bit of nitrogen, Kraus says. However, it's how these elements interact under extreme planetary conditions that really fascinates scientists. It's possible that conditions on these planets could generate a special type of water called superionic water. They might also cause diamonds to fall as rain.

Olivier Bonin / SLAC National Accelerator Laboratory

What is superionic water? "Superionic water is a predicted form of water where the oxygen atoms form a crystal lattice and the hydrogen nuclei [are] then somewhat able to move freely through this oxygen lattice," Kraus says.

The presence of this superionic water might explain the unique magnetic fields that scientists think exist on these planets, the study authors wrote.

To try and figure out what might be happening on these planets, scientists need to somehow replicate their extreme conditions—with temperatures in the thousands of degrees Celsius and atmospheric pressure millions of times greater than Earth's—in the laboratory. They do this by blasting a filmy material with a high-powered laser that can heat the film to 6,000 degrees Fahrenheit, producing a shockwave that multiplies the pressure on the material by a million. They then use the special Linac Coherent Light Source (LCLS) accelerator-based X-ray laser, located at the SLAC National Accelerator Laboratory, to look at what happens when the laser flashes hit the film.

Previous experiments blasting polystyrene—a plastic composed of hydrogen and carbon–had led to evidence that diamond precipitation really could form on these planets. However, these planets also have lots of water, and scientists think that superionic water would likely be formed when carbon and water separate.

That's why they turned to PET, which has the chemical formula C10H8O4. It was this experiment that generated the nanodiamonds–and bolstered scientific evidence that ice giants might see both diamond rain and superionic water.

"We know that Earth's core is predominantly made of iron, but many experiments are still investigating how the presence of lighter elements can change the conditions of melting and phase transitions," SLAC scientist and study co-author Silvia Pandolfi says in a SLAC press release. "Our experiment demonstrates how these elements can change the conditions in which diamonds are forming on ice giants. If we want to accurately model planets, then we need to get as close as we can to the actual composition of the planetary interior."

Blaurock / HZDR

While this wasn't the intent of the experiment, the researchers think they may have developed a new method for generating nanodiamonds from cheap material.

"The way nanodiamonds are currently made is by taking a bunch of carbon or diamond and blowing it up with explosives," SLAC scientist and study co-author Benjamin Ofori-Okai says in the press release. "This creates nanodiamonds of various sizes and shapes and is hard to control. What we're seeing in this experiment is a different reactivity of the same species under high temperature and pressure. In some cases, the diamonds seem to be forming faster than others, which suggests that the presence of these other chemicals can speed up this process. Laser production could offer a cleaner and more easily controlled method to produce nanodiamonds. If we can design ways to change some things about the reactivity, we can change how quickly they form and therefore how big they get."

Kraus says it's unlikely that the process would be scaled up as a solution to plastic pollution, but it could still give a useful second life to some plastic. Nanodiamonds are currently used in abrasives and polishing agents, according to SLAC. However, potential future applications include quantum sensors, contrast agents for medicinal uses, and accelerators for chemical reactions including the splitting of carbon dioxide, according to HZDR.

In particular, Kraus thinks that nanodiamonds might help with the photocatalysis of carbon dioxide–a process that uses light to convert the greenhouse gas into hydrogen or methane.

"[Y]ou float, for example, water with those nanodiamonds and shine sunlight on it and then you bring carbon dioxide through this water region," Kraus explains.

Some scientists have argued that recycling carbon dioxide like this could be a climate solution by generating a more sustainable source of methane that did not require extracting additional fossil fuels from beneath the Earth. However, Matteo Pasquali, the A. J. Hartsook Professor of Chemical & Biomolecular Engineering, Chemistry, and Materials Science & NanoEngineering at Rice University, throws some cold water over these claims.

"Man-made carbon dioxide emissions are the cause of climate change and cannot be the solution," he tells Treehugger. "We emit carbon dioxide because it is generated when we burn coal, oil, and gas (methane) to make energy. Of course, it takes more energy to reconvert CO2 into methane (or oil, or gas) than the energy that was extracted from the methane. This is technology-independent and is due to the first and second laws of thermodynamics which, for example, state that one cannot generate energy in a cyclical process and that external energy input is required to run cyclical processes."

He thinks in a future in which policymakers have succeeded in zeroing out greenhouse gas emissions, it might be possible to use renewable energy to recycle carbon dioxide into carbon, but he also thinks natural systems would successfully mop up excess atmospheric carbon if humans simply stopped burning fossil fuels.

He also does not believe that nanodiamonds would help with carbon-dioxide recycling.

While it seems unlikely that using lasers to transform plastic bottles into tiny diamonds will be part of the solution to the major environmental crises facing our planet, it's still a reminder of the happy accidents produced by the scientific process. Kraus says that one particularly "fun" element of the findings was that astrophysics research had led to potential earthly applications. For him, it's a reminder that science doesn't only need to be about solving problems. Sometimes, asking questions out of curiosity can lead to solutions you weren't even looking for.

"Curiosity-driven research is also very important and there are many examples of how this has transformed our world," he says.

Next, Kraus hopes to both learn more about what's happening on ice giants and figure out ways to produce more nanodiamonds.

He, Zhiyu, et. al. "Diamond formation kinetics in shock-compressed C─H─O samples recorded by small-angle x-ray scattering and x-ray diffraction." Science Advances, vol. 8, no. 35, 2 Sept 2022, DOI:10.1126/sciadv.abo0617

Kraus, D., et al. Formation of diamonds in laser-compressed hydrocarbons at planetary interior conditions. Nat Astron, vol 1, pp. 606–611, 2017., doi:10.1038/s41550-017-0219-9

Sundermier, Ali. "'Diamond rain' on giant icy planets could be more common than previously thought." SLAC National Accelerator Laboratory.

"Making nanodiamonds out of bottle plastic." Helmholtz Zentrum Dresden Rossendorf.

Ulmer, Ulrich, et al. Fundamentals and applications of photocatalytic CO2 methanation. Nat Commun, vol. 10, no. 3169 (2019). https://doi.org/10.1038/s41467-019-10996-2