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Microwaved fish could help scientists create sustainable LEDs

Supermaterial created from heated scales. Sorry about the smell

Scientists in Japan have figured out a new way to create sustainable LEDs: by microwaving fish.

That pungent breakroom smell may alienate coworkers, but when fish scales undergo microwave pyrolysis – where they are heated to temperatures as high as 800˚C – it turns out they "quickly and efficiently create a nanoform of carbon known as carbon nano-onions (CNOs)," the researchers reported

CNOs –  also known as multilayer fullerenes – have a variety of potential applications, but one major drawback, according to the research team: They're tough to make. "Some [methods] require harsh synthesis conditions, such as high temperatures or vacuum, while others demand a lot of time and energy. Some techniques can circumvent these limitations, but instead call for complex catalysts, expensive carbon sources, or dangerous acidic or basic conditions," the researchers said. 

CNOs are a cousin to carbon nanotubes (CNTs), and were first reported in 1980, roughly the same time CNTs were made practically usable. CNTs are easier to produce, and have found their way into a variety of products, including proprietary Nano-RAM built by memory maker Nantero.

Unlike the tube-shaped CNTs, CNOs are made up of concentric shells of fullerenes that resemble multiple layers of cages within cages. CNOs have a large surface area, as well as large electrical and thermal conductivity, which results in them glowing with a brightness "10 times higher than that of previously reported CNOs synthesized via conventional methods," said paper coauthor and Nagoya Institute of Technology Life Sciences and Applied Chemistry professor Takashi Shirai.

Shirai said that their CNOs emitted light with a 40 percent quantum yield, which is a measurement of photons emitted to photons absorbed.

It works, don't ask why

The researchers admit they're not quite sure why their new method, which involves extracting and cleaning fish scales from fish waste and then zapping them for a few seconds, works. They believe it has to do with collagen in the scales quickly absorbing microwave energy, allowing the scales to thermally decompose through pyrolysis. 

Once pyrolysis takes hold, the scales emit gasses that support assembly of CNOs. "What is remarkable about this approach is that it needs no complex catalysts, nor harsh conditions, nor prolonged wait times; the fish scales can be converted into CNOs in less than 10 seconds," the researchers said. 

CNOs created by applying microwave pyrolysis to fish scales have properties that make them particularly well suited to use in various applications because they automatically "functionalize," meaning they have bonds on their surface that make them easier to disperse in solvents.

"CNOs prepared with conventional methods [are] typically bare and [have] to be functionalized through additional steps," the researchers said. 

In addition to automatic functionalization, the researchers said CNOs made using their method also have "very high crystallinity," which they said is "remarkably difficult" to achieve using biomass as a starting material. 

The researchers said that they demonstrated the use of their fish-derived CNOs in blue-light-emitting thin films that worked in solid devices and while dispersed in water, ethanol and isopropanol, though no footage of the demonstration was provided. 

"The stable optical properties could enable us to fabricate large-area emissive flexible films and LED devices … [and] will open up new avenues for the development of next-generation displays and solid-state lighting," Shirai said, adding that their CNOs could make LED and QLED displays much cheaper to produce. ®

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