A new method converts fish waste into valuable carbon-based nanomaterials

In only 10 seconds?
Chris Young
Carbon-based nanomaterial.
Carbon-based nanomaterial.Takashi Shirai from NITech, Japan

Scientists from Nagoya Institute of Technology in Japan discovered a new method for turning fish waste into extremely high-quality carbon nano-onions (CNOS), a press statement reveals. The new development could lead to cheaper next-generation LED lighting and QLED displays.

CNOs are a form of carbon-based nanomaterial with low toxicity, chemical stability, and excellent electrical and optical properties. They are composed of concentric shells of fullerenes that somewhat resemble cages within cages. Their main advantage over other carbon-based nanomaterials is that they have a high surface area as well as large electrical and thermal conductivities.

Since they were first discovered in the 80s, attempts to manufacture CNOs have been met with some serious obstacles. Some CNOs, for example, require high temperature or vacuum conditions for the manufacturing process. Others take an unsustainable amount of time to produce.

Now, in their new study published in the journal Green Chemistry, the team from the Nagoya Institute of Technology describes their simple new method for turning fish waste into CNOs. The team developed a synthesis route that converts fish scales extracted from fish waste into CNOs in a matter of seconds. The key to this is microwave pyrolysis.

Interestingly, the researchers are still investigating the reason behind their discovery — they don't yet fully understand why fish scales can be so easily converted into CNOs. What they do know, is that it may have to do with the fact that the collagen contained in fish scales absorbs enough microwave radiation to produce a rapid rise in temperature. This, in turn, leads to thermal decomposition or "pyrolysis". Pyrolysis produces gases that support the assembly of CNOs.

A new CNO manufacturing method could reduce the cost of next-gen displays

Impressively, the new method requires no extreme temperatures, no complex catalysts, and it takes only 10 seconds. The process also produces CNOs with very high crystallinity, the researchers explain in their paper, also noting that this is incredibly rare for processes using biomass waste.

The scientists also note that their method creates CNOs that are selectively and thoroughly functionalized with (−COOH) and (−OH) groups. One of the benefits of their CNOs' functionalization and high crystallinity is that it lends great optical properties. Associate Professor Takashi Shirai, who worked on the new research, said, "the CNOs exhibit ultra-bright visible-light emission with efficiency (or quantum yield) of 40 percent. This value, which has never been achieved before, is about 10 times higher than that of previously reported CNOs synthesized via conventional methods."

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In the lab, the researchers demonstrated the efficiency of their fish-based CNOs by using them in LEDs and blue-light-emitting thin films. They produced a highly stable emission, they said. “The stable optical properties could enable us to fabricate large-area emissive flexible films and LED devices," explained Dr. Shirai. "These findings will open up new avenues for the development of next-generation displays and solid-state lighting." Not only that, the use of fish waste would be a more environmentally friendly way of producing electronics, and it could also lower the costs of production for the next-generation displays.