Rice University’s lab turns potential environmental hazards into useful material –...

This is what Rice University scientists call the process they have used to efficiently use plastic waste that would otherwise contribute to the planet’s environmental problems. In this case, rechemist James Tour’s lab changed its method of making flash graphene to improve it for recycling plastic into graphene.

The laboratory’s study appears in the Journal of the American Chemical Society ACS Nano.

Instead of using direct current to raise the temperature of a carbon source as in the original process, the laboratory first exposes plastic waste to high-intensity alternating current for about eight seconds, followed by a direct current surge.

The products are high quality turbostratic graphene, a valuable and soluble substance that can be used to improve electronics, composites, concrete and other materials, as well as carbon oligomers, molecules that can be drained from graphene for use in other applications.

“We produce a significant amount of hydrogen in our flash process, which is a clean fuel,” said Rice PhD student and lead author Wala Algozeeb.

Tour estimated that the ACDC process could produce graphene on an industrial scale for about $ 125 in electricity costs per tonne of plastic waste.

“We showed in the original paper that plastic can be transformed, but the quality of the graphene was not as good as we had imagined,” said Tour. “If we now use a different series of electrical impulses, we can see a big difference.”

He found that most of the world’s plastic recycling technologies are ineffective and that only about 9% of the plastic produced is recycled. Most notoriously, Tour said, is an island of plastic junk the size of Texas that formed in the Pacific.

“We have to take care of it,” he said. “And there is another problem: microbes in the ocean that convert carbon dioxide into oxygen are hindered by plastic breakdown products and they reverse the process, taking in oxygen and converting it to carbon dioxide. It will be really bad for people. ”

The flash joule conversion noted by the tour eliminates a large part of the costs associated with recycling plastic, including sorting and cleaning, which require energy and water. “Instead of recycling plastic into pellets that sell for $ 2,000 a tonne, you could upcycling it to graphene, which is much more valuable,” he said. “There is both an economic and an ecological incentive.”

Despite the overwhelming amount of plastic raw materials, having too much graphene is not a problem, Tour said. “Whatever you do with carbon, once you take it out of the ground from oil, gas or coal, it ends up in the carbon dioxide cycle,” he said. “The nice thing about graphene is that its biodegradation is very slow under many conditions. So in most cases it has not entered the carbon cycle for hundreds of years. ”

He noted that the researchers are working on refining the flash graphene process for other materials, especially food waste. “We’re working on creating a good pulse sequence to convert food waste into very high quality graphene with the lowest possible emissions,” he said. “We use machine learning programs to know where to go.”

The new study follows another recent paper that characterizes flash graphene made from soot by DC Joule heating. This paper, also in ACS Nano, combined microscopy and simulations to show two different morphologies: turbostratic graph and wrinkled graphene layers. The study described how and why the rearranged carbon atoms would take one form or another, and that the ratio can be controlled by adjusting the duration of the flash.