Over 10 million tonnes of waste, in the form of discarded peanut shells, result annually from global peanut production, yet scientists have now uncovered a technique to convert this biomass into graphene-like carbon materials. The findings of this new study have been published in the journal Chemical Engineering Journal Advances.
Graphene, composed of carbon, is frequently referred to as a “wonder material”: it possesses incredible strength, is remarkably light, and exhibits excellent thermal and electrical conductivity. It is already widely employed and promises to substantially enhance consumer electronics moving forward.
However, manufacturing it on a large scale is difficult and comes at a high cost. Therefore, alternative pathways for graphene production could significantly advance energy systems, data storage, and other cutting-edge technologies.
The new research, conducted by a team of academics at the University of New South Wales (UNSW) in Australia, indicates that common peanut shells hold the potential to boost graphene output in a manner that is both more economical and environmentally sound compared to some established synthesis routes.
“Most of the waste from production is either sent to landfill or repurposed into low-value products that don’t fully capitalize on their potential,” states Guang Yeoh from UNSW. “In this work, we demonstrated that high-quality graphene can be derived from ordinary peanut shells using substantially less energy than currently required, thus at a lower expense. Furthermore, we avoid the use of any chemicals, which is an added environmental benefit.”
The crucial component in this procedure is lignin, a naturally occurring polymer rich in carbon found in the majority of plants. Its presence in peanut shells was known previously, but the researchers needed to determine the optimal way to process it.
Before employing the method known as Flash Joule Heating (FJH), the team assessed several ways to prepare the shell waste for lignin extraction. This method uses an electrical “flash” to heat the material above 3000 degrees Celsius (5432 degrees Fahrenheit) in mere milliseconds. This sudden surge of heat reorganizes the carbon atoms into graphitic structures, a process which forms multilayer turbostratic graphene.
While FJH performed the bulk of the transformation, the manner in which the shells were prepared for FJH proved critical. The researchers found that a staged pre-treatment, involving indirect Joule heating at approximately 500°C for 5 minutes, followed by a brief period at a higher temperature, yielded the best results.
“This process is vital for eliminating impurities and obtaining the best possible carbon-rich material, which helps minimize defects in the final graphene, ensuring it is truly just a single layer of atoms,” Yeoh explains. “This is precisely what you need to guarantee the best performance regarding electrical and thermal conductivity.”
Although the concept of creating graphene from peanut shells has been demonstrated experimentally before, this specific study emphasizes just how much meticulous control over the starting material can improve the resulting graphene’s quality.
However, this does not imply the process is currently perfect. The graphene material produced is high-grade, but it typically consists of a few graphene layers arranged turbostratically, and the researchers note that commercial scaling might require three to four years.
Efforts to further refine the process, developed from this laboratory model, will continue. In the interim, the researchers intend to verify whether their specially engineered preparation and heating protocol is effective with other types of biomass.
“We also plan to conduct experiments with different materials, such as spent coffee grounds, banana peels, or anything else that might yield a good carbon source for subsequent conversion into graphene,” remarks Yeoh. “Given the widespread availability of similar organic matter, our work strikes a sound balance between energy efficiency, the quality of the derived graphene, and the overall cost-effectiveness of the approach.”
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