Researchers from Australia's University of New South Wales (UNSW), Australian Nuclear Science and Technology Organization (ANSTO) and The Hong Kong Polytechnic University have developed a rapid, highly efficient process to synthesize graphene from discarded peanut shells - turning what agricultural waste into a high-value nanomaterial.
The team, led by Professor Guan Yeoh from UNSW’s School of Mechanical and Manufacturing Engineering, used a two-stage heating strategy that dramatically improves the energy efficiency and quality of the resulting graphene compared to traditional high-temperature or chemical routes. Their work shows how precursor engineering - the controlled pre-treatment of raw biomass - determines the structural order and electronic quality of the resulting graphene.
The process begins with peanut shells, chosen for their high lignin content and stable carbon yield. In the first step, the shells undergo a short indirect Joule heating (IJH) at 500°C for five minutes, followed by 1000°C for one minute. This rapid pre-treatment removes oxygen and hydrogen species, eliminates impurities, and creates a moderately carbonized char rich in aromatic rings.
This char is then subjected to a flash Joule heating (FJH) pulse, where a high-current electric discharge drives the temperature to approximately 3000°C within milliseconds. The extreme conditions trigger a rapid reorganization of carbon atoms into few-layer, turbostratic graphene - characterized by weak interlayer coupling and a disordered rotational stacking favorable for electronic transport.
Raman spectroscopy revealed a strong I₂D/I_G ratio of 2.05, while X-ray diffraction confirmed a contracted interlayer spacing (d002≈0.342nm), indicative of few-layer graphene. XPS analysis further showed an enriched sp²/sp³ ratio consistent with the formation of high-quality graphitic domains. Transmission electron microscopy and selected-area electron diffraction (SAED) images displayed thin, transparent flakes with long-range lattice coherence, confirming the superior microstructure achieved via the IJH-assisted route.
Reactive molecular dynamics simulations (MD–ReaxFF) reproduced the atomistic sequence observed experimentally - deoxygenation, aromatic ring coalescence, and defect healing - occurring within microseconds under high thermal flux. Importantly, the FJH voltage (ranging from 90–180 V) was found to fine-tune defect density and crystallinity, but the intrinsic precursor condition remained the dominant determinant of graphene quality.
From an engineering standpoint, the approach is remarkably efficient. The specific electrical energy required for conversion is just 15.6 MJ per kilogram of graphene, equivalent to an electricity cost of about USD $1.30 per kg, significantly lower than reported for FJH synthesis from other sources such as lignin or polymeric waste. The entire process - from raw peanut shell to graphene - is completed in around 10 minutes, without any chemical reagents or fossil-derived additives like carbon black.
Prof. Yeoh said: “What we identified in the experiments was that the most important aspect of producing high-quality graphene was the pre-treatment or precursor engineering done to the peanut shells before the flash Joule heating.” This insight underscores how brief yet well-controlled pretreatment steps can modulate conductive pathways and enable the ultrafast formation of planar carbon networks.
Looking ahead, the team plans to extend this approach to other lignin-rich biomasses such as coffee grounds and banana peels, positioning precursor-engineered flash Joule heating as a broadly applicable route to low-cost, high-quality graphene.
