Researchers at The Pennsylvania State University recently demonstrated a catalyst-free strategy to convert waste polyethylene terephthalate (PET) into highly crystalline graphitic carbon using graphene-based templating additives, achieving structural ordering that in some cases surpasses natural graphite.
PET, a major contributor to single-use plastic waste, is inherently difficult to graphitize due to its oxygen-rich composition, which typically leads to non-graphitizable char during thermal treatment. To overcome this limitation, the team introduced small amounts of graphene oxide (GO) and graphene (Gr) as structure-directing agents during carbonization and graphitization, enabling precise control over crystallite formation without relying on metal catalysts.
By systematically varying additive loading (1 wt%, 2.5 wt%, and 5 wt%) and oxygen content in GO (10 at.% and 34 at.%), the researchers identified key structural parameters governing graphitization: reactive edge oxygen content, the edge-to-basal oxygen ratio, and graphene layer accessibility. These variables directly influence how carbon atoms reorganize into ordered graphitic domains.
At an optimal loading of 2.5 wt% GO with 10 at.% oxygen, the process delivered the best performance, with approximately 228% increase in lateral crystallite size (La) and ~200% increase in stacking height (Lc) compared to pure PET-derived carbon. Notably, these values exceeded those of natural graphite, indicating a highly ordered crystal structure. Among graphene additives, materials with lower stacking height showed superior templating efficiency, achieving ~167% and ~190% increases in La and Lc, respectively.
GO and graphene operate through distinct but complementary pathways. In GO-assisted graphitization, oxygen functional groups at sheet edges act as active sites that promote lateral crystallite growth, while oxygen species on basal planes induce cross-linking that facilitates coherent alignment of graphitic domains. In contrast, graphene templating follows a dual-pathway mechanism: reactive edge sites initiate lateral growth (La), while the sp2-bonded basal planes enable π–π interactions that guide vertical stacking (Lc).
The resulting materials consist of both graphitic carbon and hard carbon phases, offering tunable structures depending on processing conditions. Structural evolution and crystallinity were confirmed through X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and thermogravimetric analysis, with each technique providing complementary insight into the carbonization process.
Importantly, the catalyst-free approach avoids the need for metals such as iron, nickel, or cobalt, which are commonly used in graphitization but require post-processing removal. "By avoiding metal catalysts, we can produce cleaner graphite while reducing chemical use and waste generation," said author Shakshi Sekar.
The study also highlights the broader application potential of PET-derived graphite in energy storage. The synthesized material exhibits large, well-ordered crystallites suitable for lithium-ion battery anodes, where graphite serves as a critical charge storage component. "Most people think of a plastic bottle as waste once they're done using it," Sekar said. "Our work shows that the same material can become a valuable resource for producing graphite, which is essential for modern battery technologies."
By demonstrating that waste PET can be transformed into high-quality synthetic graphite with crystallite parameters exceeding those of natural graphite, the work establishes a pathway for converting a widespread environmental liability into a high-value material. "We're not simply finding a use for waste plastic," Sekar said. "We're creating a valuable material that could help support the growing demand for batteries and clean energy technologies."
The findings provide a foundation for scalable, additive-assisted carbonization processes and suggest a shift toward viewing plastic waste as a strategic feedstock for advanced energy materials. "If waste plastic can become a feedstock for advanced energy materials, it changes how we think about recycling," Sekar said. "Instead of viewing plastic as a disposal problem, we can see it as a resource that helps support clean energy technologies."
