Upcycling PET plastic waste: A graphenic additive templated approach to synthetic graphite

Polyethylene terephthalate (PET) is a major contributor to single-use plastic waste. Its inherent oxygen content forms non-graphitizable char during thermal treatment, making upcycling into valuable carbon materials challenging. This study demonstrates a novel catalyst-free approach for converting waste PET into highly crystalline graphitic carbon using graphene oxide (GO) and graphene (Gr) as templating additives during carbonization and graphitization. This circumvents the purification challenges associated with conventional catalytic methods. Successful graphitization leverages oxygen functional groups in GO and reactive edge sites in Gr to precisely control structure formation. The critical variables identified are: (a) reactive edge oxygen content, (b) edge-to-basal oxygen ratio and (c) graphene layer accessibility. GO facilitates graphitization, where edge oxygen groups promote lateral crystallite growth and basal plane oxygen causes cross-linking that helps coherent crystallite alignment. Gr templating operates through a dual-pathway mechanism. Edge sites serve as reactive nucleation points for lateral growth (L_a), while sp2 basal plane enables π-π templating for vertical stacking (L_c). Comprehensive characterization using X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) reveal optimal performance at 2.5 wt% GO loading. GO with 10 at.% oxygen achieved ∼228% increase in L_a and ∼ 200% increase in L_c compared to pure PET, surpassing natural graphite. Among Gr additives, the lowest stacking height demonstrated superior performance with ∼167% and ∼ 190% increase in L_a and L_c respectively. At optimal loadings, the process yields both graphitic carbon, and hard carbon offering sustainable upcycling of waste PET.