▎ 摘　　要

Producing high-quality graphene sheets from plastic waste is regarded as a significant economic and environmental challenge. In the present study, unsupported Fe, Co, and Fe-Co oxide catalysts were prepared by the combustion method and examined for the production of graphene via a dual-stage process using polypropylene (PP) waste as a source of carbon. The prepared catalysts and the as-produced graphene sheets were fully characterized by several techniques, including XRD, H-2-TPR, FT-IR, FESEM, TEM, and Raman spectroscopy. XRD, TPR, and FT-IR analyses revealed the formation of high purity and crystallinity of Fe2O3 and Co3O4 nanoparticles as well as cobalt ferrite (CoFe2O4) species after calcining Fe, Co, and Fe-Co catalysts, respectively. The Fe-Co catalyst was completely changed into Fe-Co alloy after pre-reduction at 800 degrees C for 1 h. TEM and XRD results revealed the formation of multi-layered graphene sheets on the surface of all catalysts. Raman spectra of the as-deposited carbon showed the appearance of D, G, and 2D bands at 1350, 1580, and 2700 cm(-1), respectively, confirming the formation of graphene sheets. Fe, Co, and Fe-Co catalysts produced quasi-identical graphene yields of 2.8, 3.04, and 2.17 g(C)/g(cat), respectively. The graphene yield in terms of mass PP was found to be 9.3, 10.1, and 7.2 g(C)/100g(PP) with the same order of catalysts. Monometallic Fe and Co catalysts produced a mix of small and large-area graphene nanosheets, whereas the bimetallic Fe-Co catalyst yielded exclusively large-area graphene sheets with remarkable quality. The higher stability of Fe-Co alloy and its carbide phase during the growth reaction compared to the Fe and Co catalysts was the primary reason for the generation of extra-large graphene sheets with relatively low yield. In contrast, the segregation of some metallic Fe or Co particles through the growth time was responsible for the growth small-area graphene sheets.