In order to optimize the manufacturing of polypropylene-derived few-layer graphene, an innovative utilization of nonsupported iron oxide nanoparticles generated under various fuel environment conditions was studied. Three distinct fuel combustion environment circumstances (fusion, fuel shortage, and fuel excess) produced a variety of Fe2O3 nanoparticles for cost-effective and green graphene deposition. XRD, H2- TPR, Raman, and TGA measurements were used to characterize both new and spent catalysts. Remarkably, the microstructure of the generated Fe2O3 nanoparticles could be controlled by the citric acid/iron nitrate ratio, ranging from spheroids ( Fe2O3(0)) to sheets ( Fe2O3(0.5-0.75)) and a hybrid microstructure that consists of sheets, spheroids, and interconnected strips ( Fe2O3(1-2)). According to fuel situation (citric acid/iron nitrate ratio, Fe2O3( 0-2)), various graphitization level and yields of graphene derivatives including sheets, ribbons, and onions have been developed. With the ideal fuel/oxidant ratio (ɸ = 1), the Fe2O3( 0.75) catalyst demonstrated the best catalytic activity to deposit the largest yield of highly graphitized few graphene layers (280%). Lean and rich fuel conditions (1 > ɸ > 1) have detrimental effects on the amount and quality of graphene deposition. It is interesting to note that in addition to graphene sheets, an excess of citric acid caused the production of metallic cores, hollow, and merged carbon nano-onions, and graphene nano-ribbons. It was suggested that carbon nano-onions be converted into graphene nano-ribbons and semi-onion shell-like graphene layers.

Novel concept for synthesizing carbon nano-onion, graphene layers, and graphene nano-ribbons from polypropylene waste over Fe2O3 nanoparticles
    Abstract
        Graphical abstract
    1 Introduction
    2 Experimental section
        2.1 Preparation of various monometallic iron oxide catalysts
        2.2 Conversion PP waste to graphene
        2.3 Characterization techniques
    3 Results and discussion
        3.1 Characterization of fresh Fe2O3 nanoparticles
        3.2 Impacts of citric acidiron nitrate mole ratio on the synthesis of CNMs
    4 Conclusion
    Acknowledgements 
    References

• Ahmed M. Haggar(Process Development Division, Egyptian Petroleum Research Institute, PO Box 11727, Nasr City, Cairo, Egypt) Corresponding author
• Ateyya A. Aboul‑Enein(Process Development Division, Egyptian Petroleum Research Institute, PO Box 11727, Nasr City, Cairo, Egypt)
• Ahmed E. Awadallah(Process Development Division, Egyptian Petroleum Research Institute, PO Box 11727, Nasr City, Cairo, Egypt)
• Mostafa A. Azab(Process Development Division, Egyptian Petroleum Research Institute, PO Box 11727, Nasr City, Cairo, Egypt)