Upcycling of Plastic Wastes and Biomass for Sustainable Graphitic Carbon Production: A Critical Review

Abstract

Upcycling of waste plastics diverts plastics from landfill, which helps in reducing greenhouse gas emissions. Graphitic carbon is an interesting material with a wide range of applications in electronics, energy storage, fuel cells, and even as advanced fillers for polymer composites. It is a very strong and highly conductive material consisting of weakly bound graphene layers arranged in a hexagonal structure. There are different ways of synthesizing graphitic carbons, of which the co-pyrolysis of biomass and plastic wastes is a promising approach for large-scale production. Highly graphitized carbon with surface areas in the range of 201 m²/g was produced from the co-pyrolysis of polyethylene and pinewood at 600 °C. Similarly, porous carbon having a superior discharge capacity (290 mAh/g) was developed from the co-pyrolysis of sugar cane and plastic polymers with catalysts. The addition of plastic wastes including polyethylene and high-density polyethylene to the pyrolysis of biomass tends to increase the surface area and improve the discharge capacity of the produced graphitic carbons. Likewise, temperature plays an important role in enhancing the carbon content and thereby the quality of the graphitic carbon during the co-pyrolysis process. The application of metal catalysts can reduce the graphitization temperature while at the same time improve the quality of the graphitic carbon by increasing the carbon contents. This work reports some typical graphitic carbon preparation methods from the co-pyrolysis of biomass and plastic wastes for the first time including thermochemical methods, exfoliation methods, template-based production methods, and salt-based methods. The factors affecting the graphitic char quality during the conversion processes are reviewed critically. Moreover, the current state-of-the-art characterization technologies such as Raman, scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy are discussed in detail, and finally, an overview on the applications, scalability, and future trends of graphitic-like carbons is highlighted.