Plastic waste upcycling into carbon nanomaterials in circular economy: Synthesis, applications, and environmental aspects

Since the last 5 decades, there has been a huge proliferation in the global production and utilization of plastic polymers in building, construction, electronic components, packaging, and transportation. However, these polymers pose great threat to the environment, ecosystem, and human health due to toxic components and non-biodegradable nature. The researchers worldwide are exploring ways for sustainable upcycling of polymeric plastic waste into materials exhibiting extra-ordinary intrinsic properties for application in variety of fields in circular economy. In this regard, the chemical upcycling of plastic into value-added carbon-based nanomaterials (CNMs) such as carbon nanotubes, graphene, carbon spheres, and porous carbon is an effective approach of waste management. The waste plastic polymers act as low-cost carbon source attributed to their high carbon content and large availability while simultaneously reducing plastic pollution, CO₂ emissions, and the related carbon footprint on environment when compared to the conventionally produced CNMs. Moreover, plastic-waste-derived CNMs (PWCNMs) exhibit attractive properties in terms of large surface area and porosity along with high energy content, good adsorption, catalytic, and opto-electronic characteristics for wide application in areas such as environmental remediation, energy production, and storage etc. Therefore, the present review article recapitulates the information regarding the upcycling of different types of plastic waste into a variety of CNMs exhibiting potential future applications in environmental and energy applications. Firstly, the statistics related to plastic production, consumption, contamination, and hazards along with conventional plastic waste management methods and their limitations have been discussed. Thereafter, the need and benefits of plastic waste upcycling into value-added carbon nanomaterials via different methods have been congregated. The major focus has been given to plastic waste-derived carbon nanotubes (CNTs) and graphene due to their high market value in energy and environmental applications. The factors affecting the plastic waste conversion into CNMs and various aspects including reduced carbon footprint, lifecycle assessment, and role in circular economy have been discussed. The research advancements needed to increase the overall yield, reduce the impurity levels in the final product, and upscale the production as well as applications to commercial level have also been mentioned. To summarize, plastic waste upcycling into CNMs might be in its infancy, however, holds great potential of contribution towards environmental sustainability and circular economy.