Structure-oriented conversions of plastics to carbon nanomaterials

The accumulation of waste plastics has caused serious environmental issues due to their unbiodegradable nature and hazardous additives. Converting waste plastics to different carbon nanomaterials (CNMs) is a promising approach to minimize plastic pollution and realize advanced manufacturing of CNMs. The reported plastic-derived carbons include carbon filaments (i.e. carbon nanotubes and carbon nanofibers), graphene, carbon nanosheets, carbon sphere, and porous carbon. In this review, we present the influences of different intrinsic structures of plastics on the pyrolysis intermediates. We also reveal that non-charring plastics are prone to being pyrolyzed into light hydrocarbons while charring plastics are prone to being pyrolyzed into aromatics. Subsequently, light hydrocarbons favor to form graphite while aromatics are inclined to form amorphous carbon during the carbon formation process. In addition, the conversion tendency of different plastics into various morphologies of carbon is concluded. We also discuss other impact factors during the transformation process, including catalysts, temperature, processing duration and templates, and reveal how to obtain different morphological CNMs from plastics. Finally, current technology limitations and perspectives are presented to provide future research directions in effective plastic conversion and advanced CNM synthesis.