<p>The emergence of 2D graphene-based materials has attracted development of nanocomposites for decontamination of water. In this study, iron-based graphene nanocomposites (GNCs) were synthesized from plastic and bioplastic waste using pyrolysis and chemical exfoliation methods. The GNC synthesized from bioplastic displayed surface area and micropore volume of 407 m² g^− 1 and 1.158 cm³ g^− 1, respectively. The N- and O- containing functional groups were found at 1196&#xa0;cm^− 1 and 1604&#xa0;cm^− 1 in the infrared spectrum. The existence of Fe-O bond was confirmed at 569&#xa0;cm^− 1. The GNCs achieved maximum adsorption capacities of 38.6 ± 1.6 mg g^− 1 for As(V), 39.1 ± 2.1 mg g^− 1 for Cd(II) and 28.7 ± 1.1 mg g^− 1 for Pb(II) at pH 7.0 ± 0.5. The adsorption of metal ions onto GNCs followed Langmuir isotherm and molecular models were developed to understand the binding of metal ions onto iron based GNCs. The GNCs were reusable up to 10 cycles without significant reduction in their adsorption capacity. The TCLP and Kirby-Bauer tests confirm that the spent GNCs can be disposed-off in landfills safely. This study reports upcycling of recalcitrant plastic/bioplastic waste into value-added materials for environment clean-up.</p> Graphical abstract <p></p>