Looped carbon capturing and environmental remediation: case study of magnetic polypropylene nanocomposites

Abstract

A waste-free process to recycle Fe@Fe₂O₃/polypropylene (PP) polymer nanocomposites (PNCs) is introduced to synthesize magnetic carbon nanocomposites (MCNCs) and simultaneously produce useful chemical species which can be utilized as a feedstock in petrochemical industry. The magnetic nanoparticles (NPs) are found to have an effective catalytic activity on the pyrolysis of PP. The PNCs (with a NP loading of 20.0 wt%) undergo a complete degradation with 2 h pyrolysis at 500 °C in a H₂/Ar atmosphere and the degradation components exhibit a distribution of species with different numbers of carbon, while only 40% of pure PP is decomposed after applying the same pyrolytic conditions. The coked solid waste from the conventional process has been utilized as a carbon source to form a protective carbon shell surrounding the magnetic NPs. The magnetic carbon nanocomposites (MCNCs) pyrolyzed from PNCs containing 20.0 wt% NPs demonstrate extremely fast Cr(VI) removal from wastewater with the almost complete removal of Cr(VI) within 10 min. The pH effect on the Cr(VI) removal efficiency is investigated with a preferable value of 1–3. The adsorbent exhibits much higher adsorption capacity in acidic solutions than that in alkali solutions. The large saturation magnetization (32.5 emu g⁻¹) of these novel magnetic carbon nanocomposites allows fast recycling of both the adsorbents and the adsorbed Cr(VI) from the liquid suspension in a more energetically and economically sustainable way by simply applying a permanent magnet. The significantly reduced treatment time required to remove the Cr(VI) makes these MCNCs promising for the efficient removal of the heavy metals from wastewater. Kinetic investigation reveals the pseudo-second-order adsorption of Cr(VI) on these novel magnetic carbon nanocomposite adsorbents.