Iron-doped carbon nanotubes via microwave shock: Recyclability in polypropylene pyrolysis for ORR catalyst manufacturing

The recycling and upcycling of waste plastics into high-value products by pyrolysis is a critical challenge caused by its time/energy-consuming problems, which can be overcome by employing microwave-assisted catalytic pyrolysis due to its rapid pyrolysis rates and high product yields. This study presents a facile method for the synthesis of catalysts for microwave-assisted pyrolysis of waste plastics, utilizing the pyrolytic products as raw materials. In this case, a microwave thermal shock strategy is developed to efficiently anchor iron nanoparticles on carbon nanotubes (CNTs). This method recycles a portion of pyrolysis products back into the catalyst pool for plastic transformation into new CNTs, reducing the consumption for preparing additional catalysts. The precursors exposed to 50 W microwave irradiation reaches above 2000 °C within seconds, allowing Fe nanoparticles to be uniformly impregnated within the carbon nanotube matrix. The formed iron-doped CNTs shows high activity for microwave-assisted pyrolysis, generating CNTs with D/G ratios at 0.31. The recycling and reconstruction of CNTs after multiple pyrolysis form a cross-lined network structure, which facilitates electron transition and can be utilized for fabricating electrocatalysts. Nitrogen doping further improves the onset potential to 0.923 V vs. RHE, making them viable candidates for electrocatalytic applications in oxygen reduction reactions. In summary, our findings demonstrate the feasibility of this approach to reactive pyrolysis products that serve as catalysis for microwave-assisted pyrolysis, with the potential to reduce volatile organic compound emissions and capital expenditure in catalyst preparation, offering a greener and more efficient pathway for plastic waste management and catalyst production.