Microwave-Assisted Catalytic Upcycling of Plastic Wastes over Heterojunction-Structured Layered Triple Oxides

Abstract

Chemical upcycling of plastic wastes into valuable chemical feedstocks and simultaneous mitigation of environmental deterioration are fascinating but remain extremely challenging. Herein, we report microwave-assisted valorization of plastic wastes into carbon nanotubes (CNTs) and hydrogen (H₂) over heterojunction-structured mixed metal oxides. Specifically, the CoNiFe-based layered triple oxides (LTO) arrayed on Ni-foam (CoNiFe-LTO@foam) were constructed. The special heterojunction of the LTO endows high dielectric loss, facilitating efficient conversion of absorbed microwave energy into thermal energy. Most importantly, the synergistic effect of the multiple transition metal sites boosts the cleavage of carbon chains and dehydrogenation, thereby accelerating the reaction kinetics. As a result, the CoNiFe-LTO@foam achieves an H₂ selectivity of ∼95 vol % with the yield of ∼69 $\mathrm{mmol}·{\mathrm{g}}_{\mathrm{plastic}}^{-1}$ for upcycling polyethylene in 25 cycles of measurement. Simultaneously, the CNTs attain a yield of ∼35%, which can be used for aqueous chloride-ion batteries. Additionally, the CoNiFe-LTO@foam enables facile recovery of CNTs and prevents the loss of catalytic sites, facilitating upcycling of various real-world plastic wastes. Our work thus highlights the innovations of an advanced catalytic system for forming a closed loop of plastic C/H and achieving the ultimate goal of a carbon-neutral society.