Air-Oxidizing, Solvent-Free Depolymerization of Plastic Waste to Produce Valuable Chemicals

Abstract

Polyethylene terephthalate (PET) plastic waste is highly resistant to natural degradation, and conventional chemical recycling routes typically rely on acidic, basic or hydrogen-assisted processes under harsh conditions. Here, we present a solvent-free, oxidative depolymerization strategy that converts PET plastic waste into a valuable monomer using an atomically dispersed Fe catalyst within a zeolite framework. Consequently, high-purity terephthalic acid (TPA) can be obtained with a yield of 90.7% at 260 °C under atmospheric oxygen. This conversion can also be driven using the air or solar heat. We reveal that this high efficiency is due to the reversible Fe(II)/Fe(III) redox cycle sites modulating the local oxygen environment and activating molecular oxygen to generate reactive oxygen species (ROSs). These ROSs efficiently cleave the PET ester bonds, and the reaction is sustained by hydrogen atoms derived from the polymer backbone. Meanwhile, the synergistic acid sites of the ZSM-5 framework promote substrate protonation and lower the activation energy barrier for C–O scission. This strategy could reduce net carbon emissions by 73.1% compared to conventional TPA production.