Hierarchical porous 2D α-Al2O3 nanosheet catalyst for aminolytic upcycling of PET plastic waste

Despite its wide applicability, the synthesis of α-Al2O3 with nanoscale dimensions and a well-developed porous structure continues to be a formidable challenge. This study reports the synthesis of a versatile 2-dimensional (2D) α-Al2O3 nanomaterial using a simple solution combustion method. The 2D α-Al2O3 nanomaterial calcined at 550 °C (denoted as α-Al2O3 550) exhibited unique characteristics, including a hierarchical porous structure (5–30 nm), nanosheet morphology (length: 2.81–4.97 μm, width: 0.78–0.97 μm, and thickness: 4.7–9.8 nm), surface-engineered grain boundaries, BET surface area of 56 m2/g, and optimum amount of acid sites, as confirmed by SEM, TEM, AFM, and NH3-TPD analyses. The 2D α-Al2O3 550 nanosheet catalyst showed excellent activity in upcycling post-consumer PET plastic bottles into a valuable monomer, bis(2-aminoethyl) terephthalamide (BAET), using ethylenediamine as both the reactant and solvent. An impressive 92% isolated yield of BAET was achieved over the 2D α-Al2O3 550 nanosheet catalyst, outperforming several metal oxides, such as γ-Al2O3, Nb2O5, CeO2, and MnOx. The α-Al2O3 550 catalyst is highly stable and exhibits good reusability over five consecutive cycles, with only a slight decrease in BAET yield from 92% in the first cycle to 85% in the fifth cycle. The process is scalable (5 g), efficiently employed for upcycling various post-consumer PET bottles with yields of 90%, and meets green chemistry metrics. This study highlights 2D α-Al2O3 550 nanomaterial as a robust, economically viable catalyst, offering a practical route for the upcycling of plastic waste. The exponential rise in plastic production has led to significant environmental challenges, particularly in waste management and greenhouse gas emissions. This study addresses issues by exploring the chemical recycling of polyethylene terephthalate (PET) using aminolysis with ethylenediamine and a novel α-Al2O3 catalyst. They synthesized an α-Al2O3 catalyst with hierarchical porosity and a 2D nanostructure using a low-temperature solution combustion method. This catalyst demonstrated high efficiency in PET aminolysis, achieving a 92% yield of the valuable monomer BAET under mild conditions. The α-Al2O3 catalyst’s strong acid sites and stability were crucial for its performance, and it retained activity over multiple cycles. This research highlights the potential for scalable and sustainable PET recycling, offering a promising avenue for reducing plastic waste and environmental impact. Future work could explore the application of this method to other types of plastic waste. This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author. A versatile α-Al2O3 catalyst with a nanosheet morphology and hierarchical porous structure enables efficient and sustainable aminolysis of PET plastic waste under mild reaction conditions. The optimized catalyst provides abundant active sites and enhanced surface accessibility, promoting selective PET depolymerization with high efficiency. The process achieves up to 92% isolated yield of a value-added monomer [bis(2-aminoethyl) terephthalamide]. The developed method demonstrates excellent catalytic performance, scalability, and applicability toward real-world mixed plastic waste. This work highlights the development of a novel α-Al2O3 catalyst for the chemical upcycling of PET waste into valuable monomers towards the circular plastic economy.