Hierarchical Porous 2D α-Al2O3 Nanosheet Catalyst for Aminolytic Upcycling of PET Plastic Waste

Despite its wide applicability, the synthesis of α-Al ₂ O ₃ 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 α-Al ₂ O ₃ nanomaterial using a simple solution combustion method. The 2D α-Al ₂ O ₃ nanomaterial calcined at 550°C (denoted as α-Al ₂ O ₃ 550) exhibited unique characteristics, including a hierarchical porous structure (5–30 nm), nanosheet morphology (length: 2810–4970 nm, width: 780–973 nm, and thickness: 4.7–9.8 nm), surface-engineered grain boundaries, BET surface area of 56 m ² /g, and optimum amount of acid sites, as confirmed by SEM, TEM, AFM, and NH ₃ -TPD analyses. The 2D α-Al ₂ O ₃ 550 nanosheet catalyst showed excellent activity in upcycling post-consumer PET plastic bottles into a valuable monomer, bis(amino-ethyl) terephthalamide (BAET), using ethylenediamine as both the reactant and solvent. An impressive 92% isolated yield of BAET was achieved over the 2D α-Al ₂ O ₃ 550 nanosheet catalyst, outperforming several metal oxides, such as γ-Al ₂ O ₃ , Nb ₂ O ₅ , CeO ₂ , and MnO _x . The analysis of the spent α-Al ₂ O ₃ 550 catalyst by powder XRD, XPS, and SEM/TEM techniques confirmed its structural and morphological stability. The catalytic process is scalable (5 g), efficiently applied for upcycling different types of post-consumer PET bottles with yields of 80%, and the green chemistry metrics demonstrate the process's sustainability. This study highlights 2D α-Al ₂ O ₃ 550 nanomaterial as a robust and economically viable catalyst, offering a practical route for the plastic waste upcycling industry.