Catalytic Hydrolysis of Color-Mixed Polyethylene Terephthalate-Based Fabrics Waste over Dendritic Fibrous Solid Superacid

Approximately 70% of polyethylene terephthalate (PET) production is used in textiles, generating a substantial amount of waste that is particularly challenging to recycle due to the presence of dyes, additives, contamination, degradation, and complex packaging structures. Chemical recycling via acid-catalyzed hydrolysis in the aqueous phase represents a sustainable route for recovering monomer feedstocks. In this work, super acidic dendritic fibrous WOx/ZrO2-SiO2 nanospheres (DFWZS) were prepared by the one-pot microemulsion-templated method, followed by citric acid (CA)-assisted impregnation. DFWZS possesses a significantly enhanced specific surface area, pore volume, and total acid density than conventional WO3/ZrO2. It was revealed that the aggregation state of WOx species follows a volcanic trend with Brønsted (B) acidity, wherein the intermediate Zr-WOx clusters constitute the primary source of strong B acid sites. Moreover, the W5+/(W5++W6+) ratio serves as an effective descriptor for both the WOx aggregation state and the resultant B acidity. At the optimal electronic state, a maximum B acid density of 0.28 mmol/g was achieved, enabling complete PET conversion with a 96.6% terephthalic acid (TPA) yield within 2 h at 260 °C, significantly outperforming conventional WO3/ZrO2. Moreover, DFWZS exhibited higher activity than HZSM-5, despite its weaker B acidity, owing to its dendritic fibrous morphology. Mechanistic studies revealed that B acid sites protonate the carbonyl oxygen of PET, which is then subjected to nucleophilic attack by water molecules, leading to ester bond cleavage and TPA formation. When applied to color-mixed fabrics, this catalyst maintained over 90.0% TPA yields with 99.1% purity within 3 h, meanwhile demonstrating outstanding reusability and dye tolerance. This work provides an economically viable and efficient strategy for closed-loop recycling of diverse PET wastes.