Immobilized proton ionic liquid catalyst based on ZIF-8 catalytic degradation of PET performance and mechanism study

Abstract

Polyethylene glycol terephthalate (PET) is widely utilized in industrial applications and everyday life. However, its extensive use has led to substantial environmental challenges. This study presents a highly active and selective [DBU][m-cresol] proton-ionic liquid (PIL)-immobilized ZIF-8 catalyst for PET resource utilization. Using just 15 mg of the ZIF-8@[DBU][m-cresol]-2 catalyst, PET degradation reached 97.72 %, while BHET conversion achieved 86.95 % within 60 min. The Zn²⁺ ions in the catalyst decrease the electron density of the m-cresol carbocation, thus improving the nucleophilic substitution capability of [DBU][m-cresol]. The influence of catalyst dosage, the ethylene glycol-to-PET ratio, and temperature on degradation and conversion was investigated. After five cycles, the catalyst retained a degradation efficiency of 77.71%. In practical applications, testing on three commercial PET materials demonstrated degradation efficiencies exceeding 90%. DFT calculations and LC-MS analysis indicate that hydrogen bonding among ethylene glycol (EG), PET, and ZIF-8@[DBU][m-cresol] enhances PET’s electrophilicity, while Zn²⁺ decreases the electron density of carbocations, thereby facilitating PET degradation. This work highlights the potential of proton-based ionic liquid-supported catalysts for efficiently converting PET waste into valuable resources.