Dual activation of a zinc salt and solvent-tuned dissolution enable efficient neutral hydrolysis of PET and its blends

Abstract

Neutral hydrolysis of polyethylene terephthalate (PET) waste to terephthalic acid (TPA) is a promising but very challenging recycling method due to the weak nucleophilicity of water. While some metal catalysts were reported to accelerate neutral hydrolysis under high-concentration conditions, the resulting acidic environment at elevated temperature often leads to actual acid hydrolysis rather than true neutral hydrolysis. Herein, we demonstrate a highly efficient neutral hydrolysis by coupling the activation effect of the metal salt zinc trifluoromethanesulfonate (Zn(OTf)₂) with the solvent effect of γ-valerolactone (GVL)/H₂O. Mechanistic studies reveal that Zn(OTf)₂ activates both water (through triflate–water interactions) and PET ester groups (via Zn²⁺ coordination). Meanwhile, GVL shifts the reaction from a heterogeneous to a homogeneous system and enables the non-destructive separation of other components from PET by utilizing their own physical properties and different solubilities in GVL for PET blends. This work offers a new insight into catalytic solvent systems and provides an efficient and sustainable method for the recovery of PET waste.