Sustainable latex-mediated ZnO catalysts with enhanced surface properties for energy-efficient PET hydrolysis

Poly(ethylene terephthalate) (PET) hydrolysis under subcritical water is a promising route for chemical recycling, yet it remains energy-intensive due to the high temperatures needed for efficient depolymerization. In this study, a dual strategy combining process optimization and catalyst design is proposed to enhance reaction efficiency while reducing energy consumption. Hydrothermal depolymerization of post-consumer PET was first optimized via response surface methodology (using a Box-Behnken design), identifying temperature and reaction time as the dominant factors, with complete conversion at 200 °C and 180 min under non-catalytic conditions. Then, to further intensify the process, a biogenic ZnO catalyst was prepared through a sustainable Jatropha curcas latex-assisted route, eliminating the need for conventional alkaline precipitation agents. Structural characterization confirmed that both conventional and biogenic ZnO preserve the hexagonal wurtzite phase. Remarkably, latex-mediated synthesis induces modifications in particle morphology and surface chemistry associated with improved catalytic performance. The incorporation of 5 wt% JCL-ZnO enabled high PET conversion at milder conditions, reducing the apparent activation energy by ∼35% (i.e., from 274.2 to 179.3 kJ mol⁻¹) while maintaining pseudo-first-order kinetics. Terephthalic acid yields above 90% were consistently obtained over multiple reuse cycles, and spectroscopic analyses confirmed the structural equivalence of the recovered monomer to a commercial standard. Based on these findings, this work demonstrates that bio-mediated synthesis can effectively tailor surface properties of metal oxides without modifying their crystalline structure. Notably, the resulting biogenic ZnO enabled improved catalytic efficiency and provided a scalable, environmentally benign pathway for PET chemical recycling.