High-performance green calcium oxide–biochar catalysts for the chemical recycling of PET waste

This study presents a sustainable catalytic system for the methanolysis of polyethylene terephthalate (PET). The catalytic system was prepared by a novel green synthesis, incorporating a photoactivated organic concentrated liquor derived from Jatropha fruit husk hydrothermal carbonization to enhance dispersion and control particle aggregation of the calcium oxide in a rice husk biochar matrix. Thermal depolymerization parameters were optimized using a Box–Behnken design, identifying key variables that influence PET conversion. The optimized catalyst (RHB_8.5_0.2_c) achieved 84.67% PET and >95% DMT yield conversion under mild conditions (160 °C, 1 h, 3 wt% catalyst), with an apparent activation energy of 90.39 kJ mol⁻¹. The material characterization confirmed the formation of mesoporous structures, uniform dispersion of CaO clusters, and successful phase transformation from carbonate to oxide. Techniques including SEM, EDS, XRD, FTIR, and BET analysis revealed the morphological, chemical, and textural properties responsible for the high catalytic activity. The proposed catalyst stands out for its efficiency, low material input, and alignment with circular economic principles.