Enhanced depolymerization of poly(bisphenol A carbonate) via robust mesoporous CaCO3/CaTiO3 nanocomposites featuring synergistic acid–base sites and oxygen vacancies

Abstract

Poly(bisphenol A carbonate) (BPA-PC) exhibits high resistance to natural degradation and releases hazardous bisphenol A (BPA), raising significant environmental and health concerns. Chemical recycling through alcoholysis represents a promising strategy to address this issue; however, currently available catalytic systems are hampered by several drawbacks including undesirable side reactions, poor recyclability, low catalytic activity, and complex preparation processes. Herein, we report a robust mesoporous CaCO₃/CaTiO₃ composite catalyst (CTO) fabricated via a facile sol–gel method coupled with controlled calcination, engineered to address these challenges through synergistic acid–base sites and oxygen vacancies (OVs). Calcination at 500 °C for 5 h (CTO-500-5) led to the formation of a biphasic composite with well-defined mesoporosity, balanced Lewis acid and basic sites, and abundant OVs, enabling efficient alcoholysis of BPA-PC under batch and flow conditions. For batch reactions, the catalyst demonstrated broad applicability, efficiently depolymerizing diverse commercial BPA-PC products into BPA with yields of 80–91%, while also adapting to multiple nucleophilic alcohols to generate high-value carbonates. It retained full activity across 10 reuse cycles with no discernible deactivation. For scalable recycling, the catalyst was immobilized in a fixed-bed flow reactor. This setup enabled continuous methanolysis and glycolysis with 100% BPA selectivity and stable operation for over 30 h and 40 h, respectively. Simultaneously, the catalytic activity was readily recovered via alkali treatment regeneration. This work demonstrates that the CaCO₃/CaTiO₃ catalyst, with its tunable structure, acid–base synergy, and excellent stability, provides a sustainable and industrially viable strategy for closed-loop chemical recycling of BPA-PC.