Efficient limonene epoxidation via Pickering interfacial biocatalysis by functionalized lignin nanoparticles

Chemoenzymatic epoxidation is a green route for terpene conversion but suffers from a fundamental trade-off. The high hydrogen peroxide (H₂O₂) loads required to overcome mass transfer paradoxically leads to severe enzyme inactivation. Herein, a lignin-based Pickering interfacial biocatalytic (PIB) system was constructed by covalently immobilizing Candida antarctica lipase B (CALB) onto functionalized lignin nanoparticles (CGPALPs). The resulting CGPALPs exhibit enhanced structural stability and oxidative resistance, retaining 71.4% of their activity after 12 h exposure to 1 M H₂O₂. Remarkably, this PIB system operates efficiently at a stoichiometric oxidant ratio (H₂O₂/limonene = 2:1). It achieves 92.97% limonene conversion and 92.23% total epoxide yield within 12 h. Most importantly, it delivers a 41.8% yield of limonene diepoxide without any excess H₂O₂, a result unattainable in chemoenzymatic biphasic systems. The system also demonstrates efficient H₂O₂ utilization (94.13%) and excellent reusability, maintaining over 80% activity after seven cycles. By integrating covalent enzyme immobilization with Pickering emulsion design, this work provides a sustainable and generalizable strategy to resolve the long-standing conflict between enzyme stability and mass transfer in chemoenzymatic epoxidation of hydrophobic substrates.