Engineering pH-Responsive High Internal Phase Pickering Emulsions Stabilized by Copolymer Nanoparticle–Lipase Complexes for Sustainable Enzymatic Microreactors

Enzymatic microreactors with sustainable operational stability have attracted significant interest in the development of green synthesis. In this work, a recyclable and pH-responsive enzymatic microreactor was constructed on the basis of high internal phase Pickering emulsions (HIPPEs). Oil-in-water HIPPEs were prepared via simple hand-shaking emulsification adopting amine-functionalized diblock copolymer nanoparticle/lipase complexes as Pickering emulsifiers. The amine-functionalized nanoparticles, composed of poly(oligo(ethylene glycol) methyl ether methacrylate)-b-poly(diacetone acrylamide), were synthesized through the combination of RAFT-mediated polymerization-induced self-assembly and subsequent hydrolysis. The obtained HIPPEs displayed reversible emulsification/demulsification behaviors triggered by protonation/deprotonation of amine groups on the surfaces of nanoparticles. When applied to the esterification of butyric acid with 1-butanol, the as-prepared HIPPE-based microreactor exhibited outstanding catalytic efficiency due to the large interfacial area and shortened diffusion distance provided by the high-internal-phase structure. Moreover, pH-triggered demulsification enabled convenient product separation and efficient recycling of the nanoparticle/lipase complexes for repeated catalytic runs, demonstrating good sustainability and promising potential for practical applications.