Reaction‐controlled microgel‐lipase co‐stabilized compartmentalized emulsion for recyclable biodiesel production

Abstract Pickering emulsions have been widely used for biphasic catalysis in the past decade. However, it remains a great challenge to achieve simple product collection and enzyme recovery. Poly(N‐isopropylacrylamide) (PNIPAM)‐based microgels can endow Pickering emulsions with stimuli‐responsiveness, while most microgel‐stabilized emulsions are oil‐in‐water (O/W) type and not ideal for interfacial catalysis. Besides, altering temperature or pH value for demulsification is time‐ and energy‐consuming and may cause irreversible deactivation of enzymes. In this work, inverse water‐in‐oil (W/O) Pickering emulsions were formed using hexanoic acid‐swollen microgels as the sole emulsifiers. When lipase was added in the water phase, stable oil‐in‐water‐in‐oil (O/W/O) Pickering double emulsions could be formed through one‐step emulsification, owing to the synergistic effect of the hydrophobic microgels and hydrophilic lipase at the interface. Compared with other biphasic systems, such double emulsion systems represent a desirable platform for highly efficient biodiesel production because of the ultra‐high interfacial areas and fast mass transport between two phases. More importantly, the switchable transition between hydrophobicity/hydrophilicity of microgels is controlled by the catalytic reaction. Therefore, double emulsions demulsify spontaneously when substrates are used up without the need for energy input or loss of enzymatic activity, enabling the facile collection of products and demonstrating the excellent recyclability of the biphasic catalysis system.