Light-Triggered Phase Separation of Pickering Emulsions Co-Emulsified by Amino-Functionalized SiO2 and Spiropyran-Based Ionic Liquid Surfactants

Pickering emulsions have demonstrated remarkable potential as a platform for interfacial catalysis. However, the development of simple and efficient strategies to accomplish the objectives of product separation, catalyst recovery, and emulsifier reuse remains an ongoing challenge. In this work, a class of light-responsive Pickering emulsions comprising a spiropyran-based ionic liquid surfactant (SPIL), amino-functionalized SiO2 (SM-NH2), toluene, and water was demonstrated, wherein the transition between emulsification and demulsification is reversibly regulated by visible and UV light. Upon visible light irradiation, the SPIL isomerizes from hydrophilic open-ring (MC) to hydrophobic closed-ring (SP), this kind of property change enhances its adsorption onto SM-NH2, increases zeta potential of the system, and drives the SPIL toward the toluene phase, ultimately leading to demulsification. Conversely, UV light triggers the reverse isomerization, establishing new electrostatic equilibrium with SM-NH2 to form stable Pickering emulsions. This feature enables the Pickering emulsion to serve as a light-controlled interfacial catalytic microreactor for the hydrolysis of 4-nitrophenyl palmitate. Compared with an aqueous system, this system achieves a 10-fold increase in ester hydrolyze conversion efficiency. It facilitates product separation and allows for the simple recycling of both the emulsifier and the catalyst.