Thermo-Switchable Pickering Emulsion Stabilized by Smart Janus Nanosheets for Controllable Interfacial Catalysis

Pickering emulsion has recently received widespread attention since it alleviates the mass transfer limitation between oil/water biphases for efficient interfacial catalysis. However, a convenient strategy to control the emulsification and demulsification, so as to combine the reactivity and recovery of catalytic emulsifiers in Pickering interfacial catalysis, remains challenging to date. Herein, we have developed a thermo-switchable Pickering emulsion which could undergo reversible emulsification and demulsification at its cloud point to realize the thermo-controlled Pickering interfacial catalysis for asymmetric sulfoxidation in water. Thermoresponsive Janus silica nanosheets (JNSs) were thus prepared by decorating a stimuli-responsive poly(N-isopropylacrylamide) (PNIPAAm) brush and a catalytically active chiral salen TiIV complex on the opposite sides of mesosilica nanosheets, respectively. Characterization results suggested their temperature-sensitive wettability switching behaviors which resulted in thermo-switchable emulsification/demulsification in an oil/water biphasic system. The smart JNSs could significantly accelerate the asymmetric sulfoxidation in water at room temperature through the formation of stable oil/water Pickering emulsions and then in situ-demulsified quickly for complete separation upon heating over the cloud point (T > 39 °C). The thermo-switchable emulsification/demulsification approach provided a convenient way to control the reaction and separation of Pickering interfacial catalysis on demand, which should simplify the operation in industrial applications.