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Stimuli-responsive Janus mesoporous nanosheets towards robust interfacial emulsification and catalysis

The ability to rationally design and synthesize amphiphilic Janus materials with the selective growth of catalytic species on one side represents an important endeavour towards high-efficiency phase-selective catalysis in heterogeneous reaction. Herein, we report, for the first time, the crafting of smart amphiphilic Janus mesoporous nanosheets (denoted JMNs), selectively decorated with Au nanoparticles (NPs) on the hydrophilic side, for robust and dual-functional interfacial emulsification and catalysis. First, two amphiphilic JMNs are judiciously created (i.e., C18-mSiO2-P4VP composed of mesoporous silica (mSiO2) nanosheets sandwiched by C18 and poly(4-vinylpyridine) (P4VP) on opposite sides of the nanosheets; and C18-mSiO2-NH2 with C18 and NH2 on the respective sides). Subsequently, the in situ growth of Au NPs on the hydrophilic side of the nanosheets yields C18-mSiO2-P4VP@Au and C18-mSiO2-NH2@Au. Notably, these JMNs exhibit pH-dependent catalytic activity in aqueous solution and oil-phase-type-dependent catalytic activity at the emulsion interface. Moreover, both JMNs manifest reversible interfacial emulsification/de-emulsification behaviour. Finally, they also feature excellent recyclability, rendering them promising in heterogeneous catalysis. In principle, given the diversity of functional polymers that can be easily grafted on mSiO2 nanosheets, a rich variety of JMNs with other stimuli-responsive characteristics (e.g., temperature-, light-, etc.) may be conveniently engineered. As such, a suite of properties (e.g., optical, catalytic, etc.) of these JMNs, triggered by external stimuli noted above, can be scrutinized.