Phosphotungstate-Functionalized Mesoporous Janus Silica Nanosheets for Reaction-Controlled Pickering Interfacial Catalysis

Pickering interfacial catalysis enables oil/water biphasic reactions to efficiently proceed by the formation of stable Pickering emulsions. However, a convenient approach to control the emulsion properties, so as to combine the reactivity and recovery of catalytic emulsifiers, remains challenging to date. Herein, we have reported the switchable transition between emulsification/demulsification controlled by the catalytic reaction process, to realize reaction-controlled Pickering interfacial catalysis. A novel series of phosphotungstate (PW)-functionalized mesoporous Janus silica nanosheets were thus prepared by selectively decorating ammonium PW on one side of mesosilica nanosheets. Characterization results suggested their H2O2-switched reversible emulsification/demulsification behavior in an oil/water biphasic system due to H2O2-induced wettability change in the ammonium PW moiety. The resultant H2O2-switchable Pickering emulsions induced an efficient Pickering interfacial catalysis approach for selective oxidation of alcohols by aqueous H2O2 in water, thus leading to remarkable high conversion and selectivity over a wide range of alcohols. When H2O2 was used up, they could be demulsified spontaneously, resulting in the complete separation of catalytic emulsifiers for steady reuse. The reaction-controlled emulsification/demulsification approach provided a sustainable way to combine reactivity and recovery of catalytic emulsifiers in Pickering interfacial catalysis, which was a benefit for energy-saving in industrial applications.