Redox-switchable Pickering emulsion stabilized by hexaniobate-based ionic liquid for oxidation catalysis

Abstract

Pickering emulsions provide an efficient platform for interfacial catalysis, but product separation and catalyst recycling rely on time- and energy-consuming centrifugation or filtration. Herein, three hexaniobate-based ionic liquids, [C_nMIM]Nb₆ (n = 12, 14 and 16), have been successfully synthesized by self-assembly of hexaniobate (Nb₆) with long alkyl chain-modified imidazole cations (C_nMIM). Interestingly, the surface wettability of [C₁₆MIM]Nb₆ can be regulated by redox reactions, and the rapid switch between emulsification and demulsification can be achieved by alternately adding oxidant (H₂O₂) and reductant (Na₂SO₃) agents. Furthermore, studies suggest that the redox-responsive behavior is related to the reversible transformation between [C₁₆MIM]Nb₆ and peroxohexaniobate [C₁₆MIM]Nb₆-O₂, which leads to the rearrangement of hydrophobic long chains on imidazole cations around hydrophilic Nb₆. Moreover, [C₁₆MIM]Nb₆ can effectively catalyze oxidative desulfurization (conversion > 99%), and the separation of clean model oil and the recycling of the interfacial catalyst were realized in a facile route.