CO₂/N₂ Triggered Aqueous Recyclable Surfactants for Biphasic Catalytic Reactions in the Pickering Emulsions

The utilization of Pickering emulsions in interfacial catalysis offers a promising environmental platform for biphasic reactions. However, complicated surface coating or chemical grafting methods are always required to prepare the surface-active catalysts for the Pickering emulsions, since most of them are commercially unavailable. Here, we report CO₂-switchable Pickering emulsions for biphasic reactions, in which Pd@Al₂O₃ nanoparticles are in situ modified by a CO₂/N₂ responsive surfactant. Compared with the chemical grafted methods, the in situ formed Pickering interfacial catalysts avoid complex chemical modification. Furthermore, efficient demulsification and separation of the oil phase and the products without surfactant contaminations can be achieved by CO₂ trigger. The Pickering interfacial catalysis system can also be reformed after the aqueous phase containing the catalyst nanoparticles, and the surfactant is recycled and reused. The strategy is universal for nitrobenzene reductions and alcohol oxidations, providing a convenient and green method for the preparation of Pickering catalysts with commercially available nanoparticles, efficient emulsion separation, and recovery of the catalyst nanoparticles and emulsifiers in various two-phase organic reactions.