Light-switched reversible emulsification and demulsification of oil-in-water Pickering emulsions.

Pickering emulsions have been shown to be an excellent platform for interfacial catalysis. However, developing simple and efficient strategies to achieve the goal of product separation and catalyst and emulsifier recovery is still a challenge. Herein, we report for the first time the switchable transition between emulsification and demulsification triggered by UV and visible light in a novel class of light-responsive Pickering emulsions fabricated from Pd supported silica nanoparticles, azobenzene ionic liquid surfactant, n-octane and water. It is shown that light-switchable emulsification and demulsification of the Pickering emulsions is attributed to the adsorption of azobenzene ionic liquid surfactant on the surface of the nanoparticles and the light switched surface activity of the ionic liquid surfactant. This feature enables the Pickering emulsion to be used as an easily controlled micro-reactor with the functions of catalytic reaction, product separation as well as emulsifier and catalyst recycling. As an example, highly efficient catalytic hydrogenation of some unsaturated hydrocarbons at room temperature and atmospheric pressure has been performed in this system, with product separation and emulsifier and catalyst re-use achievable in a simple way.