Pickering emulsions of alumina nanoparticles and bola-type selenium surfactant yield a fully recyclable aqueous phase

Separation of surfactants from oil or water is essential for many research and industrial applications, such as in emulsions for biphasic catalysis and oil pipeline transportation. However, it is difficult to efficiently remove or recycle surfactants from the above systems due to their amphiphilic nature. Here, we report on redox-responsive Pickering emulsions stabilized by alumina nanoparticles and a selenium-containing surfactant at concentrations as low as 0.1 wt% and 1 x 10(-6)M (approximate to 0.001 cmc), respectively. Rapid demulsification can be achieved after the surfactant is converted from bola-type to trimeric form by a redox reaction, and the oil phase can be separated with minimal surfactant contamination (<0.005 ppb). In addition, the alumina nanoparticles together with the surfactant return to the aqueous phase after demulsification and are fully recoverable and re-usable.