Redox-Responsive Pickering Emulsions Stabilized by Silica Nanoparticles and Ferrocene Surfactants at a Very Low Concentration

Here, we describe a redox-responsive Pickering emulsion stabilized by silica nanoparticles and a ferrocene surfactant (FcCOC(10)N) at a concentration as low as 0.01 mM (approximate to 0.005 cmc). The emulsions are stable and resistant to coalescence for more than one month. The ferrocene group in the structure of FcCOC(10)N can be reversibly switched between its oxidized and reduced forms by redox reactions, which would alter the amphiphilic properties of the surfactant. Consequently, the emulsion can be switched between "on" (stable) and "off" (unstable) states through electrochemical reactions without adding additional chemicals or changing the particle/surfactant concentration. Moreover, the Pickering emulsifier composed of the surfactant and the nanoparticles can be recovered and reused after removal of the original oil. It offers a new platform that provides green and sustainable operation for separation and reuse of the emulsifier in potential applications, such as biphasic catalysis and oil transportation.