Abstract
In this paper, a redox and magnetic dual responsive toluene-in-water Pickering emulsion was stabilized by negatively charged Fe3O4 nanoparticles hydrophobically modified by positively charged oxidized ferrocene azine (Fc+A) via electrostatic interaction. The results showed that the adsorbed amount was 0.24 mmol/g and the molecular area was 0.27 nm2 for Fc+A at the Fe3O4 particles surface, which was higher than that at air-water interface (0.21 nm2), implying the adsorption process was typical monolayer adsorption. Because of the adsorption and desorption of Fc+A on the Fe3O4 particles surface, the Pickering emulsion prepared by Fc+A modified Fe3O4 nanoparticles could be reversibly switched between stable and unstable states by alternately adding reducing agent N2H4·H2O and oxidant H2O2. And approximately 80% of particles adsorbed at oil-water interface were returned to water phase after adding N2H4·H2O into the emulsion. At the same time, the emulsion droplets could be close to each other by applying an external magnetic field without demulsification due to the super paramagnetic properties of Fe3O4 nanoparticles, indicating the high stability and magnetic responsiveness of emulsion. Moreover, by applying an external magnetic field, Fc+A modified Fe3O4 nanoparticles stabilized Pickering emulsion was a good extraction system for purifying the aqueous solution contaminated by rhodamine B (RhB).The extraction efficiency (about 97.5 %) was attributed to the hydrophobicity, non-covalent interaction between RhB and Fc+A modified Fe3O4 nanoparticles, and the high specific surface area of emulsion droplets. After the adsorption, the emulsion droplets could be restored to the original emulsion by washing using magnetic field, which can be used to extract contaminated water again. That is to say, the redox and magnetic field dual-responsive Pickering emulsions can not only achieve demulsification/emulsification cycles by redox regulation, but also respond to magnetic field, which provides a promising way to construct functional Pickering emulsion in situ to adsorb dye molecules from aqueous solution.
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