Synthesis of amphipathic superparamagnetic Fe3O4 Janus nanoparticles via a moderate strategy and their controllable self-assembly

Recently, amphipathic Janus Fe3O4 nanoparticles, with distinct hydrophilic and hydrophobic “faces”, have attracted tremendous attention. However, conventional synthesis methods for these nanoparticles either influenced the superparamagnetism of Fe3O4 nanoparticles or failed to endow Fe3O4 nanoparticles evident amphipathy, and thus as-prepared amphipathic Janus Fe3O4 nanoparticles hardly reveal remarkable self-assembly properties. To address these critical issues, a versatile strategy that combines activators regenerated by electron transfer for atom transfer radical polymerization (ARGET-ATRP) and Pickering emulsions is proposed here to synthesize amphipathic Janus Fe3O4 nanoparticles for the first time. Owing to the masterly integration all of the unique features of ARGET-ATRP and Pickering emulsions, Janus Fe3O4 nanoparticles with high saturation magnetization and diverse self-assembly behaviors in different solvents are successfully prepared in a gentle, simple and highly controllable reaction condition. Furthermore, these Janus Fe3O4 nanoparticles exhibit prominent emulsification in toluene–water model system as their superior amphipathy. These emulsions could not only maintain excellent stability even in an extremely low usage of Janus Fe3O4 nanoparticles, but also be easily separated by an external magnetic field because of the intrinsic superparamagnetism of Fe3O4. The result implies that the as-received Janus Fe3O4 nanoparticles may have extensive application prospects in oil purification from oil–water compounds. This synthesis strategy likewise could be a guidance to synthesize similar Janus materials.