Recyclable Amphiphilic Magnetic‐responsive Mixed‐Shell Nanoparticles With High Interfacial Activity Comparable to Janus Particles for Oily Water Purification

Abstract Amphiphilic magnetic‐responsive mixed‐shell nanoparticles (Mag‐MSNPs) with tailorable compositions are synthesized by electrostatic‐mediated cross‐linking of core‐forming blocks of two diblock copolymers, followed by in situ growth of magnetite in the cross‐linked core. The Mag‐MSNPs have a magnetic‐responsive core and hydrophilic/lipophilic mixed shells, firmly anchoring at the oil–water interface of emulsified oil droplets due to their high interfacial activity (13.1 mN m −1 at a rather low emulsifier concentration of 1.2 mg mL −1 in the n ‐hexane/water system), outperforming most of Janus particles. Driven by the magnetic field, the emulsified oil droplets with Mag‐MSNPs at the interface are drawn to one side for collection. The oil–water separation efficiency reaches 99.5%, manifesting their excellent ability to remove emulsified oil droplets from oily water. After five separation and regeneration cycles, the separation efficiency remains at 98.8%, showcasing their potential for recyclable oily water purification.