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

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.