Advanced magnetic nanospheres for oil pollutant management: Dual roles in emulsification and demulsification.

Environmental contamination from oil spills and industrial oily wastewater poses significant ecological risks due to the persistence of harmful organic compounds. To address these challenges, magnetic composite nanospheres (CMNP@CHPEI) are systematically developed, with carboxylated FeO nanoparticles (CMNP) as the core and amphiphilic hyperbranched polyethyleneimine (CHPEI) as the decorated shell. These novel nanospheres combine the controllable size and magnetic responsiveness of "hard" magnetic nanomaterials with the structural complexity and functional diversity of "soft" hyperbranched polymers. This design allows for switching between emulsification and demulsification behaviors by regulating the size of the nanospheres and the amphiphilicity of CHPEI. Specifically, the nanospheres can form Pickering emulsions with oil droplet sizes smaller than 1 µm, maintaining stability for up to 75 days, and achieve rapid oil-water separation with demulsification efficiencies up to 99.8 %. Even after seven recycling experiments, they still retain significant interfacial activity and applicability. Interfacial characteristic experiments and molecular dynamics simulations reveal that particle size directly affects the film structures formed at oil-water interface, while the amphiphilic functional molecules determine the interaction mode of nanospheres with oil-water phases. These achievements introduce a versatile, environmentally friendly material for removing hazardous oil-based pollutants, with promising applications in oil spill remediation and industrial wastewater treatment.