Fig. 3

Purification performance of the nanoparticles towards oilfield wastewater. Photographs of deionized water, oilfield wastewater before and after treated with a Fe3O4@SiO2-MPS-AM-DMC-AMPS and c Fe3O4 under external magnet field, respectively, and the corresponding desalination efficiency of b Fe3O4@SiO2-MPS-AM-DMC-AMPS and d Fe3O4 for each ion