Treatment of emulsified oil wastewaters by using chitosan grafted magnetic nanoparticles

Abstract In this study, a class of chitosan (CS)-grafted magnetic nanoparticles (MNPs) was synthesized for treating emulsified oil wastewaters. Fe 3 O 4 MNPs were synthesized by using a solvothermal method, followed by coating with aminopropyl-functionalized silica (APFS) to form a surface for further grafting of CS molecular chains. The synthesized MNPs were characterized by various technologies and their demulsification performances were evaluated under various conditions. Results showed that synthetic Fe 3 O 4 MNPs showed negligible demulsification effect, however, under both acidic and neutral conditions, APFS-coated MNPs (Fe 3 O 4 @APFS MNPs) exhibited good demulsification effect via electrostatic attraction. It was also found that demulsification performance could be further enhanced upon CS grafting, especially under alkaline condition. Results showed that, under both acidic and neutral conditions, CS-grafted MNPs (Fe 3 O 4 @APFS-G-CS MNPs) could efficiently flocculate oil droplets mainly via electrostatic attraction, thereby facilitating magnetic separation; while under alkaline condition, MNPs could overcome electrostatic repulsion and be absorbed onto oil droplet surface via hydrophobic interaction, thereby exhibiting certain demulsification effect under magnetic field. Moreover, under both acidic and neutral conditions, synthesized MNPs could be recycled up to 7 cycles without showing significant loss in demulsification efficiency. In conclusion, CS-grafted MNPs can be easily synthesized and recycled, providing a potential promising approach for efficient treatment of emulsified oil wastewater.