Fabrication of alkyl/amino siloxane-modified magnetic nanoparticles for simultaneous demulsification of O/W and W/O emulsions

"Oil-in-water" emulsion (O/W emulsion) and "water-in-oil" emulsion (W/O emulsion) are widely presented in our daily life and production activity. From the perspective of both effective resource utilization and environmental protection, it is of great significance to implement efficient oil-water separation. Although many magnetic nanoparticles (MNPs) with special wettability were successfully developed to separate oil-water mixture, they cannot demulsify O/W and W/O emulsions simultaneously. In this study, a class of amphiphilic MNPs with cationic characteristic has been facilely developed by covalently chemical modification with hydrophobic alkyl siloxane and hydrophilic amino siloxane on the surface of Fe3O4 @SiO2 nanoparticles. The fabricated MNPs were characterized by various techniques and then evaluated for their demulsification performances in both O/W and W/O emulsions. Results showed that neither alkyl siloxane-modified MNPs nor amino siloxane-modified MNPs could effectively demulsify both O/W and W/O emulsions simultaneously. However, when the MNPs were coated with appropriate proportion of alkyl siloxane and amino siloxane, the selected M3-21 could rapidly assemble at the oil-water interface and meanwhile promote droplet coalescence in both types of emulsions, leading to high magnetic demulsification efficiency; specifically, the oil/water removal ratio reached ~95% for sodium dodecyl sulfate (SDS)-stabilized O/W emulsion (SDS=20 mg/L) and Span80-stabilized W/O emulsion (Span80 =5 g/L) at the dosage of 500 mg/L and 30 g/L, respectively. Moreover, the developed MNPs exhibited satisfactory reusability. In view of its convenient synthetic process and superior demulsification performance, the fabricated MNPs were recognized as a class of promising materials for demulsification in both O/W and W/O emulsions from petroleum industry, machinery and food processing industries.