A comprehensive review on demulsification using functionalized magnetic nanoparticles

Conventional oil-water separation techniques have limited effectiveness in separating emulsified oil contaminations in wastewater in the forms of oil-in-water (o/w) or water-in-oil (w/o) emulsions. Researchers have used advances in nanotechnology to overcome the challenges with oil-water separation for emulsion systems. The use of magnetic nanoparticles (MNPs) such as iron oxide for separating emulsified oil contaminations has been extensively studied because of high adsorption capacity, high magnetic strength, low cost, low toxicity, biodegradability, reusability, and efficient separation from the aqueous phase. This review focuses on the application of MNPs in separating emulsified oil contaminations from wastewater. Although pristine magnetic iron oxide nanoparticles have excellent separation efficiency, there are challenges in using them, including high tendency for aggregation that results in their precipitation, and high chemical activity that causes oxidation by air and loss of magnetism. Thus, stabilization of the MNPs is required through developing a protecting coating layer using different organic/inorganic compounds. However, the performance of the MNPs will be affected by the coatings and their chemical structures. In general, demulsification by MNPs is affected by operating conditions (temperature and mixing time), fluid properties (viscosity, pH, salinity, and content of emulsion phases), and MNPs properties (type, size, and dosage). The effects of these variables on the effectiveness of demulsification by the MNPs are covered in this review manuscript. Finally, we provide useful tips and guidelines for designing an effective framework to implement MNPs for separation of emulsified oil droplets.