*5.2.3 Hybrid magnetic nanoparticles*

Hybrid magnetic nanostructures contain two or more nanometer-scale components with at least one component being magnetic [56]. These hybrid nanocomposites take the advantages of the magnetic nanoparticles such as their high surface area, their easy separation under external magnetic fields and their excellent recyclability after separation and prevent from their precipitation or aggregation due to their tendency to oxidation [57]. Up to date, different MNP have been researched by the scientific society. The investigated nanostructures include magnetite (Fe3O4), maghemite (-Fe2O3) and hematite (-Fe2O3). They could be functionalized with different materials such as polymers, biomolecules, inorganics, organics or carbon nanotubes [57]. This surface functionalization improves the homogeneity, selectivity and adsorption capacity of magnetic nanoparticles leading to an effective removal of toxic pollutants. Asadi et al. (2020) synthetized the spinel ferrites nanoparticles MnFe2O4 and CoFe2O4 to investigate the zinc removal from aqueous solution. High respective adsorption capacities of 454.5 and 384.6 mg/g for MnFe2O4 and CoFe2O4 were obtained at optimum pH =6, by following the Langmuir Isotherm model [58].
