Stabilizing Magnetic Nanoparticles for Improved Dispersion

The naked MNPs frequently aggregate in the solution due to the high surface energies, van der Waals, and magnetostatic interactions of MNPs that cause poor stability and dispersion [9 (link)]. Hence, in this work, the naked MNPs were first functionalized with poly(diallydimethylammonium chloride) (PPDA) to improve the MNPs’ stability and dispersion in water. The coating of PDDA on the MNPs’ surface (positive charge) could also help link the negatively charged TiO₂ or HPOM via electrostatic attraction. A 0.0025 g/mL concentration of MNPs was suspended in distilled water and ultrasonicated for at least 30 min to obtain MNP suspension without large aggregates. Simultaneously, a 0.075 g/mL concentration of PDDA solution was ultrasonicated at 60 °C for 1 h to allow the PDDA to dissolve. The MNPs’ suspension and the PDDA solution’s pH were then adjusted to pH 8. The MNPs were then added to the PDDA solution in a dropwise manner. The binding of the PDDA to the surface of the MNPs was achieved through electrostatic attraction. The binding process was carried out in an orbital shaker at a speed of 150 rpm for 2 h. Before being dispersed into distilled water during the final step, the functionalized MNPs (f-MNPs) were first separated using a permanent magnet and prewashed several times. The successfully synthesized f-MNPs were then linked with TiO_2, or HPOM particles, as explained in Section 2.5.