*2.1.3 Synthesis of magnetite nanoparticles (Fe3O4) by co-precipitation*

According to the previous work, magnetite (Fe3O4) nanoparticles were synthesized by chemical co-precipitation method. Magnetic Fe3O4 NPs were synthesized by dissolving 50 mL of FeCl3.6H2O and 25 mL of FeSO4.7H2O in 350 mL of distilled water under nitrogen atmosphere under vigorous stirring. Upon addition of (35 ml) NaOH, the pH was adjusted to about 10, the solution turned black, indicating the formation of magnetite nanoparticles. Further stirring is continued for 1 h to uniformly disperse the magnetic nanoparticles. After raising the reaction temperature to 80°C. Then, a formed black precipitate was collected with an external magnet, washed several times with ethanol and distilled water, and dried in vacuum at 60°C. The entire reaction is given by the equation as shown in **Figure 5**.
