Fe3O4 nanoparticles were prepared by co-precipitation of the Fe3+and Fe2+ions by ammonia solution and treating under hydrothermal conditions [40]. Chemical precipitation was achieved at 25 °C under vigorous stirring by adding NH4OH solution. The precipitates were heated at 80 °C for 30 min, washed several times with water and ethanol, and then finally dried in a vacuum oven at 70 °C.