Growth of iron oxide nanoparticles by hydrothermal process: Effect of reaction parameters on the nanoparticle size
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Different size of iron oxide nanoparticles were synthesized via hydrothermal process. The change of the size of nanoparticles with reaction temperatures (60, 100, 150, and 180 a"integral) was investigated. To have further insight into the growth of nanoparticles, the different reaction times were also studied at the temperatures of 100, 150, and 180 a"integral. The structural characterization was carried out with X-ray diffractometer and Fourier transform infrared spectroscopy. The nanoparticles were found to have high crystalline iron oxides with a mixture of magnetite and maghemite crystalline phases. With the increase of the nanoparticle size, the ratio of magnetite to maghemite phase increased and reached to a pure magnetite phase for the 123 +/- 44 nm particles. When the reaction temperature increased from 100 to 180 a"integral for 12 h, the size of the nanoparticles increased from 14.5 +/- 4 to 29.9 +/- 9 nm according to transmission electron microscopy analysis. At 180 a"integral, as the reaction time increased from 1 to 48 h, the size of nanoparticles increased from 20.6 +/- 6 to 123 +/- 44 nm. This means that the reaction times are more effective on the growth of the nanoparticles at high temperatures. Magnetic analysis by vibrating sample magnetometer showed that the nanoparticles are ferrimagnetic. By considering all nanoparticles, the saturation magnetization increased as the size of the nanoparticle increased. And the high size of nanoparticles reached the high saturation magnetization value at low applied magnetic fields. The structural and magnetic properties of the nanoparticles are found to be depending on the nanoparticle sizes which are substantially affected by the reaction temperature and time.