Result and Discussion Abstract Introduction Experimental Effect of temperature on the size, shape, and morphology of Zn0.3Fe2.7O4 nanoparticles synthesized by citric acid-assisted hydrothermal reduction process for magnetic hyperthermia applications  T. Zargar a,*, A. Kermanpura aDepartment of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran * Corresponding author. Tel.: +98-311-391-2751; fax: +98-311-391-2752. E-mail address: t.zargar@ma.iut.ac.ir Result and Discussion Abstract It was recently shown that the Zn-substituted magnetite (Zn0.3Fe2.7O4) nanoparticles had the highest intrinsic loss power (ILP) of 4.8 nHm2/kg which is higher than the maximum ILP of commercial nanoparticles (3.12 nHm2/kg). In the present work, the magnetic Zn0.3Fe2.7O4 nanoparticles were synthesized via hydrothermal-reduction route in the presence of citric acid, and the effect of process temperature (e.g. 150, 175 and 200 °C) on the size, shape and morphology of the nanoparticles were investigated. The synthesized nanoparticles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The results showed that the synthesis temperature in hydrothermal method had a significant effect on the phase transition of ferrihydrite to spinel, thereby on the size, shape, and morphology of magnetic Zn0.3Fe2.7O4 nanoparticles. In Fig. 1a which corresponds to sample A, only two broad peaks can be observed. Belonging to the ferrihydrite compound with the chemical formula of Fe5HO8.4H2O. Fig. 1b shows that all main peaks in the XRD pattern of sample B are related to Zn0.3Fe2.7O4 spinel, while those of sample C corresponded to hematite and spinel phases (Fig. 1c). Fig. 1. XRD patterns of the synthesized nanoparticles at different temperature: (a) 150; (b) 175 and (c) 200ºC. This shows that the synthesis temperature in hydrothermal-reduction route had a significant effect on the phase transition of ferrihydrite to spinel and phase purity of the produced nanoparticles. The stoichiometric conditions for the formation of spinel structure in hydrothermal method is M2+/M3+=0.5, Tronc et al. (1992). This ratio has been provided at 175 ° C, leading to the formation of spinel. One should note that, firstly, this spinel is not very stable in basic solution, because Fe2+ ions are oxidized to Fe3+ by oxygen and some of the spinel is converted to hematite (Fe2O3); and secondly, increasing temperature resulted in an increase in ionization of water and therefore the amount of O2- ions increases, leading to the formation Fe3+ (e.g. hematite) before converting to spinel. A comparison between XRD patterns of Fig. 1b and c shows that increasing the temperature resulted in a larger height of the spinel peaks and smaller widths. This indicated that the size and crystallinity of spinel crystal grow by rising temperature. As previously mentioned, the average crystallite sizes of synthesized nanoparticles were calculated by using modified Scherrer’s method as 19.9 and 20.7 nm for the samples B and C, respectively. Fig. 2 shows SEM images of samples A, B and C. Fig. 3a is related to the synthesized sample at 150 ° C, showing no spinel nanoparticles, that is according to the results of X-ray pattern. Uniformity in distribution of sizes, shapes and morphology of the spinel nanoparticles of samples B and C can be observed in Figs. 2b and 3c, respectively. As can be seen, nanoparticles of samples B and C have both a spherical shape. The mean particle sizes, calculated from SEM data, were 12.9 nm with a standard deviation of 4.3 nm for B sample (Fig. 2d) and 13.8 nm with a standard deviation of 5 nm for C sample (Fig. 2e). The higher size in sample C compared to that of sample B is related to the higher temperature Comparison of the values of mean particle sizes to the values of average crystallite sizes calculated by using the modified Scherrer’s method indicates that in both cases, the nanoparticle are single crystals. This shows that the synthesized nanoparticles can be considered as the superparamagnetic ones at room temperature, Behdadfar et al. (2012) are therefore suitable for hyperthermia applications. Fig. 2. SEM images of the synthesized products at different temperature: (a) 150; (b)175 and (c)200 ºC. and The size distribution of the spinel nanoparticles at at different temperature: (d) 175 and (e) 200 ºC. Introduction One example is the applications of superparamagnetic nanoparticles in magnetic hyperthermia for treatment of malignant tumors. In this method, the nanoparticles are injected into the tumor and then subjected to an external alternative magnetic field. As a result, they produce heat and the heating causing a warming cancer cells until 41 ºC, ultimately destroy them. Heat generation in the alternative magnetic field is conducted with different loss mechanisms such as hysteresis and relaxation losses. magnetite is the most frequent nanoparticles used for this application, Leach (2003). The heat generation can be improved by either substitution of other ions in the magnetite structure to improve their magnetic properties and/or by control of size and size distribution of the magnetic nanoparticles. One of the advantages of Zn ferrite is low toxicity relative to other particles such as Mn-Zn ferrite, Leach (2003), Sharifi et al. (2012). Hydrothermal-reduction method is an easy and one-step route to synthesize hydrophilic magnetite nanoparticles with different reductants such as citric acid, Roca (2006), Behdadfar et al. (2012). (a) 1000nm (b) (c) 1000nm 1000nm (d) (e) Experimental Materials : All raw materials, including Fe(NO3)3.9H2O, NH4OH 25%,ZnCl2 and C6H8O7.H2O, were purchased from Merck Co. with minimum purity of 99%. Synthesis : To synthesize Zn-substituted magnetite nanoparticles (Zn0.3Fe2.7O4), 11.8 mmol of Fe(NO3)3.9H2O and 1.3 mmol of ZnCl2 were dissolved in 25 ml of deionized distilled water. The produced solution was continuously stirred by a magnetic stirrer for 20 min. Then a solution of NH4OH 25% was added slowly to reach a pH medium of 9.5. Vigorous stirring continued for another 20 min until a reddish-brown slurry was formed. The slurry was washed and centrifuged for 10 min at the speed of 5000 rpm three times with deionized distilled water. Citric acid was then added to the mixture and it was stirred vigorously for 30 min and then transferred into a 325 ml volume teflon-lined autoclave which only 200 ml of which was filled. The autoclave was kept at different temperatures of 150, 175 and 200 °C for 15 h and then free-cooled to room temperature. For powder characterization, the precipitate was washed with acetone several times and then dried at 80ºC. The final products were synthesized at 150, 175 and 200 ºC were named as A, B and C, respectively. Conclusion In this work, the magnetic Zn0.3Fe2.7O4 nanoparticles were synthesized via hydrothermal-reduction route in the presence of citric acid at different temperatures of 150, 175 and 200 ºC for 15h.The results showed that the synthesis temperature in hydrothermal method had a significant effect on the phase transition of ferrihydrite to spinel. At 150 ºC, no spinel nanoparticles was formed, while at 175 ºC, pure magnetic Zn0.3Fe2.7O4 nanoparticles and at 200 ºC both hematite and Zn0.3Fe2.7O4 nanoparticles were formed. References Leach J., 2003. Thesis on magnetic targeted drug delivery, Virginia Polytechnic, 83. Sharifi, I., Shokrollahi, H., Sharifi, E., 2012. characterization and synthesis of magnetic nanoparticles for treatment of cancer by magnetic hyperthermia method, 2nd Congress of defense applications of nanoscience. Tehran, Iran, Feb.2012. Sharifi, I., Shokrollahi, H., Amiri, S., 2012. Ferrite-based magnetic nanofluids used in hyperthermia applications. Journal of Magnetism and Magnetic Materials 324, 903-915. Roca, A.G., 2006. Structural and magnetic properties of uniform magnetite nanoparticles prepared by high temperature decomposition of organic precursors. Journal of Nanotechnology 17, 11, 2783-2788. Behdadfar, B., PHD Project: Synthesis and characterization of magnetic nanocapsules containing magnetite and Zn-Gd substituted magnetite nanoparticles for magnetic hyperthermia application for 2012, Department of Materials Engineering, Isfahan University of Technology, Sept.2012. Behdadfar, B., Kermanpur, A., Sadeghi-Aliabadi, H., del Puerto Morales, M., Mozaffari, M., 2012. Synthesis of aqueous ferrofluids of ZnxFe3_xO4 nanoparticles by citric acid assisted hydrothermal-reduction route for magnetichyperthermia applications. Journal of Magnetism and Magnetic Materials 324, 2211–2217.