Effect of mixing sequence of citric acid in the synthesis of Zn0. 3Fe2 Effect of mixing sequence of citric acid in the synthesis of Zn0.3Fe2.7O4 magnetic nanoparticles by hydrothermal method T. Zargar*,a, A. Kermanpura, F.Sohrabib  a Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran b Department of Applied Physics, Aalto University, Espoo 11100, Finland *tzargar90@gmail.com Abstract The magnetic nanoparticles are widely used in biomedicine for magnetic hyperthermia in cancer treatment applications. In this study, Zn substituted magnetite nanoparticles of Zn0.3Fe2.7O4 were synthesized by the hydrothermal method. Hydrothermal synthesis method, by means of citric acid as the reducing agent, is a single-step, easy method for producing hydrophilic magnetite nanoparticles. In this study the effect of sequence of mixing the citric acid on purity, size and distribution of the Zn-substituted magnetite nanoparticles is investigated. X-ray diffraction patterns and scanning electron microscopy images were collected to distinguish the properties of Zn0.3Fe2.7O4 nanoparticles. Introduction Nowadays magnetic nanoparticles are widely used in research fields due to their unique magnetic properties, such as great superparamagnetic property [1]. These properties enable them to be used for medical applications including magnetic hyperthermia for malignant tumors, and targeted delivery of therapeutic molecules [2,3]. Hydrothermal method, by using citric acid as a reducing agent, is a single step, easy, environmentally friendly method to make hydrophilic magnetic nanoparticles [4]. It is observed that in this method, not only does the citric acid play a role as reducing agent, but also it results in production of a hydrophilic citrate coating in the surface of nanoparticles [4,5]. Materials and Method Materials used in synthesis were Iron Nitride III (Fe(NO3)3.9H2O), Ammonium Hydroxide solution (25%) NH4OH (25%), Zinc Chloride (ZnCl2) and Citric Acid (C6H8O7.H2O) from Merck of Germany, with minimum purity of 99 percent. Method In order to synthesis Zn0.3Fe2.7O4 nanoparticles and investigate the effect of the step of adding citric acid, we made two kind of samples, for both 11.8 mmol iron nitride (III) and 3.1 mmol zinc chloride was dissolved in 25 ml of deionized distilled water. In first sample, ammonium hydroxide was added until the pH of solution reached to 9.5 and reddish brown sediments are formed. To remove unwanted dissolved ions, The deposits were later centrifuged with 5000rpm for 10 minutes for three times. Finally, 6 mmol of citric acid was added to the solution. In the second sample, citric acid was added before ammonium hydroxide. Then the ammonium hydroxide was added gradually till the pH was 9.5. In this sample, the sediments were homogenously brown and could not be deposited; therefore, they could not be washed like the first sample, and the solution was used for next step without washing. For both samples, an autoclave with 325 ml volume, with a Teflon coating was used for synthesis. Then, the autoclave was put in oven for 15 hours in 200°C, and after this time, it had been cooled by the oven. To characterize the particles, they were dried in a heater. First sample was called A, and second sample was called B. Results Fig. 1. XRD pattern of a) sample A and b) sample B. In the XRD(Fig. 1.) pattern of sample A, the number and height of the peaks related to Zn0.3Fe2.7O4 spinel are more than sample B which represents that in order to achieve more purity, citric acid must be added before ammonium hydroxide. since the sediments could not be washed in sample B, impurities such as ammonium nitride is observed. Results Fig. 2. SEM images of: a) sample A, b) sample B. and The size distribution of: c) sample A, d) sample B. In Fig. 2a, sample A is spherical and has a uniform morphology and size distribution (Fig. 2c). Fig. 2b, shows that sample B is spherical, but the morphology and size distribution is not uniform (Fig. 2d). Of mean particle sizes of samples A and B are respectively 13.77 nm and 35.63 nm. References: [1] Y. Sahoo, A. Goodarzi, M. T. Swihart, T. Y. Ohulchanskyy, N. Kaur,Edward, P. Furlani, and P. N. Prasad, "Aqueous Ferrofluid of Magnetite Nanoparticles: Fluorescence Labeling and Magnetophoretic Control", Journal of Phys. Chem, 109 (2005) 3879-3885. [2] K. Rajendra, D. Singh, T. Kim,Kapil, C. P. Jonathan, K. K.-Won, "Biocompatible magnetite nanoparticles with varying silica-coating layer for use in biomedicine: physicochemical and magnetic properties,and cellular compatibility", Journal of Biomedical Materials Research A|Month, 2012, Vol 00a, Issue 00. [3] S. Nigam, K.C. Barick, D. Bahadur, Development of citrate-stabilized Fe3O4nanoparticles: Conjugation and release of doxorubicin for therapeutic applications, Journal of Magnetism and Magnetic Materials, 323(2011) 237–243. [4] B. Behdadfar, A. Kermanpur, H. Sadeghi-Aliabadi, del Puerto Morales, M., Mozaffari, "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 (2012) 2211–2217. [5] B. Behdadfar, "Synthesis and characterization of magnetic nanocapsules containing magnetite and Zn-Gd substituted magnetite nanoparticles for magnetic hyperthermia application", PHD Project, 2012, Department of Materials Engineering, Isfahan University of Technology.