An anionic Fe(II) complex, (BMIM)4[Fe(CN)6] (where BMIM is 1-butyl-3-methylimidazolium), was synthesized in ionic liquid [BMIM][PF6] under reflux condition. The complex was characterized by elemental analysis and spectroscopic methods. The magnetite (Fe3O4) nanoparticles were prepared by the hydrothermal and solvothermal (in ionic liquid [BMIM][PF6]) methods from (BMIM)4[Fe(CN)6] as a precursor. The nanoparticles were characterized by X-ray diffraction (XRD), FT-IR, and scanning electron microscopy (SEM). The results show that the preparation of magnetite using the solvothermal method in [BMIM][PF6] has more advantages such as smaller size and high purity

Hassan Hadadzadeh

Mohammad Kaikhosravi

Mohammad-Taghi Behnamfar

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J | P | S | Tjpst.irost.irJournal of Particle Science and Technology (2015) 65-72Journal of                   Particle Science and TechnologyH I G H L I G H T S G R A P H I C A L  A B S T R A C TA new precursor for preparation of magnetite (Fe3O4) nanoparticlesMohammad Kaikhosravi, Hassan Hadadzadeh*, Mohammad-Taghi Behnamfar Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111, Iran• A new precursor, (BMIM)4[Fe(CN)6],  was syn-thesized for preparation of nanomagnetite.• The precursor was prepared in ionic liquid [BMIM][PF6].• The magnetite nanoparticles were prepared by hydrother-mal and solvothermal meth-ods.• A high purity nanomagnetite was obtained via the solvo-thermal method.• The effect of solvothermal time on structure and size of nanomagnetite was investigat-ed.A R T I C L E   I N F OArticle history:Received 3 December 2014Received in revised form 21 December 2014Accepted 27 December 2014Keywords:Ionic liquidSolvothermal1-Butyl-3-methylimidazolium hexafluorophosphateMagnetiteHydrothermalA B S T R A C TAn anionic Fe(II) complex, (BMIM)4[Fe(CN)6] (where BMIM is 1-butyl-3-methylim-idazolium), was synthesized in ionic liquid [BMIM][PF6] under reflux condition. The complex was characterized by elemental analysis and spectroscopic methods. The magnetite (Fe3O4) nanoparticles were prepared by the hydrothermal and solvothermal (in ionic liquid [BMIM][PF6]) methods from (BMIM)4[Fe(CN)6] as a precursor. The nanoparticles were characterized by X-ray diffraction (XRD), FT-IR, and scanning electron microscopy (SEM). The results show that the preparation of magnetite using the solvothermal method in [BMIM][PF6] has more advantages over the hydrother-mal method such as smaller size and higher purity.  * Corresponding author. Tel.: +98 3133913240; fax: +98 3133912350.      E-mail address:  hadad@cc.iut.ac.ir (H. Hadadzadeh).DOI: http://dx.doi.org/10.22104/jpst.2015.8066                                                            M.Kaikhosravi et al. / Journal of Particle Science and Technology (2015) 65-72sors [7,8], engineering [9,10], membrane [11], cata-lysts [10,11], and synthesis of nanostructures [14-17]. In the synthesis methods of nanostructures, the con-trol of morphology is very important for researchers. So, using of ILs in the solvothermal method is a good choice for this control.Recently, we have been interested in the use of new precursors for the preparation of nanoparticles. In this study, the magnetite nanoparticles were prepared via hydrothermal and solvothermal methods from a new anionic Fe(II) complex, (BMIM)4[Fe(CN)6] (where BMIM is 1-butyl-3-methylimidazolium), as a precur-sor. The effects of several parameters such as reaction time, solvent and temperature on the size and morphol-ogy of the magnetite nanoparticles were also investi-gated. In comparison with the reported methods for the preparation of magnetite nanoparticles, our proposed method is simple, fast, low-cost without using any spe-cial instruments, and does not require high-tempera-ture operation.1. IntroductionIonic liquids (ILs) are a class of salts which are liq-uid at ambient conditions because they have a signifi-cantly lower symmetry. Furthermore, the charge of its cation and anion is distributed over a larger volume of the molecule by resonance (Fig. 1) [1]. Generally, ILs are composed of organic cations and organic or inorganic anions (Scheme 1). The most prominent IL cations include alkylammonium, alkylphosphonium, N,N-dialkylimidazolium,  and N-alkylpyridinium cat-ions (Scheme 2). The IL anions are chloride, bromide, iodide, [BF4]–, [AlCl4]–, [PF6]–, and [SbF6]–. ILs have specific physical properties such as thermal stability, low vapor pressure, electric conductivity, interesting solvent properties, biphasic systems possible, liquid crystalline structures, high electroelasticity, high heat capacity, and non-flammability [2-6]. These unique properties make ILs attractive for scientists in a variety of field such as: electrochemical sensors and biosen Fig. 1. Charge distribution in common salts (a) and ILs (b).Scheme 1.  The ionic liquid toolbox: important model cations and anions for ILs.  M.Kaikhosravi et al. / Journal of Particle Science and Technology (2015) 65-72                                                            67Scheme 2.  Functionalized cations of ILs.2. Experimental2.1. Materials and methodsAll chemicals and solvents were reagent grades from Merck and used without any further purification. Elemental analyses were performed by using a Leco, CHNS-932 elemental analyzer. FT-IR spectra were re-corded on an FT-IR JASCO 460 spectrophotometer in the region of 4000–400 cm–1 using KBr pellets. Elec-tronic absorption spectra were recorded on a JASCO 7580 UV–Vis–NIR double-beam spectrophotome-ter. Quartz cuvettes of 10 mm path length were used for spectrophotometric experiments. XRD patterns were recorded by a Philips, X-ray diffractometer us-ing Ni-filtered Cu Kα radiation. The morphology of the nanoparticles was observed using FE-SEM (HI-TACHI; S-4160). Prior to taking images, the samples were coated by a very thin layer of Au to make the sample surface conducting and prevent charge accu-mulation, and obtaining a better contrast.2.2. Synthesis of (BMIM)4[Fe(CN)6] In the first step, a mixture of NaCN (0.05 g, 1mmol) and tetra-n-butylammonium bromide (TBAB) (0.32 g, 1mmol) was dissolved in 20 mL methanol and stirred for 1 h at room temperature. The white precipitate, tet-ra-n-butylammonium cyanide (TBACN), was filtered, washed with methanol and dried in air. In the second step, FeCl2∙6H2O (0.28 g, 1 mmol) was added to tet-ra-n-butylammonium cyanide (TBACN) (0.27 g, 1 mmol) in 5 mL ionic liquid [BMIM][PF6] and refluxed for 10 h. The resulting yellow precipitate,(BMIM)4[Fe(CN)6], was filtered and washed with wa-ter/acetone mixture (1:1), and then air dried at ambient temperature (Scheme 3), Yield: 0.5 g, 65%. 2.3. Preparation of the magnetite nanoparticles by sol-vothermal method in ionic liquid [BMIM][PF6]The precursor complex, (BMIM)4[Fe(CN)6], (0.4 g) was added to 5 mL ionic liquid [BMIM][PF6] and stirred for 2 h. The reaction mixture was transferred to a 10 mL Teflon-lined autoclave and heated in an oven at 200˚C for three different times of 12 h, 24 h and 36 h. The resulting product was centrifugated at 3000 rpm, washed with ethanol and water to remove any impurities, and dried in an oven at 80˚C overnight. (Fig. 2). 2.4. Preparation of the magnetite nanoparticles by hy-drothermal method (BMIM)4[Fe(CN)6], (0.4 g) was added to 5 mL water and stirred for 1 h. The reaction mixture was trans-ferred to a 10 mL Teflon-lined autoclave and heated in an oven at 200˚C for 12 h. The resulting precipitate was centrifugated, washed with water, and dried in an oven at 80˚C overnight.  68                                                            M.Kaikhosravi et al. / Journal of Particle Science and Technology (2015) 65-72Scheme 3.  Synthesis route to (BMIM)4[Fe(CN)6].Fig. 2. Preparation of the magnetite nanoparticles in [BMIM][PF6].3. Result and discussion The synthesis route to (BMIM)4[Fe(CN)6] is shown in Scheme . 3. Due to the poor solubility of NaCN in the ionic liquid ([BMIM][PF6]), the sodium salt was changed into tetra-n-butylammonium  salt. The reac-tion between FeCl2∙6H2O and TBACN in refluxing [BMIM][PF6] gave (BMIM)4[Fe(CN)6] in 65% final yield. Elemental analysis of the complex was entirely consistent with its proposed composition. The complex has good solubility in acetonitrile, DMF, and DMSO. Also, (BMIM)4[Fe(CN)6] is stable in the solid as well as in solution.The magnetite nanoparticles were prepared by two dif-ferent methods vis hydrothermal and solvothermal in [BMIM][PF6] (Fig. 2). The FT-IR spectrum of the complex shows typical bands associated with (CN–) ligand coordinated toFe(II). The C–H stretching vibration bands of the aliphatic hydrogen of  BMIM counter ions are appeared around 2900–3100 cm–1. The band at 593 cm–1 is assigned to the υ(Fe–C) vibration.The cyanide anion can coordinate to a metal atom in two different modes, viz. monodentate (M–CN), and bridging mode (M–CN–M›, M = or ≠ M›). The IR stretching bands of the coordinated cyano ligand appear in the range of 2025–2200 cm–1, while the bands are generally observed at 2025, 2044, and 2070 cm–1 for a monodentate mode (M–CN). For the bridging mode, the υ(C≡N) is higher by 40–100 cm–1 than that of the monodentate mode in [Fe(CN)6]4- ion. If the complex structures are similar, this rule is very useful [3]. In (BMIM)4[Fe(CN)6], the band at 2055 cm–1 correspondsto υ(C≡N) of the monodentate cyano ligands. The broad absorption band at 3446 cm-1 is attributed to the υ(OH) vibration of the crystallization water molecules. [18] (Fig. 3).     M.Kaikhosravi et al. / Journal of Particle Science and Technology (2015) 65-72                                                            69Fig. 3. FT-IR spectrum of (BMIM)4[Fe(CN)6]. Fig. 4. FT-IR spectra of the prepared magnetite nanoparticles by two methods; solvothermal in different times: 12 h (a), 24 h (b), 36 h (c), and hydrothermal for 12 h (d) at 200˚C. The FT-IR spectra of the magnetite nanoparticles in different times (12 h (a), 24 h (b), and 36 h (c), in ionic liquid, and 12 h (d) in water) at 200˚C are shown in Fig. 4. In the case of solvothermal method in [BMIM][PF6], the band associated with the CN– ligand at 2055 cm-1 is decreased from (a) to (c), indicating the amount of the cyano ligand is decreased with increasing the solvothermal reaction time. In contrast, when the water solvent was used for the hydrothermal method, the band associated with the cyano ligand is appeared at 2055 cm-1. In this method, some carbonate salts were produced as a by-product. The carbonate vibration is appeared at 1050 cm-1. The vibrations at about 450 and 750 cm-1 are attributed to the stretching vibration of the Fe–O bonds [18-20] (Fig. 4). The electronic spectrum of the complex was recorded in acetonitrile. The d6 hexacyano complexes display very simple electronic spectra. In view of the large LF strength of the cyano ligand, the t2g─eg interval is very large, and the cyano complexes are low-spin. LMCT transitions, from lower lying CN states, must terminate on the high energy eg level because the t2g level is full of electrons. Such transitions will generally fall beyond 200 nm. In the electronic spectrum of [Fe(CN)6]4-, there is a broad MLCT band in the UV–Vis region, namely t2g→ t1u MLCT and t2g→ t2u MLCT (Fig. 5). In this complex, since the ground state is 1A1g , only transitions to 1T1u are fully allowed [21].Fig. 5. UV-Vis spectrum of (BMIM)4[Fe(CN)6] in CH3CN.   70                                                            M.Kaikhosravi et al. / Journal of Particle Science and Technology (2015) 65-72Fig. 6. XRD patterns of the prepared magnetite nanoparticles by two methods; solvothermal in different times: 12 h (a), 24 h (b), 36 h (c); and hydrothermal for 12 h (d) at 200˚C.Fig. 6d shows the typical XRD patterns of the magnetite nanoparticles prepared by the hydrothermal method at 200°C for 12 h. The reflection peaks can be readily indexed to the crystalline phases. In comparison to the solvothermal method in [BMIM][PF6], several peaks for the carbonate by-product are seen in this pattern. The crystallite size (Dc) of the nanoparticles was calculated to be 47 nm. 3.4. FE-SEM studies The morphological images of the magnetite nanoparticles were studied by FE-SEM technique. According to the FE-SEM images, the morphology of the magnetite nanoparticles has the small fragment size and the nanoparticles are formed with irregular shapes. The particle size of the magnetite nanoparticles is between 15–50 nm (Fig. 7).3.3. XRD analysisThe X-ray diffraction pattern of the magnetite nanoparticles is shown in Fig. 6. The diffraction patterns show that the nanoparticles have a crystalline morphology and haven’t any amorphous phase at their structures. The solvothermal reaction of (BMIM)4[Fe(CN)6] in [BMIM][PF6] in three different times: 12h (Fig. 6, a), 24 h (Fig. 6, b), and 36 h (Fig. 6, c) at a 200°C resulted the magnetite crystalline phase, which is in agreement with the literature [19,20]. As shown in Fig. 6, the XRD pattern of the nanoparticles reveals that the diffractogram can be determined as Fe3O4 with a cubic phase, which can be filed to (220), (311), (400), (422), (511) and (440) planes (JCPDS Card No. 082–1533).Fig. 7. SEM images of the prepared magnetite nanoparticles by the solvothermal method for 24 h at 200˚C.  The crystallite size (Dc) of the magnetite nanoparticles was calculated to be 25 nm using the Debye–Scherrer equation [22], which is in agreement with that observed from the FE-SEM images.The crystallite size was calculated using the most intensity peaks.M.Kaikhosravi et al. / Journal of Particle Science and Technology (2015) 65-72                                                            71modified glassy carbon electrode integrated with flow injection analysis, Sens. Actuators. B. 205 (2014) 136–142.[8] V. V. Singh, A. K. Nigam, A. Batra, M. Boopathi, B. Singh, and R. Vijayaraghavan, Applications of Ionic Liquids in Electrochemical Sensors and Biosensors, Int. J. Electrochem. 2012 (2012) 1–19.[9] W. Beichel, U. P. Preiss, S. P. Verevkin, T. Koslowski, I. Krossing, Empirical description and prediction of ionic liquids ‘ properties with augmented volume-based thermodynamics, J. Mol. Liq. 192 (2014) 3–8.[10] M. Usula, E. Matteoli, F. Leonelli, F. Mocci, F. C. Marincola, L. 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Humphrey, Effect of microwave heating on the synthesis of rhodium nanoparticles in ionic liquids, Inorg. Chim. Acta. 422 (2014) 65–69.[15] M. Padervand, M. Vossoughi, Fabrication and antibacterial performance of Ag–Au nanoparticles decorated ionic liquid modified magnetic core-analcime shell microspheres, J. Environ. Chem. Eng. 2 (2014) 1989–1995.[16] K. T. P. Charan, N. Pothanagandhi, K. Vijayakrishna, A. Sivaramakrishna, D. Mecerreyes, B. Sreedhar, Poly(ionic liquids) as “smart” stabilizers for metal nanoparticles, Eur. Polym. J. 60 (2014) 114–122.[17] S. Rabieh, M. Bagheri, M. Heydari, E. Badiei, Microwave assisted synthesis of ZnO nanoparticles in ionic liquid [Bmim]cl and their photocatalyticinvestigation, Mater. Sci. Semicond. 4. ConclusionsFor the first time, a mononuclear Fe(II) complex with bulky counter ions, (BMIM)4[Fe(CN)6], has been synthesized in an ionic liquid with a good yield. We have also synthesized and characterized the pure magnetite (Fe3O4) nanoparticles via a fast and facile solvothermal method in an ionic liquid. The effect of time on the structure and grain size of the magnetite nanoparticles was investigated. In comparison to the hydrothermal method, the results reveal that the preparation of magnetite using the solvothermal method in [BMIM][PF6] yields pure and smaller nanoparticles. In hydrothermal method, the final product was impure and its XRD pattern revealed several peaks for carbonate as a by-product.AcknowledgementsWe are grateful to the Isfahan University of Technology (IUT) for financial support. References[1] J. D. Holbrey and K. R. Seddon, Ionic Liquids, Clean Technol. Environ. Policy. 1 (1999) 223–236. [2] C. Method, M. S. T. Mahmoudi, CeO2 nanoparticles synthesized by a microwave-assisted hydrothermal method: evolution from, J. Clust. Sci. 23 (2012) 597–602. [3] R. M. Cornell, U. 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A new precursor for preparation of magnetite (Fe3O4) nanoparticles

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A new precursor for preparation of magnetite (Fe3O4) nanoparticles

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