A Simple Chemical Route toward Monodisperse Iron Carbide

Letter pubs.acs.org/NanoLett

A Simple Chemical Route toward Monodisperse Iron Carbide Nanoparticles Displaying Tunable Magnetic and Unprecedented Hyperthermia Properties Anca Meffre, Boubker Mehdaoui, Vinciane Kelsen, Pier Francesco Fazzini, Julian Carrey, Sebastien Lachaize, Marc Respaud,* and Bruno Chaudret* Laboratoire de Physique et Chimie des Nano Objets, INSA, Université de Toulouse, 135, Avenue de Rangueil, F-31077 Toulouse, France S Supporting Information *

ABSTRACT: We report a tunable organometallic synthesis of monodisperse iron carbide and core/shell iron/iron carbide nanoparticles displaying a high magnetization and good air-stability. This process based on the decomposition of Fe(CO)5 on Fe(0) seeds allows the control of the amount of carbon diffused and therefore the tuning of nanoparticles magnetic anisotropy. This results in unprecedented hyperthermia properties at moderate magnetic fields, in the range of medical treatments. KEYWORDS: Magnetic nanoparticles, iron carbides, iron, core/shell, hyperthermia, organometallic chemistry

M

For instance, there is presently no available method to change continuously the magnetic anisotropy while keeping constant a particle size and the saturation magnetization. Iron carbides are attractive since they combine good air stability with a high magnetization. But few reports concern their synthesis in the form of nanostructures besides their formation from Fe nanoparticles during the Fischer−Tropsch Process.13,14 Thus, this process converts syngas (mixture of CO and H2) into long chain hydrocarbons using catalysts which are initially composed of iron and/or cobalt deposited on a support. Main preparation routes of iron carbides involve either physical pyrolysis,15−18 sonolysis, 19,20 or laser ablation methods21 which lead to agglomerates and polydisperse nanoparticles and to a low magnetization or, more recently, solution chemistry methods using the intermediate formation of a gel which is then converted to iron carbide by a thermal treatment.22−24 Among their various applications, iron carbides could be especially attractive for catalysis (FTP) and for hyperthermia. Mechanistic studies of FTP have shown that using iron-based catalysts high Fischer−Tropsch activities are obtained only if carbon-rich iron carbides (Hägg carbide, Fe2.5C) phases are formed as intermediates.25 Magnetic hyperthermia requires biocompatible magnetic nanoparticles, which placed in an alternative magnetic field, convert the external energy into heat. The power generated by the magnetic nanoparticles is governed by their specific absorption rate (SAR). A SAR of ca. 1 kW g−1 is required for biomedical applications, in the range of frequency and magnetic field

agnetic nanoparticles display interesting properties which can find applications in various important domains among which permanent magnets, nanoelectronics (tunnel magneto-resistance), microelectronics (data storage, electromagnetic protection, magnetic sensors), catalysis (sustainable catalysts, catalysts recovery), biomedicine (drug delivery, cell destruction),1 and so forth. The magnetic materials constituting these nanoparticles may be magnetic metals and alloys, oxides and mixed oxides, or compounds such as borides or carbides. Most of the studies in this field are carried out on iron oxides which are both air- and water-stable and nontoxic.2 Mixed oxides such as cobalt ferrites are also of interest because of their large anisotropy.3 However, the magnetization of oxides is low, and this is amplified by the difficulty to obtain structurally perfect nano-objects which in general results in a further loss of magnetization.4 The magnetic metals are Fe, Co, and Ni and their alloys. FePt5 and CoPt6 are of interest for their high coercivity, leading to the possibility of magnetic recording, whereas FeCo7 and FeNi8 are soft magnetic materials of interest for RF applications. In our group, we have synthesized for 15 years mono- or bimetallic magnetic nanoparticles using an organometallic approach. These particles are in most cases monodisperse and display a high magnetization (bulk or higher).9,10 Concerning phases associating a metal to main group elements, some cobalt borides have been obtained during the process of cobalt reduction by NaBH4, but their properties as nanoparticles have not been systematically investigated.11,12 The development of new applications in the fields of nanomagnetism still requires versatile synthesis routes that allow for a fine-tuning of particle sizes and magnetic properties according to the specifications related to a given application. © 2012 American Chemical Society

Received: June 7, 2012 Revised: July 23, 2012 Published: July 30, 2012 4722

dx.doi.org/10.1021/nl302160d | Nano Lett. 2012, 12, 4722−4728

Nano Letters

Letter

Scheme 1. Typical Synthesis of Iron Carbide (MM1) and Iron(0)/Iron Carbides Core Shell (MM2) Nanoparticles Starting from Preformed Iron(0) Nanoparticles

Figure 1. Structural analysis of iron carbide nanocrystals (MM1) of about 13.1 nm. (a) TEM analysis of MM1. (b) HRTEM analysis of MM1. (c) Powder-XRD data of MM1. (d) Mössbauer spectrum of MM1.

compatible with human applications26 (100 kHz and 20 mT), but it remains a real challenge. We have recently made significant progresses in the optimization of the SAR values by optimizing the size of iron(0) nanoparticles,27,28 but increasing SAR values at low magnetic field requires the decrease of nanoparticle anisotropy.29,30 We report hereafter the first versatile chemical synthesis of monodisperse iron carbide nanoparticles of controlled size and composition as well as that of core−shell iron/iron carbide nanoparticles and the modulation of their magnetic and hyperthermia properties following an approach inspired by the Fischer−Tropsch process, namely, using preformed monodisperse iron(0) nanoparticles as “seeds” on which Fe(CO)5, as both Fe and carbon precursor, is reacted under Ar or H2 (Scheme 1). The synthesis of iron carbide nanoparticles was carried out in two steps. First iron(0) nanoparticles were prepared according to a previously reported method.31,32 Interestingly, the reaction does not work when using Fe nanoparticles stabilized by a carboxylic acid/amine mixture, presumably because of the strong coordination of the carboxylic acids to the nanoparticle

surface.31 This led us to change to a procedure recently reported in our group using C16H33NH2 (HDA), C16H33NH3Cl (HDAHCl), and {Fe[N(SiMe3)2]2}2 in mesitylene.32 The reaction products were fully characterized by transmission electron microscopy (TEM) and high resolution TEM (HRTEM) observations which evidenced the presence of homogeneous nanocrystals with a very narrow size distribution. Mössbauer spectroscopy confirmed the complete reduction of the iron complex to metallic ferromagnetic iron. As previously described, the average size of preformed iron(0) nanocrystals could be tuned between 8 and 12 nm by varying the experimental conditions such as acid concentration, temperature, or reaction time. The second step was carried out by adding iron pentacarbonyl (Fe(CO)5) to preformed iron(0) nanoparticles of about 9.6 nm, in a respective 1:2 molar ratio. Note that the decomposition of Fe(CO)5 in the presence of HDAHCl and HDA and without Fe(0) NPs produced an inhomogeneous mixture and polydisperse nanoparticles (see Figure S1 of the Supporting Information). In our typical reaction, the mixture was pressurized with 3 bar H2 in mesitylene and heated at 150 4723


Nano Letters

Letter

Figure 2. Structural analysis of iron/iron carbide nanoparticles (MM2) of about 13.6 nm. (a) TEM analysis of MM2. (b) Mössbauer spectrum of MM2. (c) HRTEM analysis and distribution of the iron(0) core and iron carbide shell of MM2. (d) Powder-XRD data of MM2.

°C for 24 h. A black magnetic material formed (MM1, magnetic material 1 iron carbide), which contains 80% of iron and consists of homogeneous nanoparticles displaying an average size of about 13.1 nm and a very narrow size distribution (standard deviation, σ = 0.9 nm; see Figure 1a). The contrast in the nanoparticles in the HRTEM image shows a darker core and a lighter shell that reveals a core/shell structure. HRTEM clearly showed uniform lattice fringes of ε′Fe2.2C (011) and (010) core (see Figure 1b and Figure S2 of the Supporting Information). X-ray diffraction (XRD) carried out on a powder of nanoparticles shows the complete disappearance of the three peaks corresponding to the initial bcc-iron(0) and the formation of six broad peaks characteristic of new carbon rich iron carbide phases, ε′-Fe2.2C (see Figure 1c). Using the Scherrer equation, the average size of ε′-Fe2.2C nanocrystalites estimated from the peak width of Fe2.2C (101) is 9.6 nm. Taking into account the error bars of the different methods of analysis, this value is close to the average core size of 10.4 ± 0.6 nm measured on HRTEM images. The Mössbauer spectrum recorded at 5 K on a purified sample demonstrates the presence of equal contributions of about 43% of iron carbide ε′-Fe2.2C and 43% of Hägg carbide χ-Fe5C2 together with a very minor contribution of a paramagnetic species (see Figure 1d). Only the Mössbauer spectra evidence the presence of the Hägg carbide phase, the very low crystallographic symmetry of which could prevent its identification by XRD and HRTEM studies. The ratio of each phase determined by Mössbauer agrees with the one deduced from HRTEM considering a disordered χ-Fe5C2 shell surrounding the ε′-Fe2.2C single crystal core. Remarkably, the amount of iron carbides of different compositions (carbon rich or carbon poor) can be modulated by varying the experimental conditions of Fe(CO)5 decomposition, namely, the temperature and the gas atmosphere (H2 or Ar). Thus, reacting preformed iron(0) nanocrystals of about 9.6 nm with Fe(CO)5 in a respective 2:1 molar ratio at 150 °C

under Ar for 24 h, led to core−shell nano-objects, again very homogeneous in size and shape as deduced from TEM observations (MM2, magnetic material 2 iron/iron carbide; see Figure 2a). They display a mean size of 13.6 nm (σ = 0.8 nm) with a core diameter of about 9.3 ± 0.6 nm. The Mössbauer spectra (see Figure 2b) demonstrate the presence of ferromagnetic bcc-iron (0) as the main component (52%) and iron carbide phases with two components (20% of χ-Fe5C2 and 23% of ε′-Fe2.2C) as well as a very small contribution of about 5% of an unidentified paramagnetic species. HRTEM images (see Figure 2c and Figure S5 of the Supporting Information) show uniform lattice fringes across the whole core, with characteristic interplanar distances corresponding to α-bcc-iron(0) (110) and (020). For the shell, multiple crystalline domains with lattice spacing matching those of ε′-Fe2.2C were observed. The XRD pattern (see Figure 2d) agrees with Mössbauer (see Figure 2b) and HRTEM (see Figure 2c), clearly showing the three diffraction peaks of bcciron (0) and the six very small broad peaks characteristic of iron carbide phases with high carbon content. Again, using the Scherrer equation, the average size of bcc-iron(0) nanocrystallites estimated from the peak width of Fe(110) is 8.2 nm. This value is close to the average iron(0) core size of 9.3 ± 0.6 nm measured on HRTEM images, taking into account the error bars of the different methods of analysis. Similar core−shell Fe/FexCy nano-objects are formed if the reaction is carried out under H2, but at 120 °C instead of 150 °C. Some representative results are shown in the Supporting Information (see Figure S4). Longer reaction times at 120 °C allow a slow increase of the amount of iron carbide phases at the expenses of the iron(0) one (see Figure S7). All of these elements clearly suggest that Fe(CO)5 decomposition and CO dissociation are considerably slowed down by reducing the reaction temperature under H2 or by changing to a neutral atmosphere leading to the formation of a lower amount of iron 4724


Nano Letters

Letter

Figure 3. Magnetic properties of different compositions of iron and iron carbide based nanoparticles. (a) Magnetization data of ∼9.6 nm iron(0) nanocrystals at 2 and 300 K. (b) Magnetization data analysis of ∼13.1 nm MM2 at 2 and 300 K. (c) Magnetization data analysis of ∼14.2 nm MM1 nanocrystals at 2 and 300 K. (d) Stability against oxidation of iron, MM1, and MM2 nanocrystals.

at 300 K; see Figure 3a). Iron carbide nanocrystals (MM1) of 14.2 nm (±1.0 nm) display a reduced magnetization of 161 (±10%) Am2·kg−1 at 2 K and 132 (±10%) Am2·kg−1 at 300 K (HC = 34.5 mT at 2 K and 23.3 mT at 300 K; see Figure 3c). These values are among the highest saturation magnetizations reported so far for iron carbide materials.15−24 Iron/iron carbide (MM2) core shell nanocrystals (13.1 ± 0.9 nm) display a high saturation magnetization of 202 (±10%) Am2·kg−1 at 2 K and 195 (±10%) Am2·kg−1 at 300 K (HC = 21.2 mT at 2 K and 3.5 mT at 300 K) close to that of bulk iron (see Figure 3b). In addition, iron carbide and iron/iron carbides nano-objects display a higher stability against oxidation than the initial iron (0) nanocrystals (see Figure 3d). Upon exposing iron carbide nanocrystals to air, the value of MS first decreases and saturates at a value of about 80% of initial MS after 1 month. For iron/ iron carbide nano-objects, a faster decrease is measured in first 24 h exposure to air, which corresponds to a loss of 10% of MS. However, these nano-objects even after oxidation display a saturation magnetization higher than iron oxides or core shell iron/iron oxide nanoparticles described until now in the literature.2,33 The hyperthermia properties of these new materials were first studied by measuring the temperature rise of colloidal solutions upon applying an alternating magnetic field on a homemade frequency-adjustable electromagnet.34 The SAR dependence as a function of magnetic field measured at a frequency fexc = 54 kHz is depicted for different representative samples in Figure 4a. Figure 4b displays the high-frequency hysteresis loops of the same samples measured with a specially designed setup described elsewhere.35 In both figures, the

carbides of different compositions (carbon rich or carbon poor). In both cases (MM1 and MM2), the final size of nanoobjects can be finely controlled by varying the average size of the initial iron(0) nanocrystals or the Fe(CO)5 concentration, while keeping all other parameters constant. MM1 and MM2 were obtained in a size range from 11.7 to 14.5 nm (see Figures S3 and S6 of the Supporting Information). The thickness of the iron carbide shell in MM2 can increase from 1.5 ± 0.2 nm to 2−2.3 ± 0.2 nm while keeping the bcc-Fe(0) core diameter constant. All of these results suggest that the amount of carbon formed, and its diffusion inside the preformed iron(0) nanocrystal seeds is strongly dependent upon both the presence of H2 and the reaction temperature. Magnetization measurements were performed on a Quantum Design model MPMS 5.5 SQUID magnetometer. The measurements were carried out on purified powder samples prepared and sealed under argon atmosphere to preserve the NPs from any uncontrolled oxidation. The absolute magnetization was deduced from the iron(0) total content determined by microanalysis using the inductively coupled plasma mass spectrometry technique (ICP). Initial iron(0), iron carbide (MM1), and iron(0)/iron carbide (MM2) core shell nanocrystals exhibit a soft ferromagnetic behavior at room temperature and a high magnetization (see Figure 3). As expected, the measured saturation magnetization (MS) of preformed iron(0) nanoparticles (9.6 ± 0.3 nm) is very close to that of bulk iron, 210 (±10%) Am2·kg−1 at 2 K and 198 (±10%) Am2·kg−1 at 300 K (HC = 14.5 mT at 2 K and 3.4 mT 4725


Nano Letters

Letter

Figure 4. Hyperthermia properties of samples of iron carbide and iron/iron carbide nanocrystals. (a) SAR measurements at fexc = 54 kHz. (b) Normalized hysteresis loops measured at fexc = 54 kHz and room temperature on the same samples. (c) Dependence of the coercive fields deduced from the hyperthermia measurements vs the iron content determined from XRD data. (d) Theoretical calculation of the SAR for aligned monodisperse nanocrystals.

magnetic field (see Figure 4d).27 The saturation magnetization was fixed at 200 Am2·kgFe−1 and fexc at 54 kHz according to the experimental conditions. For Keff varying from 5 × 104 to 9 × 104 J·m−3, μ0HC increases from 10 to 30 mT, and the maximum SAR from 400 to 1800 W/g. The comparison of the experimental data with these calculations shows that Keff is reduced by the presence of the iron carbide shell around the iron core, leading to a softer nanomaterial. The main properties of the different samples are summarized in Table 1 of the SI. For the different iron/iron carbide samples, we estimate Keff values in the range of 5.5 to 6.6 104 J·m−1 by using the analytical expressions of μ0HC and μ0HCHyp for aligned particles.29,30 For the iron carbide and iron NPs, only an underestimated value can be given of 6.8 and 12 × 104 J·m−3, respectively, by using the analytical expressions for randomly oriented nanoparticles of μ0HC, since only minor loops have been measured in the available fields. The analysis using the μ0HCHyp values leads to higher values of these two systems 10 and 15 × 104 J·m−3, respectively. More precise experiments are needed to quantify more precisely these latter values. We interpret the softening effect in iron/iron carbide nanocrystals as a consequence of the surface anisotropy reduction of the poorly crystallized iron carbide surface. More refined studies are required to understand the influence of the thickness, crystallinity, and interface in core shell iron/iron carbide on the magnetic anisotropy. These findings are of first importance in the context of hyperthermia. Reducing Keff and keeping high MS allowed us to substantially increase the SAR

measurements of 13 nm metallic Fe nanoparticles are also shown for the sake of comparison. Other samples have been measured and are shown in the Supporting Information (see Figure S8 and Table 1). Interestingly, the iron/iron carbide core/shell nanocrystals exhibit behaviors typical of nanoparticles in the ferromagnetic regime with anisotropy axes aligned along the magnetic field direction.29 This is evidenced by both (i) the abrupt increase of SAR above a critical field (μ0HCHyp) followed by saturation (see Figure 4a) and (ii) the square shape and saturated behavior of the hysteresis loops (see Figure 4b). The behaviors of iron and iron carbide are typical of nanoparticles with anisotropy axis randomly oriented in space:29 the drop in the SAR curve is smoother than for the previous samples. The hysteresis loops of iron carbide and Fe sample, measured in fields up to 40 mT, are characteristic of minor loops with a tilted unsaturated shape. Both hyperthermia and magnetic measurements evidence that the nanoparticle coercive field (μ0HCHyp) is strongly modulated by the carbon content resulting from the synthesis conditions. Figure 4c displays the measured μ0HCHyp versus the metallic iron phase fraction deduced from XRD. Upon increasing the carbon content, the coercive field first decreases and then further increases. To interpret these data, we performed some calculations of the SAR, as a function of the effective magnetic anisotropy constant (Keff) and the amplitude of the alternative magnetic field, considering a system of monodisperse particles with a diameter of 13 nm and an anisotropy axis along the applied 4726


Nano Letters

Letter

efficiency in moderate fields respect to pure iron(0) nanocrystals (see Table 1 of SI). For our best sample (MM2-3), measurements in the current treatment conditions used in Charity Hospital96 kHz and 20 mTlead to SAR = 415 W·g−1 and an hysteresis area A = 4.3 mJ·g−1. This value is 3 times larger than the values reported on the best chemically synthesized nanoparticles.36 Note that, in these conditions, the maximal achievable theoretical SAR value is SARMAX = 4 μ0HmaxσS f ≈ 1600 W·gFe−1 which shows that further improvements are still possible. In summary, we describe in this paper an easy and reproducible low temperature process for the tunable synthesis of monodisperse, high quality iron carbide, and iron/iron carbides nanocrystals, air-stable after some initial losses and displaying excellent magnetic properties with tunable magnetic anisotropy. These particles have no precedent, and the synthesis method based on an organometallic approach deriving from the Fischer−Tropsch mechanism is also original. Interestingly, adjusting the carbon distribution within the nanoparticles offers the possibility to tune finely their magnetic anisotropy. Hence, some of these nanoparticles display the highest efficiency so far reported for magnetic hyperthermia in the current operating treatment conditions. Such a synthetic route based on the reaction of carbonyl based precursors on preformed nanoparticles may be extended to other nanomaterials to refine their magnetic behavior to fulfill more precisely the specifications related to a defined application.

■

L. M. Lacroix for discussions concerning the synthesis procedure, R. P. Tan and J. Dugay for some magnetic and electric characterizations, Stéphanie Blanchandin for Raman measurements (Société Civile Synchrotron Soleil, L’Orme des Merisiers, Saint-Aubin, Gyf sur Yvette). We also thank the CEMES-CNRS laboratory of Toulouse and the French METSA program for giving us access for the high resolution transmission electronic microscopy platform.

■

ASSOCIATED CONTENT

S Supporting Information *

(1) Methods and characterization, (2) chemical synthesis (HADHCl preparation, iron carbide nanoparticles preparation, core/shell iron/iron carbide nanoparticle preparation), (3) TEM image of material obtained from decomposition of Fe(CO)5 in the absence of Fe(0) NPs and in the presence of HDAHCl and HDA at 150 °C under H2, (4) structural analysis (TEM, Mossbauer, HR-TEM, size distribution, XRD-pattern) of core/shell iron/iron carbide nanoparticles, (5) TEM images of different size of iron carbide and core/shell iron/iron carbide nanoparticles, (6) HRTEM analysis of MM1 and MM2, (7) experimental hyperthermia measurements, (8) SAR measurements as a function of size and composition for iron carbide and core/shell iron/iron carbide nanoparticles and magnetic field amplitude, (fixed field frequency fexc = 54 kHz), and (9) normalized hysteresis loops as a function of size and composition for iron carbide and core/shell iron/iron carbide nanoparticles and magnetic field amplitude (fixed field frequency fexc = 54 kHz). This material is available free of charge via the Internet at http://pubs.acs.org.

■

REFERENCES

(1) Lu, A.-H.; Salabas, E. L.; Schuth, F. Angew. Chem., Int. Ed. 2007, 46, 1222−1244. (2) Laurent, S.; Forge, D.; Port, M.; Roch, A.; Robic, C.; Vander Elst, L.; Muller, R. N. Chem. Rev. 2008, 108, 2064−2110. (3) Fortin, J.-P.; Wilhelm, C.; Servais, J.; Ménanger, C.; Bacri, J.-C.; Gazeau, F. J. Am. Chem. Soc. 2007, 129, 2628−2635. (4) Hou, Y.; Xu, Z.; Sun, S. Angew. Chem., Int. Ed. 2007, 46, 6329− 6332. (5) Rutledge, R. D.; Morris, W. H.; Wellons, M. S.; Gay, Z.; Shen, J.; Bentley, J.; Wittig, J. E.; Lukehart, C. M. J. Am. Chem. Soc. 2006, 128, 14210−142111. (6) Barcaro, G.; Sementa, L.; Negreiros, F. R.; Ferrando, R.; Fortunelli, A. Nano Lett. 2011, 11 (12), 5542−5547. (7) Desvaux, C.; Amiens, C.; Fejes, P.; Renaud, P.; Respaud, M.; Lecante, P.; Snoeck, E.; Chaudret, B. Nat. Mater. 2005, 4, 750−753. (8) Chen, H. M.; Liu, R. S. J. Phys. Chem. C 2011, 115 (9), 3513− 3527. (9) Dumestre, F.; Chaudret, B.; Amiens, C.; Renaud, P.; Fejes, P. Science 2004, 303, 821−823. (10) Ciuculescu, D.; Amiens, C.; Respaud, M.; Falqui, A.; Lecante, P.; Benfield, R. E.; Jiang, L.; Fauth, K.; Chaudret, B. Chem. Mater. 2007, 19, 4624−4626. (11) Rinaldi, A.; Licoccia, S.; Traversa, E.; Sieradzki, K.; Peralta, P.; Davila-Ibanez, A. B.; Correa-Duarte, M. A.; Salgueirino, V. J. Phys. Chem. C 2010, 114, 13451−13458. (12) Glavee, G. N.; Klabunde, K. J.; Sorensen, C. M.; Hadjipanayis, G. C. Inorg. Chem. 1995, 34, 28−35. (13) Smit, E.; Cinquini, F.; Beale, A. M.; Safonova, O. V.; Van Beek, W.; Sautet, P.; Weckhuysen, B. M. J. Am. Chem. Soc. 2010, 132, 14928−14941. (14) Torres Galvis, H. M.; Bitter, J. H.; Khare, C. B.; Ruitenbeek, M.; Dugulan, A. I.; de Jong, K. P. Science 2012, 335, 835−838. (15) Sajitha, E. P.; Prasad, V.; Subramanyam, S. V.; Mishra, A. K.; Sarkar, S.; Bansal, C. J. Phys.: Condens. Matter 2007, 19, 1−13. (16) Kim, J. H.; Kim, J.; Park, J. H.; Kim, C. K.; Yoon, C. S.; Shon, Y. Nanotechnology 2007, 18, 1−6. (17) Hermann, I. K.; Grass, R. N.; Mazunin, D.; Stark, W. J. Chem. Mater. 2009, 21, 3275−3281. (18) Shneeweiss, O.; Zboril, R.; David, B.; Hermanek, M.; Mashlan, M. Hyperfine Interact. 2009, 189, 167−173. (19) Nikitenko, S. I.; Koltypin, Y.; Palchik, O.; Felner, I.; Xu, X. N.; Gedanken, A. Angew. Chem., Int. Ed. 2001, 40, 4447−4449. (20) Hermann, I. K.; Grass, R. N.; Mazunin, D.; Stark, W. J. Chem. Mater. 2009, 21, 3275−3281. (21) Amendola, V.; Riello, P.; Meneghetti, M. J. Phys. Chem. C 2011, 115, 5140−5146. (22) Giordano, C.; Kraupner, A.; Wimbush, S. C.; Antonietti, M. Small 2010, 6, 1859−1862. (23) Schnepp, Z.; Wimbush, S. C.; Antonietti, M.; Giordano, C. Chem. Mater. 2010, 22, 5340−5344. (24) Giordano, C.; Erpen, C.; Yao, W.; Milke, B.; Antonietti, M. Chem. Mater. 2009, 21, 5136−5144. (25) De Smit, E.; Swart, I.; Creemer, J. F.; Hoveling, G. H.; Gilles, M. K.; Tyliszczak, T.; Zandbergen, H. W.; Morin, C.; Weckhuysen, B. M.; de Groot, F. M. F. Nature 2008, 456, 222−225. (26) Wust, P.; Gneveckow, U.; Johannsen, M.; Bohmer, D.; Henkel, T.; Kahmann, F.; Sehouli, J.; Felix, R.; Ricke, J.; Jordan, A. Int. J. Hyperthermia 2006, 22, 673−685.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]; [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank InNaBioSanté Foundation, Conseil Regional de Midi-Pyrénées, and ERC Advanced Grant (NANOSONWINGS 2009-246763) for financial support, A. Mari and J.-F. Meunier for magnetic (SQuID and Mössbauer) measurements, 4727


Nano Letters

Letter

(27) Mehdaoui, B.; Meffre, A.; Carrey, J.; Lachaize, S.; Lacroix, L.-M.; Gougeon, M.; Chaudret, B.; Respaud, M. Adv. Funct. Mater. 2011, 21, 4573−4581. (28) Mehdaoui, B.; Meffre, A.; Lacroix, L.-M.; Carrey, J.; Lachaize, S.; Gougeon, M.; Respaud, M.; Chaudret, B. J. Magn. Magn. Mater. 2010, 322, L49−L52. (29) Mehdaoui, B.; Meffre, A.; Lacroix, L.-M.; Carrey, J.; Lachaize, S.; Gougeon, M.; Respaud, M.; Chaudret, B. J. Appl. Phys. 2010, 107, 09A324. (30) Carrey, J.; Mehdaoui, B.; Respaud, M. J. Appl. Phys. 2011, 109, 083921. (31) Lacroix, L.-M.; Lachaize, S.; Falqui, A.; Respaud, M.; Chaudret, B. J. Am. Chem. Soc. 2009, 131, 549−557. (32) Meffre, A.; Lachaize, S.; Gatel, C.; Respaud, M.; Chaudret, B. J. Mater. Chem. 2011, 21, 13464−13469. (33) Peng, S.; Wang, C.; Xie, J.; Sun, S. J. Am. Chem. Soc. 2006, 128, 10676−10677. (34) Lacroix, L.-M.; Carrey, J.; Respaud, M. Rev. Sci. Instrum. 2008, 79, 093909. (35) Mehdaoui, B.; Carrey, J.; Stadler, M.; Cornejo, A.; Nayral, C.; Delpech, F.; Chaudret, B.; Respaud, M. Appl. Phys. Lett. 2012, 100, 052403. (36) Hergt, R.; Hiergeist, R.; Hilger, I.; Kaiser, W. A.; Lapatnikov, Y.; Margel, S.; Richter, U. J. Magn. Magn. Mater. 2004, 270, 345−357.

4728


A Simple Chemical Route toward Monodisperse Iron Carbide

Recommend Documents