Synthesis and Characterization of Elemental Iron and Iron Oxide Nano/Microcomposite Particles by Thermal Decomposition of Ferrocene

DOI 10.1515/ntrev-2012-0061 Nanotechnol Rev 2013; 2(3): 333–357

Review

Daniel Amara and Shlomo Margel * Synthesis and characterization of elemental iron and iron oxide nano/microcomposite particles by thermal decomposition of ferrocene

Abstract: The unique chemical and physical properties difficult to test without an independent measure of the of the nano and microscale materials have led to impor- particle sizes and shapes. With the application of the elec- tant roles in the several scientific and technological fields. tron microscopy to these systems in the 1940s and 1950s, The magnetic nano/microparticles are of great interest the particle sizes, shapes, and distribution information because of its potential applications in, e.g., hyperther- could be readily determined. There was a renewed inter- mia, magnetic resonance imaging (MRI), catalytic appli- est in the finely divided magnetic iron and iron oxides, cations, etc. The decomposition of iron pentacarbonyl as the properties could now be correlated with the sizes is one of the most common methods for the preparation and shapes of the particles. By the early 1960s, the theory of magnetic iron oxide and iron nanoparticles. However, describing the magnetism of the iron nanoparticles was

Fe(CO)5 is severely toxic and alternative precursors should fully formed and had been largely confirmed by experi- be used. Here, we describe the recent advances in the ments [1, 2]. The research on iron and iron oxide nano- synthesis and characterization of the elemental iron and particles has continued since then, but has experienced iron oxide nano/microcomposite particles by the thermal a surge in interest in the recent two decades. This is likely decomposition of ferrocene. The described synthesis pro- due to the new synthetic techniques as well as the interest cess is based on simple nontoxic approaches including, in the new applications of iron and iron oxide nanopar- for example, a solventless process. The particle size and ticles [3 – 6] . The reason for the great interest in the zero- size distribution as well as their composition, crystallin- valent iron nanoparticles arise from its special magnetic ity, shape, and magnetic properties can be controlled via properties [7] . Table 1 shows some of the properties of the the synthesis conditions. ferromagnetic elements; the table clearly demonstrates that iron is the most practical among the various mag- Keywords: Fe nanoparticles; iron oxide nanoparticles; netic elements. Although gadolinium has a higher satura- magnetic nanocomposite; thermal decomposition of tion magnetization magnetic saturation moment (Ms) at ferrocene. 0 K, it has a Curie temperature (Tc) just below the room temperature, making it impractical for use in the majority of the applications. Iron is the most useful among the fer- *Corresponding author: Shlomo Margel, Institute of romagnetic elements; it has the highest magnetic moment Nanotechnology and Advanced Materials, Department of Chemistry, Bar Ilan University, 52900 Ramat Gan, Israel , at room temperature, and a curie temperature that is high e-mail: [email protected] enough for the vast majority of practical applications. In Daniel Amara: Institute of Nanotechnology and Advanced Materials, addition, iron is a widespread element and, therefore, sig- Department of Chemistry, Bar Ilan University, 52900 Ramat Gan, nificantly cheaper than the other ferromagnetic elements Israel such as nickel and cobalt. In addition to this, iron is a very soft magnetic material, in particular, in comparison to cobalt, which has the second-highest room temperature Ms value. In addition, iron also has a low magnetocrys- 1 Introduction talline anisotropy [8, 9] , which is part of what makes the iron nanoparticles such an attractive material to work The magnetic nanoparticles have been studied for many with. The sufficiently small magnetic nanoparticles years. Theories were devised to describe the expected mag- show a superparamagnetic behavior, and the maximum netic properties of the magnetic nanoparticles, but were volume particle that can be superparamagnetic at a given 334 D. Amara and S. Margel: Synthesis and characterization of elemental iron

Table 1 Properties of the ferromagnetic elements. and iron oxide nanoparticles are typically prepared by the decomposition of the soluble iron precursors in solution Element M (emu/g) T (K) S c containing a stabilizer [34] . The decomposition of the iron Fe 218 1043 precursors is accomplished by means such as sonochem- Co 161 1388 istry [35 – 37] , thermal decomposition [38] , electrochemical Ni 54 627 [39] , and laser decomposition [40] . Among the iron precursors, iron carbonyl compounds are very useful, as they can easily be dissociated, and CO is a labile ligand that can temperature varies directly with the magnetocrystalline be removed from the reaction mixture [23, 41] . One of the anisotropy. This means that much larger iron nanoparti- most common method for the preparation of iron oxide cles are superparamagnetic than is the case with cobalt and iron nanoparticles is based on the decomposition of [7, 9]. The moment that a superparamagnetic iron particle iron pentacarbonyl in the organic continuous phase [34, can exhibit (which is the product of the moment per atom 42]. However, Fe(CO) is severely toxic, which is of concern and the number of atoms) is, therefore, much larger than is 5 because of its volatility [43] . This review demonstrates the possible in the case of any other metal. However, the main synthesis of magnetic iron and iron oxides nano/micro- shortcoming of iron is its reactivity [10 – 12] , especially at composite particles with various shapes, by the thermal ambient atmosphere (water and oxygen). This general decomposition of ferrocene. The described synthesis pro- weakness is greatly multiplied in the case of the iron nano- cesses posses simple nontoxic approaches, among them a particles, where the iron rapidly and completely oxidizes solventless process, which is a highly environmental and in air [10] . Maintaining the iron nanoparticles in its zero- economical process. valent state generally limits it to the applications where water and oxygen are largely excluded, or it is maintained in a reducing atmosphere. However, the extreme reactivity of the iron nanoparticles can be beneficial in a non-oxidiz- 2 Synthesis of magnetic ing environment. There are already a number of examples microspheres of iron nanoparticles as catalysts [13 – 17] , and certainly, more will be developed in the near future. In particular, the use of iron as a catalyst primarily involves making 2.1 Sy nthesis of porous superparamagnetic and breaking the carbon-carbon bonds [18] . The forma- and ferromagnetic composite micrometer- tion or cleavage of the carbon-carbon bonds is critical for sized particles of narrow size distribution an enormous number of industrially important chemical prepared by solventless thermal transformations [19] , from the production of clean fuels decomposition of ferrocene [22] to the production of carbon nanotubes (CNTs) [20] . In order to prevent the iron tendency to be oxidized, the Fe The uniform micrometer-sized PS/PDVB (PS/polydivinyl particles should be protected by a protective layer, e.g., benzene) composite particles were formed by a single-step carbon [21 – 23] , silica [24, 25], alumina [26] , etc. Recently, swelling process at room temperature of the PS template a few publications describe the synthesis of iron oxide particles of 2.35 ± 0.1 μ m (prepared as described in the magnetic silica particles by entrapment of iron nitrate literature) [44] with dibutyl phthalate (DBP) (a swelling within the mesopores of the silica particles, followed by solvent), droplets containing divinyl benzene (DVB) and impregnation with ethylene glycol and then annealing benzoyl peroxide (BP) (DVB as a crosslinker monomer and at 450° C [27] . Although iron oxide posses poor magnetic BP as an initiator), followed by the polymerization of the properties compared to the zero-valent iron [23] , magnet- DVB within the swollen PS template particles at elevated γ ite (Fe3 O4 ) and maghemite ( – Fe2 O3 ) particles are useful temperature. In a typical experiment, the PS template for biomedical applications [28, 29]. The applications of microspheres of 2.35 ± 0.1 μm were swollen up to 7.6 ± 0.6 μ m these iron oxide particles rely upon its biocompatibility by adding to a 20-ml vial containing 10 ml of a sodium [30] . The size, shape, composition, and structure of the dodecyl sulfate (SDS) aqueous solution (0.75% w/v) and magnetic particles are the key factors that determine their 1.5 ml of DBP containing 10 mg of BP and 1.5 ml of DVB. The magnetic properties (ferromagnetic, superparamagnetic, emulsion droplets of the swelling solvent were then formed etc.) [4, 31 – 33] . Thus, there is a great interest in the devel- by sonication (Sonics and Materials, model VCX-750, opment of simple and economical synthesis methods for Ti-horn 20 kHz) of the mixture for 1 min. An aqueous dis- the preparation of iron and iron oxides nanoparticles. Iron persion (3.5 ml) of the PS template microspheres (7% w/v) D. Amara and S. Margel: Synthesis and characterization of elemental iron 335

α ° ° was then added to the stirred DBP emulsion. After the PDVB/ -Fe2 O3 microspheres at 500 C and 800 C, respec- swelling of the PS particles was completed, and the tively, under argon atmosphere. Figure 1 summarizes the mixture did not contain any small droplets of the emul- preparation scheme of the uniform superparamagnetic sified swelling solvent, as verified by optical microscopy, PDVB/iron oxide, C/iron oxide, and C/Fe3 O4 /Fe compo site the diameter of the swollen microspheres was meas- microspheres. First, PS/PDVB composite particles were ured. For the polymerization of the monomers within the prepared by a single-step swelling of the uniform PS tem- swollen particles, the temperature of the shaken vial con- plate microspheres dispersed in an aqueous continuous taining the swollen particles was raised to 73° C for 24 h. phase with the emulsion droplets of DBP containing the The produced composite microspheres were then washed initiator BP and the crosslinker monomer DVB. The PS/ from undesired reagents by the extensive centrifugation PDVB composite particles of narrow size distribution were cycles with water, ethanol, and water again. The obtained then formed by polymerizing the DVB within the swollen particles were then dried by lyophilization. PS template microspheres at 73° C. The uniform porous The uniform crosslinked micrometer-sized PDVB par- PDVB microspheres were then prepared by the dissolu- ticles were prepared by dissolving the PS template part of tion of the PS template part of the former composite par- the PS/PDVB composite particles with Dimethylformamide ticles. The uniform superparamagnetic PDVB/iron oxide (DMF). Briefly, the PS/PDVB particles prepared as described composite microspheres were then prepared by entrap- in the previous paragraph were dispersed in 50 ml of DMF ping by vacuum sodium acetate and then ferrocene within and then shaken at room temperature for ca. 15 min. The these microspheres. At this stage, the solid mixture was dispersed particles were then centrifuged, and the super- annealed in a sealed cell at 300° C for 2 h under ambient natant containing the dissolved PS template polymer was atmosphere. The produced superparamagnetic PDVB/ discarded. This procedure was repeated five times with iron oxide composite microspheres were then washed of DMF. The obtained PDVB particles were washed twice the excess reagents, e.g., sodium acetate, with an excess with ethanol and water and then dried by lyophilization. mixture of water and THF (2:1 v/v). The ferromagnatic α The PDVB/ -Fe2 O3 composite particles were prepared as C/Fe3 O4 and C/Fe3 O4 /Fe composite microspheres were follows: 100 mg of the dried PDVB microspheres was added formed by annealing the PDVB/iron oxide composite par- to a two-neck round bottom flask equipped with a septum. ticles at 500° C or 700° C, respectively, for 2 h under inert The flask was then evacuated using an oil vacuum pump atmosphere. Figure 2 shows, by the low and high magnifi- for 1 h, after which 1 ml of a 0.25-m solution of FeCl2 · 4H2 O cation of the SEM pictures, the perfect spherical shape and THF was injected into the flask. The microspheres con- narrow size distribution of the PS (A and B) and the PDVB α taining the iron salts were then dried. The PDVB/ -Fe2 O3 (C and D) microspheres. The size and size distribution of microspheres were then produced by annealing these these particles are 2.35 ± 0.1 and 5.5 ± 0.1 μ m, respectively. ° microspheres at 250 C under ambient atmosphere. C/Fe3 O4 Figure 2 also illustrates that the surface of the PS template and the C/Fe microspheres were formed by annealing the microspheres has a smooth nonporous morphology (B),

PS Swollen PS PS/PDVB PDVB PDVB/NaAc PDVB/NaAc/Ferrocene

Swelling DVB DMF NaAC Ferrocene 300°C DVB BP Polymerization Vacuum BP

C/iron oxide

PDVB/NaAc/iron oxide PDVB/iron oxide 500°C THF Ar H2O 700°C C/Fe3O4/Fe Ar

Figure 1 The schematic scheme illustrating the synthesis of the various magnetic composite microspheres prepared by the solventless thermal decomposition of ferrocene. 336 D. Amara and S. Margel: Synthesis and characterization of elemental iron

A B

Figure 2 The low- and high-magnification SEM photomicrographs of the PS (A, B) and PDVB (C, D) microspheres. while that of the PDVB microspheres is rough and porous from the polymer particles [21] . Second, the dissolution (D). The increased roughness and porosity of the PDVB of the PS template part of the composite PS/PDVB microparticles are expressed by an increased surface area from spheres also generates the macropores within the PDVB 2.7 m2 /g, for the PS template microspheres, to 657 m2 /g particles. Figure 3 presents the low and high magnifica- for the PDVB microspheres (see Table 2 ). The measured tion SEM images of the composite microspheres annealed surface area of the PS template microspheres with a 2.45-μ m at 300° C (A and B), 500° C (C and D), and 700° C (E and F). average diameter is similar to the calculated surface area Table 2 summarizes the size, surface area, and elemental of the spherical-shaped particles with a density of 1.0 g/ml composition, including the [Fe[/[O] mole ratio of the PDVB and the same size (A = 4 π r 2 ), indicating the nonporous and these composite microspheres. Table 2 shows that the structure of these PS microspheres. The high surface area annealing of the PDVB particles containing the ferrocene and porosity of the PDVB microspheres are probably due at 300° C did not change the size and size distribution of to two main reasons. First, the swelling solvent DBP serves the particles (5.5 ± 0.1 and 5.5 ± 0.2 μ m, respectively), while as a porogen that forms macropores. Thus, the pores are the surface area decreased (657 and 512 m2 /g, respectively). formed in the spaces where the porogen was extracted These results may indicate that the ferrocene mainly

Table 2 Elemental analysis, size and size distribution, and BET surface area of the PDVB, PDVB/iron oxide, C/iron oxide, and C/Fe3 O4 /Fe composite microspheres.a

Microspheres and annealing temperature Size (μ m) Surface area (m 2/g) Mass % [Fe]/[O] (mol/mol)

CH OFea

PDVB 5.5 ± 0.1 657 91.5 8.2 1.3 0 – PDVB/ferrocene at 300° C 5.5 ± 0.2 512 69.7 6.6 8.5 15.2 0.5 PDVB/ferrocene at 500° C 2.7 ± 0.4 342 56.3 1.1 11.4 27 0.7 PDVB/ferrocene at 700° C 1.7 ± 0.3 145 26.3 0 14.5 59.2 1.1 a The Fe concentration was calculated by reducing from 100 the sum of the other elements. D. Amara and S. Margel: Synthesis and characterization of elemental iron 337

A B

C D

Figure 3 The low and high magnification SEM images of the composite microspheres annealed at 300° C (A and B), 500° C (C and D), and 700 ° C (E and F). penetrated into the PDVB particles ’ pores, so that the iron the C content for the particles annealed at 300° C decreased oxide formed at 300° C was generated there, thus leading from 69.7% to 56.3% and 26.3% for the particles annealed to the same diameter and decreased surface area. Figure at 500° C and 700° C, respectively. This decomposition 3 and Table 2 also illustrate the spherical shape and the of the particles as the annealing temperature increases decrease in the diameter and the surface area of the com- leads to the collapse of the inner structure of the parti- posite microspheres as a function of the increased anneal- cles, resulting, thereby, in the decrease in the surface ing temperature, e.g., the size of the particles annealed at area of these composite particles. The XRD patterns and 300° C, 500° C, and 700° C is 5.5 ± 0.2, 2.7 ± 0.4, and 1.7 ± 0.3 Mossbauer spectroscopy measurements of the composite μm, respectively, and the surface area is 512, 342, and 145 microspheres were demonstrated in the iron oxide phases, m 2 /g, respectively. The decrease in the size is due to the which are not well crystallized for the particles obtained increased thermal degradation of the microspheres as the at 300° C and 500° C. However, it was impossible to deter- annealing temperature increases, as illustrated in Table 2 mine whether it was the magnetite (Fe 3 O4 ) or maghemite γ by the significant decrease in the C and H contents, e.g., ( -Fe2 O3 ), due to the similarity in their unit cell parameters, 338 D. Amara and S. Margel: Synthesis and characterization of elemental iron

which leads to a similarity in the XRD patterns of these two oxide, C/iron oxide, and C/Fe3 O4 /Fe composite micro- oxides. On the other hand, the XRD pattern of the microspheres, are 0.5, 0.7, and 1.1, respectively. The increased spheres annealed at 700° C demonstrated the crystalline [Fe]/[0] mole ratio of the C/iron oxide particles obtained ° materials that match the spinel Fe3 O4 crystal structure and by annealing the PDVB/iron oxide particles at 500 C is the body centered cubic (bcc) Fe structure, which was also due to the reduction of the iron oxide at the higher oxi- ° confirmed by the Mossbauer spectroscopy. Table 2, indeed, dation state, e.g., Fe2 O3 , obtained at 300 C to magnetite, exhibits that part of the iron oxide phase obtained for the according to the following reaction: [45] composite particles annealed at 300° C and 500° C were 6Fe O + C→ 4Fe O + CO . partially reduced to a zero-valent iron at 700 °C. This can 2 3 3 4 2 be explained by the following reaction [45] : The increased [Fe]/[0] mole ratio of the C/Fe3 O4 /Fe composite microspheres obtained at 700° C is due to the Fe O + 2C→ 3Fe+ 2CO . 3 4 2 reduction of part of the magnetite phase to a zero-valent Part of the carbon formed by the carbonization of the Fe phase, as shown in the above equation. PDVB microspheres (see Table 2) served as the reducing Figure 4 A – C and Table 3 represent the magnetization agent of the iron oxide to form the elemental Fe and CO 2 , properties measured at 300 and 5 K of the PDVB/iron oxide as illustrated in the above equation. This formed carbon (A), C/iron oxide (B), and C/Fe3 O4 /Fe (C) composite micro- ° ° ° also protects the Fe, as well as the Fe3 O4 particles, against spheres obtained at 300 C, 500 C, and 700 C, respectively. the oxidation by air, thus preserving the particles ’ mag- Generally, increasing the annealing temperature resulted netic properties. Moreover, Table 2 indicates, as previously in the increase in the magnetic saturation moment (Ms) mentioned, that the [Fe]/[0] mole ratios of the PDVB/iron and coercivity at both 5 and 300 K. For example, at 5 K, the

A 10 B 20 300 K 300 K 5 10 0 0 -5 -10 -10 -20 10 20 5 K 5 K M (emu/g) 5 M (emu/g) 10 0 0 -5 -10 -10 -20 -20,000 -10,0000 10,000 20,000 -20,000 -10,0000 10,000 20,000 H (Oe) H (Oe)

C 60 40 300 K 20 0 -20 -40 -60 40 5 K M (emu/g) 20 0 -20 -40 -60 -20,000 -10,0000 10,000 20,000 H (Oe)

Figure 4 The magnetization (M) vs. magnetic field (H) at 300 and 5 K of the PDVB/iron oxide (A), C/iron oxide (B), and C/Fe3 O4 /Fe (C) composite microspheres. D. Amara and S. Margel: Synthesis and characterization of elemental iron 339

Table 3 Magnetic properties of the PDVB/iron oxide, C/iron oxide, the superparamagnetic behavior of these microspheres. and C/Fe3 O4 /Fe composite microspheres. On the other hand, the ZFC and FC curves of the C/iron

oxide and the C/Fe3 O4 /Fe composite microspheres merge Microspheres Magnetization (emu/g) Coercivity (Oe) above 300 K, indicating the ferromagnetic behavior of 300 K 5 K 300 K 5 K these particles (not shown here). Further evidence for the PDVB/iron oxide 8.3 9.8 0 190 superparamagnetic nature of the PDVB/iron oxide parti- C/iron oxide 19.5 22.1 0 370 cles and the ferromagnetic nature of the C/iron oxide and C/Fe O /Fe 55.5 58 170 340 3 4 C/ Fe3 O4 /Fe particles may be the size of the nanoparticles entrapped within these composite microspheres. The magnetic moments and the coercivities of the composite superparamagnetic behavior is typical for the nanosized particles annealed at 300° C, 500° C, and 700° C were 9.8, magnetic particles. The upper superparamagnetic volume V 22.1, and 58 emu/g and 190, 370, and 340 Oe, respectively. ( p) of a magnetic particle can be calculated by the follow- Similarly, the hysteresis increases slightly as the annealing Eq [46] : ing temperature increases, as shown in Figure 4. Table 25⋅⋅Tk 3 and Figure 4 also show that the composite particles V = B , P K annealed at 300° C, 500° C, and 700° C (PDVB/iron oxide u and C/iron oxide, C/Fe3 O4 /Fe, respectively) exhibit hys- V teresis when measured at 5 K. Similarly, when measured where p is the upper superparamagnetic volume of ° at 300 K, the particles annealed at 700 C (C/Fe3 O4 /Fe) a magnetic particle, kB is the Boltzmann’ s constant, T also exhibit hysteresis. On the other hand, no hysteresis is the temperature, and Ku is the anisotropy constant was observed for the particles annealed at 300° C and [-1.1 × 105 , 1.35 × 10 5, and 4.8 × 105 for maghemite, magnet- 500 ° C (PDVB/iron oxide and C/iron oxide, respectively) ite, and zero-valent iron, respectively]. The upper diam- when measured at 300 K. These results indicate that the eters of the superparamagnetic maghemite, magnetite, PDVB/iron oxide and the C/iron oxide composite particles and zero-valent iron nanoparticles are 26, 24, and 18 nm, obtained at 300° C and 500° C, respectively, may be super- respectively [46] . Indeed, Figure 6 demonstrates by cross- paramagnetic. In order to examine this possibility, tem- sectional typical TEM pictures that for the PDVB/iron perature-dependent magnetic-moment measurements of oxide composite particles, the iron oxide nanoparticles these composite particles were made. Figure 5 shows the entrapped within the PDVB matrix are of 15– 22 nm (Figure field cooled (FC) and zero field cooled (ZFC) curves of the 6A– B), while for the C/iron oxide and the C/Fe3 O4 /Fe PDVB/iron oxide composite microspheres measured from particles, the iron oxide nanoparticles entrapped within T 5 to 300 K at 100 Oe. The two curves merge at b of 150 K the C matrix are 50– 70 nm (Figure 6C) and 80– 120 nm and overlap completely at higher temperatures, indicating (Figure 6D), respectively. The structure of the iron oxide nanoparticles was also investigated in the high-resolution electron microscope (HRTEM) mode. Figure 7 shows a 1.2 cross-sectional HRTEM image of a typical single superparamagnetic nanoparticle entrapped within the PDVB 1.0 T FC b matrix. This micrograph clearly demonstrates the lattice fringe of the iron oxide nanoparticle. The measured size 0.8 of this nanoparticle is about 20 nm, which is in good ZFC agreement with the cross-sectional typical TEM pictures 0.6 (Figure 8 ) that may explain the superparamagnetic behav- M (emu/g) ior of the PDVB/iron oxide composite microspheres. The 0.4 sodium acetate was used as a separating media between 0.2 the formed iron oxide nanoparticles embedded within the PDVB matrix, thereby enabling the production of 0 these individual supeparamagnetic particles. The sodium 0 50 100 150 200 250 300 350 acetate was then washed from the magnetic particles by Temperature (K) extensive centrifugation cycles with a mixture of THF and water. The ferromagnetic C/iron oxide and C/Fe O /Fe Figure 5 The zero field-cooled (ZFC) and field-cooled (Fc) tem- 3 4 perature-dependent magnetization curves of the PDVB/iron oxide composite microspheres were then formed by annealing composite microspheres. the superparamagnetic PDVB/iron oxide microspheres at 340 D. Amara and S. Margel: Synthesis and characterization of elemental iron

A B

500 nm 200 nm

0.2 μm 0.5 μm

Figure 6 The cross-sectional TEM pictures of the PDVB/iron oxide (A and B), C/iron oxide (C), and C/Fe3 O4 /Fe (D) composite microspheres.

500 ° C and 700° C, respectively, under argon atmosphere. 2.2 Synthesis of superparamagnetic This thermal decomposition leads to the decomposition core-shell micrometer-sized particles of of the PDVB/iron oxide composite microspheres, thus, narrow size distribution prepared by a causing the formation of the ferromagnetic particles by swelling process [47] the partial agglomeration of the iron oxide and Fe nanoparticles within the C matrix. The uniform micrometer-sized core-shell PS/(PDVB/ ferrocene) and PS/(P(S-DVB)/ferrocene) composite particles were formed by a room temperature single-step swelling process of the PS template particles with toluene (a swelling solvent) containing S (styrene) and DVB as monomers, AIBN as initiator, and ferrocene, followed by the polymerization of the S and/or DVB at the elevated temperature within the swollen particles. In a typical experiment, the PS template microspheres of 2.35 ± 0.1 μ m were swollen up to 7.6 ± 0.6 μ m (as was observed by light microscopy) by adding to a 20-ml vial containing 10 ml of SDS aqueous solution (0.75% w/v), 2 ml of toluene containing 10 mg AIBN, 400 mg ferrocene, and 1.5 ml DVB or 1.5 ml of a mixture of DVB and S, wherein the [DVB]/ [S] volume ratio was altered: 1/1, 2/1, or 1/2. The emulsion droplets of the swelling solvent were then formed by the Figure 7 The cross-sectional HRTEM of a typical single superpara- sonication of the mixture for 1 min. An aqueous disper- magnetic particle entrapped within the PDVB matrix. sion (3.5 ml) of the PS template microspheres (7% w/v) D. Amara and S. Margel: Synthesis and characterization of elemental iron 341

PS/PDVB/Fe O ; 3 4 PDVB/Fe O ; PS/(PDVB/ferrocene); 3 4 PS Swollen PS PS/P(S-DVB)/Fe3O4 C/Fe PS/P(S-DVB)/ferrocene) P(S-DVB)/Fe3O4

Swelling DVB/S 330°C DMF 450°C AIBN Polymerization Tolune, DVB/S, Ferrocene H2 AIBN, Ferrocene

Figure 8 The schematic scheme illustrating the synthesis of the various magnetic composite microspheres prepared by the swelling process. was then added to the stirred toluene emulsion. After the stabilized by SDS, followed by the polymerization of the swelling of the template particles was completed, and the monomer/s within the swollen template PS microspheres. mixture did not contain any small droplets of the emulsi- The magnetic micrometer-sized PDVB/Fe3 O4 and P(S- fied swelling solvent, as verified by light microscopy, the DVB)/Fe3 O4 composite particles of narrow-size distribu- diameter of the swollen microspheres was measured. For tion were then formed by the decomposition of ferrocene the polymerization of the monomers within the swollen entrapped within the various composite microspheres at particles, the temperature of the shaken vial contain- 330 ° C in a stainless steel sealed cell, followed by the dis- ing the swollen particles was raised to 73° C for 24 h. The solution of the PS part with DMF. The magnetic uniform composite microspheres produced were then washed C/Fe micrometer-sized particles of narrow size distribu- from the undesired reagents by the extensive centrifugation were formed by the reduction of the Fe3 O4 nanopar- tion cycles with water, mixture of water and ethanol, and ticles entrapped within the PDVB/Fe3 O4 particles with again water. The obtained composite particles were then hydrogen at 450° C. Figure 9 demonstrates, by the low- and dried by lyophilization. high-magnification SEM pictures, the spherical shape and

The uniform superparamagnetic micrometer-sized narrow size distribution of the PDVB/Fe3 O4 (A, B) and P(S-

PDVB/Fe3 O4 oxide and P(S-DVB)/Fe3 O4 composite par- DVB)/Fe3 O4 micrometer-sized particles prepared at [DVB]/ ticles were formed by annealing of the PS/(PDVB/fer- [S] volume ratio of 1:1 (C, D). Figure 2 shows that the size rocene) and PS/(P(S-DVB)/ferrocene) composite micro- of the PS particles is 2.35 ± 0.1 μ m, while that of the PDVB/ spheres prepared at [DVB]/[S] volume ratios of 2:1 and 1:1 Fe3 O4 and P(S-DVB)/Fe3 O4 particles is significantly higher at 330° C for 2h in a stainless steel sealed cell. The various and the same: 6.0 ± 0.1 μm. It should be noted that the microspheres were then dispersed in 50 ml of DMF and measured size and size distribution of the P(S-DVB)/Fe3 O4 shaken at room temperature for 15 min. The dispersed composite microspheres prepared at [DVB]/[S] volume particles were then centrifuged and the supernatant con- ratios of 2:1 and 1:2 was also 6.0 ± 0.1 μm (see Table 4 ). It taining the dissolved PS template polymer was discarded. can, therefore, be concluded that neither the size nor the This procedure was repeated five times with DMF. The size distribution of the various composite microspheres obtained PDVB/Fe3 O4 and P(S-DVB)/Fe3 O4 composite par- is significantly changed by the adjustment of the [DVB]/ ticles were then washed twice with ethanol and water and [S] volume ratios. The surface of the PS template micro- then dried by lyophilization. The uniform ferromagnetic spheres has a smooth nonporous morphology (as showed micrometer-P(S-DVB)/Fe3 O4 composite particles were in the previous section), while that of the PDVB/Fe3 O4 formed similarly, substituting the volume ratio [DVB]/[S] and PDVB/P(S-DVB)/Fe3 O4 particles are rough and highly from 2:1 and 1:1 to 1:2. The uniform C/Fe micrometer-sized porous (B, D). The increased roughness and porosity of particles were formed by annealing the PDVB/Fe3 O4 parti- the PDVB-derived composite particles is expressed by the cles at 450° C under hydrogen atmosphere for 2 h. Figure 8 increased surface area (see Table 4) from 2.7 m2 /g for the summarizes the synthesis scheme through which the PS template microspheres to 450, 157, 96 and 84 m2 /g for various uniform magnetic micrometer-sized particles the PDVB/Fe3 O4 and the P(S-DVB)/Fe3 O4 composite parti- were prepared. First, the uniform micrometer-sized PS/ cles prepared at [DVB]/[S] volume ratios of 2:1, 1:1, and 1:2, (PDVB/ferrocene) and PS/(P(S-DVB)/ferrocene) compo- respectively. The reasons for the increase in the surface site particles were prepared by swelling of the uniform PS area are explained in the previous section. Table 4 dem- template microspheres dispersed in an aqueous continu- onstrates the mass % of C, H, O, and Fe, as well as the ous phase with the emulsion droplets of toluene contain- size and size distribution of the different composite micro- ing the initiator AIBN and the monomers S and/or DVB spheres. A simple calculation indicates that the weight 342 D. Amara and S. Margel: Synthesis and characterization of elemental iron

A B

20 μm 3 μm

Figure 9 The low and high magnification SEM pictures of the PDVB/Fe3 O4 (A, B), P(S-DVB)/Fe3 O4 micrometer-sized particles prepared at [DVB]/[S] volume ratio of 1:1 (C, D) and of the C/Fe micrometer-sized composite particles (E, F).

Table 4 Size and size distribution and BET surface area of the C/Fe and the PDVB/Fe3 O4 and P(S-DVB)/Fe3 O4 composite microspheres prepared in the presence of different [DVB]/[S] volume ratios.a

Microspheres [DVB]/[S] (ml/ml) Size (μ m) Surface area (m 2/g) Mass %

b C H O Fe Fe3 O4 ± PDVB/Fe3 O4 1.5/0 6.0 0.1 450 80.5 6.6 3.6 9.3 12.9 ± P(S-DVB)/Fe3 O4 1/0.5 6.0 0.1 157 80.9 6.8 3.4 8.9 12.3 ± P(S-DVB)/Fe3 O4 0.75/0.75 6.0 0.1 96 79.1 6.8 3.8 10.3 14.1 ± P(S-DVB)/Fe3 O4 0.5/1 6.0 0.1 84 77.4 6.5 4.5 11.6 16.1 C/Fe – 4.2 ± 1.4 147 66.3 1 0.8 32.9 –

a The various composite micrometer-sized magnetic particles were prepared in the presence of 1.5 ml DVB or 1.5 ml (DVB+ S) at different ° [DVB]/[S] volume ratios. The C/Fe composite microspheres were prepared by annealing the PDVB/Fe3 O4 particles at 450 C under hydrogen atmosphere.b The Fe concentration was calculated by reducing from 100 the sum of the other elements. D. Amara and S. Margel: Synthesis and characterization of elemental iron 343 ratio of [Fe]/[O] in magnetite is 2.6/1. Thus, the % mag- nanoparticles within the various composite microspheres netite content of the PDVB/Fe3 O4 and the P(S-DVB)/Fe3 O4 is mainly magnetite, as also demonstrated by the FTIR composite particles obtained at [DVB]/[S] volume ratios and XRD measurements. The weight ratio of [C]/[H] for of 2:1, 1:1, and 1:2 are 12.9%, 12.3%, 14.1%, and 16.1%, these samples are 12.2, 11.9, 11.6, and 11.9, respectively. respectively. The [Fe]/[O] weight ratios values for the These ratios are almost the same as those calculated various composite microspheres are 2.6, 2.6, 2.7, and 2.5, for the pure PS and PDVB ((C10 H10 )n and (C8 H8 )n , respec- respectively. Thus, the elemental analysis supplies further tively). Figure 10 demonstrates the typical low- and high- evidence that the iron oxide phase of the entrapped magnification cross-sectional TEM pictures of the PDVB/

Figure 10 The cross-sectional TEM pictures of the PDVB/Fe3 O4 (A – B) and the P(S-DVB)/Fe3 O4 composite microspheres prepared at the [DVB]/[S] volume ratio of 1:1 (C, D) and of the C/Fe micrometer-sized composite particles (E, F). 344 D. Amara and S. Margel: Synthesis and characterization of elemental iron

Fe3 O4 (A, B) and P(S-DVB)/Fe3 O4 composite microspheres Fe3 O4 microspheres were reduced to the zero-valent iron prepared at [DVB]/[S] volume ratio of 1:1 (C, D). These pic- due to the hydrogen treatment at an elevated temperature. tures clearly demonstrate the presence of the Fe3 O4 nano- This can be explained by the following reaction [48]: particles of 16.4 ± 2.1 and 23 ± 3.2 nm diameter, respectively, Fe O + 4H → 3Fe+ 4H O. caged in the entire PDVB matrix. The measured size and 3 4 2 2 size distribution of the nanoparticles entrapped within Figure 10E – F demonstrate the typical low (E) and the P(S-DVB)/Fe3 O4 composite microspheres prepared at high (F) magnification cross-sectional TEM pictures of the [DVB]/[S] volume ratios of 2:1 and 1:2 were 19 ± 3.5 and the C/Fe composite microspheres. These pictures clearly 34 ± 2.9 as shown in Table 5 . It can be deduced from the show the presence of the iron nanoparticles of 17.9 ± 3.9 nm size measurements of the entrapped magnetic nanopar- diameter caged in the entire carbon matrix (see Table 5). ticles within the various composite microspheres that the As previously discussed, the C/Fe composite particles size of the entrapped Fe3 O4 nanoparticles within the com- were prepared by reducing the Fe3 O4 entrapped within the ° posite particles decreases as the DVB content increases. PDVB/Fe3 O4 composite particles at 450 C. The comparison This can be explained by the entrapment of the ferrocene of Figure 10E – F with Figure 10A – B clearly illustrates that molecules by the PDVB or P(S-DVB) matrices. These rigid the size of the nanoparticles within the composite par- matrices may limit the growth of the Fe3 O4 nanoparticles. ticles’ matrix was relatively retained, and the hydrogen Thus, the particle size is influenced by the DVB content, reduction at 450° C did not lead to damage or aggregation so that the Fe3 O4 nanoparticle size can be controlled by of these nanoparticles. We believe that the rigid cage of adjusting the [DVB]/[S] volume ratio during the PS parti- the PDVB surrounding the entrapped Fe3 O4 nanoparticles cles swelling process. retained their size even at elevated temperatures such as ° The air-stable C/Fe composite micrometer-sized parti- 450 C in a hydrogen atmosphere. The M s as well as the cles of narrow size distribution were formed by annealing coercive fields obtained are summarized in Table 6 . At 300 ° the PDVB/Fe3 O4 particles at 450 C under a H2 atmosphere. K, the superparamagnetic behavior was observed for the

The typical low- and higher-magnification SEM pictures of PDVB/Fe3 O4 , P(S-DVB)/Fe3 O4 prepared at [DVB]/[S] volume the C/Fe composite particles are presented in Figure 2E – F. ratios of 2:1 and 1:1 due to the small size of the nanoparti- These figures clearly show the rough porous structure of cles entrapped within the various composites. However, the C/Fe composite microspheres. Table 4 indicates that for the P(S-DVB)/Fe3 O4 prepared at the [DVB]/[S] volume the formation of these C/Fe composite particles from the ratio of 1:2, the ferromagnetic behavior was observed.

PDVB/Fe3 O4 particles leads to the decrease in their size The measured size and size distribution of the nanopar- from 6.0 ± 0.1 to 4.2 ± 1.4 μ m and in the surface area from 450 ticles entrapped within this composite microspheres is to 147 m 2/g, respectively. This change in the size, rough- 34 ± 2.9 nm, which is higher from the upper diameter of a ness, and surface area can be attributed to the thermal spherical superparamagnetic magnetite particles (24 nm degradation of the PDVB part in the composite particles, as demonstrated previously). The Ms values obtained at which leads to the collapse of the rough porous structure 5 K for the PDVB/Fe 3 O4 , P(S-DVB)/Fe3 O4 prepared at the of the cross-linked microspheres. The pattern matches the [DVB]/[S] volume ratios of 2:1, 1:1, and 1:2 and for the crystal structure of bcc Fe. The XRD pattern demonstrated C/Fe micrometer-sized composite particles are 8.6, 11.2, that the Fe3 O4 nanoparticles entrapped within the PDVB/ 13.4, 14, and 37.3 emu/g, respectively (see Table 5). The

Table 5 Magnetic properties of the PDVB/Fe3 O4 , P(S-DVB)/Fe3 O4 prepared in the presence of the different [DVB]/[S] volume ratios and the C/Fe composite microspheres. a

Microspheres [DVB]/[S] Entrapped magnetic Magnetization (emu/g) Coercivity (Oe) Tb (ml/ml) nanoparticles diameter (nm) 300 K 5 K 300 K 5 K ± PDVB/Fe3 O4 1.5/0 16.4 2.1 7.5 8.6 – 300 85 ± P(S-DVB)/Fe3 O4 1/0.5 19 3.5 9.7 11.2 – 345 104 ± P(S-DVB)/Fe3 O4 0.75/0.75 23 3.2 11.8 11.3 – 360 120 ± P(S-DVB)/Fe3 O4 0.5/1 34 2.9 13.4 14 182 325 – C/Fe – 17.9 ± 3.9 35.0 37.3 – 440 220 a The various composite micrometer-sized magnetic particles were prepared in the presence of 1.5 ml DVB or 1.5 ml (DVB+ S) at the different [DVB]/[S] volume ratios. ° The C/Fe composite microspheres were prepared by annealing the PDVB/Fe3 O4 particles at 450 C under hydrogen atmosphere. D. Amara and S. Margel: Synthesis and characterization of elemental iron 345

Table 6 Elemental analysis, size, and size distribution of the nanocubes/spheres obtained by annealing the different ratios of ferrocene and PVP mixtures for different time periods.a

[Ferrocene]/ Annealing Size Mass % [PVP] (w/w) time (h) (nm) + C O N Fe [Fe3 O4 ]/[Fe3 O4 PVP] 1:1 2 49 ± 4.0 31.1 21.6 6.5 37 51 1:2 2 41 ± 5.2 46.5 18.4 8.9 20.3 28 1:5 2 29 ± 3.4 54.2 17.4 10.6 11.5 – 1:5 4 32 ± 5.4 57 16.1 11 8.8 12.1 a The size of the nanocubes and the nanospheres relates to the diagonal length of the cubes and the diameter of the spheres, respectively. The Fe amount was calculated by reducing the sum of the other elements from 100.

merging temperature of the two ZFC/FC branches is collected. The obtained magnetite nanocubes were then T defined as the blocking temperature ( b ) of the super- washed from the excess reagents by the extensive centrif- T paramagnetic particles. The measured b are summarized ugation cycles with ethanol. The Fe3 O 4 nanospheres were T in Table 5. As expected, the b values depend directly on obtained by a similar solventless process by increasing the the size of the magnetic nanoparticles entrapped in the annealing time to 4 h at a [PVP] [ferrocene] weight ratio of polymeric particles. Indeed, the PDVB/Fe3 O4 possess the 5:1. The PVP was used as a separating media and stabilizer T T lowest b value of 85 K, whereas the b values for the of the formed iron oxide nanocubes/spheres. The TEM

P(S-DVB)/Fe3 O4 composite microspheres prepared at the images of the nanocubes obtained by thermal decomposi- [DVB]/[S] volume ratios of 2:1 and 1:1 are 104 and 110 K. tion at 350° C for 2 h of the solid mixtures of ferrocene and These values are very close due to the similarity in the PVP of weight ratios of 1:1, 1:2, and 1:5 are presented in Figure size of these entrapped Fe3 O4 nanoparticles. On the other 11 A – C, respectively. The images demonstrate the cubic mor- hand, the C/Fe composite particles possess a relatively phology of the obtained nano-iron oxides. Moreover, the T high b value (220 K), which can be attributed to the fact images clearly demonstrate that the size of the nanocubes that the size of the entrapped Fe particles is very close to depends directly on the [ferrocene]/[PVP] weight ratio. The the upper diameter of the superparamagnetic zero-valent nanocubes ’ size, as measured by the diagonal length of the ± ± ± iron. The FC and the ZFC curves of the P(S-DVB)/Fe3 O4 cubes, decreased from 49 4 to 41 5.2 and 29 3.4 nm as composite microspheres prepared at the [DVB]/[S] volume the [ferrocene]/[PVP] weight ratio decreased from 1:1 to 1:2 ratio of 1:2 tend to merge above the room temperature as and 1:5, respectively (see Table 6). It should be noted that expected for the ferromagnetic particles. the ferrocene has a boiling point of 249 ° C, and the various nanocubes were formed at 350° C. Thus, the decomposition of the ferrocene was accomplished in the gas phase, resulting in the formation of the nanocubes in the PVP domain. 3 Synthesis of magnetic This process is actually a chemical vapor deposition (CVD) nanoparticles reaction in which the ferrocene is the volatile precursor, and the PVP is the solid substrate. Moreover, the TEM images clearly demonstrate the individual nanocubes for 3.1 Synthesis of magnetite nanocubes and the various samples. This may suggest that the solid PVP nanospheres prepared by solventless matrix is used in this process as a separating media during thermal decomposition of ferrocene [49] the decomposition of the ferrocene to form the iron oxide nanocubes. It is remarkable that the decomposition tem- ° The Fe3 O 4 nanocubes were formed by grinding the mix- perature of ferrocene is above 450 C, and annealing the fer- tures of ferrocene and polyvinylpyrrolidone (PVP) (of mw rocene at 350° C for 2 h in a sealed cell in the absence of PVP of 360,000) of various weight ratios (1:1, 1:2, and 1:5). Of did not lead to the decomposition of the organometallic the solid mixtures, 300 mg was then introduced into a 1-ml compounds. However, the thermal decomposition of ferro- stainless steel sealed cell. The solid mixtures were then cene in the presence of the PVP leads to its decomposition introduced into a tube furnace preheated to 350° C for 2 h to iron oxide nanocubes/spheres. This may imply that the in an ambient atmosphere. The sealed cell was then cooled PVP catalyzes the thermal decomposition of the ferrocene. to room temperature, and the resulting black powder was Figure 12 A – B show by the low- and high-magnification TEM 346 D. Amara and S. Margel: Synthesis and characterization of elemental iron

A B

Figure 11 The TEM micrographs of the iron oxide nanocubes obtained by the thermal decomposition at 350° C for 2 h of solid mixtures of ferrocene and PVP of the weight ratios of 1:1 (A), 1:2 (B), and 1:5 (C). pictures the perfect spherical shape of the nanospheres of for 4 h did not alter their cubic shape to spheres. Figure 12B 32 ± 5.4 nm obtained by annealing the solid mixture of fer- demonstrates the core-shell architecture of the iron oxide rocene and PVP of a 1:5 weight ratio for 4 h. On the other spherical particles. The core is composed of the iron oxide hand, to our surprise, the annealing of the other solid mix- phase, while the shell is composed of the PVP. Table 6 also tures of the ferrocene and PVP of 1:1 and 1:2 weight ratios exhibits that the [C]:[H]:[N]:[O] (oxygen belonging to the

Figure 12 The low- (A) and high- (B) magnification TEM micrographs of the iron oxide nanospheres obtained by thermal decomposition at 350 ° C for 4 h of a solid mixture of ferrocene and PVP of a weight ratio of 1:5. D. Amara and S. Margel: Synthesis and characterization of elemental iron 347

PVP only) weight ratios of these nanocubes/spheres are PVP in the presence of the various metal ions. According to 8.2:1.0:1.7:2.0, 7.9:1.0:1.5:1.8 and 8.0:1.0:1.5:1.8, respectively. these previous studies, this band shift is due to the interac- These ratios are almost the same as those calculated for the tion between the carbonyl oxygen of the PVP and the metal pure PVP (C 6H 9 NO). The % magnetite content of the nano- ions [54 – 56] . Indeed, the pure PVP spectrum demonstrates cubes obtained by the thermal decomposition for 2 h of the the C = O band at 1650 cm-1 (Figure 13 A), while the various solid mixtures of ferrocene and PVP of the weight ratios of nanocubes/spheres demonstrated this carbonyl peak at 1:5 cannot be calculated due to the presence of the small 1644 cm-1 , a shift of 6 cm-1 (Figure 13B). Please note that FeO phase impurity as identified by the XRD measure- Figure 13B illustrates the carbonyl PVP peak of the mag- ments. It should be noted that the mixtures obtained after netite nanocubes obtained by thermal decomposition at the decomposition of the various ferrocene/PVP mixtures, 350° C for 2 h of a solid mixture of ferrocene and PVP of a before ethanol washing, did not indicate the presence of weight ratio of 1:5. However, the same carbonyl peak was ferrocene traces, as verified by the FTIR spectra. The yield also observed for the other nanocubes/spheres. of the ferrocene decomposition to iron oxide was almost The carbonyl peak shift in the nanocubes/spheres 100%, whereas the excess PVP was removed by the ethanol samples probably implies the formation of the Fe-PVP washing. Thus, the [PVP]:[Fe] weight ratios are lower than complex, which directly relates to the previously sug- their original ratios in the reagents as shown in Table 6. gested mechanism. The magnetic saturation moments

The effect of the PVP concentration and reaction time on (MS ), as well as the coercive fields of these particles, are the particle size can be explained as follows: the previous summarized in Table 7. The Ms values obtained at 300 K studies have demonstrated, by the FTIR spectrometry, that are 29.7, 17.3, and 9.4 emu/g, for the magnetite nanocubes the PVP molecules may coordinate with the metal ions to obtained by the thermal decomposition of the mixtures of form a stable metal-PVP complex [50, 51] . The PVP used ferrocene and PVP of 1:1, 1:2, and 1:5 weight ratios, respec- in this study probably influences the nucleation, growth, tively, and 8.2 emu/g for the magnetite nanospheres. By and aggregation of the obtained magnetite crystallites, by subtracting the PVP content, the calculated MS values in forming the iron-PVP complex molecules. This complex terms of emu/(g of Fe 3 O4 ) are 58.2 and 61.7 for the nano- formation may explain the effect of the PVP concentration cubes obtained by the thermal decomposition of the on the size and morphology of the formed magnetite nano- mixtures of ferrocene and PVP of 1:1 and 1:2, respectively, cubes/spheres. The generation of this complex inevitably and 67.8 for the nanospheres (the value for the nano- increases the time for the iron atoms to reach supersatu- cubes obtained by the thermal decomposition for 2 h of ration and to their final size. This means that the growth a solid mixture of ferrocene and PVP of a weight ratio of rate of the magnetite crystallites will decrease as its face 1:5 cannot be calculated due to the presence of the FeO adsorbed the PVP molecules because the crystal growth impurity). It should be noted that the Ms bulk value of rate is generally lowered with the adsorbed polymer [52] . magnetite is 92 emu/g [46] . The relatively lower Ms values Moreover, the number of ‘ free sites ’ on the PVP surface that can be served as a bounding site to form the iron-PVP A complex increases with increasing PVP concentration, 2.0 B thereby, resulting in the nanocubes/spheres of decrea sing size. The PVP concentration and the annealing time are also 1.5 probably the key factors in explaining the shape alteration of the magnetite crystallites, by effecting the crystal growth 1.0 in different directions. It is known that the crystal growth rate generally decreases with the adsorbed polymer, and Absorbance the crystallite morphology can be altered by the presence 0.5 of the polymer specifically interacting with the crystal faces [53] . The magnetite was formed as cubes when the growth 0 in some direction was restricted by the adsorbed PVP molecules, while one direction was free to allow growth. This 16001650 1700 led to the formation of the nanocubes. Contrarily, the mag- Wavelength (cm-1) netite nanospheres were formed when the annealing time Figure 13 The FTIR spectra of the carbonyl peaks of pure PVP (A) increased, allowing the growth of the crystallites in differ- and of the magnetite nanocubes obtained by the thermal decompo- ent directions. The previous studies reported that a shift sition at 350° C for 2 h of a solid mixture of ferrocene and PVP of a of the carbonyl band was observed in the IR spectra of the weight ratio of 1:5. 348 D. Amara and S. Margel: Synthesis and characterization of elemental iron

Table 7 Magnetic properties of the nanocubes/spheres obtained a = 8.39 Å , and the pattern was indexed as magnetite. by annealing the different ratios of ferrocene and PVP mixtures for Figure 14C and E are the HRTEM micrographs of the indi- different time periods.a vidual Fe3 O4 nanocubes obtained by the thermal decomposition of 1:2 and 1:5 weight ratios of the ferrocene and [Ferrocene]/ Annealing MS (emu/g) Coercivity [PVP] (w/w) time (h) (Oe) PVP mixtures for 2 h, respectively. Both the nanocubes display a well-resolved lattice-fringe contrast as displayed 1:1 2 29.7 50 in the respective Figures (14C and D), and their identifi- 1:2 2 17.3 40 1:5 2 9.4 36 cation was based on the analysis of these high-resolution 1:5 4 8.2 15 images. The inset on the top right in Figure 14C is the com- puted Fourier transform of the portion of the image out- aThe magnetite nanocubes/spheres were prepared according to the experimental part. The size of the nanocubes and the nanospheres lined by the white square which, like a diffraction pattern, relates to the diagonal length of the cubes and the diameter of the was indexed on the basis of the unit cell of the magnet- spheres, respectively. ite. Marked are the d022 and d113 family of planes. The inset on the bottom right represents the filtered and magnified of the magnetic nanocubes/spheres compared to the bulk portion of the image outlined by the square. The dis- values arise from the nonmagnetic PVP content, which tances measured between the lattice fringes were 0.3 nm leads to the decrease in the magnetization per weight. (d022 ) and 0.25 nm (d113 ) of the cubic FCC structure of Fe3 O4 = Another explanation for the relatively low magnetiza- (a 8.35 Å ). Figure 14E shows the lattice fringe d113 (0.25 nm) tion values is the surface effect that can occur in the case plane of the nanocubes obtained by the 1:5 weight ratios of the magnetic core and the nonmagnetic shell struc- of ferrocene and PVP for 2 h. Figures 14D and F are the tures. This effect leads to the reduction in the magnetic NBD patterns taken from the nanocubes obtained by the moment by a different mechanism, e.g., the existence of thermal decomposition of 1:2 and 1:5 weight ratios of fer- a magnetically dead layer on the cubes/spheres’ surface, rocene and PVP for 2 h, respectively. All the NBD patterns the existence of canted spins, or the existence of a spin were taken from a nano-area of 4 – 7 nm of the nanocubes. glass-like behavior of the surface spins [57] . The structure The NBD pattern (14D) shows the sets of reflections of < > of the obtained nanocubes/spheres was also investigated the d022 planes and d113 family of planes, and the NBD in HRTEM mode using either the conventional selected pattern (14F) shows the sets of reflections for the d222 , d133 , area electron diffraction (SAED) and nanobeam (NBD) dif- and d115 planes. These patterns were also indexed accord- fraction technique or the Fourier transform analysis (FFT) ing to the FCC cubic structure of Fe3 O4 . Figure 14G is the of the high-resolution images, depending on the size and HRTEM micrograph of the crystalline Fe3 O4 nanosphere the orientation of the materials. The two possible oxides coated with a thin amorphous layer of PVP. The inset rep- γ maghemite ( -Fe2 O3 ) and magnetite (Fe3 O4 ) are structur- resents the magnified portion of the image outlined by the ally similar; hence, they cannot be distinguished accord- white square. The distances measured between the lattice ing to their electron diffraction patterns. All our electron fringes were 0.24 and 0.25 nm matching the interplanar diffraction patterns could be indexed in terms of the FCC spacings for the d222 and d113 family of planes, respectively. structure of both the maghemite and magnetite, a = 8.34 Å Figure 14H is the SAED pattern taken from the several and a = 8.39 Å (PDF # 000391346 and PDF # 010890950), nanospheres showing reflections that correspond to the respectively. The Mö ssbauer spectra results provided the interplanar spacing, d220 , d311, d222 , and d400 and was indexed supporting evidence that the resulting compounds are, on the basis of the FCC structure of magnetite. The utiliza- indeed, magnetite. Figure 14 A is a HRTEM of a typical tion of these advanced nanotechniques, together with the single crystalline nanocube obtained by the thermal M ö ssbauer spectra results, provided unambiguous evi- decomposition of 1:1 weight ratio of ferrocene and PVP dence that the resulting compounds are the FCC structure mixture. This figure is displaying a lattice-fringe con- magnetite with the unit cell parameter a = 8.39 Å . trast of the d022 family of planes (0.3 nm). The nanocube was identified and characterized using the SAED pattern shown in Figure 14B. This electron diffraction pattern was 3.2 Synthesis of ferromagnetic Fe3 C/C taken from an area of 300 nm comprising several nanocomposite nanoparticles as a catalyst cubes, and it shows a typical ring diffraction pattern as for carbon nanotube growth expected from the polycrystalline materials. The marked reflections correspond to the interplanar spacings, d220 , The uniform micrometer-sized PS/ferrocene composite d 311 , and d400 in the FCC structure of the magnetite Fe3 O4 microspheres were formed by a room temperature swelling D. Amara and S. Margel: Synthesis and characterization of elemental iron 349

Figure 14 The high-resolution electron micrograph of the typical magnetite nanocubes/spheres obtained by the thermal decomposition at 350 ° C for 2 or 4 h of solid mixtures of ferrocene and PVP of the weight ratios of 1:1 (A), 1:2 (C), and 1:5 (E and G) and the corresponding ED pattern (B, D, F, and H, respectively). The nanocubes (A – F) were formed by the thermal decomposition of the ferrocene for 2 h and 4 h for the nanospheres (G, H). The inset marked by the white square (C and G) is the magnified image and Fourier transform taken from the area (C). 350 D. Amara and S. Margel: Synthesis and characterization of elemental iron process of the PS template microspheres with methylene magnetic materials were prepared. First, the uniform chloride (a swelling solvent) containing ferrocene. In a typical micrometer-sized methylene chloride swollen PS/ferrocene experiment, the PS template microspheres of 2.4 ± 0.1 μ m composite microspheres were prepared by a swelling were swollen up to 4.9 ± 0.1 μ m (as observed by a light micro- process of the uniform PS template microspheres dispersed scope) by adding to a 20-ml vial containing 10 ml SDS in an aqueous continuous phase with the emulsion drop- aqueous solution (0.75% w/v), 1 ml of methylene chloride lets of methylene chloride containing the ferrocene. The containing 100 mg of dissolved ferrocene. The emulsion PS/ferrocene composite microspheres were then formed by droplets of the swelling solvent in the aqueous continuous the removal of the methylene chloride by nitrogen flow at phase were then formed by the sonication of the mixture for room temperature. The magnetic air-stable Fe 3 C nanoparti- 1 min. An aqueous dispersion (3.5 ml) of the PS template cles embedded in the amorphous carbon matrix have been microspheres (7% w/v) was then added to the stirred meth- prepared by the thermal decomposition of the PS/ferrocene ylene chloride emulsion. After the swelling was completed, particles at 500 ° C in a sealed cell. The heating of these fer- and the mixture did not contain any small emulsion rocene-containing template particles at higher tempera- droplets of the swelling solvent, as verified by optical tures, e.g., 600° C, 700 ° C, and 1000° C, led to the formation microscopy, the diameter of the swollen microspheres was of the CNTs in addition to the Fe3 C/C composite nanoparti- measured. The swelling extent of the PS template micro- cles. Figure 16 shows the light microscope pictures that spheres by CH2 Cl 2 and ferrocene was studied with the differ- allow one to compare the swelling ability of the template PS ent volumes of CH 2Cl 2 (1, 2, and 4 ml) in the absence of fer- particles by 2 ml of CH 2Cl 2 and by 2 ml of CH 2Cl 2 containing rocene and in the presence of 10%, 20%, and 30% of 20% (w/v) ferrocene. The diameter of the PS microspheres ± μ ferrocene (w/v) dissolved in the CH2 Cl 2 . The methylene before swelling is 2.4 0.1 m (Figure 16A). As a conse- chloride, after the completion of the swelling process, was quence of their swelling with the 2 ml of CH2 Cl 2 , their diam- removed by nitrogen flow for 4 h through a shaken open eter increased from 2.4 ± 0.1 to 5.4 ± 0.2 μ m (Figure 16B), a vial containing the swollen particle aqueous mixture at 225% increase in the average diameter. On the other hand, room temperature. The obtained PS/ferrocene micro- a similar swelling process with 2 ml methylene chloride spheres were then washed from the excess reagents by containing 20% ferrocene (w/v) led to an increase in the several centrifugation cycles with water, ethanol, and again particle size from 2.4 ± 0.1 to 6.0 ± 0.2 μm (Figure 16C), a 255% water, and then dried by nitrogen flow for l0 h. The air-sta- increase in the average diameter. These results may indi- ble Fe 3 C nanoparticles and CNTs were formed by heating cate that both CH 2Cl 2 and ferrocene have the ability to swell the dried PS/ferrocene obtained by swelling the PS tem- the PS template microspheres and preserve the low size dis- plate microspheres with 2 ml of CH2 Cl 2 containing 20% tribution of these template particles. As the goal of this (w/v) ferrocene at 500° C and 600, 700° C and 1000° C for 2 h study was to fill the swollen PS particles with ferrocene in a sealed cell. The sealed cell was then cooled to room while retaining their narrow size distribution, the trials temperature and opened, then, to release the gases formed using the different mixtures of methylene chloride and fer- during the formation of the various particles. Figure 15 rocene have been performed. Figure 17 demonstrates the illustrates the synthetic scheme through which the influence of the different volumes of the swelling solvents

CH2Cl2 swollen PS/ferrocence PS/ferrocene 500°C Fe3C PS Swelling Carbon N2 T≥600°C Methylene chloride Ferrocene

Figure 15 A schematic scheme illustrating the synthesis of the magnetic CNTs and the Fe 3C/C composite nanoparticles. D. Amara and S. Margel: Synthesis and characterization of elemental iron 351

Figure 16 The light microscopy pictures of the PS template microspheres before (A) and after swelling with 2 ml of methylene chloride (B) and with 2 ml of methylene chloride containing 20% (w/v) ferrocene (C). on the diameter and size distribution of the template PS increase in the volume of methylene chloride significantly particles. For each volume, four types of swelling solvents damaged the uniformity of the swollen particles. The addi- have been tested: methylene chloride alone and three mix- tion of 7 ml of methylene chloride resulted in the dissolu- tures of methylene chloride containing 10%, 20%, and 30% tion of the PS particles by methylene chloride dispersed in (w/v) ferrocene. Figure 17 illustrates that increasing the the aqueous phase. Figure 17 also shows that increasing the volume of all the types of the swelling solvents resulted, as amount of ferrocene dissolved in methylene chloride expected, in an increased average diameter of the swollen resulted in an increase in the size of the swollen particles. particles. For example, in the absence of methylene chloride, For example, in the absence and in the presence of 4 ml of and in the presence of 1, 2, and 4 ml of methylene chloride, the different swelling solvents: methylene chloride alone the diameter of the swollen particles increased from 2.4 ± 0.1 and methylene chloride containing 10%, 20%, and 30% of to 4.7 ± 0.1, 5.4 ± 0.2, and 6.5 ± 0.3 μ m, respectively. A further ferrocene, the size of the swollen particles increased from 2.4 ± 0.1 to 6.5 ± 0.3, 6.7 ± 0.2, 6.9 ± 0.3, and 8.0 ± 0.3 μ m, respectively. This observation again indicates that the ferrocene, 9 CH Cl 10% Ferrocene 2 2 in addition to the CH 2Cl 2 , has a substantial ability to swell

m) 8 μ 20% Ferrocene 30% Ferrocene the PS template particles. The kinetics studies of the swell- 7 ing of the PS template microspheres by 4 ml methylene 6 5 chloride containing various concentrations of the dissolved 4 ferrocene indicated that under the experimental condi- 3 tions, the swelling process is completed within ca. 40 min. 2 It should also be noted, as shown in Figure 17, that the 1 increase in the diameter (and volume) of the swollen parti- Swollen particles diameter ( 0 cles was not linearly proportional to the volume of the 124added swelling solvent. For example, the addition of 1.0 or Volume (mL) 4.0 ml of methylene chloride led to an increase in the average diameter of the template particles of 195% and Figure 17 The influence of the CH2 Cl2 volume and the weight ratio 275%, respectively. The first 1 ml of methylene chloride [CH2 Cl2 ]/[ferrocene] on the diameter and size distribution of the template PS particles. increased the diameter of the PS particles significantly 352 D. Amara and S. Margel: Synthesis and characterization of elemental iron more than the additional 3 ml. This nonlinear behavior is nanoparticles. The measured particle size is 42 ± 7 nm. probably due to the packing arrangement of the PS chains Moreover, the image clearly demonstrates that these nano- within the template particles. The degree of entanglement particles are embedded in a protective carbon matrix. Inter- of these chains determines the size (and volume) of the par- estingly, the annealing product at temperatures higher ticles. The swelling solvents swell the template particles by than 500° C led to the formation of the magnetic CNTs in penetrating within the PS chains of the particles, decreas- addition to the Fe3 C/C composite nanoparticles. Figure ing their degree of entanglement, and thereby increasing 18B – D illustrates the TEM images of the nanoparticles and the counter length of the PS polymeric chains. As a conse- the CNTs obtained at 600° C, 700° C, and 1000° C, respec- quence, the particles are less compact, and their size and tively. These images demonstrate that the yield of the CNT volume increase according to their degree of swelling. The formation increases significantly as the annealing tempera- magnetic air-stable nanoparticles embedded in an amor- ture is increased. The formation of the CNTs is a catalytic phous carbon matrix have been prepared by the thermal process in which the Fe3 C nanoparticles serve as the cata- decomposition of the PS/ferrocene obtained by swelling lyst for their formation from the amorphous carbon, which the PS template microspheres with 2 ml CH2 Cl 2 containing is formed by the decomposition of the PS template parti- 20% (w/v) ferrocene at 500° C in a sealed cell. On the other cles. It should be noted here that the annealing of the PS hand, heating these PS/ferrocene particles at 600° C, 700 ° C, template microspheres in the absence of the entrapped fer- and 1000° C led to the formation of the magnetic CNTs in rocene under the same conditions did not lead to the for- addition to the Fe 3 C/C composite nanoparticles. The TEM mation of the CNTs. This, of course, illustrates the impor- image of the nanoparticles obtained by thermal decompo- tance of the magnetic nanoparticles for the catalytic ° sition at 500 C is presented in Figure 18 A. This image dem- process. The measured diameters of the CNTs and the Fe 3 C onstrates the hemispherical morphology of the obtained nanoparticles obtained at 600° C, 700 ° C, and 1000° C

° ° ° Figure 18 The TEM pictures of the magnetic CNTs and the Fe3 C/C composite nanoparticles obtained at 500 C (A), 600 C (B), 700 C (C), and 1000 (D). D. Amara and S. Margel: Synthesis and characterization of elemental iron 353 are 95 ± 12, 36 ± 10, and 33 ± 6 nm and 94 ± 17, 64 ± 22, and catalyst size. Second, at higher temperatures, the growth ± 38 6 nm, respectively. The decrease in the Fe 3 C nanoparti- rate of the CNTs increases dramatically due to the enhanced cle size can be explained as follows: the thermal decompo- diffusion and reaction rates of the carbons, which led to the sition of the PS/ferrocene composite particles was fast growth of the CNTs to their final size with smaller diam- performed in a sealed cell. Upon heating, both the PS and eters. Moreover, the CNTs formed at 1000 ° C are longer com- the ferrocene decomposed to give gaseous hydrocarbon pared to those obtained at 700° C. This can also imply that products. In addition, the sealed cell contained air (mainly there are kinetic effects on the CNT growth; the mechanism oxygen and nitrogen), which was introduced into the cell of the formation of the CNTs is not yet clear. However, during the sample preparation. As the reaction tempera- recently Futaba et al. showed that the CNTs can be synthe- ture increased, the pressure within the cell increased, and sized by a “ growth-enhancer-containing oxygen’ ’ (e.g., the resulting particles were smaller in size. It is suggested water, acetone, methyl-benzoate, etc.) and a “ carbon source that the particle growth is limited by the pressure within that does not contain oxygen” (e.g., ethylene, acetylene) the cell, which allows the formation of the smaller particles [58] . In this study, the PS template microspheres serve as at higher temperatures. The above results demonstrate that the “ carbon source,” and the “ growth enhancer” is the the nanoparticle size as well as the CNT diameter can be oxygen that is present in the cell or water and CO2 that are controlled by adjusting the annealing temperature: an formed by the combustion of PS. Further study is necessary increase in the annealing temperature from 600° C to in order to confirm the mechanism. The XRD patterns of the 1000° C led to a decrease in the CNT diameter. This can be nanoparticles obtained at 500 °C, 600 °C, 700 °C, and ° explained by two main points: first, the Fe 3C catalyst parti- 1000 C, perfectly match the orthorhombic structure of cle size decreased with increasing reaction temperature, Fe3 C. The isothermal field dependence of the magnetiza- and the CNT diameter was directly influenced by the tion measured at 300 K for the nanoparticles obtained at

° Figure 19 (A) The HRTEM image of the typical Fe 3 C/C composite nanoparticles obtained at 500 C; (B) TEM, and (C) HRTEM of the CNTs obtained at 1000° C. The inset is the magnified image showing the lattice-fringes (A). 354 D. Amara and S. Margel: Synthesis and characterization of elemental iron

500° C, 600 °C, 700 ° C, and 1000° C was characterized by the of the entrapment and decomposition conditions of ferromagnetic-type curves, which show hysteresis loops. ferrocene.

The M s as well as the coercive fields obtained are 39, 54, 58, The present review describes the four different ways and 61 emu/g and 410, 490, 345, and 500 Oe, respectively. It to prepare the above magnetic nano/microparticles, as should be noted that the Ms bulk value of Fe3 C in the litera- follows: ture was found to be 140 emu/g [59] . The relatively lower Ms 1. The superparamagnetic PDVB/iron oxide composite values of the magnetic nanoparticles compared to the bulk micrometer-sized particles of narrow size distribution value arise from the nonmagnetic carbon content, which were prepared by entrapping ferrocene and a separating leads to a decrease in the magnetization per weight. media within the pores of the uniform porous PDVB Another explanation for the relatively low magnetization microspheres, followed by solventless thermal values is the surface effect that can occur in the case of the decomposition at 300° C in ambient atmosphere in a magnetic core and nonmagnetic shell structures. This effect sealed cell. The uniform ferromagnetic C/iron oxide leads to a reduction in the magnetic moment by a different and C/Fe3 O4 /Fe composite microspheres were then mechanism, such as the existence of a magnetically dead formed by annealing the superparamagnetic PDVB/ layer on the particles’ surface, the existence of canted spins, iron oxide particles at 500 °C and 700 ° C, respectively, or the existence of a spin glass-like behavior of the surface under argon atmosphere. spins [57] . In order to study the stability of the Fe 3C nano- 2. The core-shell PS/PDVB/ferrocene and PS/P(DVB-S)/ particles obtained at 500° C, 600 °C, 700 °C, and 1000° C TGA ferrocene micrometer-sized particles of narrow size measurements in the air atmosphere have been performed. distribution were prepared by a single-step swelling of

Figure 19 A is a HRTEM of a typical single crystalline Fe3 C the uniform PS template microspheres dispersed in an nanoparticle obtained at 500 ° C. The image demonstrates a aqueous continuous phase with the emulsion droplets

Fe3 C core of 47 nm coated by a thin layer of 5 nm amorphous of a swelling solvent such as toluene containing the carbon. The inset in Figure 19A represents the magnified monomers S and/or DVB, the initiator AIBN, and portion of the image outlined by the white square. The dis- ferrocene. The monomer/s within the swollen uniform tances measured between the lattice fringes was 0.2008 nm PS template microspheres were then polymerized matching the interplanar spacings for the d031 of Fe3 C. The at an elevated temperature. The superparamagnetic ° TEM and HRTEM images of the CNTs obtained at 1000 C are and ferromagnetic PDVB/Fe3 O4 and P(S-DVB)/Fe3 O4 presented in Figure 19B– C, respectively. The images clearly composite microspheres of narrow size distribution demonstrate the cylindrical structure and the curvature of were then formed by annealing the previous the sidewall of the CNTs. The walls of the presented CNTs micrometer-sized composite particles containing are composed of carbon shells with a spacing of 0.34 nm, ferrocene at 330° C for 2 h under ambient atmosphere which is consistent with that of graphite. However, the in a sealed cell, followed by the dissolution of the PS images demonstrated disordered MWCNTs in which graph- template part with DMF. The superparamagnetic C/Fe ite layers are misaligned with the primary MWCNT axis. micrometer-sized particles of narrow size distribution

were then formed by annealing the PDVB/Fe3 O4 particles at 450° C under hydrogen atmospheres for 2 h.

3. The Fe3 O4 nanocubes and nanospheres were 4 Summary and conclusions synthesized by the solventless thermal decomposition of the various mixtures of ferrocene and PVP. The The decomposition of iron pentacarbonyl is one of the magnetite nanocubes were prepared by grinding and most common methods for the preparation of magnetic mixing the solid mixtures of ferrocene and PVP. The iron oxide and the elemental iron nano/microparti- mixtures were then annealed at 350° C for 2 h in a sealed cles. However, Fe(CO)5 is severely toxic, and alternative cell. The nanocubes ’ size was controlled by adjusting precursors should be used. This review demonstrates the [ferrocene]/[PVP] weight ratio. Increasing the a new simple nontoxic approach for the synthesis of annealing time to 4 h when the [ferrocene]/[PVP] magnetic iron and the iron oxide nano/microcompos- weight ratio was 1:5 led to the formation of the ite particles with various shapes, properties, and sizes, magnetite nanospheres. The formed nanocubes/ by thermal decomposition in various ways of the iron spheres exhibit a ferromagnetic behavior at room precursor ferrocene. In all processes, the particles’ size, temperature. These magnetite nanocubes/spheres composition, shape, crystallinity, magnetic properties, were actually formed by a CVD reaction through which and surface area can be controlled by the adjustment the ferrocene molecules, which are in the gas phase at D. Amara and S. Margel: Synthesis and characterization of elemental iron 355

the reaction conditions, decomposed to the magnetite CNTs is relatively new and promising. Further studies nanocubes/spheres dispersed in the solid PVP matrix. related to this CNT formation and its applications,

4. The air-stable Fe3 C nanoparticles embedded in the particularly for catalysis, are ongoing in our laboratory.

amorphous carbon matrix (C/Fe3 C) have been prepared In addition, for future work, we plan to extend this by thermal decomposition of the ferrocene swollen study for the other applications, particularly for the template PS particles at 500° C for 2 h in a sealed cell. biomedical uses, e.g., hyperthermia, cell labeling, and The decomposition of these swollen template particles separation, drug delivery, etc. for 2 h at higher temperatures led to the formation Acknowledgements: This study was partially supported of the CNTs in addition to the C/Fe C composite 3 by a Minerva Grant (Micro and Nano Scale Particles and nanoparticles. The yield of the CNTs increased as Thin Films for Biomedical Applications). the annealing temperature was raised. The opposite behavior was observed for the diameter of the formed Received January 1, 2013; accepted March 28, 2013; previously CNTs. This method for the formation of the magnetic published online May 1, 2013

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He worked as a senior Scientist, at the Califorina Institute of Techno logy, Jet Propulsion Lab., Pasadena, CA from 1978 to 1979. From 1980 to 1984 he worked as a Senior Scientist at the Weizmann Institute of Science, Department of Materials Science, Rehovot, Israel and became an Associate Professor of this department in 1985. From 1986 to 1987 and in July to November 1990 he was a Visiting Scientist at Du Pont, Central R&D, Wilmington, DE. He was a Visiting Scientist at the University of Ulm, Department of Chemisty from July to September 1992. Polymer Section, Ulm, Germany. From 1988 to 1994 he was an Associate Professor at Dr. Daniel Amara received his PhD in Materials Science in 2012 Bar-Ilan University, Ramat Gan, and became a Full Professor there from the Institute of Nanotechnology and Advanced Materials, in 1994. In 1997 he was a Visiting Professor at theDepartment of Bar Ilan University, Israel, under the supervision of Prof. Shlomo Physical Electronics at theTokyo Institute of Electronics (TIT). From Margel. As part of his PhD research, he developed and published 1999 to 2001 he was Head of the Chemistry Department at Bar-Ilan novel methods for the synthesis of magnetic nano/microcomposite University and from 2000 to 2003 he was the Head of the National particles. These methods focused on the environmentally friendly Committe for Chemisrty in High School Education. From 2002 to synthesis. He is currently conducting research on the solventless 2003 he was the Dean of the Faculty of Exact Sciences and in 2005 synthesis of magnetic materials. hewas a Visiting Scientist at MIT’a Institute from Soldier’s Nano- technologies in Cambridge, MA. From 2006 to 2009 he wasthe President of the Israel Chemical Society and from 2010 to 2012 he was the Chairman of the National Committee of Chemistry towards IUPAC (he was nominated by the Israel Academy of Science and Humanities). The major research interests of Prof. Margel ’ s group are in the fields of polymers and biopolymers, encapsulation, synthesis of functional particles of narrow size distribution, water purification, surface chemistry, immobilization techniques, colloidal chemistry, functional thin films, and biological and Shlomo Margel received his PhD from the Weizmann institute of medical applications of nano/microparticles. Prof. Margel’ s Science, Department of Material Science, Rehovot, Israel in 1976 research group includes about 15 PhD and MSc students and and obtained a Post-Doctorate from the California Institute of four postdocs. He is the author of more than 00 publications Technology, Department of Chemistry, Pasadena, CA in 1977. and 29 patents and patent applications.