Fe nanoparticles

Fig. 10 Self-organisation of Ni-Fe nanoparticles on a carbon substrate (1) multi-layers (2) mono-layer.

Shao MH, Sasaki K, Adzic RR. 2006c. Pd-Fe nanoparticles as electrocatalysts for oxygen reduction. J Am Chem Soc 128 3526-3527. 

Fig. 6.14 Mossbauer spectra of a-Fe nanoparticles on a carbon support. The spectra were obtained at 80 and 300 K with the indicated magnetic fields applied perpendicular to the y-ray direction. The asymmetry in the spectra is due to the presence of a small amount of iron carbide particles. (Reprinted with permission from [58] copyright 1985 by the American Chemical Society)...

Murray, C. B. Sun, S. Doyle, H. Betley, T. 2001. Monodisperse 3d transition-metal (Co, Ni, Fe) nanoparticles and their assembly into nanoparticle superlattices. MRS Bulletin 26 985-991. 

The inner cavity of carbon nanotubes stimulated some research on utilization of the so-called confinement effect [33]. It was observed that catalyst particles selectively deposited inside or outside of the CNT host (Fig. 15.7) in some cases provide different catalytic properties. Explanations range from an electronic origin due to the partial sp3 character of basal plane carbon atoms, which results in a higher n-electron density on the outer than on the inner CNT surface (Fig. 15.4(b)) [34], to an increased pressure of the reactants in nanosized pores [35]. Exemplarily for inside CNT deposited catalyst particles, Bao et al. observed a superior performance of Rh/Mn/Li/Fe nanoparticles in the ethanol production from syngas [36], whereas the opposite trend was found for an Ru catalyst in ammonia decomposition [37]. Considering the substantial volume shrinkage and expansion, respectively, in these two reactions, such results may indeed indicate an increased pressure as the key factor for catalytic performance. However, the activity of a Ru catalyst deposited on the outside wall of CNTs is also more active in the synthesis of ammonia, which in this case is explained by electronic properties [34]. 

Farrell D, Ding Y, Majetich SA, Sanchez-Hanke C, Kao C-C. Structural ordering effects in Fe nanoparticle two- and three-dimensional arrays. J Appl Phys 2004 95 6636-6638. 

Many clusters of Fe atoms are formed both inside and at the surface of each alumina grain and progressively grow. When the Fe nanoparticles located at the surface of the alumina grains reach a size around 0.7-2 nm, they immediately catalyze the decomposition of CH4 and the nucleation and growth of CNTs of very small diameter ... 

The multilayer nanocomposite films containing layers of quasi-spherical Fe nanoparticles (d — 5.8 nm) separated by dielectric layers from boron nitride (BN) are synthesized by the repeated alternating deposition of BN and Fe onto a silicon substrate [54]. In this work the authors managed to realize the correlation in the arrangement of Fe nanoparticles between the layers the thin BN layer deposited on the Fe layer has a wave-like relief, on which the disposition of Fe nanoparticles is imprinted as a result, the next Fe layer deposited onto BN reproduces the structure of the previous Fe layer. Thus, a three-dimensional ordered system of the nanoparticles has been formed on the basis of the initial ordered Fe nanoparticle layer deposited on silicon substrate [54]. The analogous three-dimensional structure composed of the Co nanoparticles layers, which alternate the layers of amorphous A1203, has been obtained by the PVD method [55]. 

For synthesis of composite films with M/SC nanoparticles distributed in the volume of a dielectric matrix, method PVD is used as co-deposition of M/ SC and dielectric material vapors. A comparison of films produced by codeposition and layer-by-layer deposition PVD methods has been made on the example of BN-Fe nanocomposite films [57]. Unlike the above considered film from alternating layers of Fe and BN, which has ordered structure, co-deposited BN-Fe nanocomposite films consist of amorphous completely disorder matrix BN containing a chaotic system of immobilized Fe nanoparticles. At the same time, these particles in contrast to those of layered film have much smaller size (d — 2.3 nm) since in this case the metal atoms are inside a matrix which slowdowns the diffusion process of atoms aggregation. 

Figure 4. Fe nanoparticles (3 nm) in a silica matrix (a) hysteresis loop and (b) ZFC and FC curves indicating a blocking temperature of 27K.

The features of the electrode used in this gas-phase electrocatalytic reduction of C02 are close to those used in PEM fuel cells [37, 40, 41] (e.g. a carbon cloth/Pt or Fe on carbon black/Nafion assembled electrode, GDE). The electrocatalysts are Pt or Fe nanoparticles supported on nanocarbon (doped carbon nanotubes), which is then deposited on a conductive carbon cloth to allow the electrical contact and the diffusion of gas phase C02 to the electrocatalyst. The metal nanoparticles are at the contact of Nation, through which protons diffuse. On the metal nanoparticles, the gas-phase C02 reacts with the electrons and protons to be reduced to longer-chain hydrocarbons and alcohols, the relative distributions of which depend on the reaction temperature and type of metal nanoparticles. Isopropanol forms selectively from the electrocatalytic reduction of C02 using a gas diffusion electrode based on an Fe/N carbon nanotube (Fe/N-CNT) [14, 39, 40]. Not only the nature of carbon is relevant, but also the presence of nanocavities, which could favor the consecutive conversion of intermediates with formation of C-C bonds. 

Figure 5.1.9 PEC solar cell. Bottom scheme of the cell with electron microscopy images of a particular of the Ti02-nanotube array electrode and of the Fe nanoparticles on N-doped carbon nanotubes, used as a photocatalyst for water oxidation and an electrocatalyst for CO2 reduction, respectively. It is also shown that it may be possible to use this cell for the production of H2/O2 in separate compartments by water photoelectrolysis. Top photo of the experimental cell and of the assembly of the photoanode with the Nafion membrane. Adapted from [14, 40, 52],...

A similar reaction without the surfactants just gave smaller Fe-nanoparticles (ca. 60 nm) without such an aggregation [22], suggesting that the two surfactants have a key role... 

Figure 7 Mossbauer spectrum of nanometer-sized metallic iron particles in zeolite NaX obtained at T = 4.2K before (A) and after (B) subtraction of two Fe(ll) contributions with Si = 0.75 mm s and AEqi = 0.8 mm s (5% relative contribution) and S2 = 0.85 mm s and AEq2 = 1.85mms (6% relative contribution). The analysis of the magnetic hyperfine field distribution identifies metallic a-Fe-nanoparticles. (From Schiinemann, Winkler, Butzlaff and Trautwein. With kind permission from Springer Science Business Media)...

Xu and coworkers have demonstrated that even non-noble metals can exhibit very high catalytic activity for the AB hydrolysis reaction [119]. They found that with in situ synthesized amorphous Fe nanoparticles, the hydrolysis of AB (0.16 M aqueous AB solution, mol Fe/mol AB = 0.12) is complete within only 8 min. The as-prepared Fe-catalyst was reused up to 20 times with no obvious loss of activity. It was concluded... 

It occurs catalytically on the surface of Fe nanoparticles grown from Fe(CO)5. Also, the conventional synthesis of nanotubes by catalytic CVD from acetylene or methane can be formally considered as redox reaction. Nevertheless, the electrochemical model of carbonization (Sections 4.1.1 and 4.1.2) is hardly applicable for CVD and HiPco, since the nanotubes grow on the catalyst particle by apposition from the gas phase, and not from the barrier film (Figure 4.1). The yield and quality of electrochemically made nanotubes are usually not competitive to those of catalytic processes in carbon arc, laser ablation, CVD and HiPco. However, this methodology demonstrated that nanotubes (and also fullerenes and onions (Section 4.3)) can be prepared by soft chemistry" at room or sub-room temperatures [4,5,101]. Secondly, some electrochemical syntheses of nanotubes do not require a catalyst [4,5,95-98,100,101]. This might be attractive if high-purity, metal-free tubes are required. 

The Fe-Au nanoparticles were reported to consist of metallic cores, having an average diameter of 6.1 nm, surrounded by an oxide shell, averaging 2.7 nm in thickness, for a total average particle diameter of 11.5 nm [101]. A surfactant solution is prepared with nonylphenol poly(ethoxylate) ethers. Au-coated Fe nanoparticles were also prepared in a reverse micelle formed by cetyltrimethylammonium bromide (CTAB), 1-butanol and octane as the surfactant, the co-surfactant and the oil phase, respectively [100]. The nanoparticles were prepared in aqueous solutions of micelles by reduction of Fe(II) and Au precursors with NaBH4. The typical size of the nanoparticles is about 20 nm. The existence of Fe and Au is again confirmed by energy dispersive X-ray microanalysis. 

Figure 2(b)).Fe nanoparticles were also prepared by decomposition of Fe(CO)s in the presence of surfactants (oleic acid and oleyl amine). The monodispersity of the particles was achieved in this case either using platinum acetylacetonate (Pt(acac)2 with acac = (CFl3CO)2CFl)) as heterogeneous nucleation agent or a supersaturation of Fe(CO)s." ... 

Finally, laser pyrolysis of Fe(CO)s produces partially or fully oxidized Fe nanoparticles of 20 nm mean diameter using an infrared laser in mixtures containing SF. A similar procedure carried out in isopropanol produced 5 nm nanoparticles of 7-Fc203. ... 

As seen, freshly synthesized Fe ) as well as nano Pd/Fe bimetallic samples were more reactive than the corresponding commercial samples. For example, TCE was degraded in 1.7 h when reacted with Fe nanoparticles, while under the same reaction conditions it took only 0.25 h with Pd/Fe nanoparticles. Interestingly, when bulk iron was used to degrade TCE, other toxic products such as DCE and VC were produced. None of these toxins were detected with either Fe or Pd/Fe nanoparticles. Similar reactivity differences were noticed with PCB. 

Pd(0) nanoparticles are used as both free nanoparticles and as supported nanoparticles, where the supporting substrate may be various foams. Free Pd(0) nanoparticles produced by the bacterium Shewanella oneidensis were shown to reductively dechlor-inate PCBs in solution, and supported Pd-Fe nanoparticles have been shown to assist in reductively dechlorinating 1,2,4-trichlorobenzene (45, 101). For the most part, Pd(0) nanoparticles appear to resist the agglomeration and oxidation problems that plague Fe(0) nanoparticles (86, 101). 

Finally, Fe-based nanoparticles may be utilized to immobilize Hg contamination and prevent it from being acted upon by bacteria and becoming methy-Imercury. CMC-stabUized FeS nanoparticles have been shown to react with Hg to produce HgS, which is a highly insoluble mineral that offers httle or no Hg bio-availabihty (103). The addition of CMC-FeS nanoparticles to low Hg content and high Hg content sediments resulted in 46% and 67% reduction in leachable Hg respectively. 

Figure 3.6. The curves of Fe nanoparticles distribution on the size in a PELD matrix (m, and m2 are the first and second modes of distribution, respectively).

Arc discharge technique This is similar to that used for fullerene synthesis, was applied for the preparation of carbon-encapsulated Ni, Co, or Fe nanoparticles. 

GOX could also be incorporated into aligned CNT/PPy composite nanofibers with Fe nanoparticles on the tip of CNTs [161]. Inclusion of Fe nanoparticles was the key factor to reduce the potential of the redox reaction of H O. A near linear increase in the current up to 20 mM... 

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