Iron nanoclusters

Figure 6.58. Examples of the ordered growth of carbon nanotubes. Shown are (a) MWNT arrays grown from squared regions of iron nanoclusters (b) Side-view SEM image of a SWNT power line on Si posts (c) ahgned SWNT growth through electric-field induction. Reproduced with permission from Dai, H. Acc. Chem. Res. 2002, 35,1035. Copyright 2002 American Chemical Society.

Figure 6.59. Schematic and cross-section SEM image of a layer-by-layer (LbL) approach to deposit iron nanoclusters onto a surface to yield vertically aligned SWNTs. Reproduced with permission from Liu, J. Li, X. Schrand, A. Ohashi, T Dai, L. Chem. Mater. 2005, J 7,6599. Copyright 2005 American Chemical Society.

Aqueous exchange with iron (which is very different to other techniques) led to the formation of iron nanoclusters, which were shown to be highly active in the selective catalytic reduction of NO,j. Figure 7.9 shows the suggested structures taken from ref [13]. 

Sohn B.H., Cohen R.E., and Papaefthymiou G.C., Magnetic properties of iron oxide nanoclusters within microdomains of block copolymers, J. Magn. Magn. Mater., 182, 216, 1998. 

Ir4(CO)i2 and Ir6(CO)i6, supported metal nanoclusters, 68-69 Ir4 in zeolite NaX supported metal nanoclusters, 69 theoretical investigation, 70 Iron oxide support, preparation of gold particles on, 6-7... 

There were developed two new technologies for manufacturing of novel carbon nanomaterials (fullerenes, nanotubes, carbonic nanoclusters) based on the idea of high-energy plasmochemistry synthesis with the use of the methods of electrical wire explosion and spark erosion of graphite and metallic materials (nickel, iron, copper) in organic medium. 

Metallic species such as iron, nickel and cobalt are known to catalyze the growth of CNTs in the CVD process [168-170]. Because of the ready thermal curability of the hb-PYs, spin-coated films of organometallic polymers 81 and 82 are expected to restrict the agglomeration of the metallic nanoclusters in the CVD process and hence to provide nanoscopic catalyst seeds for the... 

Herzing AA, Kiely CJ, Carley AF, Landon P, Hutchings GJ. Identification of active gold nanoclusters on iron oxide supports for CO oxidation. Science. 2008 321 1331-5. 

For some applications, a main drawback of CVD is that MWNTs are often generated alongside SWNTs. Since the size of the catalyst governs the diameter of resultant tubes, surface-immobilized nanoclusters of iron oxide PAMAM dendrimer, with well-defined sizes, has been shown to yield only SWNTs with... 

Figure 29 Possible structural analogues of the iron-oxo nanoclusters formed within the MFI pores (a) ferredoxin (b) HIPIP (high-potential iron proteinf ...

Properties of nanoparticles and base fluid used in this study are shown in Table 1. De-ionized water was used as a base fluid. In the nanofluid, nanoparticles tend to cluster and form agglomerates which reduce the effective thermal conductivity. It is known that ultrasonication break the nanoclusters into smaller clusters. Hong et al. [41] investigated the role of sonication time on thermal conductivity of iron (Fe) nanofluids. The thermal conductivity of each nanofluid showed saturation after a gradual increase as the sonication time was increased. The thermal conductivity of 0.2 vol% Fe nanofluid exhibited 18% enhancement with a 30 min sonication and was saturated after 30 min. So, in order to obtain good quality nanofluids, it is essential that the solid-liquid mixture be exposed to ultrasonication. 

Iron oxide nanoclusters were synthesized within mesoporous MCM-41 doped with aluminum using evaporation-condensation of volatile Fe(CO)5 [53]. Subsequent calcination in an O2 flow resulted in amorphous y-Fe203 particles with diameters of 2-3 nm evenly distributed through the well-defined hexago-nally packed cyhndrical pores. These results were sohdly confirmed by combination of Mossbauer spectroscopy, XRD, TEM, and STEM (Fig. 4). 

In [4] we demonstrated for the first time that Er ions can be incorporated inside iron oxide clusters of OPS. These 5-50 nm clusters were formed by electrochemical co-deposition of Fe and Er in porous silicon followed by high temperature oxidation. The Er ions incorporated in the iron oxide nanoclusters showed a highly resolved Stark structure of emission spectmm indicating unambiguously a well-defmed configuration of Er centers in crystalline environment [4,5]. We have observed more than twenty sharp emission peaks related to highly resolved transitions between splitted spin-orbit levels of the I 13/2 and I 15/2 multiplets. The FWHM of the peaks did not exceed 0.5 meV at 77 K that is much lower than that for Er in different silica-like host materials. Two ensembles of different Er centers having cubic and lower than cubic symmetries have been identified [5]. 

The metal ion - metal nanocluster ensemble sites can contain either one or two metal components. In different forms of copper and gold catalysts, the metal can exist in both forms, i.e., as metal ion and the metal nanocluster. These systems will be considered as a mono-element metal ion - metal nanocluster ensemble sites. However, as it will be demonstrated later, systems containing two elements are more common. In most of these systems the metal ions are formed from elements of well known red-ox metals, such as tin, rhenium, iron, tungsten, molybdenum, etc. while the metal nanoparticles are noble metals, such as platinum, ruthenium, etc. 

In additional experiments it has been shown that iron is interacting with platinum, i.e., it is located in atomic closeness to Pt. In the bimetallic nanocluster, due to the high electropositivity of iron, there is an electron transfer from iron to platinum. The net result is the formation of electron deficient iron species at the Pt surface. The authors suggested that these electron-deficient or low-valent iron species on the Pt surface might act as Lewis acid adsorption sites. These sites, due... 

A. A. Turovskiy, V. I. Kopylets, V. I. Pokhmurskiy, S. A. Komiy, G. A. Zaikov Simulation of organic compound oxidation on the surfaces of iron and chromium nanoclusters, In Book Kinetics and Thermodynamics for Chemistry and Biochemistry , Nova Science Publishers, New York, 2,117-124 (2009). 

---