Fe-Au nanoparticles

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. 

Lin, J., Zhou, W., Kumbhar, A., Wiemann, J., Fang, J., Carpenter, E.E. and O Connor, C.J. (2001) Gold-coated iron (Fe-Au) nanoparticles Synthesis, characterization, and magnetic field-induced self-assembly./. Solid State Chem., 159, 26-31. 

In the case of Fe as the core, there are examples of core-shell Fe-Au [100], Fe-Fe-oxide [101], Fe-oxide/Au [102], and Fe304-polymer [103] nanoparticles. The combination of Fe core/Au shell is particularly appealing because Au is not ferromagnetic, but is noble and... 

The further study of Cho et al. [107] has showed that the structure of Fe/Au core/shell nanomaterials is somewhat complex. Mossbauer spectra were best interpreted as Fe speciation of a-Fe, Fe11, Fem and Fe-Au alloy. The Au shell was suggested to grow by nucleating from small nanoparticles on the Fe-core surface before it develops the shell structure. These nanoparticle nucleation sites form islands for the growth and coalescence... 

In contrast to the above-mentioned findings, Hofmann et al. [50] demonstrated that the active phase of the catalyst is a neutral metal. As in the experiments described in the previous paragraph, Hofmann et al. measured in situ the chemical composition of Ni, Fe, Pd, and Au nanoparticles deposited on SiOj substrates during exposure to acetylene. The authors observed low catalytic activity toward CNT formation by NiO and Fe20j, which were the most abundant chemical states of Ni and Fe, respectively, after evaporation of these metals on the support. 

Good fits between experimental and theoretical amperometric responses at the tip were obtained for the composite films incorporating Pd nanoparticles to demonstrate that the generation of hydrogen peroxide (Equation 18.10) was accelerated from fe,=0.0014 cm/s to A ,=0.00534 cm/s as more Pd nanoparticles were loaded. By contrast, data for Pt composite films did not fit well with theory, which was ascribed to the formation of an oxide layer on Pt nanoparticles. In another study, LBL approach was employed to prepare the composite of gold nanoparticles, DNA, and polyethyleni-mine (PEI). Specifically, the SAM of 3-mercapto-l-propanesulfonic acid was formed on the gold electrode to deposit a cationic PEI film, which was followed by the deposition of double-stranded DNA or citrate-stabilized Au nanoparticles and PEL Approach curves were measured to demonstrate that 1 values for both FcMeOH and ferrocenecarboxyUc acid were highly dependent on the type of the outmost layer. 

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