Surface metal particles

Variation of the content of impurities in the different CNT preparations [21] offers additional challenges in the accurate and consistent assessment of CNT toxicity. As-produced CNTs generally contain high amounts of catalytic metal particles, such as iron and nickel, used as precursors in their synthesis. The cytotoxicity of high concentrations of these metals is well known [35, 36], mainly due to oxidative stress and induction of inflammatory processes generated by catalytic reactions at the metal particle surface [37]. Another very important contaminant is amorphous carbon, which exhibits comparable biological effects to carbon black or relevant ambient air particles. 

Using this method, homogeneous alloys, segregated alloys, layered bi-metallics, and decorated particles are all readily accessible. An obvious advantage of the precursor concept over the conventional salt-impregnation method is that both the size and the composition of the colloidal metal precursors may be tailored independent of the support. Further, the metal particle surface may be modified by lipophilic or hydrophilic protective shells and coated by intermediate layers, e.g., of oxide. The modification of the precursor by dopants is also possible. 

General Observations About x. its Relationship to the Overall Partitioning Coefficient and to the Concept of Surface-Site Heterogeneity. One approach to metal/particle surface interactions which has been developed, historically, in a variety of forms, is a conceptual model that assumes only two conditions for surface sites occupied by an adsorbate or unoccupied. In applying this approach to the solid/aqueous solution interface, the adsorption... 

Hache, F., Ricard, D., Flytzanis, C. Optical non linearities of small metal particles Surface-mediated resonance and quantum size effects. J. Opt. Soc. Am. B 3, 1647-1655 (1986)... 

Interactions between the precious metal and support influence the performance of the catalyst. Beil (1987) has defined metal-support interaction as depending on contact between the metal particle and the support which can be a dissolution of the dispersed metal in the lattice. The interaction could also depend on the formation of a mixed metal oxide, or the decoration of the metal particle surface with oxidic moieties derived from the support. It is possible that in this study, the differences in catalytic performance of the same active material supported on different washcoats can be attributed to any of these phenomena. Another explanation could be that the support materials exhibit different acid-base properties. According to the Bronsted and Lewis definitions, a solid acid shows a tendency to donate a proton or to accept an electron pair, whereas a solid base tends to accept a proton or to donate an electron pair. The tendency of an oxide to become positively or negatively charged is thus a function of its composition, which is affected by the preparation method and the precursors used. Refer to the section Catalyst characterization for further discussion on the influence of support material on catalyst performance. To thoroughly examine the influence of the support... 

Figure 4.8 GASP of vinyl monomer on a metal particle surface.

For time-dependent electrical perturbation, the typical assumption is that the metal nanoparticle behaves as a dielectric, characterized by a frequency-dependent permittivity ( >). Permittivities experimentally determined on bulk sample are almost invariably used. They need to be corrected with terms depending on the particle size. In fact, when the size of the metal particle has the same order of magnitude of the mean free path of conduction electrons in the bulk of the solid (tens of nanometers), it is necessary to take into account the scattering of the electrons at the metal particle surface. This is one aspect of a more general class of phenomena, known as quantum size effects. They are tightly related to the confinement of electrons in the metal particle and hence to the loss of the band structures typical of a bulk metal. Since this phenomenon regards mainly the valence... 

---