Polyhedral Nanoparticles

Carroll, J. B., Frankamp, B. L., Srivastava, S., Rotello, V. M. (2004), Electrostatic self-assembly of structured gold nanoparticle/polyhedral oligomeric silsesquioxane (ROSS) nanocomposites, JoMwa/ of Materials Chemistry, 14, 690. ... 

Carroll JB, Frankamp BL, Srivastava S, Rotello VM (2004) Electrostatic self-assembly of stmctured gold nanoparticle/polyhedral oligomeric silsesquioxane (POSS) nanocomposites. J Mater Chem 14(4) 690-694. doi 10.1039/b311423f... 

The carbon-arc plasma of extremely high temperatures and the presence of an electric field near the electrodes play important roles in the formation of nanotubes[ 1,2] and nanoparticles[3]. A nanoparticle is made up of concentric layers of closed graphitic sheets, leaving a nanoscale cavity in its center. Nanoparticles are also called nanopolyhedra because of their polyhedral shape, and are sometimes dubbed as nanoballs because of their hollow structure. 

Figure 2 illustrates a proposed growth process[3] of a polyhedral nanoparticle, along with a nanotube. First, carbon neutrals (C and C2) and ions (C )[16] deposit, and then coagulate with each other to form small clusters on the surface of the cathode. Through an accretion of carbon atoms and coalescence between clusters, clusters grow up to particles with the size fi-... 

The shape of the nanoparticles depends on numerous parameters such as the nature of the metal and the support, the metal loading. Of the various models of polyhedral metal particles [106], the cubooctaedral structure can be used to represent small metallic particles (Scheme 31). Note that these idealized structures can vary with the nature of chemisorbed species (vide infra) and very subtle atomic rearrangements probably occur during catalytic events. 

First, polyhedral-shaped Au nanoparticles (Figure 6A) are synthesized by sodium borohydride reduction of AUCI3 dissolved in toluene in the presence of DDAB (step 1). 

A schematic illustration of the model is shown in Figure 10.2.12, together with that of polyhedral nanoparticles which grow as byproducts of MWNTs (see Fig. 10.2.3). An initial seed of an MWNT is the same as that of a polyhedral nanoparticle. Carbon neutrals [C, C2 (19)] and ions (C+) deposit and coagulate with each other to form atomic clusters and fine particles on a surface of the cathode. Structures of the particles at this stage may be amorphous with high fluidity (liquidlike) because of the high temperature ( 3500 K) of the electrode surface and ion bombardment. 

Fig. 7 Examples of polyhedral oligomeric silsesquioxane (POSS) nanoparticles used to induce homeotropic alignment in nematic liquid crystals...

Similarly, numerous different nanoparticles, including organomodified clays,3 nanoparticles of silica,4 layered double hydroxides (LDH),5 or polyhedral silsesquioxanes (POSS),6 have been combined with intumescent formulations in polymeric materials to create large synergistic effects (see Chapter 12 for more details) the nanoparticles acting as char reinforcer or char expander that result in differences in terms of FR properties. 

The 0-d nanoparticles can be nano-metal oxides (such as silica,1 titania,2 alumina3), nano-metal carbide,4 and polyhedral oligomeric silsesquioxanes (POSS),5 to name just a few the 1-d nanofibers can be carbon nanofiber,6 and carbon nanotubes (CNT),7 which could be single-wall CNTs (SWCNT) or multiwall CNTs (MWCNT) etc. the 2-d nano-layers include, but are not limited to, layered silicates,8 layered double hydroxides (LDH),9 layered zirconium phosphate,10 and layered titanates,11 etc. 3-d nano-networks are rarely used and thus examples are not provided here. 

Figure 5. TEM image of 11 nm polyhedral shaped cobalt nanoparticle assembly with the co-existence of stacking faults (S), twins (T) and particle dislocations (PD) [45].

Rotello et al. used a similar system, relying mainly on multiple thymine/2,6-diamino-pyridine interactions (Fig. 72). Small molecules (such as flavines [241], ferrocenes [242]) can be boimd via a single, thymine/2,6-di-aminopyridine interaction. This can lead to materials with reversible properties, where the redox activity of the surface-bound functional moiety can interact with a current form of the (Au-) surface. The concept has been extended to nanoparticles (Au-NP) [243] and polyhedral ohgomeric silsesquioxanes [244]. The presence of the oligomeric silsesquioxanes was proven by XPS measurements, detecting the Si(2p) peak on the surface after deposition. 

Kwon K, Lee KY, Kim M, Lee YW, Heo J, Ahn SJ, Han SW (2006) High-yield synthesis of monodisperse polyhedral gold nanoparticles with controllable size and their surface-enhanced Raman scattering activity. Chem Phys Lett 432 209-212... 

Fig. 15.5 Oxidation and reduction of epitaxially grown polyhedral Rh nanoparticles (mean size 5 nm) on alumina, monitored ex situ by HRTEM. In the as-prepared state, most of the Rh particles were half-octahedra with 111 and 100 surface facets, as revealed by combining results from HRTEM and WBDF (a, d), and SAED (b). Upon oxidation in 1 bar at 723 K, an epitaxial Rh-oxide shell developed on top of a Rh core (c, e). Reduction in 1 bar H at 523 and 723 K led to polycrystalline (f) and rounded crystalline (g) nanoparticles, respectively. The microstructural changes were correlated with changes in catalytic hydrogenolysis activity (see text for details) adapted in part from [20] with permission. Copyright (1998) Elsevier...

A signal of delocalized it-electrons, on the other hand, is not observed in spherical nano-onions. This means that the dimensions of conjugated spMomains are rather limited and that most it-elecfrons are locahzed instead. An additional broad signal arises, however, for the better graphitized, polyhedral nanoparticles obtained... 

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