Nanoparticle self-organization

Fig. 3. Methods of YAG nanopowders compaction using nanoparticles self-organization processes.

Part V, which is about interfacial photocatalysis, includes such topics as nanochemistry, nanoparticles, self-organized microheterogeneous structures, photosensitizers. 

An efficient and practically convenient method of metal nanoparticles deposition has been developed which enables covering a large semiconductor surface area with nanoparticles of various metals. One can fabricate isolated nanoparticles, self-organized ensembles, both ordered and disordered, and also dense fractal aggregates. The particle size is in the range of 5-70 nm depending on the nature of metals. The shape of the nanoparticle ensembles is determined by a microrelief of the semiconductor surface. 

B. Donnio, P. Garcia-Vazquez, J.-L. Gallani, D. Guillon, E. Terazzi, Dendronized ferromagnetic gold nanoparticles self-organized in a thermotropic cubic phase. Adv. Mater. 19, 3534-3539 (2007)... 

When the silver nanocrystals are organized in a 2D superlattice, the plasmon peak is shifted toward an energy lower than that obtained in solution (Fig. 6). The covered support is washed with hexane, and the nanoparticles are dispersed again in the solvent. The absorption spectrum of the latter solution is similar to that used to cover the support (free particles in hexane). This clearly indicates that the shift in the absorption spectrum of nanosized silver particles is due to their self-organization on the support. The bandwidth of the plasmon peak (1.3 eV) obtained after deposition is larger than that in solution (0.9 eV). This can be attributed to a change in the dielectric constant of the composite medium. Similar behavior is observed for various nanocrystal sizes (from 3 to 8 nm). 

Keywords Organometallic Nanoparticles Surface chemistry Self-organization Catalysis... 

In order to make practical use of the physical properties of nanoparticles, whether individual or collective, one has to find a way to address them. If we leave out the near field techniques, this in turn requires that the particles be monodisperse and organized in two or three dimensions. It is therefore necessary to imagine techniques allowing the self-organization and even, ideally, the crystallization of nanoparticles into super-lattices. 

In summary, super-lattices may be obtained using the estabUshed techniques of self-organization but also a technique derived from molecular chemistry, the creation of hydrogen bond networks, hi addition, the crystallization of nanoparticles inside 3D super-crystals may be achieved using ionic stabilizers. 

This study could be extended to the synthesis of iron nanoparticles. Using Fe[N(SiMe3)2]2 as precursor and a mixture of HDA and oleic acid, spherical nanoparticles are initially formed as in the case of cobalt. However, a thermal treatment at 150 °C in the presence of H2 leads to coalescence of the particles into cubic particles of 7 nm side length. Furthermore, these particles self-organize into cubic super-structures (cubes of cubes Fig. ) [79]. The nanoparticles are very air-sensitive but consist of zerovalent iron as evidenced by Mossbauer spectroscopy. The fact that the spherical particles present at the early stage of the reaction coalesce into rods in the case of cobalt and cubes in the case of iron is attributed to the crystal structure of the metal particles hep for cobalt, bcc for iron. 

The synthesis of bimetallic nanoparticles is mainly divided into two methods, i.e., chemical and physical method, or bottom-up and top-down method. The chemical method involves (1) simultaneous or co-reduction, (2) successive or two-stepped reduction of two kinds of metal ions, and (3) self-organization of bimetallic nanoparticle by physically mixing two kinds of already-prepared monometallic nanoparticles with or without after-treatments. Bimetallic nanoparticle alloys are prepared usually by the simultaneous reduction while bimetallic nanoparticles with core/shell structures are prepared usually by the successive reduction. In the preparation of bimetallic nanoparticles, one of the most interesting aspects is a core/shell structure. The surface element plays an important role in the functions of metal nanoparticles like catal5dic and optical properties, but these properties can be tuned by addition of the second element which may be located on the surface or in the center of the particles adjacent to the surface element. So, we would like to use following marks to inscribe the bimetallic nanoparticles composed of metal 1, Mi and metal 2, M2. 

Fig. 3.3 The common two-stage sol-gel process used to entrap biopolymers in a silica matrix (see Scheme 3.1). The first stage serves to hydrolyze alkoxide Equation (2) in the acidic or alkaline media. This is also attended with condensation reactions Equations (3) and (4) resulting in the formation of oligomeric silica that self-organizes in the form of sol nanoparticles. Biopolymers are entrapped in the...

Akagi T, Baba M, Akashi M (2007) Preparation of nanoparticles by the self-organization of polymers consisting of hydrophobic and hydrophilic segments potential applications. Polymer 48 6729-6747... 

This section provides a comprehensive overview of recent efforts in physical theory, molecular modeling, and performance modeling of CLs in PEFCs. Our major focus will be on state-of-the-art CLs that contain Pt nanoparticle electrocatalysts, a porous carbonaceous substrate, and an embedded network of interconnected ionomer domains as the main constituents. The section starts with a general discussion of structure and processes in catalyst layers and how they transpire in the evaluation of performance. Thereafter, aspects related to self-organization phenomena in catalyst layer inks during fabrication will be discussed. These phenomena determine the effective properties for transport and electrocatalytic activity. Finally, physical models of catalyst layer operation will be reviewed that relate structure, processes, and operating conditions to performance. 

---