Nanoparticles nanoscale templates

Finally, among other classes of nanoparticles, carbon nanotubes and graphene nanosheets deserve special attention for a number of reasons. They can be used to improve the conductivity of nanofibers, to enhance their mechanical strength and to serve as nanoscale templates inducing a higher... 

While the use of metal oxide nanoparticles is dependent on their synthesis and subsequent magnetic or ceramic properties, size homogeneity is also necessary because the nanoparticles properties are related directly to their size. Natural templates, such as butterfly scales, peptide nanorings and bacterial or protein cages, can be tuned to induce narrow size distributions that have yet to be seen within an industrial setting. These chemically engineered systems have been proven to serve as viable nanoscale templates for the constrained biomimetic synthesis of higher-ordered metal oxide nanoparticles with unique properties specific to their synthesis. 

A general approach to prepare hollow spheres of ceramic materials with func-tionaUzed interior surface has also been reported [121]. The onter surfaces of the templating PS beads are first coated with submonolayers of silver nanoparlicles, and they are assembled into a three-dimensional crystalline lattice. The beads are then coated with a titania layer. After the PS beads are dissolved in toluene, uniform hollow spheres are generated, with their interior surfaces being functionalized with the silver nanoparticles. Meanwhile, silver nanoparticles can be selectively removed using another wet etchant to produce an array of nanosized cavities on the interior surface of the hollow sphere. These nanoscale cavities may have functionality similar to that of the nanoscale template, as demonstrated in the area of molecular imprinting [122,123]. 

The coating of templates already indicated that carbonaceous hybrid materials on the nanoscale length can be produced when leaving the second material phase within the carbon frame. In the case of functional nanoparticles and nanostructures, this has tremendous importance for various applications in science and technology [18]. Consequently, hydrothermal carbonization has been also intensively used for the production of various hybrids. 

Figure 15.1 Ordered nanoscale structures of mesoporous materials such as FSM-16 and HMM-1 (Et-HMM-1) as the silica and organosilica templates for surface-mediated synthesis of metal/alloy nanowires and nanoparticles.

This chapter deals with the selective preparation, TEM/EXAFS/XPS characterization and catalysis of mono- and bimetallic nanowires and nanoparticles highly ordered in silica FSM-16, organosilica HMM-1 and mesoporous silica thin films. The mechanism of nanowire formation is discussed with the specific surface-mediated reactions of metal precursors in the restraint of nanoscale void space of mesoporous silica templates. The unique catalytic performances of nanowires and particles occluded in mesoporous cavities are also reviewed in terms of their shape and size dependency in catalysis as well as their unique electronic and magnetic properties for the device application. 

We have reviewed the state of the art of the synthesis and applications of metal/ alloy nanowires and nanoparticles by surface-mediated fabrication using different mesoporous silica templates. New nanoscale materials are appearing one after another by the use of many kinds of mesoporous materials as templates, and we are facing a rapid advance of this research field. So far, many studies have focused... 

Self-assembly of molecules and nanoparticles to build well-defined structures, constitutes another approach to make model catalysts [33,34]. Here, nano-structured surfaces are made from nanoscale building blocks that are synthesized from atoms and molecules by chemical means. There has been a tremendous development in this field during the past decade, which includes a number of different strategies, including microemulsions [33], (micellar) block copolymers [35,36], and template CVD growth [37]. Relatively little work has, however, so far been directed toward heterogeneous catalysis in the sense described in this chapter, i.e., to make supported catalysts [38]. There are many reports on preparations but relatively much fewer on evaluations of catal3dic activity, trends, or reactivity versus particle size, etc. A main issue for model catalysts prepared by self-assembly is whether they maintain the well-defined character after, e.g., template removal and calcinations and other pretreatment steps, before they can be used as model catalysts. 

Gold nanoparticles have also been chosen due to their high electronic conductivity, their thermod5mamically stable interface with C03O4, and the potential to catalyze electrochemical reactions at the nanoscale. Belcher et al. propose hybrid gold-cobalt oxide wires prepared by a virus-templated synthesis. The cell delivered 94% of its theoretical capacity at a rate of 1.12 C and 65% at a rate of 5.19 C. Thus, the authors evidenced that nanoscale battery components can be designed and assembled on the basis of biological principles [54]. 

ID assemblies of nanopaiticles refer to the controlled assembly of nanoparticles into wires, rods, belts, rings, and tubes, which have become the focus of intensive research owing to their unique application in mesoscopic physics and fabrication of nanoscale devices. The basic method for ID assemblies can be divided into template-directed method and template-free method which will be introduced in the following text. 

The nanocomposites based on cellulose can be made in two ways (a) the disintegrated microfibrils/nanoscale whiskers can be used for reinforcing polymers and (b) cellulose or cellulose derivatives can be reinforced by other nanoscale particles. In nanoscience and nanotechnology, cellulose and its derivatives are used as templates and surfactants for synthesizing inorganic nanoparticles for many industrial and biomedical applications. 

G.A. Seisenbaeva and V.G. Kessler, Precursor directed synthesis - molecular mechanisms in the Soft Chemistry approaches and their use for template-free synthesis of metal, metaloxide and metal chalcogenide nanoparticles and nanostructures, Nanoscale, Vol. 4, pp. 6229-6244,2004. 

Another self-assembly concept that provides a nanoscale linear template for protein and inorganic nanoparticles was developed by the Zuckermann group. For instance, they demonstrate a reversible molecular tool for assembly of modified peptides in the presence of divalent metal ions. The generated nanofibres could be disassembled by adding a strong metal-chelating reagent such as EDTA [38]. 

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