Nanostructures silica metallized

A size-selective synthesis of nanostructured transition metal clusters (Pd, Ni) has been reported166, as has the preparation of colloidal palladium in organic solvents167, the latter of which is an active and stable catalyst for selective hydrogenation. The use of microwaves in the preparation of palladium catalysts on alumina and silica resulted in hydrogenation catalysts with improved crystallite size and activity168. 

Many nanostructural possibilities for creating very effective nanomaterials for photocatalytic decontamination are possible. The doping (or docking) of transition metal ions of visible light chromophores (e.g., vanadinm, chromium, manganese, iron, or cobalt) into the backbone of nanostructured silica (SiO ), titania (TiOj), silica-titania, as well as POMs, has been demonstrated. Other possibilities, such as halogens, metal nanoparticles, or other POMs with particular tuned potentials could be stored in pores as special chromophores. 

When precursors are sonicated in high-boiling alkanes, e.g., decane or hexa-decane, nanostructured powders are formed. Using a polymeric ligand [e.g., polyvinylpyrrolidone (PVP)] or inorganic supports (silica, alumina, etc.), nanophase metal colloids, and nanostructured supported metal catalysts are generated, with very interesting catalytic activity. 

Examples of dense silica, hybrid silica, metal oxides, solid-state metal oxide solutions, or colloidal self-assembly are unlimited. However, the recent developments to accurately control processing conditions (e.g., atmosphere, temperature, and motion) led to films with unique properties (see Figure 9.6) [52,53]. These progresses concern mesoporous coatings with controlled pore size and structure [26], hard template infiltration and/or replication [54-58], nanostructured epitaxial low-quartz thin films [59], ultrathin nanostructured supported networks [60,61], ultrathick porous Ti02 layer prepared from aqueous solutions [51], coatings with hierarchical porosity [62], multilayer porous stacks [63], colloidal MOF layers [64,65], pillar planar nanochannels (PPNs) for nanofluidics [66], and so on. 

An interesting variation on template deposition is to self-assanble ordered nanostructures (e.g., surfactants) and microstructures (e.g., polystyrene or Si02 beads) on the surface of an electrode and then electrodeposit into the self-assembled pores. The order in the resulting nanostructure is imposed by the self-assembled layer, not by the substrate. Schwartz and coworkers have extended this idea to the use of crystalline protein masks to produce ordered nanostructures of metals (such as Ni, Pt, Pd, and Co) and metal oxides (such as Cu20). Braun and coworkers have used the electrodeposition of materials into self-assembled colloidal crystals or silica or polymer opals. The template is then removed (see Figure 17.11) to produce an inverse opal. This type of templating produces periodic microstructures that can be used to produce functional photonics. Figure 17.11 shows the production of CdSe and Ni inverse opals by electrodeposition into a colloidal crystal with subsequent removal of the colloidal crystal template. ... 

P. Mazzoldi, G. Mattel, C. Maurizio, E. Cattaruzza, F. Gonella, in E. Knystautas (ed.) Metal Alloy Nanoclusters by Ion Implantation in Silica, in Engineering Thin Films and Nanostructures with Ion Beams, Chapter 7, CRC Press, New York, 2005, 82. 

Epoxy-silica hybrids are well known for their abrasion resistance and low thermal expansion due to the presence of nanostructured bi-continuous domains. Most recently they have entered the market as anticorrosion coatings in the marine held, for yachts and for large metal vessels, such as oil tankers, and in particular for cargo or ballast tanks and on hulls (Figure 4.9). 

Figure 5 shows two typical core-shell structures (a) contains a metal core and a dye doped silica shell [30, 32, 33, 78-85] and (b) has a dye doped silica core and a metal shell [31, 34]. There is a spacer between the core and the shell to maintain the distance between the fluorophores and the metal to avoid fluorescence quenching [30, 32, 33, 78-80, 83]. Usually, the spacer is a silica layer in this type of nanostructures. Various Ag and Au nanomaterials in different shapes have been used for fluorescence enhancement. Occasionally, Pt and Au-Ag alloys are selected as the metal. A few fluorophores have been studied in these two core-shell structures including Cy3 [30], cascade yellow [78], carboxyfluorescein [78], Ru(bpy)32+ [31, 34], R6G [34], fluorescein isothiocyanate [79], Rhodamine 800 [32, 33], Alexa Fluor 647 [32], NIR 797 [82], dansylamide [84], oxazin 725 [85], and Eu3+ complexes [33, 83]. 

More pragmatically, one can attempt to address the question of the benefits of nanostructured catalysts by comparison against the properties of similar catalysts prepared by traditional methods. There are a couple of well-known reactions that are thought to be catalyzed by atomically dispersed metals on supports [95]. Epoxi-dation of olefins by titanium on silica is one [96, 97]. 

NIR-absorbing metal nanostructures are appealing for biomedical imaging applications for reasons discussed previously, and this includes biological applications of SERS. For example, NIR-active core-shell superparticles have been prepared by the electrostatic assembly of densely packed Au nanoparticles on submicron silica spheres.34 Such superparticle probes can be implanted into mammalian cells by cationic transfection,186 and have produced SERS signals from absorbed DNA.187 Biocompatible SERS nanoparticle tags can also be used as contrast agents for in vivo detection, as previously discussed.169... 

Potential applications of peptide-polymer conjugates include drug delivery materials, optoelectronics, biosensors, tissue scaffolds, tissue replacement materials, hydrogels, adhesives, biomimetic polymers, lithographic masks, and templates for metallic or silica nanostructures. 

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