Silver nanoparticles core-shell structures

Bimetallic nanoparticles, either as alloys or as core-shell structures, exhibit unique electronic, optical and catalytic properties compared to pure metallic nanopartides [24]. Cu-Ag alloy nanoparticles were obtained through the simultaneous reduction of copper and silver ions again in aqueous starch matrix. The optical properties of these alloy nanopartides vary with their composition, which is seen from the digital photographs in Fig. 8. The formation of alloy was confirmed by single SP maxima which varied depending on the composition of the alloy. 

Competitive reduction of Au(III) and Ag(I) ions occurs simultaneously in solution during exposure to neem leaf extract leads to the preparation of bimetallic Au-core/Ag-shell nanoparticles in solution. TEM revealed that the silver nanoparticles are adsorbed onto the gold nanoparticles, forming a core/sheU structure. Panigrahi et al. [121] reported that sugar-assisted stable Au-core/Ag-shell nanoparticles with particles size of ca. 10 nm were prepared by a wet chemical method. Fructose was found to be the best suited sugar for the preparation of smallest particles. 

Fig. 7.4 (a) Carbon spheres loaded with silver nanoparticles at room temperature (b) carbon spheres loaded with palladium nanoparticles by refluxing (c) silver core of carbon spheres from encapsulation of silver nanoparticle seeds, (d) layered structure with an silver core, a platinum shell, and a carbon interlayer, formed by seeded encapsulation followed by the reflux method. 

Surface-Enhanced Raman Spectroscopy, Fig. 4 Overview of the broad diversity of SERS substrates (a) aggregates of silver nanoparticles fabricated by means of a modified Lee-Meisel protocol, (b) aggregates of gold nanoparticles, (c) enzymatic generated silver nanoparticles with flowerlike shape, (d) nanosized gold cores coated by a silica shell for an application as SERS label, (e) silver nanotriangle structures prepared by means... 

The simplest way of inclusion of inorganic nanoparticles in the microcapsule shells is their adsorption. Thus, a usual layer-by-layer assembly technique is used to embed nanoparticles in a capsule shell structure. For example, microcapsules containing various number of metal (silver or gold) nanoparticles were fabricated. Magnetite particles were included into the inner volume of polyelectrolyte capsules to obtain magnetic-driven delivery system. In this case magnetite was adsorbed on the surface of a melamine formaldehyde latex core, then polyelectrolyte layers were placed, after that the core was dissolved. Also microdrops of octane-based iron oxide nanoparticles suspension emulsificated in polyelectrolyte water solution were used as template cores. 

Analysis of the internal structure of layers of nanoparticles was carried out on samples having typical characteristics for all nanoelements. We determined the particle radius and diameter, and then detected the structure and composition of each layer of the nanoparticles as a function of the relative radius of the nanostructure. Graph of the relative density of the layers nanoparticles is shown in Fig. 4.9. The total value of the relative density of each layer was assumed to be 100%. Internal analysis nanoelements showed uneven distribution of metal nanoparticles in the structure under study. The core of the particle consists mainly of gold, the middle layers are formed by atoms of silver, zinc atoms form a shell. There are transition layers in which there are several metals. 

The nanoscale coating of colloid particles with materials of different compositions has been an active area of research in nanoscience and nanotechnology [2]. Deposition of metal nanoparticles on different colloid particles to form core-shell particles has been one of the most effective tools for achieving such composite nanostructures [172]. In particular, a number of studies on such composite structures were concentrated on the fabrication of metal coated latex particles, because of their potential applications in the fields of surface-enhanced I man scattering (SERS), catalysis, biochemistry, and so forth [173]. Conventionally, silver shells on polymer latex were prepared via wet-chemistry methods, which involve the activation of a latex surface by seeds of a different metal, followed by the deposition of the desired metal [174], or the modification of the latex with groups capable of interacting with the metal precursor ions on the latex surface via complex or ion pairs, and subsequent reduction [175]. 

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