Silver nanoparticles chemical reduction

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. 

Recently, novel nanomaterials have become a new frontier for SERS experiments, where different metals are collected together to form, for example, bimetallic particles. Thus, the same nanoparticle could be responsible for both SERS effect and catalytic activity. This is the case of the Ag/Pd colloids synthesized by chemical reduction with sodium borohydride (NaBH4) of silver nitrate (AgNOs) and palladium nitrate (Pd(N03)2), with a 96 4 Ag/Pd molar ratio [11]. The silver nanoparticles provide the SERS enhancement for the ligand molecules, while palladium may induce catalytic reactions. Also, in this case, TEM microscopy provides an important help to characterize these composite materials. In Fig. 20.6 TEM images at different magnifications are reported for bimetallic Ag/Pd particles, in comparison with those constituted by pure silver. While these latter present spheroidal shapes, bimetallic particles show more irregularities, due to palladium clusters in contact with the silver core surface. 

Silver nanoparticles of 23 nm size were formed in aqueous medium by chemical reduction of silver nitrate in excess of aqueous sodium borohydride. To examine the aggregation of the produced silver nanoparticles they were coated either with polyethylene glycol or poly(diallyldimethylammonium chloride). 

Various approaches were developed to prepare silver nanoparticles with the size less than 100 nm photolytic [7] and radiolytic reduction [8], the sonochemical method [9], solvent extraction reduction [10]. Among these methods, chemical reduction is the most common one. One could control the intrinsic properties of synthesized silver nanoparticles during chemical synthesis [11] by reducing the concentration of silver salts and using larger amount of stabilizer to avoid aggregation of the nanoparticles. 

FIGURE 20.6 Schematic representation of silver attachment onto silica NPs. (a) Binding a linker to the silica NPs. (b) Binding silver ion to the linker, (c) Reduction of the silver ions. (From Zidki, T., Cohen, H., Meyerstein, D., and Meisel, D., Effect of silica-supported silver nanoparticles on the dihydrogen yields from irradiated aqueous solutions, J. Phys. Chem. C, 111, 10461-10466. Copyright 2007, with permission from American Chemical Society.)... 

Similarly, using the same particles as those used for the synthesis of CdS QDs (see Sect. 6.2, Fig. 36), silver nanoparticles could be deposited onto carboxylated poly(MMA-co-MAA) particles using silver salts as precursors [315, 316]. As for the case of CdS, periodic structures of polymer/silver hybrid colloids were elaborated. The method obviously opens a new avenue for production of optically responsive materials with a controlled periodicity. In another work using commercial llOnm carboxylate-functionalized PS particles as templates, Hao et al. reported the synthesis of silver nanodisks formed through chemical reduction of silver salts in DMF [332]. The composite particles obtained (Fig. 39) exhibited an intense electronic spectrum differing markedly from those of spheres. Still using... 

Processes for the preparation of silver nanoparticles were carried out using a one-step chemical reduction in the aquatic environment. The studies were conducted using raw materials which are safe for the environment. The properties of chemicals used make it possible to treat them as friendly for human and nature. 

Figure 8.12. TEM image of silver nanoparticles at pH 6, synthesized by NaBH4 reduction of AgNOs Inset particle size histogram from >100 particles. Taken with permission from [105], P. Rijiravanich, M. Somasun-drum,andW. Surareungchai,Ana/. Chem. 80, 3904-3909 [2008], Supporting Information. American Chemical Society.

Two chemical ways were used to include metal nanoparticles inclusion in the microcapsule shell. It was photoreduction of silver under of UV-irradiation and chemical reduction of silver by acetaldehyde oxidation (reaction of a "silver mirror"). The polystyrene latex and calcium carbonate were used as a template for the formation of polyelectrolyte shells. 

Kem and coworkers have also explored controllable, uniform metal deposition by employing TMV as a biotemplate. In their studies, the addressable amino acid side chains that function as metal nncleation sites are first activated with a metal complex, followed by incubation with the desired metal for metallization and its subsequent chemical reduction to form metal nanoparticles. By employing this approach of electroless deposition, discrete nickel, silver, and cobalt nanoclusters were selectively formed on the interior or exterior of the virus by controlling the pH and the activation complex used in the reaction. In addition... 

Chemical reduction is the most frequently applied method for the preparation of silver nanoparticles as stable, colloidal dispersions in water or organic solvents. However, a number of alternative green chemistry synthesis routes have been reported. Inspired by mussel adhesive proteins, a novel functional polyurethane based on hydrolyzable tannins that contain a number of catechol groups was... 

Using silver(I)-bis(oxalato)palladate(II) complex, Rhee et al. reported synthesis of ultrafine Ag-Pd bimetallic nanoparticles. The advantage of this complex, which contains both metal ions, is prevention of formation of silver halides. Moreover, the oxalate ligand rapidly decomposes by light irradiation or chemical reduction. It was demonstrated that the particle size distribution is dependent on the Ag/Pd ratio [46],... 

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