Metal nanoparticles synthesis aqueous phase

Single step synthesis of transition metal nanoparticles in aqueous phase for catalytic applications... 

A number of other reports have been made relating to the use of surfactants, reverse micelles, microemulsions, membranes and polyelectrolytes for the synthesis of noble metal nanoparticles [157-159]. This type of synthetic method generally involves a two-phase system with a surfactant causing the formation of a microemulsion or micelle, and maintains a favorable microenvironment together with extraction of metal ions from aqueous phase to organic phase. In such cases, the surfactant not only acts as a stabilizer but also plays an important role in controlling crystal growth. 

This method has been successfully applied for the synthesis of metals, metal oxides, alloys and core-shell nanoparticles. The synthesis of metal oxides from reverse micelles is similar in most aspects to their synthesis in aqueous phase by a precipitation process. For example, precipitation of hydroxides is obtained by addition of a base such as NH3(aq) or NaOH to a reverse micelle solution... 

The formation and stabilization of noble metal colloids in the aqueous phase are widely known. Platinum and palladium are most widely used in hydrogenation of C=C bonds but some results have been described with rhodium. Generally, surfactants are investigated as stabilizers for the preparation of rhodium nanoparticles for biphasic catalysis in water. In many cases, ionic surfactants, such as ammonium salts, which provide sufficiently hydrophilic character to maintain the catalytic species within the aqueous phase, are used. The obtained micelles constitute interesting nanoreactors for the synthesis of controlled size nanoparticles due to the confinement of the particles inside the micelle cores. Aqueous colloidal solutions are then obtained and can be easily used as catalysts. 

Keywords Solution Combustion Synthesis, Metal Nanoparticles, Aqueous Phase Synthesis, Heterogeneous Catdysis... 

Two systems were used by Chen et al. [428] for synthesis of cobalt metal nanoparticles. One of them was the well-known system AOT/isooctane/aqueous solution. Two reverse microemulsions (w = 11) were prepared with 0.3M C0CI2 or 0.6M NaBH4 dissolved in water as the aqueous phase. The microemulsions, when mixed, yielded a black colloid. Removal of the isooctane led to the formation of a paste containing Co particles in AOT. The surfactant was removed by washing with water. The product in this form, or as a powdery material, yielded 3-4 nm sized Co particles. Heating at 550°C/2 h produced crystalline Co. 

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