Abstract
Binary gold–silver nanostructures of preformed gold nanoparticles (25 nm) in silver nitrate solutions are produced by a two step sonication (20 kHz). Ultrasonic treatment of gold–silver mixtures is carried out in the presence of sodium dodecyl sulfate in water or 2-propanol, and poly(vinyl pyrrolidone) in ethylene glycol solutions. Gold–silver nano-worms, which consist of ripened gold particles connected by ultrasonically reduced silver, are formed after 1 h of sonication in the presence of sodium dodecyl sulfate aqueous solution. In 2-propanol bimetallic nano-worms have a well defined core–shell structure. Polygonal alloy nanoparticles with gold as a core material and a silver shell are produced after 180 min of sonication in the presence of poly(vinyl pyrrolidone) in ethylene glycol solution. Bimetallic gold–silver nanostructures have defected face centered cubic structure and represent polycrystals with a large number of crystallites randomly oriented. For the first time, the mechanism of gold particle design by ultrasound is examined in detail. The role of additives (sodium dodecyl sulfate, polyvinyl pyrrolidone, ethylene glycol and 2-propanol) as reductants of silver at the gold contact surface or stabilizers of particles is highlighted.
Highlights
Colloidal gold is the most stable metal dispersion towards moisture, oxygen and most corrosive reagents
The examined surface plasmon resonance band, crystalline structure and elemental composition of ultrasonically treated gold sols without silver nitrate in the presence of sodium dodecyl sulfate in aqueous solution proves that gold–silver nano-worms consist of ripened gold nanoparticles, which are connected by reduced silver in between
Sodium dodecyl sulfate in aqueous solution 17.28 mg of SDS in 30 mL of H2O was stirred for 15 min and 7.5 mL of 40 mmol dmÀ3 AgNO3 was added, and the mixture was sonicated for 30 min at 23.8 W cmÀ2. 7.5 mL of 5 mmol dmÀ3 concentration of preformed colloidal gold solution was mixed with 4.25 mg of SDS, shaken for 15 min and added to the sonicated SDS–silver solution for ultrasonic treatment for 60 min at 38.9 W cmÀ2
Summary
Colloidal gold is the most stable metal dispersion towards moisture, oxygen and most corrosive reagents. In contrast to the descriptive nature of the earlier article, the present manuscript elucidates the role of surface active additives (sodium dodecyl sulfate and poly(vinyl pyrrolidone)) and solutes (2-propanol and ethylene glycol) in the silver reduction to produce gold–silver nanostructures with different morphology. The examined surface plasmon resonance band, crystalline structure and elemental composition of ultrasonically treated gold sols without silver nitrate in the presence of sodium dodecyl sulfate in aqueous solution proves that gold–silver nano-worms consist of ripened gold nanoparticles, which are connected by reduced silver in between. The kinetics formation of silver shell at the surface of preformed gold nanoparticles in the presence of polyvinyl pyrrolidone in ethylene glycol solution is expanded by the study of elemental composition versus time and crystalline structure of binary nanostructures. Preformed gold nanoparticles in silver nitrate solution are substituted by silver sols in order to elucidate the silver reduction during sonication
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