Mechanism Study For Shape-Control Of The Gold And Silver Nanoparticles By Chlorine Ions

Recently, gold and silver nanoparticles, two of the important noble metals, have been extensively studied as active components in a wide variety of fundamental researches and technical applications due to their unique structures, optical, electric, catalytic properties and biocompatibility. Great efforts have been devoted to control the size and shape of the metal nanopaticles since it is well documented that their properties are both size- and shape-dependent. Many publications about the synthetic methods of the gold and silver nanoparticles have been reported. For example, many people utilized sodium borohydride or sodium citrate as the reducing agent to synthesis the gold or silver nanoparticles in one step. The nanoparticles with monodisperse dimension can be tuned from several nanometers to a few dozens. Other people fabricated the nanoparticles/composites with solid/hollow interior using seeding approach. Many perspectives about the growth mechanism have been proposed in the literature, such as nucleation-growth, aggregation and ripening. In addition, the organic molecules and some inorganic ions have been found to affect the morphology of the nanoparticles. For instance, some researchers utilized CTAB as the template to synthesize gold nanoparticles with anisotropic structures. And other researchers also reported that inorganic ions, such as silver ions and iodine ions, can manipulated the shape of the nanoparticles. However, just like water effect was neglected for synthesis of nanoparticles in the aqueous solution, the effect of some inevitable factors introduced by reactants for the synthesis as well as shape-control of the nanoparticles has not been taken into account.In this dissertation, the growth kinetics of the gold and silver nanoparticles was investigated systematically and quantitatively. The effect of Cl- on the synthesis of nanoparticles were revealed and used to effectively manipulate the shape of the nanoparticles.1,The seeding approach for preparation of gold nanoflowers in which 25 nm gold nanoparticles were used as the seeds and mixture of HAuCl4 and hydroxylamine as growth solution were investigated systematically. It is revealed that the formation and stability of the nanoflowers were affected greatly by the intraparticle ripening induced by the chlorine ions existed in the reaction system. In this seeding approach, hydroxylamine promoted the rapid reduction of HAuCl4 and thus rapid formation of small Au particles with diameter around 3 nm in the growth solution. The attachment of the small particles on the seed surface contributed to the growth of the nanoflowers. The branch length of the nanoflowers increased with the increased pH of the growth solution due to the suppressed ripening at higher pH. Stability of the nanoflowers can be improved by increasing the pH of the storing solution and/or removal of the chlorine ions.2,For the reactions to synthesize Ag/Au hollow nanostructures by using silver nanoparticles as the seeds and the mixtures of HAuCl4 and hydroxylamine as the growth solutions, the existence of Cl- is likely to affect the shape of the nanostructures. For the reactions of low pH (4.2?10.3), the hollow Ag/Au nanostructures were irregular in shape due to the suppressed reduction and deposition of metallic precursors induced by AgCl. However, for the reactions of high pH (10.6?12.5), the disappearance of AgCl due to the competition of hydroxyl groups with chlorine ions to Ag+ in the solution facilitated the reduction and deposition of metallic ions, resulting in the hollow Ag/Au nanoflowers.3,We have found the chlorine ions can accelerated the intraparticle ripening and AgCl can suppressed the reducing rate and deposition of the metallic ions in above works. So the Cl- and other related ions were used to control the branch of the gold nanoflowers. It is found that the halide ions accelerated the intraparticle ripening of the gold nanoflowers and the branch can be tuned by simply changing the concentration of the halide ions at high pH. However, the introduction of Ag+ into the reaction solution suppressed the intraparticle ripening and the gold nanoflowers with longer branch were obtained at low pH. These results further proved the understanding for the synthesis of metallic nanoparticles in my previous work.4,In this chapter, the shape control of the nanoparticles using the Cl- and other related ions was applied in the Frens method. It is conclude that the accelerated ripening induced by chlorine ions and suppressed ripening by hydroxyl groups and AgCl were also applicative in Frens method. When the chlorine ions were introduced into the reaction solution, the nanoparticles transformed from ellipsoidal to spherical shape. However, when the hydroxyl groups or Ag+ were introduced into the reaction solution, the nanoparticles became more anisotropic and exhibited as short line and tadpole. Besides, the different reaction time at which the ions were introduced into the reaction solution have greatly effect on the introparticle ripening, thus the formation of the nanoparticles.