Abstract
Here we report a study on controllable synthesis of hierarchical silver structures via regulating reaction kinetics. Silver particles with various morphologies are synthesized by a solution-based reduction approach at the addition of amino acids. The amino acid is used to coordinate with silver ions to slow down the reduction of silver ions. With the increase of glycine concentration, the morphologies of silver particles switch from dendrites, to flowers and to compacted spheres, which is attributed to the decrease of reaction rate as a result of the coordination. Three more amino acids are examined and confirms the role of reaction kinetic in shaping silver particles. Furthermore, by increasing the concentration of the reductant, the silver morphologies change from compact spheres to loose flowers as a result of the increase of reaction rate. Therefore the silver hierarchical structure can be reversibly switched by reaction kinetics. The silver particles synthesized are tested for surface enhanced Raman scattering (SERS) property and the dendritic particles present a remarkable SERS activity. This study shows that reaction kinetics is a powerful tool to tune hierarchical structures of silver particles, which is expected to be transferable to other material systems.
Highlights
Speaking, hierarchical structures are not thermodynamically favored shape but should be the products of kinetics
To understand why the reaction kinetics dominates the morphology of silver products, we have to consider the formation mechanism of silver dendrites
The growth of dendritic structures is dependent on the chemical concentration around the growth front, which is determined by the diffusion and reaction rates of chemicals
Summary
Hierarchical structures are not thermodynamically favored shape but should be the products of kinetics. Diffusion and reaction rates are two general parameters influencing the structure development of materials[20,21]. By regulating diffusion and reaction rates, we have synthesized calcium carbonate particles with various morphologies[26]. To determine the role of diffusion and reaction separately, we have designed reactors to regulate the diffusion of chemicals, which leaded to the morphologies of platinum products switching from cubic to spherical[27]. The reduction rate is regulated by changing the concentration of amino acids. By regulating the ratio of reductant and amino acids, the reaction rate can be reversibly switched, which leads to a reversible change of silver hierarchical structures from dendrites to spheres. The SERS activity of silver particles with diverse morphologies is investigated and the silver dendrites show excellent SERS enhancement
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