Synthesis And Characterization Of Morphology Controllable Silver Nanostructures And Ag/ZnO Composite Materials

Silver nanostructures have great advantages, such as unique optical properties, high electrical conductivity, high catalytic ability, high antibacterial activity. These advantages determine that Silver nanostructures play an important role in photoelectric materials, electrode materials, catalytic materials, and antibacterial materials. However, the excellent properties of silver nanostructures are mainly dependent on their shapes and sizes. Thus, the shape-controllable synthesis of silver nanostructures has garnered a significant attention. In this paper, the synthesis and growth mechanism of shape-controlled silver nanostructures were investigated systematically by microwave assisted polyols method. The wormlike Ag/ZnO and firecracker-like Ag/ZnO were synthesized with prepared silver nanowires by microwave method and hydrothermal method. And their formation mechanisms were also clarified. These main results are listed as below:1. Uniform silver nanoparticles were prepared with ethylene glycol (EG) as reducing agent and solvent and with poly (vintlpyrrolidone)(PVP) as surfactant. The effects of reaction time, microwave power, PVP concentration, and AgNO3 concentration on the morphology and size of silver nanostructures were studied. The results show that the dispersivity of Ag nanoparticles was good, and the surfaces of silver nanoparticles were easily absorbed and covered by PVP, which prevented the agglomeration of silver nanoparticles. As the reaction time increased, the adsorption effect of PVP was greater than that of growth rate, promoting the formation of small size Ag nanoparticles. As the microwave power and the AgNO3concentration increased, the nucleation rate became higher than growth rate, promoting the formation of small size Ag nanoparticles.2. Silver nanowires and nanocubes were obtained by adding different concentrations of Na2S into the solution. Silver nanocubes were synthesized under low concentration of Na2S. The low concentration of Ag2S, which is an n-type semiconductor as catalytic agent, catalyzed Ag+reduction, increased the rate of Ag+reduction, and promoted supersaturation with silver seeds and subsequent formation of single-crystalline seeds. The seeds fast grew into silver nanocubes with the PVP adsorption. Silver nanowires were synthesized of high concentration of Na2S. A high concentration of Ag2S as controlling agents reduced the concentration of free Ag+in the solution, decreased the rate of Ag+reduction, and promoted the formation of the decahedral twinned nanoparticle. In the subsequent reaction, Ag+ions were gradually released from Ag2S colloids into the solution, keeping the equilibrium concentrations of in soluble and soluble salts. The twincrystal nanparticles fast grew into silver nanowires with the adsorption of PVP on the{100} facets. When the concentration of Na2S gradually increased (rang from2.0mM to3.5mM), silver nanowires with large diameters were obtained.3. Silver nanowires were obtained using CuCl2as controlling agents. The results show that AgCl colloids were formed from Cl-and free Ag+in the solution, reducing the concentration of Ag+ions in solution, decreasing the rate of Ag+reduction, and resulting in formation of multiply twinned seeds of decahedral shape. In the subsequent reaction, Ag+ions were gradually released from AgCl colloids into the solution. Cu2+was reduced Cu+, and then Cu+was oxidized Cu to consume O2and thus to prevent the silver seeds from being etched by Cr/O2.These multiply twinned seeds of decahedral shape can grew into silver nanowires due to selective adsorption of PVP on{100} facets.4. Wormlike Ag/ZnO core-shell structures were synthesized by microwave method with silver nanowires, zinc acetate, and triethanolamine (TEA) as raw materials. The structures were composed of single crystal Ag nanowires (core) and dense regular ZnO particles (shell) grown on Ag nanowires. Firecracker-like Ag/ZnO heterojunction was synthesized by hydrothermal method using silver nanowires, zinc nitrate, and hexamethylene tetramine (HMT) as raw materials. The structures were formed by the growth of about100nm ZnO nanorods perpendicular to the axis of Ag nanowires.