Study On The Preparation And Catalytic Properties Of Micro/nano-structured Silver Particles

Uniform micro/nano-structured silver particles have attracted extensive attention dueto their importance in a wide range of applications including electronics, catalysis, optics,and surface-enhanced Raman scattering （SERS）. These applications are due to the uniqueproperties of silver particles, which mainly depend on the morphology and size of silverparticles. The morphology and size of as-obtained particles are affected by synthesismethods and conditions. As a result, interest in the synthesis of micro/nano-structuredsilver particles has been growing steadily over the past decades. Among many synthesismethods, wet chemical reduction method is probably the most popular one for itssimplicity, low cost and easiness of manipulating. Therefore, wet chemical reductionmethod was used to synthesize micro/nano-structured silver particles with differentmorphologies and sizes in this work. Controlled synthesis of silver particles wasinvestigated by reducing silver nitrate with ascorbic acid. We synthesized not onlymono-dispersive silver particles with dispersing agents, such as polyvinyl pyrrolidone（PVP, K30） and gum arabic, but also clean silver particles without dispersing agents. Thestructure and morphology of these particles were investigated by X-ray diffraction （XRD）,feld-emission scanning electron microscopy （FESEM） and transmission electronmicroscopy （TEM）. The influence factors, such as reactant concentrations, reaction timeand temperature were investigated. The catalytic activity of these micro/nano-structuredsilver particles was tested by catalytic reduction of p-nitrophenol by sodium borohydride.This work mainly includes the following aspects:PVP and gum arabic were used as dispersing agents to synthesize silver particles,respectively. It was found that the reactant concentrations and reaction, the adding methodof gum arabic and reaction temperature all have important influences on the morphologyand size of silver particles. Adjusting these parameters, mono-dispersive silver particlescould be controllably synthesized. The catalytic activity of these obtained silver particleshad been studied. The results indicated that these silver particles have relative highcatalytic activity compared with silver nanoparticles reported in literatures.Clean micro/nano-structured silver particles were synthesized by rapid reducing silver nitrate with ascorbic acid in the absence of dispersing agents. The influence factorsfor morphology were also investigated. The formation process of micro/nano-structuredsilver particles was investigated. It was found that these silver particles were formed byaggregation of subunits. The shape of these subunits was dominantly affected by molarratio of ascorbic acid to silver nitrate. The size of these subunits can be controlled byaddition of dispersing agents and changing the reactant concentrations.The catalytic activity of these clean silver particles had also been studied. It wasfound that silver particles prepared by reduced0.3M silver nitrate with0.21M ascorbicacid exhibited the highest catalytic activity, and the Kappis9.68×10^-3s^-1, which is about10times higher than that of silver nanoparticles. And it is also higher than that of silverparticles with dispersing agents in our study. It was also found that silver particles withlonger plate-like subunits and higher crystallinity showed better catalytic activity.Considering the facile synthesis and high catalytic activity, these micro/nano-structuredsilver particles may find wide applications in catalytic fields.