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Synthesis of Nanosilver with PVP-SDS as Soft Templates

Author: WuMengJie
Tutor: FangYun
School: Jiangnan University
Course: Chemical processes
Keywords: Nano-silver Soft template Quintet twins Nanorods Nanosheets Bound micelles Polyvinylpyrrolidone Sodium dodecyl sulfate
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 154
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Abstract

Nano-silver as a special form of metallic silver, with a small particle size, surface area and high catalytic activity, low melting point, while retaining the metallic silver good conductivity, high thermal conductivity, anti-bacterial performance advantages, catalysis, information storage, biomarkers, antibacterial and surface-enhanced Raman spectroscopy has potential applications in the field and scientists close attention. Nano silver depending on the nature of their size, shape, composition, degree of crystallization and structure (solid and hollow). Principle, adjust to any one of the above performance parameters can remote control the nature of the nano-silver. In the method for preparing a large number of nano-silver material, wherein the polyol wears needed for other methods by means of other equipment while having a simple, low-cost and high yield advantages in preparing a special morphology of the nano-material much concern. Of polyol method prototype phase in water at room temperature, under conditions not add a seed crystal, the use of surface active agents and macromolecules silver nanoparticles was prepared as a template, green organic pollution, and also having a high yield, the advantages of low energy consumption. Soft template for a long time, its full protection nanoparticles, the significant advantages of nanoparticle morphology control has been widely used as surfactants and macromolecules. There is interaction between the surfactant and the macromolecule, in a certain concentration of the surfactant within the scope of surfactants and macromolecular soft cluster structure will occur changes in the micelle structure, i.e. the double critical micelle concentration characteristic. In the first critical concentrations c ₁ before, no interaction between macromolecules and surfactant molecules; c ₁ and the c ₂ between the adsorbed surfactant molecules of bound micelles are formed in the macromolecular chains, on the macromolecular chains of bound micelles reach saturation in the c ₂ after freedom micelles begin to form in the solution. PVP is a common water-soluble macromolecules, SDS is a typical anionic surfactant, both a mixed aqueous solution having the above characteristics, and Join silver ammine ions bis critical micelle concentration characteristics are not changed. PVP-SDS mixed aqueous solution as nano prepared soft template has a special meaning, it has two template role, the second control the growth of nanoparticles. In the early stage of the reaction, SDS bound micelles silver ammonia complex ion adsorption solution, the silver ammonium ion in the reaction process is enriched in SDS bound around the micelles is reduced to form a primary nanocrystals, auxiliary homogeneous nucleation process This level role template. With the further increase in the original class of nanocrystalline, dependent on the macromolecular chains of the original nano-silver grains due to the traction of the macromolecular chains to each other near the fusion growth was further nanostructure this second template role. In addition, the PVP molecules having both directional adsorption and weak reduction function, the the PVP molecular chain can be directed adsorption in certain crystal faces of silver nanoparticles, it is conducive to the growth of the silver nanoparticles Orientation; under appropriate conditions PVP chain having a weak reductive role to act as a weak reducing agent silver ammonium ion. Soft template to PVP-SDS at room temperature, the aqueous phase, without adding a seed crystal and an organic solvent under conditions with glucose to restore the silver ammine ions Built quintet twinned silver nanoparticles. The nano silver ion resonance absorption peak at 441 nm, XRD showed that its face centered cubic, the strongest absorption in the (111) crystal plane; confirmed as to lattice fringes of silver nanoparticles observed by HRTEM and twin plane multiple twins (MTP), selected area electron diffraction (SAED) confirmed the quintet twin structure. The nano-particles have a high growth activity, may further growth of silver nanorods. Experimental Investigation of the mechanism of action of the template, in the first stage of the silver nanorod growth, SDS Bound to Micellar main template effect, to obtain a diameter of approximately 5-10 nm of the original nano silver grains. In the second growth phase, PVP macromolecular chains play a major template role of a diameter of about 50 ± 5 nm of sub-nano-silver particles; quintet twins in the third growth stage, crystal growth pattern of dominance of Ostwald ripening growth, synthesis diameter of 40 nm and a maximum length of 700 nm silver nanorods, soft template only secondary crystal growth by selective adsorption play. Using silver nanoparticles prepared from the seed crystal flake soft template under the protection of the PVP-SDS sodium borohydride as a reducing agent quickly restore silver ammonia complex ions of silver seed crystals act as a weak reducing high concentrations of PVP chain in the subsequent reaction agent, slow restore silver ammonia complex ions of silver, regulate the concentration of SDS in the PVP-SDS template, the PVP concentration as well as pH change the morphology of the nano-silver, triangular flakes, disc-shaped, and truncated triangular sheet nano-silver . By assembling dendritic nano-silver structure.

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