Synthesis Of Nanosilver With PVP-SDS As Soft Templates

As a special form of silver, the nano-silver not only has advantages of small particle size, large surface area, high catalytic activity and low melting point, but also maintains good characteristics of metal silver, such as high electrical conductivity, high thermal conductivity and good performance in anti-bacterial. Since then it has been widely used in catalysis, information storage, biological labeling, anti-bacterial and surface enhanced Raman scattering (SERS). The properties of the nano-silver are mainly determined by its size, shape, composition, crystallinity and morphology (solid versus hollow). In principle, one could control any of these parameters to fine-tune the properties of the nano-silver.Compared with other preparation of the nano-silver, polyol process has been increasing popular, which has various advantages, such as simple, inexpensive, high yield and without needing the help of machine. In this paper, based on the prototype of polyol process, the nano-silver were synthesized by using surfactants and macromolecules as soft templates in normal temperature, but without adding seed or organic solvent. This method was totally green, and has many significant advantages such as without organic solvent pollution, high yield and low energy consumption.It was a long time to use surfactants and macromolecules as soft templates, since they can fully cap nanoparticles and significantly control the morphology of nanoparticles. The interaction between surfactants and macromolecules has been confirmed. At a certain range of surfactants concentration, the micelle structures of the soft clusters which consist of surfactants and macromolecules were changed with the change of surfactants concentration, which showed the characteristic of two critical concentrations.Before the first critical micelle concentration c₁, there is no interaction between surfactants and macromolecules; between c₁ and the second critical micelle concentration c₂, surfactants adsorb on macromolecules chain to form bound micelles; after c₂, the bound micelle has been saturated and the free micelles begin to form. In our research, since PVP is a common water-soluble macromolecule and SDS is a typical anionic surfactant, the complex of PVP-SDS aqueous solution can provide the above characteristics. Simultaneously, by adding silver ammonia complex ion in solution the two critical micelle concentrations remain the same.The complex of PVP-SDS aqueous solution as soft templates to prepare nano-silver has special meanings. It has two-level template effect, which can control the growth of nanoparticles twice. In the initial stage, silver ammonia ion was adsorbed to the SDS bound micelles. With the reduction of silver ammonia ion, the amount of Ag was enriched by SDS bound micelles and finally nano-crystals were formed. This stage was the process of assisting homogeneous nucleation. This is the first level of template effect. Then with the number of nano-crystals increasing, more and more nano-crystals attached on the chains of polymers, which made nano-crystals close to each other and grow to nanostructures in the end. This is the second level of template effect. Meanwhile, PVP chains acted as oriented adsorption and a weak reducer. PVP chains can be absorbed to a certain crystal face of silver nanoparticles, which was benefit to oriented growth of silver nanoparticles. Besides, PVP chains also have a weak effect of reduction in the appropriate condition, which can act as a weak reducer to reduce silver ammonia ions.Multiply twinned particles (MTP) of nanosilver were synthesized from ammoniacal silver ion reduced by glucose in aqueous solution of polyvinylpyrrolidone (PVP) and sodium dodecyl sulfate (SDS) aggregations. In this method, there was normal temperature, water phase, without adding seeds and on organic solvents. The Plasma resonance absorption of MTP was at 441 nm, the size was 50±5 nm in diameter. The XRD diffraction pattern shows the face centric structure (fcc) of MTP with the strongest diffraction peak at (111) lattice plane. The lattice fringes and twin planes were observed by the high-resolution transmission electron microscopy (HRTEM) and the quintuple twinned structure of silver nanoparticles was further validated by selected area electron diffraction (SAED). The as-prepared MTP of nanosilver with high growth activity could further grow into silver nanorods by the inducing of the template. We present an explanation to the growth mechanism of soft template. In the first stage, SDS bound micelles played a major role of the template to get the original silver nano-crystals of 5-10 nm in diameter. Second, PVP chains play a major role of the template, got 50±5 nm in diameter of the secondary silver nanoparticles. Third, the five-twinned crystal self growth became dominance, finally 40 nm in diameter and 700 nm in length of silver nanorods were synthesized by Ostwald ripening, the soft template only play a supporting role by selective adsorption in crystal growth.Flake-like silver nanoparticles was prepared by self-seeding in the PVP-SDS aqueous solution. In this method, sodium borohydride was used to fast reducer to obtain silver seed, in the subsequent of reaction, high concentration of PVP chains acted as weak reduction agent to slowly reduce of silver ammonia complex ion. Modified the pH and the concentration of SDS or PVP, the morphology of silver nanoparticles were changed. By this means, we obtained triangular, flakes and truncated triangular of nanosilver. We also got dendritic silver nano-structure through base assemble.