Preparation Of Silver And Gold Nanoparticles Via Ion-Exchange Self-Assembly Technique Using Water-Soluble Poly (Amic Acid) As Intermediate

Silver and gold nanoparticles (Ag and Au NPs) have been extensively studied due to their excellent properties, which enable them to have a wide application in various fields such as electronics, optics, biological science and catalysis and so on. In this dissertation, we report our efforts on the preparation of Ag and Au NPs based on water-soluble poly (amic acid) (PAA) via a novel ion exchange self-assembly technique. The method works by using oxydiphthalic anhydride/oxidianiline (ODPA/ODA)-based water-soluble PAA as the intermediate to capture silver and gold cations in aqueous solution through an ion exchange reaction to obtain metal polycarboxylate complex, followed by heating the complex to yield Ag and Au NPs in the liquid solution and on the solid ultra-thin films, respectively.In the liquid solution, Ag and Au NPs were synthesized by heating the metal polycarboxylate complex solution at 90℃for 2h. The as-synthesized Ag and Au NPs are characterized by transmission electron microscope (TEM), ultraviolet spectrophotometer (UV-Vis), energy dispersive X-ray (EDX) and X-ray diffraction (XRD). The results suggest that the Ag and Au NPs are predominantly spherical with diameter ranging from 10 to 20 nm. The temperature exerted great influence on the synthesis of metal NPs. The size of Ag NPs increased with the increasing time of thermal treatment and it growed to around 25nm at 90℃for 24 h. The NPs were able to be obtained in shorter time at 120℃. This work provides a novel intermediate and an efficient and facile approach for the synthesis of metal NPs.In the solid ultra-thin films, the method works by casting polycarboxylate complex solution onto a glass slide via spin-coating to form an ultra-thin film. Subsequent thermal treatment of the ultra-thin films derived from the poly(amic acid)-silver(Ⅰ) complex induces the silver reduction, anisotropic aggregation and restricted growth in the ultra-thin polymer film yielding silver and gold nanocubes (Ag and Au NCs) with uniform shape. The as-synthesized Ag and Au NCs were characterized by SEM and TEM, suggesting that the diameter of Ag and Au NCs were 110±10nm and 150±10nm, respectively.Factors influencing the synthesis of Ag NCs and related mechanism were investigated. The results suggest that the shape and size of Ag NPs were greatly dependent on the temperature, metal ion concentration, thickness of solid films(the PAA content) and the incorporation of chloride ion.300℃was the minimum temperature for the synthesis of Ag, below which it was hard to obtained cubic NPs, above which the Ag NCs with larger size were obtained.1% was an ideal Ag+ content for the preparation of Ag NCs. The solid films with moderate thickness were beneficial to the formation of Ag NCs. Ag NCs with smaller size were obtained by introducing chloride ion in the synthesis, which facilitated the growth of crystal nucleus. Ag and Au nanobars were also synthesized in solid ultra-thin films by combining the seed-mediated growth with ion-exchange self-assembly technique. The dimension of Ag and Au NPs were able to be controlled by tuning the concentration of seeds.To the best of our knowledge, it is the first successful utilization of poly(amic acid) as an intermediate in the preparation of metal nanoparticles with well-defined shape. And it is also for the first time to prepare metal NPs with well-defined shape in solid phase. And our present work provides a new and efficient solid phase approach for the synthesis of Ag and Au NCs in large scale.