Fabrication Of Composite Polymer/Noble Metal Nanoparticle Free-Standing Thin Films At The Liquid/Liquid Interface

Free-standing thin polymer films have macroscopic size and molecular scale thickness, and combine the properties of macroscopic materials and individual molecules or nanoparticles. These thin films without substrates would extend the field of applications, such as sensors, actuators, nanodevices and catalysts. So the free-standing thin films have aroused substantial interest in recent years. In this thesis, we described a simple and convenient approach to fabricate functional inorganic/polymer free-standing composites. The composite thin films of amphiphilic poly(2-vinylpyridine)(P2VP, Mw:21500) doped with metal ions were fabricated at the interface through co-adsorption and combination of the related species and further self-assembly of the composite polymer molecules at the liquid/liquid interface under ambient conditions. The films were composed of planar thin layers decorated with separated microcapsules and foam structures of conglutinated microcapsules. After treatment, the metal nanoparticles (Ag and Pt) with the diameter between2and4nm are generated and disperse in the films homogeneously, and exhibit high catalytic activity and durability of the composite free-standing films for a certain reaction system.1. Free-standing polymer foam films doped with Ag nanoparticlesFree-standing films of poly(2-vinylpyridine)(P2VP) doped with Ag+ions were fabricated at the planar liquid-liquid interface of an aqueous solution of AgNO3and a chloroform solution of the polymer through adsorption and self-assembly of the composite species at room temperature. Transmission electron microscopic (TEM) investigations indicated that the films were composed of planar thin layers decorated with separated microcapsules and foam structures of conglutinated microcapsules, and no Ag nanoparticles formed in the pristine films. The coordination between Ag+and pyridine group was confirmed by FT-IR spectroscopy in the composite. After UV-light irradiation and KBH4aqueous solution treatment, Ag nanoparticles with the average size of3.2nm appeared and incorporated in the polymer matrices homogeneously. X-ray photoelectron spectra (XPS) investigations revealed that silver exits in the form of Ag+before the treatment and after the treatment it exits as Ag atoms. UV-vis spectroscopy (UV-vis) also suggested the formation of Ag nanoparticles. These were consistent with the TEM observations. Thermogravimetric analysis (TGA) showed good thermal stability of the composite films. The silver content was estimated to be24.0%from the TG curve, closing to the calculated value. The catalytic performance of the composite films was evaluated by using the reduction of nitro-compounds, including nitrobenzene,4-nitrophenol, and4-nitrobenzoic acid by KBH4in aqueous solutions. The results indicated that the composite films have high and durable catalytic activity. The catalytic reaction rate constants are related to the size of the nitro-compounds, suggesting that the Ag nanoparticles were incorporated in the matrices, and the reaction depends not only on the size and distribution of the nanoparticles, but also on the diffusion of the reactant molecules.2. Free-standing polymer foam films doped with Pt nanoparticlesFree-standing thin films of poly(2-vinylpyridine)(P2VP) doped with PtCl62-and PtCl42-complex ions were fabricated at the planar aqueous solution of H2PtCl6/chloroform solution of P2VP interface at room temperature. The films were composed of thin layers decorated with separated and conglutinated microcapsules. FTIR spectroscopy investigations revealed that the formation of the protonated pyridine groups in the composite, and the electrostatic attraction between the protonated pyridine groups and the an ions. TEM observations indicated that no platinum nanoparticles formed in the pristine films. But XPS investigations revealed that these composites were mainly made up of PtCl62-and PtCl42-ions, indicating that during the formation of the composite film some PtCl62-ions were reduced to PtCl42-ions. We think that the reduction of PtCl64-should be attributed to small quantity of ethanol in the chloroform. After treatment with KBH4aqueous solution, the platinum complex ions incorporated in the polymer matrices transformed to platinum nanoparticles with the mean size of2.2nm, which was confirmed by XPS analysis of the samples. Both the contents of the platinum element in the untreated and treated composite films estimated based on the TGA were close to each other, indicating no loss of platinum during the treatment process. The catalytic activity of the composite films was evaluated by using the reduction of4-nitrophenol by KBH4in aqueous solutions. The results indicated that the composite films have high and durable catalytic activity.