Synthesis, Assembly And Catalytic Properties Of Gold Or Platinum Nanoparticle-doped Polymer Foam-like Thin Films At The Liquid/Liquid Interface

In recent years, synthesis and assembly of noble metal nanoparticles and investigation of their properties have been attracted much attention due to their unique optical, electronic and catalytic properties. Polymer micro- and nanocapsules have been paid continuous attention due to their high specific surface area, good permeability, mechanical property, and potential applications in many areas. In this thesis, we described a new, simple, and convenient one-step synthesis and assembly process to prepare noble metal nanoparticle-doped poly(2-vinylpyridine) microcapsules and solid foams at the liquid/liquid interface under ambient temperature. The noble metal nanoparticles with the diameter less than 4 nm dispersed in the capsule and foam walls homogeneously, and exhibit high catalytic activity for a certain reaction system.I Gold nanoparticle-doped poly(2-vinylpyridine) (P2VP) microcapsules and solid foam films were prepared at the P2VP chloroform solution/HAuCl4 aqueous solution interface through a one-step synthesis and assembly process at room temperature. It was also found that these composite nanostructures formed at the liquid/liquid interface moved to and adsorbed by the air/HAuCl4 aqueous solution interface. The morphology, structure, compositions and optical properties of the capsules and the solid foam films were characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), FTIR spectroscopy, UV-visible spectroscopy, and fluorescence spectroscopy. The results indicated that the concentration of polymer P2VP and HAuCl4 aqueous solution have a impact on the morphology of the capsules and the solid foam, and Au nanoparticles with the average diameter of 2.1 nm were embedded in and/or adsorbed on the walls of the capsules and foams homogeneously, the nanoparticles were composed of Au(0) and Au(III) with the molar ratio of about 75/25, and the mass percent of Au elements in the composites formed at the liquid/liquid interface was measured to be 19.65%. The formation of the nanostructures was attributed to the self-assembly of P2VP at the liquid/liquid interface, the simultaneous reduction of AuCl4-ions by a small amount of ethanol in the chloroform and adsorption of AuCl4- ions. After irradiated by UV-light for 1 hour, the average diameter of the nanoparticles was found to be 2.2 nm, and the AuCl4-ions were transformed to Au(0) completely. The catalytic performance of these composite nanostructures were evaluated by using the reduction of 4-nitrophenol (4-NP) by potassium borohydride in aqueous solutions as a model reaction. The catalytic activity was very high in the first cycle, decreased rapidly and slightly in the second and third cycles due to the aggregation of some nanoparticles as the TEM observations shown, it can be clear seen the nanopaticles with the average diameter of 4.1 nm, and even a diameter of more than 10 nm particle formation. However, this composite structure can still be used as a reusable, efficient catalyst.ⅡPtCl62- and PtCl42- ions-doped polymer foam-like thin films were prepared via an one-step synthesis and assembly process at the liquid/liquid interface of a chloroform solution of poly(2-vinylpyridine) and an aqueous solution of chloroplatinic acid hydrate. It was also found that these composite nanostructures formed at the liquid/liquid interface moved to and adsorbed by the air/H2PtCl6 aqueous solution interface. Transmission electron microscopy and high-resolution transmission electron microscopy observations indicated that the foam-like thin films were composed of microcapsules polymer molecules and Pt(II) and Pt(IV) ions. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) investigations revealed that the mass percent of Pt elements in the composites formed at the liquid/liquid interface was measured to be 17%. X-ray photoelectron spectroscopy investigations revealed that these composites were mainly made up of Pt(II) and Pt(IV) ions. The formation of the composite nanostructures at the interface was attributed to self-assembly of the polymer molecules at the liquid/liquid interface, reduction of PtCl64- by small quantity of ethanol in the chloroform, and adsorption of PtCl64- and intermediate PtCl42- ions due to the electrostatic attraction between the ions and the protonated pyridine groups. In order to further reduce the metal ions to the metal atoms and improve the stability of the composite structures, UV-light irradiation process was used. Platinum nanoparticles with the average diameter of 2.7 nm appeared after UV-light irradiation, which were embedded in and adsorbed on the walls of the foams. X-ray photoelectron spectroscopy investigations indicated the presence of Pt atoms, Pt(Ⅱ) and Pt(Ⅳ) ions in the UV-light irradiated samples. The catalytic activity of the composite film for the reduction of methylene blue by potassium borohydride in aqueous solutions was evaluated. The apparent rate constant decreased gradually with increasing the number of runs due to the partially leaching of Pt nanoparticles and became stable after the third cycle, indicating that the composite film can be used as an effective, stable and reusable catalyst. Enhanced the stability of the catalyst is in progress.