Fabrication And Characterization Of Polyoxometalate/layer-by-layer Composite Nanostructured Multilayer Films

Nanocomposites of nanometer-sized materials embedded within a polymer matrix have attracted much attention, for their potential applications in catalysis, magnetics, and photonics. This thesis focuses on the preparation of such nanocomposite films based on polyoxometalates by combination of layer-by-layer self-assembly technology with in situ chemical reaction.The effective method of nucleation and growth of nanoparticles as applied to synthesize W- and Mo- containing polyoxometalates nanoparticles in precursor films by making use of their acidity or oxidative property. The controllable synthesis of nanoparticles can be achieved by increasing synthetic cycle of polyoxometalates. The composition, structure, and properties of the as prepared composite films have been characterized in detail by UV-vis, FTIR, X-ray photoelectron spectra, scanning electron microscopy, atomic force microscopy, transmission electron microscopy and cycle voltammograms. The results indicate that the polyoxometalates nanoparticles in-situ formed in the films and their identities were preserved. The characteristic absorbance increased nearly in line with the number of synthetic cycle. The nanocomposite films showed different roughness before and after synthesis.By using the acidity of polyoxometalates, the substrate modified by polyelectrolyte precursor film was alternately dipping into polyoxometalates solution and solution of tetraalkylammonium salts as precipitator. The experiments show that different polyoxometalates as starting materials or reaction condition can lead to different results. Both the size and morphology of the nanoparticles changed with synthetic cycle when H3PMo12O40 was as raw material. Moreover, the morphology of them changed from global to egg-shaped. While, well dispersed nanorods were achieved when H4SiW12O40 was as raw material and the size of them increased with the reaction cycle. The length of nanorods can be tailored by choosing tetraalkylammonium with different alkyl chain. However, the manipulative sequence was exchanged when AgNO3 was as precipitator. The substrate was dipping into AgNO3 solution first and then H4SiW12O40 solution. The well defined global nanoparticles can be obtained and the size of them also increased with synthetic cycle, whereas, the morphology of them didn't change.By using the strong oxidative property of polyoxometalates, the precursor films were immersed in pyrrole monomer solution with pH=4 and then in H3PMo12O40 solution. The positive charged pyrrole monomer was adsorbed and then polymerized in the films. Repeating above steps, the polypyrrole nanoparticles doped with polyoxometalates were formed and the size of them increased with the increasing of synthetic. Moreover, the...