Study On Preparation And Properties Of Organic/Inorganic Nanocomposite Thin Films

Organic/inorganic nanocomposite thin film made of organic materials and nanoparticles with different functionalities are assembled through supermolecular chemistry, the film with controllable thickness, ordered and stable structure can be prepared at molecular level, which is one of the research focuses in contemporary materials science. Organic/inorganic nanocomposite thin films have potential applications in the fields of optical devices, solar cell, biosensors, filtration, and so forth. In this paper, the vitamin E (VE) monolayer was used to prepare silver and gold nanoparticles, and then the monolayers with Ag and Au nanoparticles were fabricated by LB technique. By means of layer-by-layer self-assembly technique(LBL), Ag nanoparticles were synthesized by in-situ chemical reaction, and tungstosilicate-Ag (TSA-Ag) composite nanoparticles were as-prepared, respectively, the organic/inorganic nanocomposite films consisting of poly(ethyleneimine)-silver ions (PEI-Ag⁺) and phosphotungstate acid (PTA), tungstosilicate acid (TSA)-Ag composite nanoparticles and chitosan (CTS) were fabricated. TiO₂ nanocomposite films were prepared by LBL and coating methods, and the photoelectrochemical properties of the TiO₂ nanostructured porous films sensitized by dye were studied. The composition, structure, and properties of the as-prepared composite films were characterized by transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared transmission spectroscopy (FTIR), atomic force microscopy (AFM), Field emission scanning microscopy (FESEM), X-ray photoelectron spectra (XPS), X-ray diffraction analysis(XRD), profilometer and cyclic voltammetry (CV).The main contents and results of the work are as follows:1. Silver and gold nanoparticles were synthesized firstly by one-step reduction of silver ions in alkaline subphase and chloroaurate (AuCl₄^-) in acid subphase beneath vitamin E (VE) Langrnuir monolayers. Suface pressure-area (Ï€-A) isotherms showed that the area per molecule of VE monolayer increased with reaction time, which indicated that more and more silver and gold nanoparticles had inserted into the monolayer. TEM images showed that the ellipsoidal and spherical silver nanoparticles with a diameter of about 3-14nm formed at the surface pressure of 20raN/m, and the arrangement of the nanoparticles changed from sparseness to compactness with reaction time. The morphologies of Au particles such as spherical-like, triangular, and multiply-twinned particles (MTPs) could be observed. The ED patterns indicated that the silver nanoparticles were face-centered cubic (fcc) polycrystalline, and triangular gold particle was single crystalline. Silver and gold particles with different morphology and size formed at air-water interface. The formation mechanism of the nanocomposite film was discussed, which revealed that the phenolic groups in the VE molecules changed to quinone after being oxidated.2. Poly(ethyleneimine)-silver ions (PEI-Ag+) and phosphotungstate acid (PTA) were fabricated on solid substrates by alternating adsorption. Ag nanoparticles formed in-situ by the photochemical reduction of the PTA under UV-irradiated in Polyelectrolyte multilayer nanoreactors, wherein the PTA played the roles of a UV-switchable reducing agent, photocatalytic agent and a polyelectrolyte. {PEI-Ag/PTA}n multilayer films containing Ag nanoparticles were prepared. The spherical silver nanoparticles with sizes of ca.4-7 nm were well-dispersed in the multiplayer films. The results showed that the film had a rough surface. The UV-vis characteristic absorbances of PTA and Ag increased almost linearly with the number of bilayers, which indicated a process of uniform assembling. The multiplayer films exhibited good electrocatalytic activity for the oxidation of uric acid and dopamine, which may be used in electrochemical biosensor.3. Tungstosilicate acid (TSA)-Ag composite nanoparticles were synthesized based on the reduction of silver nitrate by UV-irradiated tungstosilicate acid solution. The nanocomposite films consisting of TSA-Ag composite nanoparticles and chitosan (CTS) were fabricated by layer-by-layer self-assembly technique. The coverage degree of TSA-Ag composite nanoparticles on the surface of the film increased with the number of the bilayers and depositing time. TSA-Ag composite nanoparticles grew in the normal growth mode as well as in a direction normal to the surface. Large overlap existed between adjacent of TSA-Ag and CTS layers. The composite thin film exhibited linear, uniform and regular layer-by-layer growth. The multiplayer films exhibited good electrocatalytic activity for dioxygen reduction.4. Polyacrylate sodium (PAAS)/Titania (TiO₂) multilayers were assembled by LBL electrostatic deposition technique, which were then sensitized by cyanine dye to fabricate a dye-sensitized solar cell (DSSC). FESEM showed that the TiO₂ thin film was nanoporous. An efficiency of 1.29ï¼…was obtained for the solar cell made from TiO₂/PAAS (40 bilayers) precursor film. Thermogravimetric analysis of PAAS showed that the thermal stability of the polyelectrolytes may have a direct effect on the overall device efficiency. PAAS/TiO₂ multilayers can be used as photocatalytic degradation of methylene blue, and exhibited self-cleaning functionalities. PbS nanoparticles formed in the holes of TiO₂ nanoporous film, named as TiO₂/PbS composite semiconductor nanoporous film, which were then sensitized by cis-X₂Bis (2,2'-bipyridyl-4,4'-dicarboxylate) ruthenium(â…¡) (Ru(bpy)₂(NCS)₂). The conversion efficiency of light to electricity for the TiO₂/PbS/Ru(bpy)₂(NCS)₂ composite semiconductor nanoporous films was measured as a function of the depositing time of PbS on TiO₂ nanoporous film and it was proved that the energy conversion efficiency was dependent on the depositing time.