Surfactants/Polyoxometalates Electrostatic Composite Thin Film

Polyoxometalates (POMs) are the polyoxoanion of the early transition metal elements, especially vanadium, molybdenum and tungsten. They are discrete and uniform cluster anions that assembled from small metal oxysalt fragments in water solution with a certain pH value. The variety of their composition and structures endowed them with many functional properties, such as catalyst, proton conductivity, nonlinear optics, medicine, photophysics and magnetism. However, the development of materials and devices based on POMs was restricted because of their high lattice energies, low stability and poor processibility. It is necessary that new methods should be explored to combination, position and orient the clusters, indicative of the physical and chemical properties of the POMs. Construction of well-ordered inorganic materials under the influence of organic molecular assemblies is an effective and facile strategy. The recent research presents that the different nanostructures can lead to different functional properties of POMs. It is possible that new property may be generated through the synergy between the organic and inorganic part. If we can introduce these hybrid materials into thin film system, it should be advance the process of practicality.Firstly, we have demonstrated that a polyoxometalate-based organic amine hybrid film could be prepared by LB technique at air/water interface. The Keggin structure of PMo12 is basically preserved during the deposition. Based on XRD and polarized infrared spectral results, combining the molecular length of DOA and the diameter of PMo12, we propose a possible structural model of this hybrid film, where each inorganic PMo12 monolayer is incorporated into the hydrophilic interlayer of DOA bilayer to form a regular periodic layer structure with layer spacing of 4.4 nm. The mean tilting angle of the alkyl chains in the LB film is calculated to be about 40 o. The PMo12 that incorporates into the bilayer film of DOA keeps its inherent photochemical and electrochemical properties elementarily. When exposed to the UV light, the hybrid LB film turns blue due to the reduction of PMo12 and oxidation of DOA. The fading of the colored film occurs under ambient air or O2 and can be accelerated by heating over the temperature of phase transition. Of interesting is that the packing structure of LB film maintains despite the color change. In addition, comparing the cyclic voltammograms of the modified electrodes with the DOA/PMo12 hybrid LB film before and after the photochromism, we reveal different kinetics of electrochemical process.The colored reduced PMo12 can reduce metal ions into metal nanoparticles. Then we successfully realize the in situ synthesis of metal nanoparticles in the hybrid film with the reduction ability of PMo12 in two different ways. One is the penetration, in which the photochromic film is immersed in AgNO3 solution for 2 days to incorporate the silver ions into the hybrid film, and reaction at 40°C for 1hour to prepare silver nanoparticles. The silver nanoparticle size is 5-20 nm, which is characterized by UV-vis spectroscopy and TEM. The layered structure has been broken thoroughly after the formation of Ag nanoparticles. There is SERS can be observed in the resulting film. From the Raman spectra, we can investigate that the Ob atoms of PMo12 interact with Ag nanoparticles, which band is strongest enhancement. As the volume of AuCl4- ions is bigger than silver ions, the permeation into hybrid LB film becomes more difficult and needs much longer time. To avoid the decomposition of hybrid LB film due to the long time immersion in aqueous solution, we modified the route by introducing AuCl4- into the thin film through spreading the mixture solution of AuCl4- and DOA on the subphase of aqueous PMo12. Then prepare the film by LB technique. After UV irradiation, the film turns to purple due to the formation of the Au nanoparticles. The nanoparticles dispersed uniformly in the hybrid film through the method of mixing. And the Au nanoparticles can improve the rate of the photochromism.The cast film have no especial requirement for the sample, and the operate process is easy. Therefore, we synthesized polymerizable surfactant-encapsulated europium-substituted POM complex. We studied the structure and the photophysical properties of the cast film. Then we can in-situ polymerize the thin film through UV irradiation. Through 1H NMR and FT-IR spectra, we can conclude there is about 68 % polymerizable surfactant polymerized in the cast film. The incomplete polymerization lead to the appearance of two kinds of lamellar structure, that is, there are two different chemical microenviroments, which bring on the two different lifetimes of Eu3+. And we can improve the stability of the cast film through the method of in-situ polymerization.In summary, we have fabricated different organic/inorganic hybrid thin film consisting of different functional polyoxometalates and multifunctional surfactants through electrostatic interaction. Then we studied the properties of the hybrid film, and explored the synergistic effects between the organizations and the functions of POMs primarily.