Polyoxometalates (pom), The Function Of Composite Membrane, Characterization And Characteristics Of Study

Two types of the POM-containing composite films such as PW11/SiO2, SiW11/SiO2, GeW11/SiO2, PW11/TiO2 , SiW11/TiO2 and GeW11/TiO2 were prepared by the method of sol-gel via spin-coating and calcination techniques. Rention of the structure integrity of the starting POMs in the as-synthesized composites were confirmed by UV/DRS, FT-IR, solid state NMR and ICP-AES. Also it was shown from the results that the strong chemical interactions between POM molecules and Silica or Tatiana networks existed on the films. The surface morphology of the composite films was confirmed by the SEM measurements; indicating the films are smooth and the thickness of the films are in the range of nanometers (250-400 nm) .Under UV-irradiation of the XW11/SiO2 (X=P, Si, Ge) composite films, all as-synthesized films exhibited high photocatalytic activity on the degradation of aqueous formic acid (FA). It has been shown that aqueous FA can be totally degraded into CO2 and H2O. The photocatalytic reactions followed Langmuir-Hinshelwood first-order kinetics.Little leakage of the POM from the silica matrix was owing to strong chemical interactions between the lacunary POM molecules and silica matrix. The results indicate that the silica composite films based on lacunary Keggin-type polyoxometalates is stable, and they are more easily handled than that of the powdered photocatalytic materials, therefore, as-synthesized film exhibits the potential for practical applications.The photocatalytic activities of the XW11/TiO2(X=P, Si, Ge) composite films were tested via degradation of aqueous azo-dyes, Congo Red (CR) and naphthol blue black (NBB). It was observed that the photocatalytic activities of the three composite films are much higher than that of the pureTiO2 film, mainly attributed to the synergetic effect between XW11 and TiO2, i.e., XW11-catalyzed electron transfer from the conduction band (CB) of photoexicited TiO2 to itself. The leakage of the active component from the films was hardly observed during the degradation reaction, indicating that the as-synthesized composite films were stable.The gas-adsorption abilities of the POM/TiO2 film was tested by using NH3, NO2, C2H5OH and C6C6 as gas resources. The gaseous adsorption properties of the films to noxious gases such as NH3 and NO2 show that the composite is much better than that of the pure TiO2 films, which may be attributed to the enhancement of the gaseous adsorption ability on the film surface as well as the modified charge transfer process between the adsorbed gases and the films due to the inducing of POM in TiO2 film. In addition, compared with the pure TiO2 films, the POM/TiO2 films also showed relative lower working temperature, indicating that the films have great potential to be used in the gas-sensor field.