Preparation Of AgBr/TiO₂Nanocomposites And Investigation Of Their Visible Light Photocatalytic Activity

Environmental contamination has been one of the biggest problems which always block up thesustainable development of the society. So a large number of man power and resources have been used toseek a proper method for solving them. There are many disadvantages for the common means of physical,chemical and biological methods, such as: complex operation, secondary pollution or an expensive cost.Until the last70s, it took us new hopes after the emergence of the semiconductor photocatalysis. Amongthe so many semiconductor metal oxides, TiO₂has been attracted much attention for a good deal ofadvantages, such as strong oxidability, stable chemical properties, environmentally friendly and obtainedeasily. But it also exists some disadvantages. Firstly, only4%-5%ultraviolet light in the sun light can beused. Secondly, the photogenerated charge carriers always recombine quickly. Many methods have beenapplied to modify TiO₂to extend the visible light absorption, and suppress the recombination ofphotogenerated charge carriers. In the so many modifiedmethods, coupling with a narrow bandgapsemiconductor is a good way. Silver halide photocatalyst caused more enthusiastic attention recently. Underthe light irradiation, AgCl, AgBr, AgI surface will form a layer of Ag0, and the obtained Ag0can protect theAgX to be decomposed continually, so that the stability of the photocatalyst is improved. ThisAgX/semiconductor nanocomposites as the highly active photocatalyst has been studied in-depth and havea wide range of applications.In this thesis, the titanic acid nanomaterials obtained from the hydrothermal method were used as theprecursor sourece of TiO₂, and then coupled with AgX nanoparticles through different methods, theirphysico-chemial properties were characterized, and their photocatalytic properties was evaluated undervisible light irradiation, the main research contents include the following four parts:（1） AgBr/TiO₂nanocomposites were prepared by an ion-exchange following calcination methodusing titanic acid nanobelts as the substrate materials. TEM images indicated that AgBr nanoparticles weresuccessfully grafted on TiO₂nanobelts. And the TiO₂nanoblets transformed to nanoparticles gradually asthe increase of the calcinated temperature, at the same time, the particle size of AgBr increased a little.UV-vis DRS spectra showed that the AgBr/TiO₂nanocomposites exhibited good visible light absorption atthe wavelength of400-470nm. And as the increase of the calcination temperature, the absorption band edge was almost unchanged. The AgBr/TiO₂nanocomposites showed an excellent photocatalytic activityfor MO decomposition under visible light irradiation. AgBr/TiO₂-300composites showed the highestphotocatalytic activity, and its degradation yield reached over95%within30min. As the increase of thecalcination temperature, the photocatalytic activity decreased gradually. The high activity ofAgBr/TiO₂-300may be due to the better one-dimensional structure of the TiO₂nanobelt and larger BETsurface areas. Moreover, comparing with the pure AgBr, TAN, and AgBr/P25mixture, the AgBr/TiO₂nanocomposites exhibited a higher photocatalytic activity for MO degradation.（2） AgBr/titanic acid nanotubes （TAN） nanocomposites were prepared by thecoprecipitation-calcination method. TEM images showed that the one-dimensional morphology of titanicacid nanotubes transformed into nanoparticles as the increase of the calcination temperature. And the XRDresults illustrated that the crystal structure of TAN transformed from the orthorhombic into anatase. TheUV-vis DRS spectra indicated that the absorption of TAN was obviously expand after sensitization by AgBrnanoparticles. The presence of the surface Ag species in the AgBr/TAN composites was estimated to be Ag+by XPS analysis. The photo-degradation of methyl orange （MO） was selected as the model chemicals toevaluate the photocatalytic activity of AgBr/TAN composites. AgBr/TAN-200showed the highestphotocatalytic activity, the degradation yield of MO reached more than90%within30min. As the increaseof the calcined temperature, the photocatalytic activity of AgBr/TAN decreased gradually.（3） Anatase TiO₂nanotube （TN） films were prepared by calcination of the titanic acid nanotubes at400℃for4h. TEM image show that the diameter of the TiO₂nanotubes is8-10nm. And SEM imagesshowed that the NT films consisted by a lot of TiO₂nanotubes, and many nanotubes intertwined together toform a porous and incompact structure. AgBr nanocrystals were successfully sensitized on the TN film. Thenanotubes structure of the film was kept after sensitization, but the visible light absorption was remarkablyincreased. The sensitization content of AgBr was estimated to be2.42%by EDS. The AgBr-TN filmshowed a higher photocatalytic activity for MO degradation compared to the bare TN film and AgBr-TiO₂nanoparticle film, which may be caused by the large BET surface areas and one-dimensional morphologyof the TiO₂nanotubes, and more lights harvesting in the pores and channels of the nanotube film. WhenAgBr-TN film was calcined, a stronger visible light absorption and a much higher photocatalytic activity were achieved. The EIS result indicated that the separation efficiency of the photo-generated charge carrierswas increased after annealing.（4） AgX/TiO₂nanocomposites were prepared by an ion-exchange following calcination method usingtitanic acid nanobelts as the substrate materials. UV-vis DRS spectra showed that the AgX/TiO₂nanocomposites exhibited good visible light absorption at the wavelength of400-470nm. The AgX/TiO₂nanocomposites showed an excellent photocatalytic activity for MO decomposition under visible lightirradiation. AgBr/TiO₂-300composites showed the highest photocatalytic activity compared withAgCl/TiO₂-300and AgI/TiO₂-300, which may be due to the better matching binding energy of the AgBrand TiO₂and a electronic can transferred to the valence of the TiO₂easily, reducing the electron-holerecombination.Anatase TiO₂nanotube （TN） films were prepared by calcination of the titanic acid nanotubes at400℃for4h. TEM image show that the diameter of the TiO₂nanotubes is8-10nm. And SEM images showedthat the NT films consisted by a lot of TiO₂nanotubes, and many nanotubes intertwined together to form aporous and incompact structure. AgX nanocrystals were successfully sensitized on the TN film. Thenanotubes structure of the film was kept after sensitization, but the visible light absorption was remarkablyincreased. AgBr-TN-C composites showed the highest photocatalytic activity compared with AgCl-TN-Cand AgI-TN-C.