Preparation And Photocatalytical Property Research Of Bi-radicle Oxides

Since the water splitting on TiO₂ electrode discovered by Honda and Fujishima, an epoch for photocatalytic technic research began. The detailed researched semiconductor photocatalyst-TiO₂ has been broadly applied in many regions including degradation of organic and inorganic pollutants, water splitting, photocatalytic sterilization and photocatalytic synthesis. But the intrinsic defects of TiO₂ have limited the industrial applications and development, for example low photon efficiency, narrow response spectrum and so on. For dealing with these problems, two foreland domains about semiconductor photocatalysts, modification of TiO₂ and exploiture of new photocatalysts, have been developed.On the basis of these, Bi-radicle compound oxides were prepared and the photocatalytic activities were studied in this paper. The following is the content of the paper.Layered perovskite structure Bi₃TiNbO₉ was prepared by sol-gel method and XRD, TEM, SEM and UV-Vis instruments were used to show the crystal phase, particle morphology and photophysic property. XRD patterns indicated that Bi₃TiNbO₉ with good crystallinity can be obtained by annealing at 500°C for one hour. With TEM and SEM photos, we can know that Bi₃TiNbO₉ was composed of clubbed particles with homogeneous size about 100nm. The phtocatalytic activity of Bi₃TiNbO₉ was tested by degradation of methyl orange under UV light. The result of the photocatatical experiment showed the high photocatalytic activity of Bi₃TiNbO₉. The reasons for the superior photocatalytic activity contain two. Ti-O-Ti bond and Nb-O-Nb bonds are close to 180 degrees which is in favor of the mobility of photogenerated charge carriers. The interelectric field between (Bi₂O₂)²⁺ layer and (BiTiNbO₇)^2- layer within the layered perovskite structure will accelerate the separation of photogenerated electron and hole, which can improve the photocatalytical activity.Sol-gel method was used to prepare pyrochlore structure oxides Bi₂Ti₂O₇. The effect of Bi/Ti molar ration in the precursor solution on the structure formation of Bi₂Ti₂O₇ was studied through XRD analysis. The experiment results indicated that the molar ratio of Bi/Ti used can not correspond to the stoichiometric proportion of Bi₂Ti₂O₇ and pure Bi₂Ti₂O₇ was obtained when Bi/Ti was 1:1.5. The obtained Bi₂Ti₂O₇ was used in the degradation of methyl orange under UV light which showed the high photocatalytic activity. To seek after the photocatalytic mechanism of Bi₂Ti₂O₇, it was considered that there may be two reasons. The active oxygen offered by Bi-0 tetrahedra will be reduced by photogenerated electrons which can lower the recombination of photogenerated electrons and holes and the endless [TiO₃] chains will improve the mobility of charge carriers.The sillenite phase Bi₂₅FeO₄₀ and bismuth tungstate Bi₁₄W₂O₂₇ were obtained by chemical solution decomposition method. XRD and UV-Vis instruments were used to depict the crystal structures and photophysical properties. The degradations of methylene blue under visible light were processed which revealed high photocatalytical activities of Bi₂₅FeO₄₀ and Bi₁₄W₂O₂. The author has given primary interpretation of these phenomena. The reasons for Bi₂₅FeO₄₀ involve that the high photosensitivity and good charge carriers mobility of sillenite phase oxides and the visible light response by the iron oxide dopant. The reasons for Bi₁₄W₂O₂₇ contain that Bi₁₄W₂O₂₇ was the solid solution to stabilize δ-Bi₂O₃ at room temperature. δ-Bi₂O₃ is an excellent oxide ion conductor and therefore Bi₁₄W₂O₂₇ possesses this property. In photocatalytical reactions, the combination of oxygen and photogenerated electrons specially influences the process. Additionally, Bi₁₄W₂O₂₇ with the band gap of 2.8eV has visible light adsorption. All these results the high photocatalytical activity of Bi₁₄W₂O₂₇ under visible light.In this paper, metastable phase β-Bi₂O₃ appeared in the preparation process of photocatalysts was simply researched. XRD, TEM, SEM instruments were used to reveal the formation mechanism, particle morphology.