Mechanism Of Brookite-Photocatalyzed Biphase TiO₂ Mixture And Exploitation Of Rutile TiO₂ Photocatalytic Activity

Using semiconductor photocatalytic technology to decompose environmental organic pollutants is a sort of effective and clean way. Among a great number of photocatalysts, TiO2 has attracted widely attention as it is effective, stable, economic and eco-friendly. But there are still two issues to be noted. Firstly, when we were evaluating the’apparent’photocatalytic activity (APCA) of different TiO2 specimens, their different oxygen adsorption capacities were awalys did not be token into account, especially in explaining mechanism of TiO2 mixtures, which leads the unreasonable conclusion. Secondly, the low quantum efficiency could not satisfy the practical application. As the rutile TiO2 owns a high ’intrinsic’ photocatalytic activity (IPCA), exploiting its IPCA is the most important work about improvement in TiO2 activity.In this thesis, brookite/rutile and brookite/anatase mixtures were synthesized, and the oxygen transfer mechanism was reinvestigated through inspecting the APCA and IPCA; The IPCA of rutile was exploited through directly adding CUWO4 or noble metal and anion. The main contents and results are as follows:In the first part, the biphase effect of brookite with anatase or rutile has been reinvestigated by using phenol degradation in aqueous solution as a model reaction. In order to avoid the influence of its physical properties change, each oxide was sintered at 500 ℃, and then mixed in isopropanol, followed by dry and sitering at 450 ℃. Solid characterization showed that each oxide remained intact. In addition, the oxygen transfer direction of mixture was studied though H2O2 generation experiment.In the second part, we reported that upon the addition of trace CuWO4, phenol degradation in the aerated aqueous suspension of rutile was greatly accelerated, the magnitude of which was much larger than those obtained from anatase and brookite made at the same sintering temperature (600 ℃). This result indicates that the high intrinsic photocatalytic activity of rutile at high sintering temperature can be exploited by using co-catalyst CuWO4. Importantly, the CuWO4-caused photocatalytic activity enhancement of rutile continuously increased with the sintering temperature of rutile from 150 ℃ to 800 ℃. Furthermore, as the amount of CuWO4 added in the suspension increased, the amount of H2O2 produced in the presence of excess phenol increased, and then decreased and the trend was similar to that observed from phenol degradation. Such positive effect of CuWO4 is largely due to the solid CuWO4, other than to the dissolved Cu2+ ions in aqueous solution. A (photo)electrochemical measurement shows that there is an interfacial electron transfer from the irradiated rutile to CuWO4. This would improve the efficiency of the charge separation, and consequently increase the rates of O2 reduction and phenol degradation.In the third part, adding Ag nanopowders into rutile successfully improved the photocatalytic activity of rutile. Moveover, adding B4O72- into above system further increased the photocatalytic degradation of phenol, ascribed to the synergetic effect between Ag nanopowders and B4O72-. The optimal pH for Ag and B4O72- synergetic effect was 7.0, which had a more scope of application than TiO2 modification with Cu2+ and F~-.