| Semiconductor photocatalysis are important for many current environmental and energy issues, it can utilize solar energy to splitting water to supply clean and recyclable hydrogen energy, in addition to decompose harmful organic and inorganic pollutants present in air and aqueous systems. TiO2is the mostly studied photocatalyst, owing to its high reactivity, stability and non-toxic. However, the band gap of TiO2is about3.2eV, can only absorb UV light at wavelength shorter than380nm and those only represent the5%of the solar energy reaching the earth surface. The band gap of WO3is about2.6eV, can absorb visible light at wavelength shorter than460nm effectively. But the quantum yield of organic disappearance over TiO2or WO3is still very low, it is meaningful to promote the photocatalytic activity for organic degradation with semiconductors by modified with some electron acceptors.In this work, we studied on the metal ions modified on the TiO2and WO3semiconductors for phenol degradation under UV or visible light. Moreover, the influence factors and mechanism of these systems were also studied in detail. Fe3+is an excellent electron acceptor, can scavenger the conduction band electron of TiO2or WO3efficiently then reduced to Fe2+. However, Fe2+is hard to re-oxide by O2under air condition. So the reaction of iodine photo-oxide Fe2+to Fe3+was studied. And the mechanism of this reaction was discussed. There are two chapters in this thesis, the main contents and results are as follows:First part, we studied on the photocatalytic activity for organic degradation by addition of Fe3+, Cu2+into the suspension of TiO2or WO3, respectively. We find that the effects of Cu2+and Fe3+are determined by the activity of photocatalysts used. Phenol photodegradation was conducted in the aerated aqueous suspensions of WO3and TiO2(P25, anatase, and rutile). On the addition of Fe3+ions, the initial rate of phenol degradation over each catalyst became increased, but continual rate enhancement was only observed with TiO2, not with WO3. On the addition of Cu2+ions, phenol degradation over P25was inhibited, while the reactions over other catalysts were not only accelerated, but also followed well the apparent first-order kinetics. Control experiments with the metal ions showed that only Fe3+in aqueous solution underwent significant photolysis and dark adsorption onto the catalysts. Through a kinetic analysis, it becomes clear that as electron scavengers of TiO2and WO3, both Fe3+and Cu2+are better than O2, while Fe3+is better than Cu2+, the observation in agreement with those expected in thermodynamics. Moreover, Fe2+ions formed from Fe3+reduction over TiO2can be reoxidized to Fe3+by the photogenerated reactive species such as H2O2, while Cu particles, produced from Cu2+reduction over rutile, anatase and WO3, can be reoxidized to Cu2+by O2dissolved in aqueous solutions.Second part, we studied on the photoactivity for Fe2+photo-oxidization with I2and I3-. Under UV and visible light at wavelengths longer than320and420nm, respectively, both I2and I3-in acidic aqueous solution can oxide Fe2+, with the stoichiometric formation of Fe3+and I-. Comparatively, the I2-sensitized reaction was fast, while the I3--sensitized reaction significantly occurred only in the presence of excess Fe2+. This is ascribed to the fact that I-radicals generated in the former are more reactive than I2-· radicals produced in the latter. The quantum yields for the I2and I3--sensitized formation of Fe3+, measured at456nm were0.119and0.118, respectively. Moreover, under I2and visible light, the initial rate of Fe3+production increased with the initial concentration of I2and with the reaction temperature as well, but it was independent of Fe2+concentration. The reaction was determined to the first order to I2, and Arrhenius activation was29.3kJ-mol-1. These observations suggest that the reaction between Fe+and I· is fast, while the formation and self-recombination of I· radicals are the rate determining step for the I2-sensitized reaction. |
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