| In recent years, resource problem and environmental pollution are difficult problems which still puzzlehuman survival and development. To solve these problems, people started to control pollution and protectenvironment by photocatalytic technology. Photocatalysts of semiconductor generate conduction bandelectrons and valence band holes by light absorption, these electron-hole pairs not only can react withorganic pollutants on the catalysts to remove contaminants, but also can decompose water to generatehydrogen. Meanwhile, photocatalytic technology can be used as an effective method to solve environmentaland energy problems through the conversion from solar energy to chemical energy. As a photocatalyticmaterial, TiO2is widely used in the field of environmental pollution and photocatalysis because of itscharacteristics of proper conduction band and valence band, non-toxic, photocatalytic activity, goodphysical and chemical stability, low cost etc. Since the band gap of TiO2semiconductor catalyst is around3.2eV, which limits its absorption in the ultraviolet region (<380nm), so the conversion efficiency of solarenergy is pretty low. Therefore, exploring and developing new semiconductor photocatalysts to improve thecatalytic activity is the focus of today’s research. There are many ways to modify TiO2, including metaldoping, nonmetal doping, narrow-band semiconductors as well as fuel photosensitizing and so on.Modifying and doping metal ions is one of the candidates to extend the absorption edge of TiO2to visibleregion.This thesis focuses on the study of catalytic property of metal ion-TiO2systems, by using fluorescenceprobe as the detecting technique. To this end, we prepared visible response catalysts of Sb-doped TiO2photocatalyst and Fe (Ⅲ) modified AgBr/TiO2composite, used terephthalic acid fluorescent probe methodto characterize the catalytic performance respectively and explored its photocatalytic mechanism.(1) In the study of Sb-doped TiO2photocatalyst, we obtained the catalysts of the0.1%~5%Sb-dopedTiO2by co-precipitation method, and studied the influence of Sb doping on structure, optical absorptionperformance and photocatalytic activity of TiO2. The characterization results of XRD, SEM, BET andUV-Vis indicate Sb doping has an influence on grain size, surface area and light absorption range of TiO2.From the Sb concentration-dependent experiments, the results show that the different dopant concentrationshave different catalytic activity, the appropriate amount of Sb doping concentration may increase theactivity of the catalyst with the doping concentration. However, the excess Sb doping concentration will accelerate TiO2internal electron-hole pairs recombination probability and thus the catalytic activitydecreases simultaneously. From our experiment, the1%Sb-doped TiO2demonstrates the highest catalyticactivity. With the Sb doping into TiO2, a new doping level is generated in the band gap to reduce the bandgap and transition path of valence band electrons changes, thereby changing the spectral response andcatalytic properties. Sb-doping not only extends the light absorption range of catalyst from the ultraviolet tovisible region, but also improves the catalytic activity of the photocatalyst, which is better than DegussaP25TiO2. Based on Sb-doped TiO2catalysts can generate hydroxyl radicals (OH) and superoxide anionradicals (O2-) under visible light (>420nm), we employed a2-hydroxy terephthalic acid (2-HTA)fluorescence probe method for evaluate the catalytic activity rapidly, and the two quenchers of DMSO andp-benzoquinone are used to quench hydroxyl radicals (OH) and superoxide anion radicals (O2-), and thuscan finally confirm the existence of two types of free radicals.(2) In the study of Fe(Ⅲ)/AgBr/TiO2composite system, based on TiO2composite and metalcompounds depositing on TiO2can improve the absorption of visible light, we prepared0.0005M~0.01MFe(Ⅲ)/AgBr/TiO2composite photocatalyst by simple chemical deposition method. The AgBr/TiO2composite photocatalyst could be obtained by loading AgBr on TiO2. Then Fe(Ⅲ) was deposited onAgBr/TiO2and a new type of Fe(Ⅲ)/AgBr/TiO2composite photocatalyst could be prepared. We use XRD,UV-Vis, SEM to characterize Fe(Ⅲ)/AgBr/TiO2catalysts and the results show that the deposition of Fe (Ⅲ)have an influence on the light absorption of AgBr/TiO2. The terephthalic acid was used as a fluorescentprobe to study the catalytic activity of Fe(Ⅲ)/AgBr/TiO2. The results indicate that an appropriateconcentration of Fe(Ⅲ) can improve the catalytic activity of the catalyst, which demonstrated the highestcatalytic activity when Fe(Ⅲ) concentration is0.001M.In summary, the photocatalytic activity of metal ion-TiO2systems was studied by using fluorescenceprobes, and the mechanisms for improving the photocatalytic properties in visible region of TiO2wasdiscussed in this thesis. The obtained results is of significance in understanding the catalytic process andexpanding the applications of semiconductor materials. |
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