| Heterogeneous photocatalysis has caused much attention owing to its potential application in many areas, especially in the treatment of environmental pollution. Among various semiconductor photocatalysts, the TiO2 is most frequently employed because of its non-toxity, low cost, high activity, strong stability against both heating treatment, acid and base. Usually, TiO2 particles are prepared via Sol-gel method, followed by calcinations at desired temperature. In the present thesis, Both the direct drying and supercritical drying methods are used in preparing TiO2 photocatalysts, which are further modified with either the Fe3+ or the SO42- dopants. The photocatalytic degradation of phenol in aqueous solution is used as a probe to evaluate the catalytic activities of the as-prepared photocatalysts. Based on various characterizations, such as XRD, XPS, TEM, SEM, BET, FLS, RAMAN, IR, DRS of pyrodine adsorption, nitrogen-adsorption etc., the relationship between the photocatalytic performance of the TiO2 particles and either the structural characteristics or the surface electronic states have been discussed briefly. The researching work could be classified into following parts:1. The TiO2 particles are prepared via Sol-gel method, followed by calcinations at high temperature in a furnace (direct drying method). The optimum R (H2O/Ti, mol/mol) is determined as 4 and the optimum calcinations temperature is determined as 673 K. Modification of the as-prepared TiO2 particles with Fe3+ ions could greatly enhance the photocatalytic activity of TiO2 particles with the optimum Fe/Ti (mol/mol) at 0.05, which could be understood by considering the following aspects: (1) The addition of the Fe3+ ions resulted in the larger particle size, more crystal defects, higher crystalline degree of the anatase phase in the TiO2 particles; (2) The formation of Ti-O-Fe oxygen-bridge due to the combination between Fe3+ and TiO2 results insome hybrid intermediate energy levels, which may enlarge the photo-responsing range of the TiO2 particles. (3) The special half-full electron structure of the Fe3+-dopant may capture the photoelectrons shallowly. Such kind of capture will be beneficial for the rapid movement and effective separation of ephotolectron-hole couples and in turn, promote the photocatalytic activity. 2. The supercritical drying is employed to treat the precursor of the TiO2, resulting in a novel TiO2 photocatalyst, which exhibits much higher photocatalytic activity than the TiO2 obtained though direct drying. According to the characterizations, the excellent photocatalytic activity of the TiO2 obtained based on supercritical drying is mainly attributed to the higher crystalline degree of the anatase phase, larger specific surface area and pore size as well as pore volume. The kinetic studies reveal that the phenol degradation reaction is first order with respect to phenol concentration. The reaction rate is also greatly influenced by phenol initial concentration, TiO2 amount and co-oxidant, and light intensity etc. 3. When SO42- was added in the sol of TiO2 precurssor, followed by supercritical drying. a novel SO42-/TiO2 photocatalyst is synthesized which displays excellent activity during phenol degradation. On one hand, promoting effect of the SO42--dopant is mainly attributed to the larger pore size and pore volume as well as specific surface area of the SO42-/TiO2 sample. On the other hand, it is also attributed to the increase in both the strength and number of Lewis acid sites and Bronsted acid sites on the surface of the SO42-/TiO2 photocatalyst. Furthermore, the formation of the complex of SO42-and TiO2 via a bridge-model may also influence the electronic states of the active sites. These factors may account for the positive effect of the SO42-dopant on the photocatalytic activity. |
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