Preparation Of CeO₂-TiO₂ Coated Photocatalyst And Study On Dye Wastewater Microwave Assisted Photocatalytic Degradation

Photocatalytic oxidation is a kind of photosentive oxidation method using n-style semiconductor as a photocatalyst, which is based on the energy band theory of the photocatalyst. TiO₂ is close to being an ideal photocatalyst in several respects, for example, it is nontoxic, relatively inexpensive, highly stable chemically, and the photogenerated holes are highly oxidizing. In addition, photogenerated electrons are reducing enough to produce superoxide from dioxygen. In order to avoid the use of conventional suspended reaction system, which entails later separation TiO₂ powder from the water and causes secondary pollution, various researchers began to work on ways of immobilizing TiO₂ particles, for example in coated photocatalyst form, which has showed bright future in wastewater treatment. But it still has some shortcomings, for example, the photocatalytic effect is not very ideal and the coating is not very firm. Physics assisted photocatalytic oxidation is a novel water treatment technique. Based on the fact that the photocatalytic effect can be improved obviously when the photocatalytic oxidation is associated with microwave technique, we did some research in improving photocatalytic effect by adulterating TiO₂ with rare earth element ceric and using microwave assisted photocatalytic oxidation. Sol-gel processing is one of the most common methods to produce TiO₂ in form of coatings. In this paper, the technic of sol preparation was improved so that the stable time of the sol could be prolonged to 76 days and the coating effect could be better. Ethanol was chosen as solvent, and the molar ratio between ethanol and Ti(OBu)4 was controlled to 17, the molar ratio between H₂O and Ti(OBu)₄ was controlled to 2.7. HAc acted as acid catalyst and chelate reagent. Surfactant was added to increase the specific surface area and improve the photocatalytic activity. In the presence of proper stabilizer, the sol can exist longer time for preparing coated photocatalyst, and the photocatalyst can be coated on the carrier more firmly. TiO₂ and CeO2-TiO₂ powder photocatalysts were prepared, and the catalysts were determined by XRD, SEM, TGA and FTIR, respectively. The photocatalytic activity of the catalysts were investigated by microwave assisted photocatalytic degradation of Acid Mordant Red B. XRD characterization manifested that the TiO₂ crystal transition could be prevented by doping rare earth element ceric. SEM measurement results showed the diameters of the particles were in the range of 20～30nm and the samples were porous. TGA analysis indicated that the process of TiO2 and 0.0003CeO2-TiO2 gel powders' loss of weight were consistent. FTIR results demonstrated that CeO2-TiO2 and pure TiO2 had better surface hydrophilicity. Microwave assisted photocatalytic oxidation experiment results revealed that doping ceric could distinctly improve the photocatalytic activity. CeO2-TiO2 coated photocatalyst was prepared by dip-coating technique, using glass and γ-Al2O3 as carriers, respectively. The result indicated that CeO2-TiO2 photocatalytic activity was higher than pure TiO2 and the photocatalytic activity of CeO2-TiO2/γ-Al2O3 was higher than CeO2-TiO2/glass. The optimum Ce content was 0.0003(molar ratio), the optimal calcinations temperature was 400 ℃ . The optimal coating layers of CeO2-TiO2/glass and CeO2-TiO2/γ-Al2O3 were 2 and 3, respectively. The degradation rates of Acid Mordant Red B were compared in four different reaction systems, the result demonstrated that the degradation rate of Acid Mordant Red B in MW+UV+0.0003CeO2-TiO2 system was much higher than the other systems, which revealed that microwave could improve the photocatalytic activity obviously. Some factors influenced the degradation rate were studied, such as the amount of H2O2, initial concentration and pH value of solution. The optimum pH value was 2, the optimum amount of H2O2 was 900mg/l. The degradation rates of three dyes were compared, the result showed the photocatalytic degradation rate was correlative with the molecular structure of the dyes. The two coated photocatalysts could be coated on carriers firmly, and there?s no significant loss on photocatalytic activity after long time illumination. The COD removal ratio of dye Acid Mordant Red B solutions was investigated under the microwave assisted photocatalytic oxidation. The results indicated that after 150 minutes reaction, the COD removal ratio increased about 24% by adding H2O2, compared with the process without H2O2.