Preparation And Optimization Of Coated Photocatalyst

Photocatalytic oxidation is a kind of photosensitive oxidation method using n-style semiconductor as a photocatalyst ,which is based on the energy band theory of this photocatalyst. Of most photocatalysts used in wastewater treatment, TiO2 has been used most commonly because it is more effective and stable, and is cheap and nontoxic. Since the conventional suspended reaction system has much disadvantage ,which mainly lie in the fact that it is difficult to recycle the TiO2 powder after reaction and so will cause secondary pollution, many researchers have thought of coating TiO2 on a kind of carrier. As a result, coated photocatalyst has showed bright future in degrading organic wastewater though there are still many aspects to be improved. For example, the photocatalytic effect of coated photocatalyst is still not very ideal, and the fastness can't meet the requirement. This paper has done some work in optimizing the coated photocatalyst by adulterating TiO2 with other semiconductors such as Fe2O3 and CdO in order to improve the photocatalytic activity.Sol-gel method is one of the main method in preparing TiO2 coated photocatalyst, and so the stability of sol is of much importance. The technics of sol preparation was improved in this paper so that the stable time for coat-dipping could be prolonged to 45 days . C4H9OH was choosed as a solvent, and the molar ratio between Ti(OBun)4 and H2O was controlled to 1:2 , HAc acted as acid catalyst and chelate reagent, NH(C2H5O)2 and CH3COCH2COCH3 were used as stable reagent. Under this condition, not only can the sol exist long time for preparing coated photocatalyst, but also the film can be coated on carrier firmly. The technics of TiO2 coated photocatalyst adulterated with Fe was improved, and the photocatalyst coated on glass was prepared. It was found that the photocatalytic activity of Fe2O3-TiO2 coated photocatalyst with x(Fe2O3)=3.9%, coated mass=9-11mg/piece and calcined at 500℃ for 2h is much higher than pure TiO2 film when degrading dye Acid Mordant Red B. The photocatalyst can be coated on glass firmly, and there's no significant loss on photocatalytic activity after long time illumination.The conception of adulterated TiO2 with Cd was obtained basing on energy band theory of semiconductor and taking the preparation method of Fe2O3-TiO2 coated photocatalyst for reference. The CdO-TiO2 photocatalyst coated on glass was prepared. It was found that the 0.04 molar ratio of CdO-TiO2 coated photocatalyst with 5 coating layers, calcined at 550℃ for 0.5h, has highest activity. The degradation rate for 1h is 3.4 times of that of pure TiO2 film. The CdO-TiO2 can be coated on glass firmly: after 20 days' dipping in water, the lost rate of mass is about 0.65%, and the photocatalyst can be used for a long time without significant loss on photocatalytic activity. The decoration of Acid Mordant Red B accords with pseudo first grade reaction. Dynamical study shows that the reaction rate constant is 0.0095min-1 at normal temperature(25℃)and the apparent activation energy of this reaction is 21.2kJ·mol-1,which is lower than the activation energy of normal chemical reactions.