| Photocatalytic oxidation of water contaminants is a new type of method for wastewater treatment. It is widely and deeply studied by many people for its high photodegradation efficeiency, none secondary pollution caused and the potential of utility of solar energy. Therefore, the way of the preparation of the effective laden photocatalysts and the way of improving the effect of solar energy use are two impending problems in the domain of photocatlytic oxidation presently.On the basis of surveying current situation and advances in photocatalytic oxidation technology, the azo dye -Acid Orange 7(AO7) was chosed in this study as a representative target contaminants for studying its photocatalytic degradation mainly within a visible photocatalytic reactor, using supported TiO2 made by sol-gel preparation as photocatalyst.Photocatalyst of supported TiO2 on SiO2, with 1:2 ratio of TiO2:SiO2 was prepared using the modified sol-gel method. The results of XRD analysis showed that the crystalloid of the catalyst was anatase and the average size was 5.3 nm. The measurement of the ratio of TiO2 in the photocatalyst showed that there was only about 6 percent of TiO2 being lost during its preparation.Factors controlling the photocatalytic oxidation reaction, including initial concentration of AO7, initial solution pH, different catalysts amounts added, reaction time and different light sources were studied in details. The results obtained indicated that :(1) The constant of reaction rate decreased and the initial reaction rate increased with the initial concentration of AO7 increased. The possible reason for this might be that the former related to the adsorption ratio of AO7 on catalysts while the latter related to the amounts of them adsorbed. (2)The pH of the solution had obvious effects on the photodegradation reaction. The reactions were favored under acidic conditions and inhibited to sme extecnt under alkaline conditions. And the effect of pH on photodegradation efficiency was consistent with the adsorption efficiency. Therefore, we might conclude that the adsorption of AO7 on catalysts played an important role on the photodegradation reaction.(3)The addition of catalysts wasindirect active factor in enhancing the photodegradation reactions. (4)AO7 could be faded completely with the reaction time increased, but it was not a process of thorough mineralization for some intermediates being exitsted in the process of photodegradation reaction. (5)The effect of the visible light on photodegradation reaction was better than the UV light, that was to say, photodegradation under visible light might be more depended on the adsoption capability of the catalyst while photodegradtion under UV light was dependent more on the crystalloid of the catalysts.The kinetic studies showed that all of the reactions could be better fitted by a pseudo-first-order kinetics, which is rationalized in terms of the Langmuir-Hinshelwood model.Finally, under some conditions, the photocatalytic efficiency of TiCVSiO: prepared was better than the standard of P25, the AO7 degradation rate constant of it was 1.99 times of that of P25. The PZC of the photocatalyst was only 2.66 , and it was even lower than that of P25 ,which had the PZC of 4.7 and it might be an important factor to control the activity of photocatalysts.
|
PDF Full Text Request