| Summary: | 碩士 === 國立高雄第一科技大學 === 環境與安全衛生工程所 === 91 === The purpose of this research is to study the effect of surfactants on liquid-phase photocatalysis of perchloroethylene (PCE) by using TiO2 as a photocatalyst. Series of photocatalytic experiments are conducted in a batch photocatalytic reactor in which 2000 mg/L anatase TiO2 powder is suspended and four near-UV light lamps are surrounded as the light source. Several experimental parameters including different types of surfactants (SDBS, TX100 and CPC), the concentrations of surfactants, solution pH levels ranging from 3 to 11, and light illumination time are investigated to discuss their influence on PCE degradation.
The experimental results indicate that the photocatalytic degradation of PCE basically follows a first order reaction but it is usually inhibited in the presence of surfactants. The inhibited reaction rates may be due to the adsorption-competition for activated sites on photocatalysts. For the inhibition on PCE decomposition by different types of surfactants, the tendency for the inhibition is in the order of SDBS > TX100 > CPC. That is, the decomposition rates of PCE are more easily inhibited by anionic surfactants and those may be enhanced in the presence of proper amount cationic surfactants. There are two reaction patterns for the change in the degradation rates of PCE resulting from different concentrations of surfactants. As surfactant concentrations are below its CMC, the obviously inhibited decomposition of PCE is observed and the reaction rates are decreased quickly as surfactant concentrations are increased. On the other hand, although the habited decomposition of PCE is also observed as the concentrations of surfactant higher than its CMC, the retarded reaction rates for PCE photocatalysis approach to constant values for both PCE-SDBS and PCE-TX100 reaction systems, but the rates are continually decreased for the PCE-CPC system.
In addition, pH has an important effect on degradation of PCE. Not only surfactants can be decomposed under the acid environment and may cause the breakage in their molecular structures, but also surfactants may become more active to as short molecules, which are more easily adsorbed by TiO2 and result in the deterioration in the PCE degradation rates. Thus, more complex reactions for PCE photocatalysis accompanied with different types of surfactants under various solution pH levels would be expected. More inspections would be required for future investigations.
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