| Summary: | 碩士 === 弘光科技大學 === 環境工程研究所 === 96 === The purpose of this research is trying to investigate the photochemical processes (UV/P25 TiO2, UV/Pt-TiO2) and non-photochemical processes (Fenton, Fenton-like) for the removal of Crystal Violet (CV) dye. The Pt-TiO2 was platinized by a photochemical impregnation method. The ratios of platinum (Pt) applied onto TiO2 surface include 0.4, 0.8, 1.6, 4, 8, 16, and 40 wt %/g TiO2. The experimental results indicated that Pt-TiO2-F (16 wt %/g TiO2) had the highest photocatalytic activity. For example, under alkaline conditions (up to about pH 9), degradation of the dye (50 mg/L) by UV/Pt-TiO2 and UV/P25 TiO2 was 97.64 and 91.07%, respectively. In the case of pH 3, the oxidation efficiency was 98.93 and 83.45%, respectively. The illumination time by UV (365 nm) was 8 hr.
This research also investigated degradation of CV by Fenton and Fenton-like processes. Parameter investigated includes pH, Fe2+, Fe3+, and H2O2 dosage. The experimental results showed optimum pH for Fe2+/H2O2 (0.5 mM：50 mM) and Fe3+/H2O2 (1 mM：50 mM) was about 3.
In order to obtain a better understanding of the mechanistic of UV/TiO2 and Fenton’s reagent for the degradation of the CV dye, the intermediates of these processes were identified and characterized by HPLC-ESI-MS with GC-MS technique in this study. The probable photodegradation pathway was N-de-methylated, hydroxylation, and cleavage of conjugated chromophore structure by UV/Pt-TiO2 processes. In UV/P25 TiO2 and Fe2+/H2O2 processes, a probable mechanism was N-de-methylated and cleavage of conjugated chromophore structure. The intermediates generated sequence indicated that the N-de-methylation degradation of CV dye took place in a stepwise manner to yield mono-, di-, tri-, tetra-, penta-, and hexa-N-de-methylated CV species.
The removal efficiencies of these processes were in the order of Fenton＞Fenton-like＞UV/Pt-TiO2＞UV/P25 TiO2. The reaction mechanisms proposed in this study might be useful for future application of advanced oxidation technology for decoloration of dyes.
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