Photo-Assisted Degradation Of Organic Dyes Over Supported Ferric Catalyst

Over the past decades, water contamination becomes increasingly a worldwide problem that affects continuable development of human being. The wastewater produced from industrial manufacture and agricultural processes contain abundantly toxic and nonbiodegradable organic pollutants such as phenol, chlorophenol, sulfide and textile dyes. These pollutants could not be thoroughly eliminated by conventional ways. Based on various reactive oxygen radicals, advanced oxidation technologies aims to oxidize and/or minerailize hazardous organic compounds into CO₂, H₂O and other inorganic substances. Therefore, these technologies are actively studied in the recent years in environmental science. The most promising AOTs is the homogenous Photo-Fenton reaction that employs ferric ion, H₂O₂ and UV light for degradation of organic pollutants in water. For the practical use, however, the immoblized Fe catalyst is preferred for convenient separation and reuse of the catalyst. In this thesis, the Fe-laded catalyst was prepared by several methods. And their potoreactivity and stability were examined for degradation of organic dyes in the presence of H₂O₂ and visible light irradation.In chapter three, was studied the effect of ferric ions added directly into TiO₂ suspension on the photocatalytic degradation of textile dye X3B in water under UV irradiation. It was found that the prensence of Fe³⁺ could significantly promote the X3B photodegradation. However, this enhancement disappeared as all Fe³⁺ were transferred into Fe²⁺. This was attributed mainly to electron trapping at the semiconductor surface, and both X3B and Fe³⁺ adsorption facilitate as well the separation of photogenerated electron-hole pairs. It was Fe²⁺ that was hardly adsorbed on the TiO₂ surface inhibiting its reoxidation by the photogenerated hole and thus the recycle of Fe³⁺/Fe²⁺. The results obtained in this work will be relevant to the study on Fe-doped photocatalyst.In chapter four, the ferric species was immobilized on an ionic exchange resin, and thereafter was investigated as a heterogeneous catalyst for degradation of dye pollutants by H2O2 under visible light irradiation. The experiment revealed that the cationic (anionic) dyes were efficiently photodegraded only on cationic (anionic) resin-supported Fe catalyst, while the Fe catalyst supported on amphoteric exchange resin was found to be effective for photodegradation to both cationic and anionic dyes. This significant difference was attributed mainly to their notabl distinction in adsorption on the Fe-resin catalyst. All the catalysts were stable upon visible light irradiation, but the Fe-loaded amphoteric resin corroded to a certain level upon UV irradiation. In the presence of H2O2, however, such UV-induced Fe dissolution was greatly depressed.In chapter five, natural clay was employed as a support for ferric species. It was found this photocatalyst could adsorb and photodegrade both cationic and anionic dyes in water even under netural pH valves in the prensence of H2O2 and visible light irradiation. Seven repeating experiments showed that this catalyst was stable and recyclable for MG degradation.