Synergistic Effects Of Ferric And Fluoride Ions On Photocatalytic Degradation Of Methyl Orange

In recent years, photocatalytic degradation of dye waste waters by nanomaterials has attracted a great attention over the world. This technology usually uses sunlight and other light such as ultraviolet radiation, laser light with the addition of photooxidant or photosensitizer as O₂, H₂O₂ to photocatalytic degrade the dyes, and the decolorization rate of organic dyes can achieve more than 90%. The method is promising because its low cost and simple requires of only light, photocatalyst and air for the reaction.In this thesis, synergistic effects of ferric and fluoride ions were investigated on photocatalytic degradation of methyl orange in TiO₂ (Degussa P25) suspensions at pH=6 under 20w UV irradiation. The results are as follows, under all the tested conditions, the methyl orange photodegradation was observed to follow a pseudo-first-order reaction in kinetics. In the suspensions with the addition of Fe³⁺ or F^-, the best addition quantity of Fe³⁺ is 1～10μM, and this addition enhances the photodegradation rate of MO by 74.1%. The best addition quantity of F^- is 0.76～7.6mM, leading to an enhancement of the photodegradation rate of MO by 41.3%. In the suspensions with the simultaneous addition of Fe³⁺ and F^-, the synergistic effects of ferric and fluoride ions greatly enhanced the degradation rate of MO by 135%. The optimized addition quantity of Fe³⁺ and F^- in the photocatalytic system is: 1μM Fe³⁺ and 1mM F^-.The effect of catalyst load, methyl orange initial concentration, the circularly use of the photocatalyst of Fe³⁺/F^-/TiO₂ is explored. The best load of TiO₂ is 1 g/L. The degradation of MO was completed in 30min when the initial concentration of MO was between 6～12 mg/L. The photocatalyst of Fe³⁺/F^-/TiO₂ even had higher photocatalytic activity after five cycle use. At last, the mechanism of synergistic effects of ferric and fluoride ions in the TiO₂ suspensions was discussed.