The Research On Iron Oxyhydroxides' Absorption And Photocatalyse Decoloration On Azo Dye

A huge amount of waste water, which is incapable treated by conventional methods, is produced during the manufacturing process. In the late 1980s, using solar energy as the main energy sources in heterogeneous pHotocatalytic oxidation is applied in environmental fields, but the mechanism and kinetics of the heterogeneous pHotocatalytic oxidation is still a grey area. In this dissertation, FTIR spectra is used to analyze the decoloration mechanism of the azo dye solution by two kinds of nanometer sized iron oxyhydroxides: α-FeOOH (Goethite) and β-FeOOH (Akaganeite), the different decoloration process under solar light and ultra violet light with or without the presence of hydrogen peroxide are discussed. The article is focused on decoloration process and mechanism of azo dyes.The results showed that after 2 hours' absorption of dyes , the FTIR spectra of iron oxyhydroxides showed sulfonic group peaks at 1033 or 1030cm^-1 , whereas the absorption band between 1450¹400cm^-1 which assigned to the stretching vibration of azo bond weakened or disappeared respectively in the samples of a-FeOOH and P-FeOOH, these indicated that azo dye molecules were absorbed to the surface of iron oxyhydroxides due to the negative charge of sulfonic group, and the electron transfer occurred between the azo dye molecules and the Fe³⁺ center on the surface of iron oxyhydroxides , this may lead to the rupture of azo bond. We can infer that the decoloration of azo dyes molecules was the co-effect of the selective chemical absorption and the oxidation effect on the surface of iron oxyhydroxides.Even without the presence of hydrogen peroxide, and either under solar light and UV light radiation, the remarkable decoloration of azo dyes are observed, we can infer that FeOOH can break the azo band under visible light radiation.With the presence of hydrogen peroxide, the azo band vibration in FTIR spectra disappeared after 5h pHotocatalytic oxidation in α-FeOOH (β-FeOOH) /UV(visible light)/H₂O₂ systems;a weak C — H group stretching vibration appeared at 2927cm^-1, 2847cm^-1, benzene ring was ruptured. In FeOOH/UV(visible light)/H₂O₂systems, it can be inferred that the first step of methyl orange decoloration process is the azo band rupture, and then with the big amount of hydroxyl radicals emerged under the condition of light radiation and the presence of hydrogen peroxide, which could lead to the rupture of benzene ring, and decomposed methyl orange organic molecules.It can be concluded that the decoloration process of azo dye by iron oxyhydroxides is: firstly azo dye molecules are absorbed to the surface sites of iron oxyhydroxides, which is through forming complex on the surface of iron oxyhydroxides;with the presence of light radiation and H2O2, the hydroxyl radicals (-OH) will decompose organic compounds yielding to CO2 -. H2O and other productions.