[FTIR study of nano-iron oxyhydroxides' decoloration on the azo dye]

IR spectra were used to analyse the azo dye solution decoloration action by two kinds of iron oxyhydroxides. It was discovered that: (1) Acid Red G and methyl orange are apt to form complex on the surface of iron oxyhydroxides > FeOH, especially Acid Red G. which possesses two -SO3Na structures has a relatively high decoloration efficiency as a result of complexation reaction; (2) after 2 hours adsorption, the IR spectra of iron oxyhydroxides show characteristic wave numbers at 1 033 and 1 030 cm(-1) which belong to -SO3Na, whereas the peaks at wave numbers between 1 450 and 1 400 cm(-1), which belong to azo dye, disappear. These phenomena indicate that azo dye molecules are adsorbed on the surface of iron oxyhydroxides due to the negative -SO3Na structure, and at the moment azo dye molecules are adsorbed on the surface of iron oxyhydroxides, the electron transfer occurs between the azo dye molecules and the iron oxyhydroxides surface's Fe3+ centre, which could lead to the rupture of azo bond. It can be infered that the decoloration of azo dye molecules is the co-effect of the selective chemical absorption and the oxidation-deoxidation effect on the surface of iron oxyhydroxides.