Adsorption and Photocatalytic Degradation of Azo Dyes with Different Structures on the Surface of TiO2 Nano-particles
不同结构偶氮染料在TiO2纳米颗粒表面的吸附和光催化降解

Four water-soluble azo dyes widely used for the dyeing and printing of fabrics including Reactive Red MS, Reactive Blue B, Mordant Black PV and Acid Orange 156 were selected to study the adsorption and photodegradation of water-soluble azo dyes with different structures on TiO2 particulate photocatalyst in water. And adsorption behavior and modes of these dyes on the surface of TiO2 particles were investigated under various pH levels and in the presence of sodium chloride, respectively. The adsorption parameters of the dyes were obtained using experimental data fitting method. In addition, these azo dyes were degraded photocatalytically in the presence of TiO2 photocatalyst under varied pH levels in water. The results indicated that high pH values caused low adsorption quantity of the dyes on TiO2 particles, and their adsorption decreased significantly with the pH range from 4 to 8. Moreover, the amounts of four dyes adsorbed on TiO2 particles were increased in the presence of sodium chloride, and those of the two acid dyes were much higher than the two reactive dyes in terms of the amounts adsorbed on TiO2 under the same conditions. In addition, the adsorption isotherms of four dyes were described well by Langmuir adsorption model, and the reactive dyes showed higher adsorption constants and coverage on the surface of TiO2 particles than the acid dyes. On the other hand, increasing pH values reduced the photocatalytic decoloration percentages and first order reaction rate constants, and the reactive dyes were decomposed more easily than the acid dyes under the same conditions.