Removal of binary azo dyes from water by UV-irradiated degradation in TiO₂ suspensions

Photodegradation and mineralization of single and binary Acid Orange 7 (AO7) and Reactive Red 2 (RR2) under UV irradiation in TiO₂ suspensions was examined. Experiments were conducted as a function of initial pH, TiO₂ dose, and initial dye concentration. First-order derivative spectrophotometric method was used to simultaneously analyze AO7 and RR2 in binary solutions. The Langmuir-Hinshelwood kinetic model was applied to evaluate and compare the apparent rate constants for the photodegradation of both dyes in single and binary solutions. It was shown that photodegradation of both dyes in binary solution was slower than those in single solution under comparable conditions. Moreover, the difference between the apparent rate constants of RR2 and AO7 became smaller in contrast to the cases of single solutions. After 20-min UV irradiation with 0.5g/L TiO₂, complete removal of single 0.086mM AO7 and 0.086mM RR2 at pH 6.8 was obtained, but only 60% and 45% of binary 0.086mM AO7 and 0.086mM RR2 was removed, respectively.