UV/TIO2 PHOTOCATALYTIC OXIDATION OF COMMERCIAL DYES IN AQUEOUS-SOLUTIONS

Photocatalytic oxidation kinetics of five commercial dyes, namely Acid Blue 40, Basic Yellow 15, Direct Blue 87, Direct Blue 160, and Reactive Red 120 was studied in a TiO2/UV slurry reactor. The oxidation kinetics of Direct Blue 160 and Reactive Red 120 follows the Langmuir-Hinshelwood kinetic model at all the pH values studied. However, the oxidation kinetics of Acid Blue 40 fits the model at pH 3, Basic Yellow at pH 3, 5, and 11, and Direct Blue 87 at pH 7 and 9 only. In neutral solution of pH 7, the oxidation rates follow the decreasing order: Direct Blue 87 > Reactive Red 120 > Basic Yellow 15 > Acid Blue 40 > Direct Blue 160. At pH 3, the number of azo linkages in dye molecules seems to be the most important factor. For example, the oxidation rate of monoazo dye of Basic Yellow 15 is faster than disazo dye of Reactive Red 120 which in turn is faster than triazo dye of Direct Blue 160. The fastest reaction rate constants are 0.0160-0.0109 mM/min for monoazo dye of Basic Yellow 15, and the slowest reaction rate constants are 0.0013-0.0021 mM/min for the triazo dye of Direct Blue 160. The effect of Fe2+ and H2O2 on the reaction kinetics was also explored.