Kinetics of decolourising methylene blue by peracetic acid in the presence of Co2+ and UV light

Abstract

The kinetics of decolourising methylene blue (MB) by peracetic acid (PAA) in the presence of Co²⁺ ion and ultraviolet (UV) light at the temperature of 25±1^oC were examined in this study. All experiments were conducted with a solution volume of 0.5 l, where the concentration of PAA was over 100 times higher than that of MB. The effects of two main factors (pH and Co²⁺ concentration) on the rate of MB decolourisation, and the enhancement of combining PAA with UV light were examined in this study. The obtained experimental results showed that the pH value of the reaction solution strongly affected the reaction rate of decolourisation. When pH increased from 4 to 6, the reaction rate increased about 7 times. The Co²⁺ ion revealed high catalytic activity for the reaction, concentrations of Co²⁺ varied from 0.01 mg/l to 0.1 mg/l, resulting in a rate increase of nearly 11 times. Under UV light irradiation, PAA exhibited more powerful activity compared to H₂O₂, achieving a decolourisation efficiency of 95% in 420 seconds. This observation can be explained by the low energy of intramolecular bonding O-O in PAA molecule.