Kinetics of decolorization of an azo dye in UV alone and UV/H_2O_2 processes

摘要

The decolonization of C.I. Acid Red 27 (AR27), a monoazo anionic dye, was studied in the ultraviolet radiation (UV) alone and UV plus hydrogen peroxide (UV/H_2O_2) processes. The experimental results indicated that the kinetics of both oxidation processes fit well by pseudo-first order kinetics. The reaction rate was sensitive to the operational parameters and increased with increasing H_2O_2 concentration and light intensity. The reaction orders of H_2O_2 concentration and light intensity in both processes were obtained with linear regression method. A regression model was developed for pseudo-first order rate constant (k_(ap,UV/H_2O_2)) as a function of the H_2O_2 concentration and UV light intensity. k_(ap, UV/H_2O_2)= (2 x 10~(-4) I_0~(0.75) + k_3I_0~(1.38)[H_2O_2]_0~n)φ_(AR27) As a result of two opposing effects of H_2O_2 concentration at low and high concentrations, n has a value of 0.49 and —0.39 and k_3 has a value of 3 x 10~(-4) and 0.1 for the regions of 0 mg l~(-1) < [H_2O_2]_0 < 650 mg l~(-1) and 650 mg l~(-1) < [H_2O_2]_0 < 1500 mg l~(-1), respectively. φ_(AR27) is the initial dye concentration correlation index for developing of model for different initial concentrations of AR27. This rate expression can be used for predicting k_(ap, UV/H_2O_2) at different conditions in UV alone and UV/H_2O_2 processes. The results show that UV alone cannot be an efficient method for decolorization of AR27 in comparison with UV/H_2O_2 process, therefore the first term of the model can be neglected.