Abstract:
This study focused on the elimination of three dyes by several advanced sonochemical and photochemical oxidation processes in a homogeneous and heterogeneous medium as well as by direct photolysis at 254 and 365 nm. In most of the cases studied, a pseudo-first order kinetic law applies correctly to a large part of the reactions. The results obtained in this study indicated that photolysis (UV only) was found to have little effect on the degradation of the three dyes. The removal efficiency can be improved by increasing the intensity of the photonic flux or by decreasing the initial concentration of pollutant.
The coupling of H2O2/UV increases considerably the degradation rate of the three dyes, the efficiency is enhanced by raising the dose of H2O2 up to a limit imposed by the self-inhibition reactions. The DT-DFT method allowed recalculating the theoretical UV-Visible spectra of the three dyes which are comparable to that obtained experimentally. Adsorption and heterogeneous Photocatalysis were influenced by various factors (initial substrate concentration, catalyst type and loading, pH of the solution, addition of hydrogen peroxide, and the presence of inorganic salts). The results showed that the degradation yield of the three dyes is very high when using TiO2-P25, where a complete photocatalytic degradation of 10 mg L-1 of GV, BF and AF was obtained in 25, 30 and 50 minutes in the presence of 1 g L-1 of TiO2 Degussa P25 at natural pH. First-order kinetics described the photocatalytic reaction of the three substrates andthe Langmuir-Hinshelwood model correctly described the photocatalysis processes of the substrates tested. The comparison between various types of catalysts (Degussa P25, Millenium PC500, PC105, PC100, and PC50) gave varied results but Degussa P25 was the most efficient photocatalyst from which it was chosen for this study. The optimum catalyst concentration was 1 g L-1 of TiO2 with an initial concentration of 10 mg L-1 of dye. Finally, the sonochemical degradation of GV by sonolysis at 516 kHz shows that this method is effective for the degradation of this dye. However, this process can be affected by several parameters including, applied electrical power, initial substrate concentration, pHof the solution, the addition of H2O2 and S2O82- and the presence of someinorganic ions.
