Degradation of '' Bromocresol Green'' by direct UV photolysis, Acetone/UV and advanced oxidation processes (AOP's) in homogeneous solution (H2O2 /UV, S2O8 2- /UV).Comparative study.

The aim of this work is to verify the ability of some photochemical processes to eliminate an acidic dye in aqueous medium, used as molecule model: The Bromocresol Green. The obtained results showed that system like: H2O2/UV and S2O8 2- /UV were better than direct UV photolysis at.254 nm and acetone/UV at the same wavelength. This improvement seems to be linked to production of OHand SO4 •- radicals issued from the photolysis of H2O2 and S2O8 2- , always at this same wavelength. The influence of concentration of H2O2 has permitted to find the optimal dose in order to avoid the scavenger effect by H2O2 itself The UV spectral change of Bromocresol Green has been also studied for both processes. One can conclude that it was easier to destroy the partial π -π* conjugated system and n- π* bonding related to OH groups. On the other hand, the rate of decolourization was found to follow first order kinetic in almost cases (except in photolysis).The effect of parameters like: alcohols, oxygen and initial concentration of the dye were also studied. One observes that alcohols inhibit the elimination of the dye in the H2O2/UV case, whereas oxygen has a minor effect on it. About, the third parameters, the initial concentration of the dye affects the decolourization process: it decreases as its concentration increases.