Decolorization of methyl green and bromocresol purple in mono and binary systems by photochemical processes: direct UV photolysis, Acetone/UV and H2O2/UV. A comparative study

The aim of this study is to test the ability of photochemical processes (photolysis, Acetone/UV and H2O2/UV at 254nm) to eliminate the Methyl Green (MG, cationic structure) and Bromocresol Purple (BCP, anionic structure) in aqueous solution in mono and binary systems. The obtained results show that the rate of decolorization by UV photolysis at 254nm in single system is weak for BCP (25%) and acceptable for MG (66%). In dark conditions, preliminary experiments show no decolorization of the two dyes in the presence of acetone and in the presence of H2O2 for BCP. However, classical oxidation has been observed for MG in H2O2 for concentrations superior to 5x10(-4)M. In the presence of light, a real improvement in the decolorization rate of both dyes is obtained using H2O2/UV (acting via issued from photolysis of H2O2 at 254nm) and Acetone/UV (acting via energy transfer from the sensitizer which is Acetone to the dye). In the mixture systems, the Acetone/UV process is more effective than direct UV photolysis and H2O2/UV. In the three photochemical processes used, each dye decreases the removal efficiency of the other. The dyes removal kinetics follows the pseudo-first-order model in Acetone/UV and H2O2/UV systems for both dyes in single and binary systems.