Comparative study on photooxidation of methyl orange using various UV/oxidant systems

In the present work, a comparative study of the photooxidation of an aqueous solution of Methyl Orange (MeO) has been realized using H2O2 and IO3 −, BrO3 −, ClO3 −, ClO4 −, BO3 − ions in the presence of UV low pressure mercury lamp (UV-C light at λ max = 254 nm). The initial concentration of MeO in all experiments was 6 × 10−5 mol L−1. The degradation rate of MeO follows pseudo-first-order kinetics in all UV/Oxidant systems. The highest degradation rate of MeO was in the BrO3 −/UV254nm system. Different systems were compared for an oxidant concentration of 10−2 mol L−1 and the obtained results showed that decolorization followed the decreasing order: BrO 3 − /UV 254 nm > IO 3 − /UV 254 nm > H 2 O 2 /UV 254 nm > BO 3 − /UV 254 nm > ClO 3 − /UV 254 nm = ClO 4 − /UV 254 nm = UV 254 nm . The optimization of oxidants concentration for each process was determined (10−2 mol L−1 for IO3 − which gives almost the same k app for 5 × 10−3, 10−2 mol L−1 for BO3 − and 5 × 10−2 mol L−1 for H2O2). No degradation of MeO in presence of ClO3 − and ClO4 − because these ions do not absorb at 254 nm, therefore they do not generate radical species which degrade organic pollutants. The mineralization was also studied where it was reached 97% after 5 h of irradiation for both H2O2/UV254 nm and BO3 −/UV254 nm systems.