Photooxidation of naphthalenesulfonic acids: Comparison between processes based on O3, O3/activated carbon and UV/H2O2

The aim of the present study was to analyze and compare the efficacy of UV photodegradation with that of different advanced oxidation processes (O3, UV/H2O2, O3/activated carbon) in the degradation of naphthalenesulfonic acids from aqueous solution and to investigate the kinetics and the mechanism involved in these processes. Results obtained showed that photodegradation with UV radiation (254 nm) of 1-naphthalenesulfonic, 1,5-naphthalendisulfonic and 1,3,6-naphthalentrisulfonic acids is not effective. Presence of duroquinone and 4-carboxybenzophenone during UV irradiation (308–410 nm) of the naphthalenesulfonic acids increased the photodegradation rate. Addition of H2O2 during irradiation of naphthalenesulfonic acids accelerated their elimination, due to the generation of OH radicals in the medium. Comparison between UV photodegradation 254 nm and the advanced oxidation processes (O3, O3/activated carbon and UV/H2O2) showed the low-efficacy of the former in the degradation of these compounds from aqueous medium. Thus, among the systems studied, those based on the use of UV/H2O2 and O3/activated carbon were the most effective in the oxidation of these contaminants from the medium. This is because of the high-reactivity of naphthalenesulfonic acids with the OH radicals generated by these two systems. This was confirmed by the values of the reaction rate constant of OH radicals with these compounds kOH, obtained by competitive kinetics (5.7 × 109 M−1 s−1, 5.2 × 109 M−1 s−1 and 3.7 × 109 M−1 s−1 for NS, NDS and NTS, respectively).