Enhanced degradation of 2,6-dimethylphenol by photocatalytic systems using TiO2 assisted with H2O2 and Fe(III).

In this study, several photocatalytic degradation systems were investigated using 2,6-dimethylphenol (2,6-DMP) as a model compound. Highly reactive species are formed in four systems, Fe(III), TiO2, TiO2/H2O2 and TiO2/Fe(III) where complete degradation of 2,6-DMP was achieved under UV radiation. Photodegradation of the 2,6-DMP has been described by pseudo-first order kinetic model in presence of TiO2. In UV/TiO2 - H2O2 system, the addition of H2O2 in the TiO2 suspension improves the degradation rate of 2,6-DMP from 70% to 100% for a H2O2 concentration of 10-2 M in 3 h. In Homogeneous system, HO• and Fe2+ can be generated by the irradiation of Fe(III) solution. The speciation of Fe(III) obtained from Visual MINTEQ soft showed the formation of several species and Fe(OH)2+ were the most predominant and active species in a pH range of 2.5 - 3.5. At low concentration of TiO2 (30 mg L-1), an important positive effect due to the iron addition has been shown in TiO2/Fe(III) system, the entrance of metallic ions at different concentration enhanced the photocatalytic activity of TiO2. A degradation percentage of 90% was achieved in UV/TiO2 - Fe(III) system under optimal conditions against 57% in UV/TiO2 system. Strong synergistic effect was observed in UV/TiO2 - H2O2 binary system. On the basis of literature, a pathway for 2,6-DMP degradation was proposed. The mechanism of degradation of the 2,6-DMP did not involve only HO• radicals an interaction of Fe(III) in the excited state with 2,6-DMP occurred giving rise to the formation of 2,6- dimethylphenoxyl radical.