Abstract:
This study focused on the application of photochemical processes (direct photolysis and advanced oxidation processes) in the degradation of an ionic liquid; 1-hexylpyridinium bromide (HPyBr) in aqueous solution. These experiments were conducted in homogeneous phase and in heterogeneous phase. In homogeneous medium, the degradation of HPyBr was studied by different photochemical processes (UV254 nm, UV365 nm, solar irradiation and H2O2/UV254 nm) and by Fenton reagent (Fe2+/H2O2) and photo-Fenton (Fe2+/H2O2 /UV365 nm).
Various physico-chemical parameters have been tested in order to optimize the efficiency of these processes. The comparison of the performances of the various processes studied shows that H2O2/UV254 nm and Fe2+/H2O2/UV365 nm processes are the most efficient. In heterogeneous medium, two metal oxides such as ZnO and TiO2 p25 Degussa were used to compare their photoactivity on the degradation and mineralization of HPyBr. The results obtained show that the percentage of HPyBr adsorption is negligible in the presence of both catalysts. The photocatalytic degradation tests of HPyBr showed that ZnO/UV system was more efficient than the TiO2/UV system, and the disappearance kinetic of HPyBr is correctly described by the Langmuir-Hinshelwood model. The influence of the experimental parameters on the rate of degradation (substrate concentration, catalyst concentrations, pH, the addition of hydrogen peroxide, humic substances, inorganic ions, etc.) was studied. The significant inhibition of the photocatalytic reaction by the addition of chemical scavengers such as isopropanol and triethanolamine confirms that the major pathway for the degradation of HPyBr is due to the hydroxyl •OH radicals formed by irradiation of the photocatalyst surface. The oxidation (COD) and the mineralization (TOC) decrease according to the treatment but more slowly than the degradation, this confirms that the treatment of HPyBr by the photocatalytic process leads to the decrease of the organic matter content, however it requires a relatively slow processing time. In order to verify the feasibility of the photocatalytic process in the environment, both systems were studied under solar irradiation. The results show that the efficiency at this scale is greater than artificial radiation.
