Photocatalytic reactions of imazamox at TiO₂, H₂O₂ and TiO₂/H₂O₂ in water interfaces: Kinetic and photoproducts study

The photocatalytic transformation of imazamox, a herbicide of imidazolinone family, is investigated in aqueous solution containing titanium dioxide, hydrogen peroxide or the combination of TiO₂/H₂O₂ under simulated sunlight irradiation. The effect of parameters such as the amount of catalysts, the concentration of herbicide, and the pH were investigated by measurement of the rate constant of degradation. Experimental data obtained under different conditions describe the dependency of degradation rate on the above mentioned parameters. Consequently, kinetic parameters were experimentally determined and a pseudo-first-order kinetic was observed. Mulliken charge distributions calculated by the DFT method B3LYP/6-31+G(d) level of theory for key cationic, anionic and neutral structures of imazamox give interpretation for the dependency of photodegradation rate constant on pH. The degradation rate constants were always higher for the heterogeneous catalysis in reactions (TiO₂/UV, TiO₂/UV/H₂O₂) compared to the homogeneous systems (UV alone, H₂O₂/UV). In parallel, five photoproducts could be tentatively identified using Electrospray ionization Fourier transform ion cyclotron resonance mass spectroscopy based on precise chemical formula assignments.