Photocatalytic Degradation of Michler's Ketone in Water by UV Light Illumination Using TiO2 Photocatalyst: Identification of Intermediates and the Reaction Pathway

The TiO2/UV photocatalytic degradation of Michler's Ketone (MK) has been investigated in aqueous heterogeneous suspensions. Results obtained show rapid and complete oxidation of MK after 24-h, and more than 97.5% of MK was mineralized after a 32-h exposure to UV-365 nm irradiation. Establishment of the reaction pathway was made possible by a thorough analysis of the reaction mixture identifying the main intermediate products generated. Nine intermediates have been detected by HPLC/ESI-MS and GC/MS techniques. The photocatalytic degradation of MK proceeds through competitive reactions such as N-de-methylation and destruction of the bis-aminobenzophenone structure. The former reaction took place in a stepwise manner to yield mono-, di-, tri-, tetra-demethylated species, while the latter reaction yielded N-methylaminobenzene and aminobenzene. The reaction mechanisms of TiO2/UV proposed in this study should shed some light on future applications of the technology to the destruction of organic pollutants.