Titanium dioxide mediated photocatalytic degradation of monochlorobenzene in aqueous phase

The reaction sequence for the photocatalytic degradation of monochlorobenzene (MCB) in UV/TiO 2 process, including substrate adsorption, degradation, and mineralization, was studied. The theoretical maximum quantity of MCB that could be adsorbed onto TiO 2 surface in aqueous phase was 0.18 ± 0.04 μmol m −2 of TiO 2 . In accordance with the upper limit of the relative surface coverage of MCB molecules to surface hydroxyls of TiO 2 was around 2.2%, the water molecules as the major adjacent species near TiO 2 surface would compete with MCB molecules. Increasing the initial substrate concentration to an appropriate value or enhancing the affinity between the MCB and the TiO 2 surface by adjusting the solution pH would promote the photocatalytic degradation. Experimental results revealed that the neutral medium was beneficial for the degradation of MCB. In comparison, the mineralization was most improved at acidic condition. Generally, 90% of the total organic carbon (TOC) was mineralized after 240 min illumination time in the examined pH range except solution pH 11. The suppressed mineralization of MCB at solution pH 11 was ascribed to the lack of adsorption. A simplified 2-step consecutive kinetic model was used to simulate the mineralization.