TiO2-mediated photomineralization of 2-chlorobiphenyl: the role of O2

Photocatalytic mineralization of 2-chlorobiphenyl (2-CB) in aqueous TiO2 suspensions was conducted under four different oxygen partial pressures (Po2) in closed reactors. The observed O2 adsorption equilibrium constant in TiO2 aqueous suspension was 0.88 (kPa)−1 based on the Langmuir–Hinshelwood rate function. Apart from the conventional electron-scavenging function, the dissolved oxygen was critical for the degradation of the hydroxyl intermediates, i.e., 2-chlorobiphenyl-ols and biphenyl-2-ol, which are potentially toxic. Degradation of 2-CB in the irradiated H2O2 aqueous solutions under two different Po2 was also studied for comparison. For UV/H2O2, Po2 does not affect the removal of 2-CB, while reducing the Po2 from 21 to 2 kPa resulted in 35% less CO2 formation after 5 h irradiation. The similar O2-dependent destruction of the hydroxyl intermediates was also observed in the UV/H2O2 system. We propose that molecular O2 acts as a key reactant following the attack of a second •OH radical during the ring opening in the degradation of the hydroxyl byproducts.