Effect of Oxygen and Hydrogen Peroxide on the Photocatalytic Degradation of Monochlorobenzene in TiO2 Aqueous Suspension

The influences of oxygen and hydrogen peroxide (H2O2) on the degradation and mineralization of monochlorobenzene (MCB) during UV/TiO2 process were investigated. Experimental results indicated that oxygen was a determining parameter for promoting the photocatalytic degradation. The presence of oxygen reduced the illumination time needed for the complete decay of MCB from 240 to 120 min. The photocatalytic degradation of MCB in UV/TiO2/O-2 photocatalysis followed a simplified two-step consecutive kinetics. The rate constants of degradation (k(1)) and mineralization (k(2)) were increased from 0.016 to 0.046 min(-1) and from 0.001 to 0.006 min(-1), respectively, as the initial concentration of dissolved oxygen (DO) was increased from 1.6 to 28.3 mg L-1. Owing to the fact that H2O2 acted as an electron and hydroxyl radicals (center dot OH) scavenger, the addition of H2O2 should in a proper dosage range to enhance the degradation and mineralization of MCB. The optimal H2O2 dosage for MCB degradation was 22.5 mg L-1, whereas the most efficient H2O2 dosage for MCB mineralization was 45.0 mg L-1. In order to minimize the adverse effects of higher H2O2 dosage, including the capture of center dot OH radicals and competitive adsorption, and to improve the photocatalytic degradation of MCB, the sequential replenishment of H2O2 was suggested. For the stepwise addition of a total H2O2 dosage of 45.0 mg L-1, a complete destruction of MCB was observed within 120 min of irradiation. Additionally, the mineralization efficiency was about 87.4% after 240 min of illumination time.