Ozone enhanced activity of aqueous titanium dioxide suspensions for photodegradation of 4-chloronitrobenzene.

The TiO(2)/UV/O(3) process has been employed to remove 4-chloronitrobenzene (4-CNB) and compared to UV/air, O(3), TiO(2)/O(3), TiO(2)/UV/O(2) and UV/O(3) five parallel oxidation pathways. The reaction activities of these six processes were tested in aqueous using electron paramagnetic resonance (EPR) spin trapping technique with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trap. Moreover, the effects of ozone dosage, catalyst dosage and initial solution pH on the degradation of 4-CNB by TiO(2)/UV/O(3) process were also investigated. Results showed that the TiO(2)/UV/O(3) is the most efficient process for complete mineralization of 4-CNB since the combination of photocatalytic oxidation with ozone has a synergistic effect. The relative intensity of DMPO-OH follows the order of UV/air<O(3)<TiO(2)/O(3)<UV/O(3)<TiO(2)/UV/O(2)<TiO(2)/UV/O(3). In TiO(2)/UV/O(3) process, the ozone and catalyst dosage are found to have a significant impact on the process efficiency whereas initial pH has relatively less effect. Chlorine atoms of 4-CNB are absolutely oxidized to chloride anions when the ozone dosage in the range of 5-18 mg/min, or the catalyst dosage ranging from 1.0 to 2.0 g/L. Part of chloride anions would be further oxidized to chlorate(V) ions if the ozone dosage exceeds 24 mg/min, or the catalyst dosage exceeds 2.0 g/L.