Destruction of o-chloroaniline in UV/TiO₂ reaction with photosensitizing additives

The photodecay of o-chloroaniline (o-ClA) in TiO2 suspension with and without the use of additives was examined under an ultraviolet light at 300 nm. An analysis showed that the disappearance of o-ClA followed a pseudo first-order reaction and can be described by the Langmuir-Hinshewood (LH) model. The application of various dosages of TiO2 indicated a discontinuous linear increment at a break point of 0.1 g L-1 TiO 2. The change in the system pH has a significant effect on the performance of the process. This is a mixed result of the surface charge of TiO2 and the chemical characteristic of o-ClA, which is discussed in detail in this paper. The further enhancement of the UV/TiO2 process by adding H2O2 is feasible if the dosage is carefully controlled. The addition of excess amounts of H2O2 should be avoided to minimize the scavenging of hydroxyl radicals in the solution and valence-band holes at the TiO2 surface. The use of the sensitizer Rose Bengal (RB) in the UV/TiO2 process, however, is not suggested. This is because RB is not sensitive at the optimal wavelength for the photocatalytic process involving TiO2; in addition, the RB may become an additional competitor (with the probe) for the free radicals and active sites on the TiO2 surface.