CHEMICAL MECHANISM OF INORGANIC OXIDANTS IN THE TIO2/UV PROCESS - INCREASED RATES OF DEGRADATION OF CHLORINATED HYDROCARBONS

Particulate suspensions of TiO2 irradiated with UV light at wavelengths shorter than 385 nm catalyze the autooxidation of chlorinated hydrocarbons such as I-chlorophenol (4-CP). The addition of oxyanion oxidants such as CIO2-, CIO3-, IO4-, S2O82-, and BrO3- increases the rate of photodegradation of 4-CP in the following order: CIO2- > IO4- > BrO3- > CIO3-. In the absence of TiO2, CIO3- shows no photoreactivity toward 4-CP, while HSO5- and MnO4- exhibit rapid thermal reactivity with 4-CP. BrO3- appears to increase photoreactivity by scavenging conduction-band electrons and reducing charge-carrier recombination. With CIO3- as an oxidant, the degradation of 4-CP appears to follow three concurrent pathways. Kinetic equations for the rate of degradation of 4-CP as a function of [4-CP], [CIO3-], and [O-2] and of the light intensity are derived from a proposed mechanism.