Primary mechanism for the iron(III) photoinduced degradation of 4-chlorophenol in aqueous solution

The photoinduced degradation of 4-chlorophenol by iron(III) has been investigated by continuous irradiation at 365 nm as well as by nanosecond laser flash photolysis at 355 nm. The process involves the most photoreactive species of iron(III), namely Fe(OH)2+. Upon irradiation, an intramolecular redox process leads to the formation of hydroxyl radicals and iron(II). The continuous formation of OH radicals causes the complete mineralization of 4-chlorophenol. Laser flash photolysis experiments clearly showed that two different pathways are initially present in the degradation of 4-chlorophenol: formation of the OH adduct, 4-chlorodihydroxycyclohexadienyl radical, and of the chlorophenoxyl radical. The quantum yields of these processes have been determined to be 0.056 and 0.015, respectively.