Iodine-sensitized oxidation of ferrous ions under UV and visible light: the influencing factors and reaction mechanism

摘要

The sensitized oxidation of Fe~(2+) ions by I2 or l3~-in acidic aqueous solution has been examined. The reactions could occur either under UV or visible light, with the stoichiometric formation of Fe~(3+) and l~-. However, the l3~--sensitized reaction was fast and complete only in the presence of excess Fe~(2+). Through a kinetics study, it becomes clear that I and l2~-are the main reactive species for the I2 and l3~-sensitized oxidation of Fe~(2+), respectively. Moreover, the quantum yields determined with the l2 and l3~-sensitized formation of Fe~(3+) at 456 nm were 0.119 and 0.118, respectively. The l2-sensitized reaction was first order only in l2, and had an Arrhenius activation energy of 29.3 kJ mol~(-1). It is proposed that the process of Fe~(2+) oxidation by I is fast, while the rate-determining step is the formation and self-recombination of I' radicals.