Enhancement of gaseous iodine emission by aqueous ferrous ions during the heterogeneous reaction of gaseous ozone with aqueous iodide.

Gaseous I2 formation from the heterogeneous reaction of gaseous ozone with aqueous iodide in the presence of aqueous ferrous ion (Fe(2+)) was investigated by electron impact ionization mass spectrometry. Emission of gaseous I2 increased as a function of the aqueous FeCl2 concentration, and the maximum I2 formation with Fe(2+) was about 10 times more than without Fe(2+). This enhancement can be explained by the OH(-) scavenging by Fe(3+) formed from Fe(2+) ozonation to produce colloidal Fe(OH)3. This mechanism was confirmed by measurements of aqueous phase products using a UV-vis spectrometer and an electrospray ionization mass spectrometer. We infer that such a pH-buffering effect may play the key role in general halogen activations.