Production of Molecular Iodine via a Redox Reaction between Iodate and Organic Compounds in Ice.

Abstract

The abiotic mechanism of molecular iodine (I2) production from iodate (IO3-) remains largely unknown. Here, we demonstrate the production of I2 in the presence of IO3- and organic compounds in ice. When the solution containing IO3- (100 μM) and furfuryl alcohol (100 μM) at pH 3.0 was frozen at -20 °C, 13.1 μM of I2 was produced with complete degradation of furfuryl alcohol after 20 min. However, there was little change in the IO3- and furfuryl alcohol concentrations in water at 25 °C. The production of I2 in ice is due to the freeze concentration effect, which induces the accumulation of IO3-, furfuryl alcohol, and protons in the ice grain boundaries. This behavior facilitated the production of I2 via a redox reaction between IO3- and organic compounds. The production of I2 increased with increasing furfuryl alcohol concentration and decreasing pH. However, freezing temperature had a minor effect on the maximum production of I2. The production of I2 is highly dependent on the type of organic compounds. It was higher for organic compounds with higher electron-donating properties. This study suggests a new mechanism for I2 production, which is helpful for predicting precisely the atmospheric I2 budget in cold regions.