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

Abstract

The abiotic mechanism of molecular iodine (I 2 ) production from iodate (IO 3 − ) remains largely unknown. Here, we demonstrate the production of I 2 in the presence of IO 3 − and organic compounds in ice. When the solution containing IO 3 − (100 μM) and furfuryl alcohol (100 μM) at pH 3.0 was frozen at −20 °C, 13.1 μM of I 2 was produced with complete degradation of furfuryl alcohol after 20 min. However, there was little change in the IO 3 − and furfuryl alcohol concentrations in water at 25 °C. The production of I 2 in ice is due to the freeze concentration effect, which induces the accumulation of IO 3 − , furfuryl alcohol, and protons in the ice grain boundaries. This behavior facilitated the production of I 2 via a redox reaction between IO 3 − and organic compounds. The production of I 2 increased with increasing furfuryl alcohol concentration and decreasing pH. However, freezing temperature had a minor effect on the maximum production of I 2 . The production of I 2 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 I 2 production, which is helpful for predicting precisely the atmospheric I 2 budget in cold regions.

Record High Iodate Anion Capture by a Redox‐Active Cationic Polymer Network

“…Besides, the iodine species in SCU‐CPN‐6‐I are classified as the reduced state (I − ) and the intermediate state (I 2 ) rather than the oxidation state as IO 3 − (V) in I 3d XPS spectrum (Figure 5b), indicating that IO 3 − is reduced after being adsorbed to SCU‐CPN‐6 in aqueous solution. This finding is closely similar to the research reported on the reduction of IO 3 − by furfuryl alcohol [38] . In addition, partial C−O converts to C=O in SCU‐CPN‐6‐I (Figure 5d), concomitant with no obvious changes observed for other elements of SCU‐CPN‐6.…”

“…À by furfuryl alcohol. [38] In addition, partial CÀ O converts to C=O in SCU-CPN-6-I (Figure 5d), concomitant with no obvious changes observed for other elements of SCU-CPN-6. The phenol groups in SCU-CPN-6 were transformed into benzoquinone, which is the primary cause that makes IO 3 À reduced, bearing a resemblance to the phenol reduction effect to uranyl ions in Redox-COF1.…”

Freezing-Enhanced Photoreduction of Iodate by Fulvic Acid

“…The reductive conversion of iodate by FA under dark or irradiated conditions at an initial pH (pH i ) 3.0 is shown in Figure . A small fraction of iodate (<10%) can be reduced by FA in frozen solution under a dark condition after 24 h. Kim et al reported that freezing enhanced the degradation of some organic pollutants by iodate, indicating that iodate can exhibit stronger oxidative reactivity in ice. The reductive activity of FA in ice was also reported in our previous work on the freezing-enhanced reduction of bromate under dark condition .…”

“…22,25−28 Gaĺvez et al 29 revealed that the photolysis of frozen iodate salts in the presence of low water content (@100−253 K) serves as a source of RI. Most recently, Kim et al 30 reported that freezing the iodate solution in the presence of various organic pollutants enhances the production of molecular iodine under dark condition, which indicates the accelerated reaction between iodate and organic substances in ice. It has also been reported that freezing enhances bromate reduction by NOM under both dark and light conditions.…”

“…Over past decades, many environmental chemical reactions taking place in frozen solution have been found to be very different from their counterparts in aqueous solution, which offers valuable insights into understanding the chemical mechanisms behind distinctive reactions that occur in polar caps and the atmospheric boundary layer. − Various redox reactions are markedly accelerated in the frozen reaction media, which include the abiotic transformation of iodide to OICs by Fe­(III)/Mn­(IV) oxides. − The solar photochemistry can provide new paths to various chemical reactions occurring in frozen solution (e.g., iodide oxidation). ,− Gálvez et al revealed that the photolysis of frozen iodate salts in the presence of low water content (@100–253 K) serves as a source of RI. Most recently, Kim et al reported that freezing the iodate solution in the presence of various organic pollutants enhances the production of molecular iodine under dark condition, which indicates the accelerated reaction between iodate and organic substances in ice. It has also been reported that freezing enhances bromate reduction by NOM under both dark and light conditions .…”