- “Enhanced redox reactions of inorganic species in ice grain boundary”
Prof. Wonyong Choi (Pohang University of Science and Technology (POSTECH))
The surface and interface (water/ice or air/ice) of ice provides a unique chemical environment wherethe chemical transformations proceed very differently from their counterparts in water and air. Ourrecent study found that the photoreductive dissolution of iron oxide particles (a common dustcomponent) is highly enhanced in the ice phase (1). The iron oxide particles are concentrated andaggregated in the liquid-like ice grain boundary region where enhanced photodissolution occurs andsubsequently release more bioavailable ferrous iron upon thawing. The enhanced photogeneration ofFe(II) in ice was confirmed regardless of the type of iron oxides [hematite, maghemite, goethite] andthe kind of electron donors. The chemical reactions taking place in polycrystalline ice may differdramatically from those in the aqueous phase. The results imply that the ice(snow)-covered surfacesand ice-cloud particles containing iron-rich mineral dusts provide a source of bioavailable iron in thepolar and cold environments. Other environmental chemical reactions occurring in the ice grainboundary were also investigated, which include the reduction of hexavalent Cr(VI) (as chromate) bymodel organic acids (e.g., citric and oxalic acid), the simultaneous removal of Cr(VI) and As(III) (asarsenite) (2), and iodide oxidation to triiodide in ice phase in comparison with their counterparts inaqueous solution. The reduction of Cr(VI) in the presence of various organic acids was negligible inambient aqueous solution but was markedly accelerated in ice. The simultaneous reduction of Cr(VI)and oxidation of As(III) in ice phase proceeded stoichiometrically, whereas their mutual conversionwas insignificant in aqueous solution. The oxidation of iodide to triiodide proceeded slowly inaqueous solution but was significantly accelerated in ice as well. The environmental implications ofvarious redox reactions in ice will be discussed.
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