얼음 내 무/유기 물질의 산화환원 반응 이해 및 지구 환경 영향 연구

Abstract

Ice chemistry is relatively new research area and it has attracted a lot of scientific interests due to its unique phenomenon. Not like common sense, chemical reactions could be vigorously occurred in frozen solution because of the existent of a liquid-like layer within the ice structure. This grain boundary in ice was observed from real nature ice samples which shows concentration of inorganic salts in this narrow region. It has been reported that ice in polar region significantly affect surface atmospheric environment of the areas. In polar region, most of surface is covered with ice. The photochemical reaction of nitrate (NO3−) in the ice produce hydroxyl radicals (∙OH) which results in the formation of nitrogen oxides, aldehyde, and halogen gases from the polar region surface ice. It could explain the high concentration of active halogen and exceptional chemical composition of troposphere in polar region. Chemical reactions in ice could lead to unexpected consequences and effect on the ecosystem. Nature ice with liquid-like grain boundary was reproduced in laboratory scale and geochemical reactions in the frozen solution was studied. It has been confirmed that frozen media shows unique chemical reactions which were not found in aqueous condition. In frozen solution nitrite (NO2−) could oxidize phenolic compounds, which results in the formation of phenolic radicals which induce the polymerization of monomers and production of high molecule organic compounds. Decrease of pH in ice grain boundary imposed the formation of nitrosonium (NO+) from nitrite which is strong active oxidant. Specific chemical reactions were dramatically accelerated in frozen solution. Bromate (BrO3−) reduction into bromide was remarkably accelerated in ice while the reduction was negligible in aqueous solution. Hydrogen peroxide (H2O2) generation from cupric ion (Cu2+) and hydroquinone was enhanced in frozen solution than aqueous solution. It was due to the freeze concentration effect during freezing the sample solution. When the solution is freezing solutes are expelled from ice crystal and aggregate in solution, which eventually leads to an increase of concentration in ice grain boundary. However, it was found out that the distribution in frozen solution is different depending on the type of solute. For Cr(III) oxidation, several oxidants showed prohibition of the oxidation under frozen condition. When the oxidant was localized in grain boundary, the chemical reaction was accelerated in frozen condition. In several cases, the oxidants were not concentrated in the liquid-like layer and spread among bulk ice crystal, which results in inhibition of chemical reaction. It identifies that physical behavior of chemical compounds in frozen solution determine the chemical reaction rate in ice.