Heterodyne-Detected Sum Frequency Generation Study of Adsorption of I– at Model Paint–Water Interface and Its Relevance to Post-Nuclear Accident Scenario

Abstract

Organic iodides constitute a significant fraction of radioactive iodine released into the environment in the event of a nuclear power plant accident. The painted surfaces inside the reactor containment play a key role in the formation of organic iodides. In this study, heterodyne detected vibrational sum frequency generation (HD-VSFG) spectroscopy has been used to gain insight into the origin of organic iodides from paint surfaces. Model polymeric compounds dimethylhexadecyl amine (DHDA) and Nylon6, which resemble the constituents of containment paints, are selected for this study. Our investigations on the DHDA–water interface and Nylon6–water interface reveal the existence of positive surface field at acidic conditions (bulk pH: 2, 6) due to protonation at amine functional group and adsorption of H+ at amide groups; and a negative surface field at pH 11 due to adsorption of OH– ions at both amine and amide functional groups. In the presence of CsI in the aqueous phase, this surface field is altered by t...