Iodine detection in Ag-mordenite based sensors: Charge conduction pathway determinations

Detection of radiological iodine gas after nuclear accidents or in nuclear fuel reprocessing is necessary for the safety of human life and the environment. The development of sensors for the detection of iodine benefits from the incorporation of nanoporous materials with high selectivity for I-2 from common competing gases in air. Silver mordenite zeolite (Ag-MOR) is widely-used material for capture of gaseous iodine (I-2). Herein, thin film zeolite coatings were applied to Pt interdigitated electrodes (IEDs) to fabricate iodine gas sensors with direct electrical readout responses. Correlations between occluded ion, exposure to iodine gas, resultant AgI nanoparticle polymorphs and location in zeolite with resultant impedance spectroscopy (IS) properties are described. Furthermore, IS is leveraged to elucidate the changes in charge conduction pathways as determined by the cation-zeolite film incorporated in the sensor. Silver mordenite reveals a significant change in impedance upon exposure to gaseous I-2 at 70 degrees C, and the magnitude and direction of the response is dependent on whether the Ag+-mordenite is reduced (Ag-0) before I-2 exposure. An equivalent circuit model is developed to describe the movement of charge along the surface and through the pores of the mordenite grains. Relative changes in the impedance of these conduction pathways are related to the chemical changes from Ag+ or Ag-0 to resultant AgI polymorph phase. Together, these results inform design of a compact Ag-mordenite sensor for direct electrical detection of gaseous I-2.