Using Impedance Spectroscopy to Detect the Selective Sorption of Iodine By MOF ZIF-8

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Detection of iodine species is important for the safety of the population in cases of nuclear accidents or advanced nuclear fuel reprocessing. Here we leverage the selective sorption of I2 by metal organic framework (MOF) ZIF-8 to create an impedance spectroscopy-based sensor for the real-time detection of gaseous I2. Methanolic ZIF-8 suspensions were cast onto interdigitated electrodes, dried, and exposed to gaseous I2 at 25, 40, or 70 °C. Equivalent circuit models were developed to separate the response of the extremely resistive ZIF-8 from that of the underlying glass substrate. While high fidelity measurements enable electrical characterization of pure ZIF-8, such precision is woefully unnecessary to detect I2; a >105× decrease in ZIF-8 resistance was observed upon sorption of 116 wt% I2 by ZIF-8 at 70 °C. Such large changes in impedance open the door for I2 detection schemes using inexpensive electronics. Tests for interfering gases such as air, argon, methanol, and water revealed minimal changes in impedance and equivalent circuit response. Using an unoptimized sensor geometry, I2 was readily detected at 25 °C in air. Further optimization of sensor geometry, decreasing MOF film thicknesses and maximizing sensor capacitance, will enable faster detection of trace I2, providing a rapid, robust, and reliable iodine sensor for the safety of the populace. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.