Direct Electrical Detection of Iodine Gas by a Novel Metal-Organic-Framework-Based Sensor

High-fidelity detection of iodine species is of utmost importance to the safety of the population in cases of nuclear accidents or advanced nuclear fuel reprocessing. Herein, we describe the success at using impedance spectroscopy to directly detect the real-time adsorption of I₂ by a metal-organic framework zeolitic imidazolate framework (ZIF)-8-based sensor. Methanolic suspensions of ZIF-8 were dropcast onto platinum interdigitated electrodes, dried, and exposed to gaseous I₂ at 25, 40, or 70 °C. Using an unoptimized sensor geometry, I₂ was readily detected at 25 °C in air within 720 s of exposure. The specific response is attributed to the chemical selectivity of the ZIF-8 toward I₂. Furthermore, equivalent circuit modeling of the impedance data indicates a >10⁵× decrease in ZIF-8 resistance when 116 wt % I₂ is adsorbed by ZIF-8 at 70 °C in air. This irreversible decrease in resistance is accompanied by an irreversible loss in the long-range crystallinity, as evidenced by X-ray diffraction and infrared spectroscopy. Air, argon, methanol, and water were found to produce minimal changes in ZIF-8 impedance. This report demonstrates how selective I₂ adsorption by ZIF-8 can be leveraged to create a highly selective sensor using >10⁵× changes in impedance response to enable the direct electrical detection of environmentally relevant gaseous toxins.