ZIF-8-based chemiresistive CO₂ sensor: fabrication, performance evaluation, and comparison with NDIR and colorimetric...

Carbon dioxide (CO₂) is a gas prevalent in the environment, but at higher concentrations can be highly toxic or even lethal. This work studies the fabrication and evaluation of chemiresistive sensing of carbon dioxide using ZIF-8 and compares it against a conventional NDIR-based SCD40 sensor and a ZIF-8-based colorimetric sensor. ZIF-8 was chosen due to its high porosity, and selective adsorption of CO₂ at room temperature, while the conventional chemiresistive sensors used metal oxides, which require higher temperatures for accurate sensing. ZIF-8 was fabricated using the solvothermal method, drop-cast on a custom etched ITO glass substrate, connecting the two portions of the ITO with the ZIF-8 layer electrically and the sensor was calibrated using the NDIR-based SCD40 sensor (400-1600 ppm) with varying CO₂ values. The calibrated sensor was evaluated for sensing behaviour against SCD40 and the colorimetric sensor across various CO₂ values and environments. The measured resistance response was subjected to curve fitting using calibration data, and the resulting model was implemented on the ESP32 microcontroller to convert resistance values into corresponding CO₂ concentrations (ppm). This work provides a practical, scalable, energy-efficient alternative for environmental monitoring, industrial safety, and healthcare applications.