Visual and Gravimetric CO₂ Sensing at High Humidity Levels Enabled by MOF‐804 Cofunctionalized with Ionic Liquid and m‐Cresol Purple

Abstract Real‐time monitoring of carbon dioxide (CO₂) is imperative for medical diagnosis and effective environmental preservation. Despite the formidable challenge posed by the inherent chemical inertness of CO₂ molecules, a pioneering CO₂ sensor based on MOF‐804 cofunctionalized with ionic liquid (IL) and m‐cresol purple (mCP) is successfully developed. By ingeniously integrating hydrogen bonding, electrostatic interactions, and hydrophobic properties within the sensitive layer, the sensor achieves a state‐of‐the‐art sensitivity (Δf = 384 Hz), an exceptionally vast detection range spanning 400–80 000 ppm, and remarkable stability with minimal sensitivity drift even at relative humidity (RH) levels exceeding 80%. Furthermore, the inherent gasochromic property, stemming from the zwitterionic mechanism, paves the way for innovative self‐sustaining CO₂ test strips and groundbreaking applications, including CO₂ tracking and CO₂‐encrypted security labeling technology. Collectively, the realization of this ultra‐sensitive and robust CO₂ monitoring approach, coupled with its CO₂‐triggered visual and multifunctional capabilities, opens up novel avenues for dynamic CO₂ detection, advanced military encryption strategies, and enhanced health management systems.