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

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.