Room-Temperature CO2 Monitoring Platform Enabled by Alkali Metal Functionalization of a Mg-MOF-74-Based QCM Sensor

Carbon dioxide (CO2) detection is indispensable for monitoring climate change, ensuring air quality, managing industrial processes, and safeguarding human health. Nevertheless, the chemical inertness and stability of CO2 pose significant challenges in advancing detection technologies in practical applications. In order to overcome these challenges, nanoscale MOF-74 metal–organic frameworks (MOFs) functionalized with alkali metals (Li, Na, and K) have been synthesized for the effective detection of the CO2 gas. The sensing results indicate that the Li–Mg-MOF-74-based quartz crystal microbalance (QCM) CO2 sensors demonstrate excellent properties, such as very high sensitivity, rapid response/recovery time (84 s/69 s), broad detection range (300–10000 ppm), and remarkable selectivity at room temperature. The enhanced performance benefits from the increased electrostatic force and Lewis’s acidity resulting from alkali metal ions (Li+) and open metal sites (Mg2+). In addition, the equilibrium constant of CO2 on the sensor surface was calculated by the Langmuir adsorption isotherm model, revealing spontaneous and robust adsorption behavior. These results indicate that alkali-metal-modified Mg-MOF-74 materials have great potential for practical CO2 detection and provide a feasible solution for the design of high-performance, room-temperature CO2 sensing platforms.