Mixed-MatrixMembrane-Based Piezoelectric CO₂ Sensor with Self-HumidityCompensation

Monitoring the CO₂ concentration is crucial for assessing respiratory illnesses in humans and safeguarding the environment. The ongoing difficulty lies in achieving highly sensitive detection while also eliminating the interference caused by humidity. There is an unmet need for portable sensors with both high sensitivity and good moisture resistance to monitor CO₂ in real time. In this study, a novel sensor capable of capturing the piezoelectric signals induced by CO₂ gas is developed. A quartz crystal microbalance (QCM) coated with a mixed- matrix membrane of metal–organic framework (MOF)/polyether block amide (Pebax) is designed as a transducer to detect CO₂ at room temperature. The change in the concentration of CO₂ can be detected by the frequency shift of the QCM sensor. The sensor shows an ultrahigh sensitivity of 371.8 Hz to 1000 ppm of CO₂ because of the abundant polar group and nitrogen Lewis basic groups. Furthermore, the implementation of a self-humidity compensation algorithm significantly enhances the accuracy and reliability of CO₂ concentration monitoring by effectively addressing the issue of humidity interference. Our research underscores the immense potential of MOF/Pebax QCM sensors with self-humidity compensation ability in the field of CO₂ gas monitoring.