Study on a quartz crystal microbalance sensor based on chitosan-functionalized mesoporous silica for humidity detection

Chitosan-functionalized mesoporous silica MCM-41 (Chi/M41) was prepared by a mild method. In the composite materials, the spherical MCM-41 particles were regarded as supporting skeletons, which reduced the effect of chitosan swelling on the repeatability and reliability of quartz crystal microbalance (QCM) sensors at high relative humidity (RH), and chitosan provided good film-forming properties of the final composite. The composite structure effectively improved the sensitivity of the QCM sensors compared to that of chitosan and MCM-41 sensors. The QCM sensor based on the Chi/M41 composites showed excellent sensitivity (58.4 ± 0.3 Hz/% RH). In addition, the optimal sensor exhibited excellent reliability, such as negligible humidity hysteresis (0.8 ± 0.1% RH), a small variation coefficient (1.1 ± 0.1), short response and recovery times (18 s/15 s) and good long-term stability. Furthermore, the Langmuir adsorption isotherm model and the Gibbs free energy were used to investigate the adsorption mechanism of water molecules on the sensitive films in this work.