Abstract
In this paper, a high sensitivity and high stability quartz crystal microbalance (QCM) humidity sensor using polydopamine (PDA) coated cellulose nanocrystal (CNC)/graphene oxide (GO) (PDA@CNC/GO) nanocomposite as sensitive material is demonstrated. The PDA@CNC was prepared by the self-polymerization action on the surface of CNC, and it acted as filler material to form functional nanocomposite with GO. The material characteristics of PDA@CNC, CNC/GO and PDA@CNC/GO were analyzed by transmission electron microscope (TEM) and Fourier transform infrared spectroscopy (FTIR), respectively. The experimental results show that the introduction of PDA@CNC into GO film not only effectively enhanced the sensitivity of GO-based nanocomposite-coated QCM sensor but also significantly maintained high stability in the entire humidity range. The PDA@CNC/GO30-coated QCM humidity sensor exhibited a superior response sensitivity up to 54.66 Hz/% relative humidity (RH), while the change rate of dynamic resistance of the sensor in the humidity range of 11.3–97.3% RH is only 14% that is much smaller than that of CNC/GO-coated QCM. Besides, the effect of the PDA@CNC content on the sensitivity and stability of GO-based nanocomposite-coated QCM humidity was also studied. Moreover, other performances of PDA@CNC/GO-coated QCM humidity sensor, including humidity hysteresis, fast response and recovery and long-term stability, were systematically investigated. This work suggests that PDA@CNC/GO nanocomposite is a promising candidate material for realizing high sensitivity and high stability QCM humidity sensor in the entire humidity detection range.
Highlights
The precious measurement of humidity level plays a critical and increasing role in modern industry and daily life, such as industrial process control, electrostatic protection, SF6 gas leakage monitoring, grain storage, weather forecast, etc. [1,2] To meet this growing demand of the development of Internet of Things (IoT) [3,4], many types of transducers including resistance [5], capacitive [6], mechanical [7,8] and microwave [9] have been adopted to develop humidity sensors
The material characteristics of the as-synthesized graphene oxide (GO), cellulose nanocrystal (CNC)/GO30 and polydopamine coated CNC (PDA@CNC)/GO30 were analyzed by transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and XRD, respectively
We observed that the change rate of dynamic resistance of PDA@CNC/GO30-coated quartz crystal microbalance (QCM) humidity sensor is only 14%, which was much smaller than that of CNC/GO30- and GO-coated QCM sensors
Summary
The precious measurement of humidity level plays a critical and increasing role in modern industry and daily life, such as industrial process control, electrostatic protection, SF6 gas leakage monitoring, grain storage, weather forecast, etc. [1,2] To meet this growing demand of the development of Internet of Things (IoT) [3,4], many types of transducers including resistance [5], capacitive [6], mechanical [7,8] and microwave [9] have been adopted to develop humidity sensors. Benefiting from its superior ability to detect nanogram mass variations, QCM can achieve high humidity response sensitivity by functionalizing the electrode with humidity sensitive materials. Several researchers have found that some QCM humidity sensors have abnormal frequency responses that deviate from Sauerbrey’s relationship when many water molecules are adsorbed on the sensitive material [18,21,22]. Wang experimentally found that PEI-coated QCM humidity sensors showed abnormal frequency responses (e.g., positive frequency shifts) in the high humidity range [18]. The above results suggest that the frequency stability of QCM humidity sensors should be especially concerned when enhance the QCM sensor’s sensitivity by increasing water molecular adsorption capacity of sensitive materials. The physical and chemical properties of humidity sensitive materials are crucial to the performance of QCM humidity sensor, because they determine the sensitivity and influence the frequency stability of the sensor
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