High-sensitivity, fast-response quartz crystal microbalance humidity sensors coated with nanodiamond/halloysite nanotube composites

This paper develops a composite mixture of halloysite nanotubes (HNTs) and nanodiamond (ND) as a humidity-sensitive material for a quartz crystal microbalance (QCM) to achieve a balance between rapid response/recovery times and high sensitivity. The ND-HNTs composite-integrated QCM sensor exhibited rapid response/recovery times of 2/1 and 4/2 s when transitioning from an environmental humidity of 55 % RH to both low (11.3 % RH) and high (97.3 % RH) humidity levels. Throughout the humidity range of 11.3 %similar to 97.3 % RH, the sensor demonstrated a sensitivity of up to 98.14 Hz/%RH and low humidity hysteresis of around 1.95 % RH, good repeatability and stability. Furthermore, a detailed analysis of the response mechanism for the ND-HNTs composite-integrated QCM humidity sensor was conducted by integrating a bimodal exponential kinetic adsorption model. This paper introduces a new approach for fabricating QCM humidity sensors that possess both heightened sensitivity and rapid response/recovery times.