Nanodiamond/Ti₃C₂ MXene-coated quartz crystal microbalance humidity sensor with high sensitivity and high quality factor

To address the challenge of achieving both high sensitivity and a high quality factor in quartz crystal microbalance (QCM) humidity sensors, a nanodiamond (ND)/Ti₃C₂ MXene composite-coated QCM humidity sensor was fabricated. The material characteristics of ND, Ti₃C₂ MXene, and ND/Ti₃C₂ MXene composite were analyzed by transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. The experimental results demonstrated that the hydrophilic ND nanoparticles coated on Ti₃C₂ MXene nanosheet prevented the self-stacking of Ti₃C₂ MXene and enhanced the sensitivity of Ti₃C₂ MXene-based QCM humidity sensor. Moreover, the high mechanical modulus of Ti₃C₂ MXene material helped ND/Ti₃C₂ MXene composite-coated QCM humidity sensor to achieve a high quality factor (> 20,000). ND/Ti₃C₂ MXene composite-coated QCM humidity sensor exhibited a sensitivity of 82.45 Hz/%RH, a humidity hysteresis of 1.1%RH, fast response/recovery times, acceptable repeatability, and good stability from 11.3%RH to 97.3%RH. The response mechanism of ND/Ti₃C₂ MXene composite-coated QCM humidity sensor was analyzed in combination with a bi-exponential kinetic adsorption model. Finally, the potential application of ND/Ti₃C₂ MXene composite-coated QCM humidity sensor was demonstrated through its frequency response to wooden blocks with different moisture contents.