Miniaturized High-Frequency QCM Ammonia Sensor Based on MXene/ZnO Heterojunction at Room Temperature

Ammonia (NH3) has a significant impact on human health, merely 300 ppm of which could pose a risk of irreversible harm to human life. Size and sensitivity are two primary factors for real-time sensing of NH3. Through dry grinding, we develop a novel 61-MHz quartz crystal microbalance (QCM) sensor with dimensions of only 5.0 mm in length and 3.2 mm in width. In this study, the MXene/ZnO heterojunction solution is created using the liquid phase method, and it is uniformly sprayed onto the surface of the QCM. The large specific surface area of the MXene/ZnO heterojunction provides additional adsorption sites for NH3 detection, enhancing sensitivity across a wide dynamic range and offering superior selectivity toward ammonia. At a temperature of 25° C, the sensitivity of the MXene/ZnO sensor for detecting NH3 is 1.319 Hz/ppm, surpassing that of the ZnO sensor (0.166 Hz/ppm). Furthermore, the sensor's recovery time is significantly reduced from typically 300 s under normal conditions to 40 s after exposure to ultraviolet (UV) light. The proposed QCM sensor boasts advantages of compact size, high sensitivity, short recovery time, and exceptional selectivity for ammonia, which presents a novel solution for detecting harmful gases such as NH3 at room temperature.