Low-Temperature Ethanol Gas Sensor Based on MoO₃/Nb₂C MXene Composite via Crystal Engineering and Facet Release

High-performance ethanol sensors with low power consumption show critical applications in environmental monitoring, personal health diagnosis, industry and traffic safety. Herein, MoO₃/Nb₂C MXene heterojunction gas-sensing materials were constructed via a one-step hydrothermal method for MoO₃ nanotube synthesis. The dominant facets of MoO₃ were shifted from the (040) orientation in MoO₃ nanotubes to the (110) and (021) orientations in the MoO₃/Nb₂C MXene composite. Nb₂C nanosheets provide a large number of crystallization sites, preventing the growth of MoO₃ nanotubes during synthesis, inducing a strategic facet release. The sensing performance shows MoO₃/Nb₂C MXene composite reduces the operating temperature down to 120 °C. The 15 wt% Nb₂C MXene-precursor-mixed MoO₃ sensor exhibits an enhanced response of 6.1 toward 100 ppm ethanol, which is higher than that of pristine MoO₃ nanotubes at 120 °C, with response and recovery times of 19 s and 72 s, respectively. The sensors show high selectivity toward ethanol over other VOC gases and good long-term stability over 30 days. This work confirms that crystal engineering is an effective method for reducing operating temperature and enhancing gas-sensing performance, and the sensor shows potential application for ethanol sensing.