Zn(OH)F Nanorods for Highly Sensitive NO₂ Gas Sensor Applications

In this study, Zn(OH)F nanorods were synthesized via a microwave-assisted hydrothermal process and employed for NO₂ gas sensor, for the first time. Without adding NH₄F in the synthesis process, caltrop-like ZnO structure was formed. The characteristics of Zn(OH)F nanorods were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), and compared to those of caltrop-like ZnO. Additionally, the Zn(OH)F nanorods were further systematically studied by annealing them at 250, 350, and 450 °C to examine thermal stability. The Zn(OH)F nanorods start to transform after annealing at 350 °C. The sensor based on the Zn(OH)F nanorods showed very high response of 63.4 toward 1.3 ppm of NO₂ gas at 100 °C, which is 8.6 times higher than the response of the sensor based on the caltrop-like ZnO. In addition, the sensor based on Zn(OH)F nanorods showed an excellent selectivity toward H₂ (5 ppm), C₂H₅OH (10.6 ppm), NH₃ (10.6 ppm), C₆H₅CH₃ (36.2 ppm), and CH₃COCH₃ (2.8 ppm).